SOUTH AFRICAN NATIONAL STANDARD · 2021. 8. 12. · SANS 1024, Welded steel fabric for reinforcement of concrete. SANS 1083, Aggregates from natural sources – Aggregates for concrete

ISBN 978-0-626-30485-0 SANS 10100-2:2014Edition 3

SOUTH AFRICAN NATIONAL STANDARD

The structural use of concrete

Part 2: Materials and execution of work

WARNING This document references other

documents normatively.

Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS

SANS 10100-2:2014 Edition 3

Table of changes

Change No. Date Scope

Acknowledgement

The SABS Standards Division wishes to acknowledge the valuable assistance derived from The Concrete Institute.

Foreword

This South African standard was approved by National Committee SABS/TC 081/SC 01, Construction materials, products and test methods – Cement, lime and concrete, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement.

This document was published in October 2014.

This document supersedes SABS 0100-2:1992 (edition 2).

This document is referenced in the National Building Regulations and Building Standards Act, 1977 (Act No. 103 of 1977).

Reference is made in 3.1.1.3 to the "relevant national body". In South Africa this means the South African National Accreditation System (SANAS).

Reference is made in table 1 to the "relevant national body". In South Africa this means Transnet.

SANS 10100 consists of the following parts, under the general title The structural use of concrete:

Part 1: Design.

Part 2: Materials and execution of work.

Annexes A and B are for information only.

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Contents

Page Acknowledgement Foreword 1 Scope .................................................................................................................................... 7 2 Normative references ........................................................................................................... 7 3 Terms, definitions and abbreviations .................................................................................... 9 4 Materials for concrete ........................................................................................................... 13 4.1 Cementitious binder .................................................................................................... 13 4.1.1 General ........................................................................................................... 13 4.1.2 Properties of concrete made with a blend of common cement and cement extenders .................................................................................... 14 4.2 Water ........................................................................................................................... 14 4.3 Aggregates .................................................................................................................. 14 4.3.1 Natural aggregates covered by SANS 1083 ................................................... 14 4.3.2 Aggregates not covered by SANS 1083 ......................................................... 15 4.3.3 Nominal maximum size ................................................................................... 15 4.3.4 Aggregates for high-strength concrete ........................................................... 15 4.3.5 Aggregates and fire resistance ....................................................................... 15 4.3.6 Use of "plums" ................................................................................................ 15 4.3.7 Storage ........................................................................................................... 15 4.4 Admixtures .................................................................................................................. 16 4.4.1 General ........................................................................................................... 16 4.4.2 Storage ........................................................................................................... 17 4.5 Deteriorated material................................................................................................... 17 5 Plant for concrete ................................................................................................................... 17 5.1 General ....................................................................................................................... 17 5.2 Batching plant ............................................................................................................. 17 5.3 Mixing plant ................................................................................................................. 17 5.4 Vibrators ...................................................................................................................... 17 6 Proportioning ........................................................................................................................ 18 6.1 Quality of concrete ...................................................................................................... 18 6.1.1 General ........................................................................................................... 18 6.1.2 Strength .......................................................................................................... 18 6.1.3 Density ........................................................................................................... 18 6.1.4 Transportation ................................................................................................ 18 6.1.5 Workability ...................................................................................................... 18 6.1.6 Settlement and bleeding ................................................................................. 19 6.1.7 Chloride content .............................................................................................. 19 6.1.8 Sulfates in concrete ........................................................................................ 19 6.1.9 Alkali-silica reaction ........................................................................................ 20 6.1.10 Drying shrinkage ............................................................................................. 20

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Contents (continued) Page

6.2 Durability .................................................................................................................... 20 6.2.1 General ........................................................................................................... 20 6.2.2 Conditions of exposure .................................................................................. 21 6.2.3 Exposure to freezing and thawing .................................................................. 22 6.2.4 Exposure to aggressive chemicals ................................................................. 22 6.2.5 Exposure to salt-laden air ............................................................................... 24 6.2.6 Exposure to corrosive fumes .......................................................................... 24 6.2.7 Exposure to polluted air .................................................................................. 24 6.3 Mix proportions ............................................................................................................ 24 7 Production of concrete .......................................................................................................... 24 7.1 General ....................................................................................................................... 24 7.2 Batching ...................................................................................................................... 25 7.2.1 Cement ........................................................................................................... 25 7.2.2 Water .............................................................................................................. 25 7.2.3 Aggregates ..................................................................................................... 25 7.2.4 Admixtures ...................................................................................................... 25 7.2.5 Equipment ...................................................................................................... 25 7.3 Mixing ......................................................................................................................... 25 7.3.1 General .......................................................................................................... 25 7.3.2 Control of admixtures ..................................................................................... 26 7.3.3 Tempering and control of mixing water .......................................................... 26 7.3.4 Adverse weather ............................................................................................ 26 7.4 Transportation ............................................................................................................ 27 8 Reinforcement ....................................................................................................................... 27 8.1 General ...................................................................................................................... 27 8.2 Cover to reinforcement .............................................................................................. 27 8.3 Bending ...................................................................................................................... 29 8.3.1 General .......................................................................................................... 29 8.3.2 Preheating before bending or straightening .................................................. 29 8.4 Fixing .......................................................................................................................... 29 8.4.1 General .......................................................................................................... 29 8.4.2 Steel reinforcement ........................................................................................ 30 8.4.3 Zinc-coated (galvanized) reinforcement ........................................................ 31 8.4.4 Epoxy-coated reinforcement .......................................................................... 31 8.5 Welding ...................................................................................................................... 31 8.5.1 General .......................................................................................................... 31 8.5.2 Use of welding ............................................................................................... 32 8.5.3 Types of welding ............................................................................................ 32 8.5.4 Location of welded joints ............................................................................... 32 8.5.5 Strength of structural welded joints ............................................................... 32 8.5.6 Welded lapped joints ..................................................................................... 32

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Contents (continued)

Page 9 Formwork ........................................................................................................................ 33 9.1 General ...................................................................................................................... 33 9.2 Design and construction of formwork ......................................................................... 33 9.2.1 Loads ............................................................................................................. 33 9.2.2 Deflection ....................................................................................................... 33 9.2.3 Form accessories .......................................................................................... 33 9.2.4 Temporary openings ...................................................................................... 34 9.3 Preparation of formwork ............................................................................................. 34 9.4 Reuse of formwork ..................................................................................................... 34 9.5 Removal of formwork and falsework .......................................................................... 34 10 Placing and protection of concrete ....................................................................................... 36 10.1 General ...................................................................................................................... 36 10.2 Placing ....................................................................................................................... 36 10.3 Compaction ................................................................................................................ 37 10.4 Construction joints ...................................................................................................... 38 10.4.1 General .......................................................................................................... 38 10.4.2 Location ......................................................................................................... 38 10.4.3 Bonding .......................................................................................................... 39 10.4.4 Reinforcement ............................................................................................... 39 10.4.5 Construction ................................................................................................... 40 10.5 Embedded items ........................................................................................................ 40 10.5.1 General .......................................................................................................... 40 10.5.2 Waterstops ..................................................................................................... 40 10.5.3 Pipes and conduits ........................................................................................ 40 10.6 Concrete for water-retaining structures ...................................................................... 40 10.7 Concrete in saturated ground .................................................................................... 41 10.8 Protection and curing of concrete .............................................................................. 41 10.8.1 General .......................................................................................................... 41 10.8.2 Concreting in hot weather or in windy conditions .......................................... 42 10.8.3 Concreting in cold weather ............................................................................ 42 10.8.4 Concreting during rainfall ............................................................................... 43 10.9 Surface finish of concrete .......................................................................................... 43 10.9.1 Upper surfaces of concrete ............................................................................ 43 10.9.2 Concrete surfaces cast against forms ........................................................... 43 10.9.3 Repair of surface defects ............................................................................... 43 10.10 Records ...................................................................................................................... 44

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Contents (continued)

Page 11 Massive concrete .................................................................................................................. 44 11.1 General ...................................................................................................................... 44 11.2 Construction ............................................................................................................... 44 12 Prestressing .......................................................................................................................... 45 12.1 Prestressing tendons ................................................................................................. 45 12.1.1 General .......................................................................................................... 45 12.1.2 Handling and storage ..................................................................................... 45 12.1.3 Surface condition ........................................................................................... 45 12.1.4 Straightness ................................................................................................... 45 12.1.5 Cutting ............................................................................................................ 45 12.1.6 Formwork ....................................................................................................... 46 12.1.7 Sheathing ....................................................................................................... 46 12.2 Tensioning .................................................................................................................. 46 12.2.1 General .......................................................................................................... 46 12.2.2 Safety precautions ......................................................................................... 47 12.2.3 Tensioning apparatus .................................................................................... 47 12.2.4 Pre-tensioning ................................................................................................ 47 12.2.5 Post-tensioning .............................................................................................. 48 12.3 Positioning of tendons and sheathing ........................................................................ 49 12.4 Tensioning procedure ................................................................................................ 49 12.5 Grouting of prestressing tendons ............................................................................... 50 12.5.1 General .......................................................................................................... 50 12.5.2 Grouting equipment ....................................................................................... 50 12.5.3 Materials ........................................................................................................ 51 12.5.4 Ducts .............................................................................................................. 51 12.5.5 Mixing ............................................................................................................. 51 12.5.6 Strength of grout ............................................................................................ 52 12.5.7 Injection of grout ............................................................................................ 52 12.5.8 Grouting during cold weather ........................................................................ 52 12.5.9 Protection and bonding of prestressing tendons ........................................... 52 13 Precast concrete ................................................................................................................... 53 13.1 General ...................................................................................................................... 53 13.2 Permissible deviations ............................................................................................... 53 13.3 Prestressed units ....................................................................................................... 54 13.4 Handling and erection of precast concrete units ........................................................ 54 13.4.1 Lifting equipment ........................................................................................... 54 13.4.2 Handling and transportation .......................................................................... 54 13.4.3 Assembly and erection .................................................................................. 55 13.4.4 Temporary supports during construction ....................................................... 55 13.4.5 Forming structural connections ..................................................................... 56 13.4.6 Protection ....................................................................................................... 57

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Contents (concluded)

Page 14 Testing and acceptance of concrete ...................................................................................... 57 14.1 General ...................................................................................................................... 57 14.2 Testing services ......................................................................................................... 57 14.2.1 Basic site testing services .............................................................................. 57 14.2.2 Testing services required by the engineer for compliance verification .......... 58 14.2.3 Additional services when required ................................................................. 58 14.2.4 Test reports .................................................................................................... 58 14.2.5 Responsibilities and duties of the contractor ................................................. 58 14.3 Strength tests of concrete during construction .......................................................... 59 14.3.1 General procedures ....................................................................................... 59 14.3.2 Evaluation of strength test results ................................................................. 59 14.3.3 Acceptance criteria for strength test results .................................................. 59 14.4 Strength tests of concrete in place ............................................................................. 60 14.4.1 Non-destructive testing .................................................................................. 60 14.4.2 Core tests ...................................................................................................... 61 14.4.3 Acceptance of concrete on the basis of core strengths ................................. 61 15 Load tests ............................................................................................................................. 61 15.1 Individual precast units .............................................................................................. 61 15.1.1 General .......................................................................................................... 61 15.1.2 Non-destructive tests ..................................................................................... 62 15.1.3 Destructive tests ............................................................................................ 62 15.1.4 Special tests .................................................................................................. 62 15.2 Structures and parts of structures .............................................................................. 62 15.2.1 General .......................................................................................................... 62 15.2.2 Age at test ...................................................................................................... 62 15.2.3 Test loads ...................................................................................................... 62 15.2.4 Measurements during the tests ..................................................................... 63 15.2.5 Assessment of results .................................................................................... 63 16 Procedure in the event of failure ........................................................................................... 64 Annex A (informative) Recommended specialist literature on massive concrete ................... 65 Annex B (informative) Technical data for prestressed structural elements ............................ 66 Bibliography .............................................................................................................................. 68

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The structural use of concrete

Part 2: Materials and execution of work

1 Scope 1.1 This part of SANS 10100 covers the materials and execution of work related to the structural use of concrete in buildings and structures where the design of reinforced, prestressed and precast concrete is entrusted to appropriately qualified structural or civil engineers and the execution of the work is carried out under the direction of appropriately qualified supervisors. 1.2 This part of SANS 10100 does not cover the structural use of concrete made with high-alumina cement.

2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Information on currently valid national and international standards can be obtained from the SABS Standards Division. 2.1 Standards BS 5896, Specification for high tensile steel wire and strand for the prestressing of concrete. BS 8500-1, Concrete – Complementary British standard to BS EN 206-1 – Part 1: Method of specifying and guidance for the specifier. BS 8500-2, Concrete – Complementary British standard to BS EN 206-1 – Part 2: Specification for constituent materials and concrete. EN 206, Concrete – Specification, performance, production and conformity. SANS 163-1/ISO 10304-1, Water quality – Determination of dissolved fluoride, chloride, nitrite, orthophosphate, bromide, nitrate and sulphate ions, using liquid chromatography of ions – Part 1: Method for water with low contamination. SANS 282, Bending dimensions and scheduling of steel reinforcement for concrete. SANS 374, Standard test methods for chloride ion in water.

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SANS 878, Ready-mixed concrete. SANS 920, Steel bars for concrete reinforcement. SANS 1024, Welded steel fabric for reinforcement of concrete. SANS 1083, Aggregates from natural sources – Aggregates for concrete. SANS 2001-CC1, Construction works – Part CC1: Concrete works (structural). SANS 5213, Water – Dissolved solids content. SANS 5217, Water – Free and saline ammonia content. SANS 5218, Water – Albuminoid ammonia content. SANS 5856, Bulking of fine aggregates. SANS 5861-2, Concrete tests – Part 2: Sampling of freshly mixed concrete. SANS 5861-3, Concrete tests – Part 3: Making and curing of test specimens. SANS 5862-1, Concrete tests – Consistence of freshly mixed concrete – Part 1: Slump test. SANS 5862-2, Concrete tests – Consistence of freshly mixed concrete – Part 2: Flow test. SANS 5863, Concrete tests – Compressive strength of hardened concrete. SANS 5865 (SABS SM 865), Concrete tests – The drilling, preparation, and testing for compressive strength of cores taken from hardened concrete. SANS 6085, Concrete tests – Initial drying shrinkage and wetting expansion of concrete. SANS 6252, Concrete tests – Air content of freshly mixed concrete – Pressure method. SANS 6265, Water – Calcium and magnesium content – Atomic absorption spectrometric method. SANS 10100-1 (SABS 0100-1), The structural use of concrete – Part 1: Design. SANS 10109-2, Concrete floors – Part 2: Finishes to concrete floors. SANS 10144, Detailing of steel reinforcement for concrete. SANS 10155, Accuracy in buildings. SANS 17025/ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories. SANS 50197-1/EN 197-1, Cement – Part 1: Composition, specifications and conformity criteria for common cements. SANS 50450-1/EN 450-1, Fly ash for concrete – Part 1: Definition, specifications and conformity criteria. SANS 50450-2/EN 450-2, Fly ash for concrete – Part 2: Conformity evaluation.

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SANS 50934-2/EN 934-2, Admixtures for concrete, mortar and grout – Part 2: Concrete admixtures – Definitions, requirements, conformity, marking and labelling. SANS 50934-6/EN 934-6, Admixtures for concrete, mortar and grout – Part 6: Sampling, conformity control and evaluation of conformity. SANS 51008/EN 1008, Mixing water for concrete – Specifications for sampling, testing and assessing the suitability of water, including water recovered from processes in the concrete industry, as mixing water for concrete. SANS 53263-1/EN 13263-1, Silica fume for concrete – Part 1: Definitions, requirements and conformity criteria. SANS 53263-2/EN 13263-2, Silica fume for concrete – Part 2: Conformity evaluation. SANS 55167-1/EN 15167-1, Ground granulated blast furnace slag for use in concrete, mortar and grout – Part 1: Definitions, specifications and conformity criteria. 2.2 Other publications Fulton’s Concrete Technology1). Concrete in aggressive ground. Building Research Establishment (BRE), 3rd ed. BRE, 2005. Special Digest 1. Parts 1–42).

3 Terms, definitions and abbreviations For the purposes of this document, the following terms, definitions and abbreviations apply. 3.1 Terms and definitions 3.1.1 General 3.1.1.1 acceptable acceptable to the engineer 3.1.1.2 approved approved by the engineer 3.1.1.3 approved laboratory laboratory accredited by the relevant national body (see foreword) under SANS 17025 for the necessary tests, or laboratory that can demonstrate to the satisfaction of the engineer its ability to carry out the necessary tests and to deliver reliable results 3.1.1.4 cementitious binder common cement that complies with the requirements of SANS 50197-1 or blends of certain types of common cement and cement extenders that comply with the requirements of SANS 55167-1, SANS 50450-1, SANS 50450-2, SANS 50934-6, SANS 53263-1, SANS 53263-2, or SANS 50934-2

1) Available from http://www.tci.org.za 2) Available from www.brebookshop.com

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3.1.1.5 concrete cover characteristic minimum thickness of concrete between the face of the concrete, as cast, and the outer face of reinforcing steel, prestressing steel, or any embedded steel 3.1.1.6 contractor individual or organization that has entered into an agreement to carry out the work specified 3.1.1.7 engineer appropriately qualified and experienced representative appointed by the owner to administer the requirements of a project specification for specific concrete work 3.1.1.8 formwork all temporary aids and material required to support, and to provide the shape of, the concrete in a structure while the concrete is in the fresh state 3.1.1.9 ready-mixed concrete concrete that complies with the relevant requirements of the project specification and as further defined in SANS 878 3.1.2 Weather 3.1.2.1 adverse weather cold weather or a combination of a high ambient temperature, low relative humidity and high wind velocity or driving rain, which may tend to impair the quality of fresh or hardening concrete or otherwise cause hardened concrete to have undesirable properties 3.1.2.2 cold weather weather of which the minimum ambient temperature is 5 °C or less 3.1.2.3 hot weather weather of which the maximum ambient temperature exceeds 30 °C 3.1.3 Conditions of exposure 3.1.3.1 extreme descriptive of concrete surfaces that are exposed to the abrasive action of sea water or very aggressive water NOTE See table 1. 3.1.3.2 moderate descriptive of concrete surfaces that are above ground level and protected against alternately wet and dry conditions caused by water, rain and sea water NOTE See table 1.

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3.1.3.3 severe descriptive of concrete surfaces that are exposed to hard rain and alternately wet and dry conditions NOTE See table 1. 3.1.3.4 very severe descriptive of concrete surfaces that are exposed to aggressive water, sea water spray or a saline atmosphere NOTE See table 1. 3.1.4 Concrete – General characteristics 3.1.4.1 consistence extent (usually measured by slump or flow tests) to which fresh concrete flows or can be deformed 3.1.4.2 grade of concrete identifying number for a particular concrete, which is numerically equal to the characteristic strength at 28 d, expressed in megapascals 3.1.4.3 high-density concrete concrete that has an air-dry density in excess of 2 600 kg/m3 3.1.4.4 low-density concrete concrete intentionally made to have an air-dry density not exceeding 2 000 kg/m3 or concrete produced with air-entraining additives 3.1.4.5 mixed concrete concrete for which the engineer has prescribed the mix proportions 3.1.4.6 normal-density concrete concrete that usually has an air-dry density in the range 2 000 kg/m3 to 2 600 kg/m3 3.1.4.7 precast concrete concrete that consists of units cast and cured in a position other than their final position, and placed in position to form an integral part of the structure 3.1.4.8 strength concrete concrete that is designed primarily for strength considerations and designated by its characteristic strength in conjunction with the maximum nominal size of stone used in its manufacture EXAMPLE 30 MPa/19 mm.

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3.1.4.9 target slump measured value for the slump of concrete at the point of delivery to ensure compliance with the slump specified 3.4.10 workability property of fresh concrete that determines the ease of placing and compacting the concrete without segregation of its constituent materials 3.1.5 Concrete — Strength characteristics 3.1.5.1 characteristic strength value for the compressive strength of concrete, below which not more than 5 % of the valid test results obtained on cubes of concrete of the same grade fall 3.1.5.2 margin difference between target strength and characteristic strength of concrete 3.1.5.3 specified strength characteristic strength required by the engineer 3.1.5.4 target strength mean value of the strength of concrete that is higher than the specified strength, and that is aimed for to ensure that the characteristic strength is attained 3.1.5.5 valid test result mean result obtained from three test cubes of concrete that have been tested in accordance with SANS 5860, SANS 5861-2 and SANS 5863 3.1.6 Prestressing 3.1.6.1 anchorage device used to anchor a tendon to the concrete member 3.1.6.2 bonded tendon prestressing tendon that is bonded to the concrete throughout its effective length, either directly (by being cast into the concrete) or by grouting 3.1.6.3 coating material applied to unbonded tendons to protect them from corrosion, or material applied to either bonded or unbonded tendons to lubricate them during stressing 3.1.6.4 sheathing enclosure in which tendons intended to be post-tensioned are encased, to prevent bonding during concrete placement

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3.1.6.5 tendon assemblage of steel elements used to impart prestress to concrete when the assemblage is tensioned NOTE Examples of steel elements are wires, bars and strands. 3.1.6.6 unbonded tendon tendon that is not bonded to the concrete 3.2 Abbreviations CSF silica fume FA fly ash FACT fines aggregate crushing test GGBS ground-granulated blast-furnace slag

4 Materials for concrete 4.1 Cementitious binder 4.1.1 General 4.1.1.1 The cementitious binder shall be a) a blend of cement that complies with SANS 50197-1 and that has an appropriate proportion cement

extender that complies with SANS 55167-1, SANS 50450-1 and SANS 50450-2 or SANS 50934-6, SANS 53263-2 and SANS 50934-2, or

b) a suitable type of cement that complies with SANS 50197-1 and that has an appropriate proportion

of suitable cement extender, or c) any type of cementitious binder other than those referred to above when so required in terms of the

project specification or when specifically authorized by the engineer. NOTE It is recommended that users of cement extenders consult producers of the extender or appropriate publications of recognized institutions. 4.1.1.2 Cementitious binders for sulfate-resisting concrete shall be chosen in accordance with the procedures given in BRE Special Digest 1 taking into account the factors described in 6.2.3. 4.1.1.3 In the case of concrete exposed in a marine environment, the binder shall contain a cement extender that complies with the requirements of SANS 55167-1, SANS 50450-1 and SANS 50450-2 or SANS 50934-6, SANS 53263-1, SANS 53263-2 and SANS 50934-2, or shall be a blended cement that contains ground slag, fly ash or silica fume which complies with SANS 50197-1. 4.1.1.4 Where there is any danger of a particular combination of cement and aggregate giving rise to a harmful alkali-aggregate reaction, the aggregate shall be tested. Where the result points to such a reaction, either the aggregate or the cementitious binder (or both) shall be replaced so that an acceptable combination may be obtained. The recommendations given in Fulton’s concrete technology shall be followed. Testing shall be conducted as specified by the engineer.

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4.1.1.5 The type of cementitious binder to be used in each part of the structure shall be specified by the engineer, and the cement used in the structure shall correspond to that specified. The type and source of cementitious binder may not be changed during the duration of a contract without the approval of the engineer. 4.1.1.6 Separate storage facilities shall be provided on the site for each type of cementitious binder used and clearly identified. Cementitious binder shall be stored in weatherproof conditions. Cementitious binders shall be stored in such a manner that the oldest binder is used first. Storage of cementitious binder in bulk is permissible provided that the cementitious binder drawn for use is measured by mass and not by volume. Provision shall be made to ensure that different types of cementitious binder are stored in different, clearly marked silos. 4.1.1.7 A cement extender on its own or masonry cement shall not be used as cement for concrete works. 4.1.2 Properties of concrete made with a blend of common cement and cement extenders Generally, as the cement extender content is increased, the early rate of strength development is reduced, particularly at lower temperatures. At ages exceeding 28 d, water-cured ground-granulated blast-furnace slag (GGBS), fly ash (FA) and silica fume (CSF) concretes may show an increase in strength over concretes manufactured with CEM I cements of equivalent 28 d strengths. Provided sufficient GGBS, FA or CSF is incorporated and the concrete is properly cured there is likely to be an increased resistance to some forms of chemical attack and a reduction of the early heat of hydration. 4.2 Water 4.2.1 Water shall be clean and free from injurious amounts of acids, alkalis, chlorides, organic matter and other substances that could impair the strength or durability of concrete or metal embedded in the concrete and shall comply with the requirements of SANS 51008. (It shall be noted that sea water contains injurious amounts of chlorides and alkalis.) 4.2.2 Should the suitability of water be in doubt, particularly in remote areas or where water is derived from sources not normally utilized for domestic purposes, such water shall be tested as specified by the engineer. 4.3 Aggregates 4.3.1 Natural aggregates covered by SANS 1083 4.3.1.1 Normally, both coarse aggregate (stone) and fine aggregate (sand) should comply with the requirements of SANS 1083. 4.3.1.2 Acceptable variations in accordance with the requirements of SANS 1083 in the project specifications shall be clearly specified. NOTE Guidance on the use of aggregates can be obtained from the Cement and Concrete Institute publication, Commentary on SANS 1083.

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4.3.2 Aggregates not covered by SANS 1083 Where aggregates other than those covered by SANS 1083 are to be used, such aggregates and their quality requirements shall be clearly specified. 4.3.3 Nominal maximum size The nominal sizes of coarse aggregate are 37,5 mm; 26,5 mm; 19 mm; 13,2 mm and 9,5 mm. The nominal maximum size of coarse aggregate shall not exceed a) one-quarter of the minimum thickness of the concrete component’s cross section, and b) the specified cover over reinforcement. In elements with closely spaced reinforcement, the use of a nominal size of 9,5 mm or 13,2 mm shall be considered. 4.3.4 Aggregates for high-strength concrete Where high-strength concrete is required, both the source and the type of aggregate may need careful selection, based on results of previous use or of trial mixes, for example the 10 % fines aggregate crushing value (10 % FACT-value) shall exceed 150 kN. 4.3.5 Aggregates and fire resistance It may be necessary to use an aggregate that behaves satisfactorily when exposed to high temperatures, for example, low-density aggregate and certain slag aggregates or igneous rocks. 4.3.6 Use of "plums" In plain concrete of thickness at least 300 mm, hard, clean, stone "plums" of mass 15 kg to 55 kg may, if approved, be used to displace concrete to a maximum of 20 % of the volume of the concrete, provided that a) such "plums" have no adhering films or coatings, b) no "plum" has a minimum dimension of less than 150 mm but shall not exceed 300 mm or one-third

of the smallest dimension of the concrete element, whichever is less, c) each "plum" is surrounded by at least 80 mm of concrete, d) the strength of the rock that makes up the "plums" (as indicated by the aggregate crushing value or

the 10 % fines aggregate crushing test) is at least that specified for coarse aggregate in SANS 1083, and

e) "plums" are clean, durable and inert. 4.3.7 Storage 4.3.7.1 Aggregates of different nominal sizes shall be stored separately and in such a way that a) contamination by foreign matter is prevented, and b) intermixing of aggregates is minimized.

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4.3.7.2 Stockpiles of sand shall be free-draining to ensure a relatively uniform moisture content throughout the stockpile. 4.4 Admixtures 4.4.1 General 4.4.1.1 Admixtures are added to a concrete mix to change certain properties of concrete by their chemical effect or physical effect (or both). In changing certain properties, an admixture can significantly affect other properties, for example, a water-reducing admixture may retard setting times, or an air-entraining agent may reduce the compressive strength of the concrete. 4.4.1.2 Admixtures that may impair the durability of the concrete, or combine with the ingredients to form harmful compounds, or increase the risk of corrosion of the reinforcement shall not be used. When an admixture is used in concrete that is made with any type of cement and that is to contain prestressing tendons, reinforcement and embedded metal, the chloride content of the admixture, expressed as a mass fraction of chloride ions, shall not exceed 2 % of the admixture or 0,03 % of the cementitious binder. 4.4.1.3 Admixtures shall not be used without the approval of the engineer, who may require tests to be conducted before admixtures are used. To facilitate approval, the following information shall be available: a) the trade name of the admixture, its source and the manufacturer's recommended method of use; b) typical dosages and possible detrimental effects of underdosages and overdosages; c) whether compounds likely to cause corrosion of the reinforcement or deterioration of the concrete

(such as those containing chloride in any form as an active ingredient) are present and, if so, the chloride content of admixtures, expressed as a mass fraction of chloride ions or expressed as an equivalent mass fraction of anhydrous calcium chloride; and

d) the mean expected air content of freshly mixed concrete containing an admixture that causes air to

be entrained (see 4.4.1.7) when the admixture is used at the manufacturer's recommended dosage. An air-entraining admixture shall be of such a type and the dosage of sufficient quantity that the air content (see table 2) is maintained at the point of placing. 4.4.1.4 If two or more admixtures are to be used simultaneously in the same concrete mix, all available data shall be used to assess the interaction of the admixtures and to ensure their compatibility. 4.4.1.5 Admixtures used in the work shall be of the same composition as those used in establishing the concrete mix proportions. 4.4.1.6 The effect of an admixture can be highly specific to the combination of ingredients in the mix and its time of addition. It is therefore important that trial mixes be made before an admixture is used in concrete for construction and if any mix ingredient is changed during the course of the project. 4.4.1.7 An air-entraining admixture shall be of such a type and the dosage of sufficient quantity that the air content (see table 2) is maintained at the point of placing. When another admixture (or cement extender) is present in the concrete mix, a different dosage of the air-entraining mixture may be required. The entrainment of air tends to reduce the strength of concrete. Trial mixes should be made to determine the extent of strength reduction, and mix proportions adjusted if necessary.

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4.4.2 Storage Admixtures shall be stored in a manner that will prevent contamination, evaporation or damage. For admixtures used in the form of suspensions or non-stable solutions, agitating equipment shall be provided to ensure thorough distribution of the ingredients. Liquid admixtures shall be protected from temperature changes that would adversely affect their characteristics. 4.5 Deteriorated material Material that has deteriorated or that has been contaminated or otherwise damaged shall not be used in concrete and shall be removed from the site without delay.

5 Plant for concrete 5.1 General The plant for concrete shall be maintained in good working order. 5.2 Batching plant 5.2.1 Regular examination, calibration and tests shall be carried out at frequent intervals that will ensure that the batching system functions effectively and accurately, and that hoppers and cement containers are kept dry and clean. 5.2.2 The batching plant shall be such that the batching accuracy complies with 7.2. 5.2.3 In the case of an automatic plant, the mass batching scales shall be so interlocked that a new batch of materials cannot be delivered until the hoppers have been completely emptied of the previous batch and the scales are in balance. Where the discharge of materials from the hoppers is manually controlled, a method of signalling shall be employed to ensure that ingredients are not omitted, or added more than once, when a batch of concrete is being made up. 5.3 Mixing plant The type and capacity of mixing machines shall be such that the rate of output of concrete is suitable for the rate of concreting. Each machine shall be capable of producing a uniform distribution of the ingredients throughout the batch within the time specified by the manufacturer. Worn or bent blades and paddles shall be replaced. The inner surfaces of the mixer shall be clean and shall have no hardened concrete adhering to them. 5.4 Vibrators Where compaction by vibration is specified, vibrators shall be capable of fully compacting each layer of concrete. It is recommended that at least one standby vibrator be available for every three (or lesser number of) vibrators necessary to maintain the rate of placing.

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6 Proportioning 6.1 Quality of concrete 6.1.1 General Concrete for all parts of the work shall be of the specified quality and capable of being placed and compacted without excessive segregation. When hardened, concrete shall have developed all the properties required by this part of SANS 10100 and by the project specification. The engineer shall ensure that representative samples of the constituent materials of the concrete, together with evidence that they comply with the provisions of clause 4, are supplied for approval in good time before concreting of the works begins. Evidence shall be in the form of a) a statement, from an approved laboratory, of the results of tests, or b) an authoritative and acceptable report or record of the previous use of, and experience with, the

material concerned, or c) a quality certificate from an independent certification body. 6.1.2 Strength 6.1.2.1 Compressive strength The specified compressive strength of concrete shall be based on the 28 d characteristic compressive strength fcu, unless a different test age is specified. 6.1.2.2 Maximum cement content Cement content shall normally not exceed 550 kg/m3 of concrete (see 6.3). 6.1.3 Density For certain purposes, for example to provide radiation shielding, a high-density concrete may have to be specified. These densities are normally achieved by selecting suitable aggregates (see 4.3). 6.1.4 Transportation Unless otherwise dictated by general workability of the concrete, the method of transportation or conditions of placement, or unless otherwise specified by the engineer, slump values for different types of construction should normally not exceed 150 mm for hand-placed concrete and 100 mm for vibrated concrete. 6.1.5 Workability The concrete shall be of such workability that it can be readily compacted into the corners of the formwork and around reinforcement without the materials in the mix segregating.

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6.1.6 Settlement and bleeding The concrete shall be so proportioned with suitable materials that the upward migration of water in compacted fresh concrete is not excessive and that settlement is minimized. The consequences of bleeding and settlement are: a) bleeding and development of voids under coarse aggregate particles and reinforcement; NOTE 1 To assess the bleeding behaviour of concrete, tests such as ASTM C 232 should be used. NOTE 2 Initially, bleeding is accompanied by the settlement of solid particles (i.e. cement and aggregates). b) plastic settlement cracking; and

NOTE Where settlement is prevented by reinforcement or by changes in cross section, differential settlement occurs and cracks and voids are formed in the concrete. This phenomenon is especially troublesome in columns, in T-beams and I-beams, and in beams and slabs with top reinforcement.

c) plastic shrinkage cracking.

NOTE A film of bleed water on the surface of an element such as a slab will prevent or retard plastic shrinkage of the concrete and is therefore beneficial.

Methods of dealing with the detrimental consequences of settlement and bleeding are discussed in 10.3.8. 6.1.7 Chloride content The presence of chloride ions in concrete increases the risk of corrosion of embedded metal. Chlorides could be present in concrete as a result of inclusion in the raw materials (see SANS 374). To minimize the chloride content in reinforced or prestressed concrete a) the chloride content of the mixing water shall not exceed 500 mg/L (sea water shall not be permitted

as mixing water), b) calcium chloride and chemical admixtures that contain chlorides in excess of that given in 4.4.1.2

shall not be permitted, c) the chloride content of fine aggregate obtained from river estuaries, the sea or other sources likely

to be contaminated by chlorides shall not exceed the limiting values given in SANS 1083, d) for reinforced concrete the chloride content of the concrete shall not exceed 0,2 % by mass of

cementitious material where the concrete might be exposed to additional chloride ingress from external sources, or 0,4 % where there is no possibility of additional chloride contamination, and

e) for prestressed concrete the chloride content of the concrete shall not exceed 0,2 % by mass of

cementitious material under all conditions. 6.1.8 Sulfates in concrete Although sulfates are present in most cements and in some aggregates, excessive amounts of sulfate in mix constituents can cause expansion and disruption of concrete. To prevent this, the total acid-soluble sulfate content of the concrete mix, expressed as SO3, shall not exceed a mass fraction of 4 %, of the cementitious binder in the mix. The sulfate content shall be determined in accordance with SANS 5213 and be calculated as the total from the various constituents of the mix.

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6.1.9 Alkali-silica reaction 6.1.9.1 Some aggregates containing particular varieties of silica may be susceptible to attack by alkalis (Na2O and K2O) originating from the cement or other sources, producing an expansive reaction that can cause cracking and disruption of the concrete. This is likely to happen only when all of the following are present together: a) environmental conditions that will promote the reaction, i.e. internal relative humidity greater than

75 %; b) a sufficiently high alkalinity of the pore solution; and c) a sufficient amount of deleteriously reactive minerals in the aggregate. The total alkali-content (Na2O-equivalent) of concrete shall be limited to 0,6 % taking into account the degree of reactivity of the aggregate. In this regard the recommendations in Fulton’s concrete technology shall be adhered to. 6.1.9.2 Either use a blend of common cement that complies with SANS 50197-1 and cement extenders, or use selected common cements that comply with SANS 50197-1 such that at least 40 % of GGBS or 20 % of FA or 10 % of CSF, by mass, of the binder is introduced in the mix. Where used as separate ingredients at the mixer, extenders shall comply with SANS 55167-1, SANS 50450-1 and SANS 50450-2 or SANS 50934-6, SANS 53263-1, SANS 53263-2, and SANS 50934-2. 6.1.10 Drying shrinkage All concretes shrink when they dry out after the cessation of moist curing. Where this shrinkage is restrained, tensile stresses develop and may cause cracking or curling (or both). The concrete shrinkage shall be determined in accordance with SANS 6085. Factors in the proportioning of concrete that influence shrinkage are a) water content, b) paste content, and c) properties of aggregates. 6.2 Durability 6.2.1 General 6.2.1.1 Ability Durability may be defined as the ability of the material or structure to withstand the service conditions for which it was designed without significant deterioration. 6.2.1.2 Impermeability One of the main characteristics that enhances the durability of any concrete is its impermeability. Suitable impermeability is achieved with normal-density aggregates if there is a sufficiently low water content, water/binder ratio, complete compaction of the concrete, and sufficient hydration of the binder through proper curing methods.

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6.2.1.3 Binder content The binder in the concrete is the component most vulnerable to attack by aggressive substances and thus the binder type and content of the concrete will determine the degree of resistance of the concrete to attack by such substances. 6.2.1.4 Detailing Since many processes of deterioration of concrete occur only in the presence of free water, the details of shape and design of exposed structural elements shall be such as to promote good drainage of water and to prevent standing pools. The minimum cover to reinforcement to comply with the durability requirements for normal-density concrete and low-density concrete are given in 8.2. 6.2.2 Conditions of exposure The conditions of exposure (see 3.1.3) are described in table 1.

Table 1 — Conditions of exposure

1 2

Condition of exposure Description of member or surface to which the cover applies

Moderatea

1 Surfaces protected by the superstructure, namely the sides of beams and the undersides of slabs and other surfaces not likely to be moistened by condensation

2 Surfaces protected by a waterproof cover or permanent formwork not likely to be subjected to weathering or corrosion

3 Enclosed surfaces 4 Structures or members permanently submerged 5 Limited structures of the relevant national body (see foreword): i) Surfaces of precast elements not in contact with soil ii) Surfaces protected by permanent formwork not likely to be subjected to

weathering or corrosion iii) Surfaces in contact with ballast iv) All other surfaces

Severe

1 All exposed surfaces 2 Surfaces on which condensation takes place 3 Surfaces in contact with soil 4 Surfaces permanently under running water 5 Structures of the relevant national body (see foreword): i) Surfaces of precast elements not in contact with soil ii) Surfaces protected by permanent formwork not likely to be subjected to

weathering or corrosion iii) Surfaces in contact with ballast iv) All other surfaces 6 Cast in-situ piles: i) Wet cast against casing ii) Wet cast against soil iii) Dry cast against soil

Very severe 1 All exposed surfaces of structures within 30 km from the sea 2 Surfaces in rivers polluted by industries 3 Cast in-situ piles, wet cast against casings

Extreme 1 Surfaces in contact with sea water of industrially polluted water 2 Surfaces in contact with marshy conditions

a Concrete exposed to mild conditions: The specified strength shall be determined by structural design considerations. If the concrete is to include embedded metal, the characteristic strength shall not be less than 20 MPa. There is no requirement for a maximum water/cement ratio or for minimum cement content.

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6.2.3 Exposure to freezing and thawing 6.2.3.1 Normal-density concrete that is likely to be subjected to freezing and thawing under wet conditions shall contain entrained air and shall conform to the air-content limits given in table 2 as determined in accordance with SANS 6252.

Table 2 ― Total air content for various sizes of coarse aggregate for normal-density concrete

1 2

Nominal maximum size of coarse aggregate

Total air content by volume

mm %

9,5 13,2

19 37,5

6-10 5-9 4-8 3-6

The water/binder ratio shall be not more than 0,53 by mass. 6.2.3.2 Low-density concrete that is likely to be subjected to freezing and thawing shall contain (6 ± 2) % total air when the nominal maximum size of aggregate exceeds 9,5 mm, or (7 ± 2) % total air when the nominal maximum size is 9,5 mm or less. Proportions shall be so selected that a characteristic strength fcu of 20 MPa or more is attained. 6.2.4 Exposure to aggressive chemicals 6.2.4.1 General Deterioration of concrete by chemical attack can occur by contact with gases or solutions of many chemicals, but is generally the result of exposure to acidic solutions or to solutions of sulfate salts. Concrete made with common cement is not recommended in persistently acidic conditions (with a pH value of 5,5 or less). Solutions of naturally occurring sulfates of sodium, potassium, calcium or magnesium, as may be present in some soils and groundwater, can cause expansion and disruption of concrete. The presence of specific chemical substances shall be determined in accordance with SANS 163-1, SANS 374, SANS 5213, SANS 5217, SANS 5218 or SANS 6265. In extreme conditions, some form of approved protective coating shall be used to prevent access by deleterious solutions. Corrosive attack by water is one of the most serious conditions of exposure. All the materials found in concrete are to some extent soluble in water. The aggregates normally used are generally more resistant to attack than is the cementitious binder, which is the most vulnerable constituent owing to its greater chemical activity. (Steel reinforcement is also susceptible, if embedded in a pervious concrete or if corrosive attack on an initially impervious concrete has reached a relatively advanced stage and the corrosive agents have penetrated to the depth where reinforcement is embedded.) The two properties of water that contribute most towards its high corrosiveness are the following: a) water is an extremely effective solvent; and

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b) water is able to dissociate dissolved salts and enable them to participate in ion-exchange and non-

addition reactions. The corrosiveness of water depends on the rate of dissolution of concrete in the water, which is influenced by the factors given in 6.2.4.2 to 6.2.4.6. 6.2.4.2 Concentration gradient between the solid phase (concrete) and the liquid phase (water) In the case of concrete wetted by water, the concentration of calcium compounds in the concrete is usually much higher than that of these compounds in the water. In the case of distilled or very soft water, the concentration of dissolved calcium salts in the water is almost zero and the concentration gradient becomes very large. The resultant dissolution rate can consequently be very high and rapid attack will take place. It is this mechanism that is responsible for the extremely aggressive behaviour of distilled water and very soft water towards concrete, which can result in the rapid leaching-out of the components of the concrete, especially calcium hydroxide, the presence of which is essential for maintaining the integrity of the binder. On the other hand, where water already contains a high concentration of the compounds present in the concrete, the concentration gradient is lower and can disappear when saturation of the aqueous phase is achieved. 6.2.4.3 Acidity of the water The materials normally found in concrete have a higher solubility in acidic water than in alkaline water. The acidity of water shall be determined in accordance with SANS 5011. 6.2.4.4 Temperature of the water Warm water is usually more aggressive than cold water. 6.2.4.5 Movement of the water relative to the concrete Corrosion rates proceed much more rapidly if the water is in motion and the interface layer is constantly replenished. (Thus wave movements in tidal zones or turbulent flow in pipelines are accelerating agents by virtue of their effective mixing action.) 6.2.4.6 Presence of dissolved gases The presence of dissolved gases is required for certain corrosion reactions to proceed and the concentration of the gases in the water influences the corrosion rate. In the case of many concrete structures in contact with water, the water level is variable and certain areas of the concrete are subjected to cycles of wet and dry conditions. The following factors can influence the corrosion rate in such areas: a) Enhanced concentration of dissolved salts: If the water level drops, previously wetted areas dry off

as a result of evaporation of the surface layer of water. Any salts present in this layer become more and more concentrated as evaporation proceeds and eventually crystallize out of solution.

b) Exposure to gases present in the atmosphere: In heavily polluted industrial atmospheres, gases

may be significant corrosion accelerators.

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6.2.5 Exposure to salt-laden air In coastal environments, concrete structures are exposed to wind-driven, salt-laden air. When a critical concentration of free chlorides is reached, depassivation of the reinforcement could occur, leading to corrosion and to subsequent spalling of the concrete. Salts that enter the pore structure of the surface concrete could also crystallize on drying. This process causes surface damage, allowing the rate of chloride ingress to increase. The degree of aggressiveness of a coastal environment depends on the salt content of the air and the atmospheric relative humidity. In areas where the salt content and relative humidity of the air are high, it may be necessary to undertake protective measures similar to those for concretes in marine environments. EN 206 or BS 8500 (parts 1 and 2) provides detailed guidance on how to deal with concrete exposed tosuch salt-laden air. 6.2.6 Exposure to corrosive fumes The deterioration of concrete as a result of exposure to corrosive fumes (with a pH value of less than 5) is usually associated with a high relative-humidity environment, which presents a special case of concrete deterioration caused by aggressive water. Corrosive fumes are often characterized by a high concentration of corroders. Special protection measures are usually required for the concrete. Depending on the degree of aggressiveness of the fumes, protective measures could range from the provision of a high-strength, low-permeability concrete to the application of a chemically-resistant barrier to isolate the concrete from the aggressive fumes. A careful assessment of the degree of aggressiveness of the fumes, together with specialist advice, is essential in determining the most effective protection method. 6.2.7 Exposure to polluted air The deterioration of concrete in heavily polluted industrial areas is caused by a number of mechanisms, depending on the nature of the atmospheric pollutant. For example, in areas around coal-burning power stations where the emission of carbon dioxide and sulfates results in the precipitation of acid rain. Both acid attack and sulfate attack could cause concrete deterioration. NOTE Additional information can be obtained from publications given in the bibliography. 6.3 Mix proportions A cementitious binder content in excess of 550 kg/m3 of concrete is high and should normally not be used because such a cement content tends to make concrete sticky and difficult to handle, place and compact. NOTE Additional information can be obtained from publications given in the bibliography.

7 Production of concrete 7.1 General Where concrete is delivered to the site ready mixed, the requirements of SANS 878 shall apply.

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7.2 Batching 7.2.1 Cement The mass of cement in a standard sack is 50 kg. All cement taken from bulk storage containers and from partially emptied bags shall be batched by mass to an accuracy of 2 % (or better) of the mass required. 7.2.2 Water Mixing water for each batch shall be measured either by mass or by volume and the amount of water adjusted to allow for the moisture content of the aggregates. The true quantity shall be measured to an accuracy of 2 % (or better). 7.2.3 Aggregates If batching is by mass, the mass of the aggregates of each size shall be measured and a correction made for the moisture content of the aggregates. The true mass shall be measured to an accuracy of 3 % (or better). If batching is by volume, the fine and coarse aggregates shall be measured separately in suitable measuring boxes of known volume and of such capacity that the quantities of aggregates for each batch are suitable for direct transfer into the mixer. Bulking tests on the fine aggregate (or moisture determination if the relation between bulking and moisture content of the specific fine aggregate is known) shall be conducted at least daily (in accordance with SANS 5856) and the results used to adjust the batch volume of fine aggregate to give the true volume required. Additional tests for bulking shall be carried out after rain has fallen or if there has been any other reason for variation in the moisture content of the aggregate. 7.2.4 Admixtures The amount of admixture to be used shall be measured to an accuracy of 2 % to 5 %. The measuring device shall be cleaned frequently. 7.2.5 Equipment All equipment shall be checked regularly and calibrated or approved at least once a year by a competent external agency, which can show traceability to national standards. 7.3 Mixing 7.3.1 General 7.3.1.1 Mixing of materials for concrete shall be conducted by an experienced operator. 7.3.1.2 The total volume of material per batch shall not exceed the rated capacity of the mixer. 7.3.1.3 Concrete shall only be mixed in quantities required for immediate use. Concrete that has set shall be discarded. In the event of delay in the concreting operations, concrete may be retained in the mixer for a maximum period of 2 h, provided that, subject to the requirements of 7.3.3 on the water/cement ratio, and by taking down the actual amount added, only just enough water is added to the mixer to maintain the target slump. During this time, the mixer shall be restarted and run for about 2 min every 15 min. The period of 2 h shall be reduced if the ambient temperature, or any other factor, tends to produce early setting. Alternatively, if concrete is being cast under cold conditions, this time may be extended. (See also 10.2.)

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7.3.1.4 At the start of each concrete production run and before any concrete is mixed, the inner surfaces of the mixer shall be cleaned and all hardened concrete removed. Sand, cement and water, proportioned as for the concrete to be made, shall then be introduced into the cleaned mixer in sufficient quantities to cover the entire inside surface of the mixer. The mixer shall then be operated (to mix these materials and to coat the interior surfaces of the mixer with the mixture) and discharged immediately before charging of the mixer with the first batch. 7.3.1.5 Instructions for the sequence of charging the particular mixer shall be given before operations begin. Control systems shall be introduced to ensure that the batch is not discharged until the required mixing time has elapsed. At least three-quarters of the required mixing time shall take place after the last of the mixing water has been added. 7.3.1.6 The period of mixing shall be measured from the time when all the materials are in the drum or pan, to the start of discharge and shall be such as to ensure that all the constituents are thoroughly mixed. 7.3.1.7 The mixed concrete shall be so discharged that there is no significant segregation of the materials in the mix. 7.3.2 Control of admixtures 7.3.2.1 Chemical admixtures shall be charged into the mixer as solutions, and shall be measured by means of an acceptable dispensing device. Admixtures that cannot be added in solutions may be weighed or may be measured by volume if so recommended by the manufacturer. 7.3.2.2 If two or more admixtures are used in the concrete, they shall be added separately to avoid possible interaction that could interfere with the effectiveness of either admixture or that could adversely affect the concrete. 7.3.3 Tempering and control of mixing water When concrete delivered at the place of operation has a slump below that suitable for placing, as indicated by the project specifications, water may be added, provided that the water/cement ratio is not increased to above the maximum limit permissible for strength and durability and the maximum slump is not exceeded. The water shall be incorporated by additional mixing equal to at least half of the total mixing time required. Any addition of water in excess of that permitted by the limitation on the water/cement ratio shall be accompanied by a quantity of cement sufficient to maintain the proper water/cement ratio. The approval of the engineer (or his/her representative) for such addition shall be obtained before the water is added. 7.3.4 Adverse weather 7.3.4.1 Cold weather Concrete shall not be placed during falling temperatures when the ambient temperature is below 7 °C. When the concrete is placed at ambient temperatures below 5 °C, appropriate precautions shall be taken to protect the concrete (see 10.8.3). Under these conditions the required concrete temperature from the time of mixing until the concrete has hardened (see 10.8.3) may be obtained in several ways, such as by: a) heating the mixing water and the aggregate (cement shall not be mixed with mixtures of water and

aggregate at temperatures exceeding 60 °C); b) using a cement that hardens more rapidly; or c) incorporating an accelerator (chloride-free accelerators shall be used when the concrete contains

reinforcement or other embedded metal).

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7.3.4.2 Hot weather When the temperature of the fresh concrete is likely to exceed the permissible maximum of 35 °C during hot weather conditions as defined in 10.8.2, the concrete temperature can be limited by a) using cement extenders, b) minimizing the cement content, c) avoiding the use of rapid hardening cement, d) using the largest size coarse aggregate that is practical, e) cooling the aggregates, for example by shading the stockpiles and by wetting the stone to cause

evaporative cooling, f) cooling the mixing water or substituting flaked or well-crushed ice for part or all of the mixing water

but the ice particles have to be small enough to melt completely during the mixing process, g) injecting liquid nitrogen into the mix during mixing, or h) avoiding placing delays. 7.4 Transportation The mixed concrete shall be discharged from the mixer and transported as rapidly as practicable to its final position by means that will prevent segregation, contamination, loss of ingredients and ingress of foreign matter or water and that will maintain the required workability at the point of placing. Concrete may only be conveyed through pipes made with materials that are non-reactive with cement. Aluminium pipes shall be suitably protected. The capacity of conveying equipment shall be sufficient to ensure that placed concrete does not set before adjacent concrete of the same pour is placed. Conveying equipment shall be cleaned at the end of each operation or work day.

8 Reinforcement 8.1 General Reinforcement shall comply with the relevant requirements of SANS 282, SANS 920 and SANS 1024. NOTE See also the relevant section of SANS 10100-1. 8.2 Cover to reinforcement The minimum cover to reinforcement shall be clearly indicated on all reinforcing drawings. The characteristic minimum cover to reinforcement for normal-density concrete and low-density concrete is given in table 3 for various conditions of exposure (see 3.3). Detailing of reinforcement shall allow for fire resistance (see SANS 10100-1), dimensional tolerances in cutting, bending and fixing of reinforcement (see SANS 10144), and permissible deviations in dimensions of concrete work (see SANS 10155). NOTE Additional information can be obtained from publications given in the bibliography.

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Table 3 — Concrete cover of outermost reinforcement

1 2 3 4 5 6 7

Condition of exposure

Description of member/surface to which the cover applies

Class of concrete

20 25 30 40 50

Characteristic minimum covermm

Moderate

1.1 Surfaces protected by the superstructure, such as the sides of beams and the undersides of slabs and other surfaces not likely to be moistened by condensation

1.2 Surfaces protected by a waterproof cover or permanent formwork not likely to be subjected to weathering or corrosion

1.3 Enclosed surfaces 1.4 Structures or members that are permanently

submerged in water

50

45 40 30

25

Severe

2.1 All exposed surfaces 2.2 Surfaces on which condensation takes place 2.3 Surfaces in contact with soil 2.4 Surfaces permanently under running water

NA 50 45 40 35

2.5 Cast in-situ piles: i) Wet cast against casing ii) Wet cast against soil iii) Dry cast against soil

50 75 75

50 75 75

50 75 75

50 75 75

50 75 75

Very severe

3.1 All exposed surfaces of structures within 30 km from the sea

3.2 Surfaces in rivers polluted by industries 3.3 Cast in situ piles, wet cast against casings

NA NA NA

NA NA NA

NA NA NA

60 60 80

50 50 80

Extreme 4.1 Surfaces in contact with sea water or industrially

polluted water 4.2 Surfaces in contact with marshy conditions

NA NA NA 65 65

NOTE 1 The cover values are characteristic minimum cover values and not more than 5 % of cover measurements should fall below these values. In addition, no single cover measurement should fall below 5 mm less than the relevant cover value indicated above. NOTE 2 In uncracked concrete the degree of protection that the concrete affords the reinforcing steel depends on the quality and thickness of the cover. Apart from the class of the concrete, the quality of the cover will among other things be affected by the method and duration of curing and the type of binder used, for example well-cured fly ash concrete without extenders. If the quality of the cover can be proven to be satisfactory to the requirements of the engineer, by for example using improved curing techniques or extended cement, the requirements in table 3 can be relaxed at the discretion of the engineer. For additional information see 2.2 and the bibliography. NOTE 3 NA = Not applicable.

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8.3 Bending 8.3.1 General The following provisions shall apply: a) all reinforcement shall be bent to the dimensions shown on the drawings and in accordance with the

requirements of SANS 282; b) all reinforcement shall be bent cold unless otherwise permitted (see 8.3.2); c) bending shall be carried out slowly, using a steady, even pressure without jerk or impact; d) it is permissible to bend grade 250 reinforcement protruding from concrete elements, provided that

care is taken to ensure that the radius of bend is not less than that specified in SANS 282. After arrival on site, 450 MPa bars shall not be bent, rebent or straightened without the engineer's approval; and

e) where it is necessary to reshape steel previously bent, this shall only be done with the engineer's

approval and each bar shall be inspected for signs of fracture. 8.3.2 Preheating before bending or straightening No preheating of bars is permitted without the express permission of the engineer who shall supply the appropriate specification and procedure with which to do this, provided that the bars do not depend on cold working for their strength. In such cases, the engineer may permit bars to be bent or straightened hot, subject to the following provisions: a) the preheating procedure shall be such as not to harm the bar material (or to cause damage to the

concrete in the case of bars already cast in); b) the preheat shall be applied to a length of bar equal to at least five bar diameters in each direction

from the centre of the bend. The temperature of the bar at the concrete interface shall not exceed 260 °C;

c) the preheat temperature shall not exceed 650 °C; d) the preheat temperature shall be maintained until bending or straightening is complete; and e) heated bars shall be cooled slowly in air. (Hot bars shall not be quenched with water.) 8.4 Fixing 8.4.1 General The grade of accuracy for the cover over reinforcement shall comply with the requirements of SANS 2001-CC1. Reinforcement shall not be subjected to mechanical damage, rough handling, dropping from a height, or shock loading.

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8.4.2 Steel reinforcement 8.4.2.1 All reinforcement, at the time of placing of the concrete, shall be free from rust, scale, oil and other coatings that may reduce the bond between the steel and surrounding concrete, or initiate corrosion of the reinforcement. The reinforcement shall not be contaminated by any substance used as a release agent for the formwork. All reinforcement shall be well and cleanly rolled. Rust, seams, surface irregularities and mill scale shall not be cause for rejection, provided that the mass per metre, dimensions, cross-sectional area and tensile properties of a test specimen comply with the applicable requirements for the specified bar. 8.4.2.2 Reinforcement shall be placed as shown on the drawings and shall be maintained in that position within the specified tolerances. Reinforcement shall be tied with annealed wire of diameter 1,6 mm or 1,25 mm or by acceptable clips, at sufficient intersections to avoid displacement of bars. It may also similarly be secured by welding if permitted by the engineer. Reinforcement shall be supported in its correct position by hangers or saddles, and aligned by means of chairs and spacers of approved design. The chairs shall be suitably robust, and fixed securely to retain the critical position of the reinforcement. The strength and design of reinforcing supports shall take into account, amongst others, temporary loads such as the mass of workmen and wet concrete, and forces caused by vibrators and other methods of compacting the concrete. Spacers required for ensuring that the specified cover is obtained shall be of an acceptable material, shape and design. Spacers shall be durable, shall not lead to corrosion of the reinforcement and shall not cause spalling of the concrete cover. Concrete spacer blocks made on the construction site shall not be used unless they are made and cured under strictly controlled conditions in accordance with the engineer’s instructions. Spacers and chairs shall be placed at the spacing recommended in SANS 10144. 8.4.2.3 The clear distance between reinforcing bars shall be determined in accordance with SANS 10100-1. 8.4.2.4 In the detailing and dimensioning of bars (in particular bends, hooks and stirrups), the designer shall take into account the diameters of all the bars intersecting at any point, the sweep or curve of bends, the need for the use of ties to fix steel, the shuttering and reinforcement tolerances, the cover specified for various exposure conditions and the tolerances permitted for the fabrication of reinforcement and erection of formwork. The concrete cover specified is equally applicable to the upper layer of reinforcing steel in floors and slabs. For any slab, cognizance shall be taken of the specified concrete cover, and the detail dimensions and diagrams of the reinforcing bars to which the steel is to be bent shall be such that the specified concrete cover can be achieved. 8.4.2.5 The design of the laps and the lengths of main bars in vertical reinforcement shall be such as to suit the position of construction joints shown on the drawings or as specified. It is particularly important that where a kicker or starter stub for a wall is specified or shown on the drawings or will be permitted, the lap in the vertical reinforcement start above the kicker. A lap shall not start below a joint at the top of a kicker and shall not finish above it. 8.4.2.6 Templates shall be furnished for placement of all column dowels, unless otherwise permitted. 8.4.2.7 Welded wire fabric for slabs on grade shall extend to within 100 mm of the concrete edge. Welded wire fabric shall be adequately supported during the placing of the concrete, to assure proper positioning in the slab.

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8.4.2.8 Where exposed aggregate, ribbed or patterned finishes are to be achieved, the detail dimensions of reinforcing bars shall be such that the specified concrete cover can be maintained after the texture, ribbing or pattern is applied. NOTE The contractor cannot provide the specified cover unless the outside dimensions of reinforcement cages and the like provide for greater cover than would be provided for plain finishes of concrete. 8.4.2.9 Supporting steel shall be included in the reinforcing schedule by the engineer. The use of other supporting materials is subject to the approval of the engineer. 8.4.2.10 Laps and joints of reinforcing bars shall be formed only as and where shown on the drawings or as approved by the engineer. Bars left exposed for bonding of future extensions to the structure shall be well protected from corrosion, using suitable means. Laps shall be constructed in such a way that the cover is not reduced below the limits specified. 8.4.2.11 Reinforcement in elements cast on the ground shall rest on precast concrete blocks at least 100 mm square, and having a compressive strength at least equal to the specified compressive strength of the concrete being placed. Other means of support may be used, if approved by the engineer. 8.4.3 Zinc-coated (galvanized) reinforcement Zinc-coated reinforcing bars supported away from formwork shall rest on zinc-coated wire bar supports or on wire bar supports made of dielectric material or other acceptable materials. All other reinforcement and embedded steel items in contact with zinc-coated reinforcing bars, or within a minimum clear distance of 50 mm from zinc-coated reinforcing bars, shall be zinc-coated, unless otherwise approved. Zinc-coated reinforcing bars shall be fixed with zinc-coated tie wire or non-metallic-coated tie wire or other acceptable material. 8.4.4 Epoxy-coated reinforcement Epoxy-coated reinforcing bars supported away from formwork shall rest on epoxy-coated wire bar supports, or on bar supports made of dielectric material or other acceptable materials. Wire bar supports shall be coated with dielectric material for a minimum distance of 50 mm from the point of contact with the epoxy-coated reinforcing bars. All reinforcing bars used as support bars or as spreader bars shall be epoxy-coated or coated with dielectric material. Epoxy-coated reinforcing bars shall be fastened with nylon-coated, epoxy-coated or plastics-coated tie wire, or with other acceptable materials. Epoxy coating shall be free of damage due to pin-holes and handling. 8.5 Welding 8.5.1 General Generally, all welding should be carried out under controlled conditions in a factory or workshop and welding on site should be avoided if possible. Welding on site may be undertaken when required and permitted by the engineer, provided that suitable safeguards and techniques are employed and the types of steel (including high-yield steels in accordance with SANS 920) have the required welding properties. Such welding should follow the procedure supplied by the engineer. The competence of the operators shall be demonstrated before, and periodically during, welding operations.

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8.5.2 Use of welding Welding may be used for a) fixing in position, for example, by welding between crossing or lapping reinforcement, or between

bars and other steel elements (metal-arc welding or electric-resistance welding may be used on suitable steels), or

b) structural welds that involve the transfer of load between reinforcement or between bars and other

steel elements. Butt welds may be carried out by flash-butt welding or metal-arc welding. For lapped joints, metal-arc welding or electric resistance welding may be used. 8.5.3 Types of welding 8.5.3.1 Flash-butt welding Flash-butt welding shall be carried out with the correct combination of flashing, heating, upsetting and annealing, and with the use of only those machines that automatically control this cycle of operations. 8.5.3.2 Metal-arc welding Metal-arc welding of reinforcement shall be carried out in accordance with the recommendations of the reinforcement manufacturer, as approved by the engineer. 8.5.3.3 Electric resistance welding Electric resistance welding is done by the use of welding machines that can be adequately controlled, but that require the correct preparation of the bars to be welded. 8.5.3.4 Other methods Other methods of welding may be used, subject to their satisfactory performance in trial joints. 8.5.4 Location of welded joints Structural welds shall not occur at bends in reinforcement. Unless otherwise agreed by the engineer, joints in parallel bars of the principal tensile reinforcement shall be staggered in the longitudinal direction. For joints to be regarded as staggered, the distance between them shall be at least equal to the end anchorage length for the bar. Laps shall be constructed in such a way that the cover is not reduced below that which is specified. 8.5.5 Strength of structural welded joints The strength of all structural welded joints shall be assessed by means of testing trial joints. 8.5.6 Welded lapped joints The length of run deposited in a single pass shall not exceed five times the diameter of the bar. If a longer length of weld is required, it shall be divided into sections and the space between runs shall be at least five times the diameter of the bar.

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9 Formwork 9.1 General 9.1.1 Materials that have a deleterious effect on concrete (for example untreated timber) shall not be used for formwork. 9.1.2 Forms shall have sufficient strength to withstand the pressure resulting from placement and compaction of the concrete and shall have sufficient rigidity to maintain the specified tolerances, the required shapes, finishes, positions, levels and dimensions shown on the drawings. 9.1.3 Tolerances shall comply with the relevant requirements of SANS 10155. 9.1.4 Forms shall be sufficiently tight to prevent loss of grout. 9.1.5 The formwork shall be capable of being dismantled and removed from the cast concrete without shock, disturbance or damage to the concrete. 9.1.6 Earth cuts shall not be used as forms for vertical surfaces, unless permitted or unless so required. 9.1.7 Shop drawings for formwork, including the location of shoring and reshoring, shall be submitted for review as required by the contract documents. 9.1.8 Where formwork is to be erected over a road, a street or a railway, the formwork shall be so designed that the full clearances required for the free movement of traffic are maintained to the satisfaction of the authority controlling such road, street or railway. It is recommended that, before erection is started, the approval of such authority be obtained for the design of the formwork. 9.2 Design and construction of formwork 9.2.1 Loads The forms shall be designed to withstand the worst combination of self-mass, wet concrete mass, concrete pressure, construction loads and wind loads, together with all incidental dynamic effects caused by placing and compacting the concrete. 9.2.2 Deflection To maintain the specified tolerances, the formwork shall be cambered to compensate for anticipated deflections in the formwork before hardening of the concrete. 9.2.3 Form accessories NOTE Requirements for spacers are given in 8.4. Form accessories such as ties and hangers shall be of a commercially manufactured type. Non-fabricated wire shall not be used. Form ties and spacers left in situ shall not impair the desired appearance or durability of the structure, for example by causing spalling or rust staining or by allowing the passage of moisture. After the ends or end fasteners of form ties have been removed, any embedded portion of the tie shall terminate at a distance of not less than the specified minimum cover from the formed surface of the concrete.

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Runways for moving equipment during concreting shall be provided with struts and legs, shall be supported directly on the formwork or structural member, and shall not rest on the reinforcing steel. 9.2.4 Temporary openings Temporary openings shall be provided at the base of column forms and wall forms and at other points where necessary to facilitate cleaning and observation immediately before concrete is placed. Subsequently, the openings shall be so closed as to provide the finish specified and to conform to the applicable tolerances given. 9.3 Preparation of formwork All matter that could contaminate the concrete, including rubble and dust, shall be removed from the interior of the forms before the concrete is placed. Surfaces that are to be in contact with fresh (wet) concrete shall be clean and covered with an acceptable coating material that will effectively prevent absorption of moisture, will prevent bond with the concrete, and will not stain the concrete surfaces. A mineral oil or other approved material may be used. 9.4 Reuse of formwork Before reuse, all formwork shall be reconditioned, and all form surfaces that are to be in contact with the concrete shall be thoroughly clean. 9.5 Removal of formwork and falsework 9.5.1 General 9.5.1.1 Falsework and formwork shall not be removed until the concrete has reached the acceptable strength to a) resist damage to surfaces during the striking, b) support its own mass and any other actions imposed on the concrete member at that stage, c) avoid deflections beyond the specified tolerances due to the elastic and inelastic (creep) behaviour

of the concrete, and d) avoid cracking beyond specified tolerances. 9.5.1.2 Where formwork is part of the curing system, the time of its removal shall be taken into account in accordance with the requirements of 10.8. The determination of minimum formwork striking times is conducted in the following two stages: a) determine the appropriate criterion for striking; and b) determine when the structure has satisfied the criterion in (a). In all cases it is the engineer’s responsibility to indicate the strength at which the formwork and falsework for the concrete can safely be struck, and the contractor’s responsibility to prove that the in-situ concrete has reached the acceptable strength before striking.

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It may be possible to reduce striking times by using accelerated curing methods or concrete with high early strength and such proposals may be considered where appropriate. When considering such proposals the engineer should take into account the mix proportions, including the binder type and content, proposed for the concrete, and the effect of these proportions on concrete properties such as setting time, heat development, shrinkage and stiffness, and the effect of these properties on the structure as a whole. Low temperatures may depress the rate of strength gain. 9.5.2 Striking 9.5.2.1 Only safety aspects are covered for the striking of the beam and soffit formwork. No provisions are made for the serviceability criteria. The strength at which the formwork may be removed shall be determined by the engineer by assessing the proportion of the total design load on the structure at the time of striking. All relevant loads including self-weight of formwork, loads due to construction operations and, where there are several other levels of construction, additional loads that may require support need to be taken into account. To calculate the characteristic strength required by cubes of equal maturity to the structure before soffit formwork can be struck, it is necessary to analyse the structure for moment, bond, shear, deflection, cracking, etc. as given in SANS 10100-1. 9.5.2.2 For the striking of the vertical formwork the time is the greatest of the values derived from consideration of the following: a) strength required to withstand wind load; b) striking time to avoid early thermal contraction cracking; and c) a minimum in-situ cube strength, fmin, of 2 MPa is required to resist mechanical damage caused by

removal of shutters. 9.5.2.3 Striking shall be done in a manner that will not subject the structure to impact, overload or damage. Sudden removal of wedges could be the equivalent of an impact load on the partially hardened concrete. 9.5.3 Releasing of loads The loads on falsework shall be released in a sequence that ensures that other falsework members are not subject to excessive loads. The stability of falsework and formwork shall be maintained when loads are released and during dismantling. 9.5.4 Propping The procedure for propping or re-propping, when used to reduce the effects of the initial load, subsequent loading or to avoid excessive deflections (or both), should be detailed in a method statement for approval by the engineer. 9.5.5 Curing If formwork is part of the curing system, adequate curing should be provided after its removal. 9.5.6 Strength estimation 9.5.6.1 Methodologies to be used to obtain an estimate of the strength of the concrete in the structure are given in 9.5.6.2.

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9.5.6.2 To determine the strength of concrete in the structure the following test methods may be used: a) Lok-tests. b) Capo tests. c) In-situ maturity measurements. d) Compressive strength tests on cubes made on site and stored under conditions simulating field

conditions. Cubes cured alongside the structure generally have a lower maturity than the in-situ concrete due to the effect of section size and formwork insulation, and will generally give conservative estimates. In all cases it is important to protect the cubes to ensure that field conditions, and especially temperature, are properly simulated.

e) Compressive strength tests on temperature-matched cubes. f) Any method for which confidence in the strength predictions has been established. Strength measurements need to be converted to characteristic strength of cubes of equal maturity as in-situ concrete. Specialist literature such as the CIRIA Report 136 should be consulted where necessary.

10 Placing and protection of concrete 10.1 General All placing and compacting shall be carried out under suitable supervision and the engineer shall be given adequate notice of the intention to place concrete. Concrete shall be placed continuously, or in layers of such thickness that no concrete will be placed on concrete that has so hardened as to cause planes of weakness within the section. If a section cannot be placed continuously, construction joints (see 10.4) shall be located as indicated in the contract documents or as permitted. Concrete that has hardened to the extent that it no longer responds plastically to compactive efforts or that has been contaminated by foreign matter shall not be placed. 10.2 Placing 10.2.1 The concrete shall be placed within 1 h from the time of discharge from the mixer. Retempering is allowed under specific controlled conditions (see 7.3.1.3). 10.2.2 Placing shall be carried out at such a rate that the concrete that is being integrated with fresh concrete is still plastic. 10.2.3 Wherever practicable, the concrete shall be placed vertically into its final position to avoid segregation and displacement of reinforcement and other items that are to be embedded. 10.2.4 Placed concrete shall not be so reworked (whether by means of vibrators or otherwise) as to cause it to flow laterally in such a way that segregation occurs. Where practicable, the concrete shall be placed in horizontal layers of compacted thickness not exceeding 450 mm, to avoid "heaping". Use of vibrators to move concrete laterally within forms shall not be allowed.

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10.2.5 Where a chute is used to convey the concrete, its slope shall be such that it will not cause segregation and a suitable spout or baffles shall be provided for the discharge of the concrete. Generally, the chute should be at an angle exceeding 30° to the horizontal. 10.2.6 Unless permitted by the engineer, the concrete shall not be allowed to fall freely through a height of more than 3 m. 10.2.7 Placing of concrete in an element that is supported shall not be started until the concrete previously placed in supporting elements (columns, walls or beams) is no longer plastic and has been in place for at least 2 h. When elements that are supported and supporting elements are placed in one operation, the concrete in the vicinity of the junction between these elements shall be revibrated shortly before it sets. This procedure is necessary to eliminate defects such as cracks caused by the settlement of solids in the fresh concrete. This is also relevant for horizontal reinforcement in deep sections and in slabs. (See 10.3.8.) 10.2.8 When a closed circuit is being concreted, work shall begin at one or more points in the circuit and shall so proceed in opposite directions at the same time that, at completion of the circuit, the junctions are formed with freshly placed concrete. 10.2.9 When the placing of concrete underwater is permitted owing to exceptional circumstances because, in the opinion of the engineer, it is not practicable to dewater before placing, it shall be placed by means of a tremie or by using an appropriately designed mix (or both). During placing, the lower end of the tremie shall be continuously so immersed in the concrete being placed that the fresh concrete enters the mass of previously placed concrete from within, causing water to be displaced with minimum disturbance at the surface of the concrete. During concreting by tremie, the pipe shall be kept filled with concrete at all times to prevent air and water from entering the tremie. If the seal between the tremie and placed concrete is broken, the tremie shall be lifted and plugged before concreting is started. The mix proportion of the concrete shall be adjusted to provide a concrete suitable for placing by tremie. Full details of the method proposed and of the adjusted concrete mix proportions shall be submitted for approval before placing starts. During and after concreting underwater, pumping or dewatering operations in the immediate vicinity shall be suspended if there is any danger that such operations will interfere with the freshly placed concrete before it has set and gained adequate strength. 10.2.10 The lift height to be concreted at any one time shall be agreed between the contractor and the engineer. In massive sections, it will be necessary to consider the effect of lift height on the temperature rise because of the heat of hydration. 10.3 Compaction 10.3.1 All concrete shall be so compacted (by vibration, spading, rodding, etc.) during and immediately after placing, to ensure that the concrete is thoroughly worked around the reinforcement, around embedded items and into corners of formwork and forms a solid void-free mass having the required surface finish. Where compaction is only by means other than vibration, approval shall be sought. 10.3.2 The concrete shall be free from honeycombing and planes of weakness. Successive layers of the same lift shall be thoroughly worked together. 10.3.3 Vibration shall be applied continuously during the placing of each batch of concrete until the expulsion of air has virtually ceased. 10.3.4 Immersion vibrators shall be inserted vertically into the concrete to be compacted, at regular spacings not exceeding 0,6 m or 10 times the diameter of the vibrator, whichever is less.

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Systematic spacing of insertions of the vibrator at the recommended intervals is essential to ensure that no concrete remains outside the sphere of energy released by the vibrator. As soon as a water sheen is visible on the surface, the vibrator shall be slowly withdrawn from the concrete, care being taken to avoid the formation of voids. 10.3.5 When external vibrators are used, the design of formwork and the disposition of vibrators shall be such as to ensure efficient compaction and to avoid surface blemishes. 10.3.6 The rate of concrete placing shall be commensurate with the available compaction equipment, and compaction by vibration shall be executed by skilled operators only. The number of vibrators used shall be compatible with the rate at which concrete is placed. Standby vibrators shall also be made available. 10.3.7 Where permanent formwork is incorporated in the structure, its energy absorption shall be taken into account when the method of vibration to be used is being decided upon. Extra care is required to ensure full compaction of the concrete, since this cannot be checked as usual when the formwork is removed. 10.3.8 To overcome the detrimental effects of bleeding (see 6.1.6) and settlement, the technique of "revibration" or "recompaction" shall be used. The technique consists of recompacting the concrete at a time that is as long as possible after initial compaction but while the concrete retains sufficient workability to respond plastically to compactive energy. In practice, this energy is normally applied by means of immersion vibrators. Recompaction is especially necessary in upper zones of columns, forms that have abrupt changes in cross section (such as T-beams, I-beams and coffered slabs), elements that have horizontal reinforcing bars placed near the top of the concrete, liquid-retaining structures, and structures exposed to aggressive conditions (see also 10.2.7). 10.4 Construction joints NOTE See SANS 10100-1. 10.4.1 General The number of construction joints shall be kept to the minimum necessary for the execution of the work. Their type and locations shall be acceptable to the engineer. The concrete at the joint shall be bonded with that subsequently placed against it, without provision for relative movement between the two. To ensure that the load-bearing capacity of the concrete in the area is not impaired, high quality workmanship is necessary when the joints are being formed. Stub columns, stub walls and stays on footings shall be cast integrally with the footings and not afterwards, even where another class of concrete is to be used for the wall or column. 10.4.2 Location 10.4.2.1 In general, joints shall be located near the middle of the spans of slabs, beams and girders, unless a beam intersects a girder at this point, in which case the joint in the girder shall be offset at a distance equal to twice the width of the beam. Joints at the top end of walls and columns shall be at the underside of floors, slabs, beams or girders. Joints at the bottom of walls and columns shall be at the top of footings or floor slabs making allowance for a stub wall or column ("kicker") of 75 mm. Joints shall be perpendicular to the main reinforcement. 10.4.2.2 The term "unforeseen joint" is used to identify a joint formed during concreting when plant failure, inclement weather or some other unforeseen event has enforced a halt in the placing of concrete and thus created a situation in which a construction joint has to be made in a location that was not approved before the start of concreting.

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If an unforeseen joint occurs at a critical section (for example at a section of maximum shear), it may be possible to remove part of the fresh concrete in order to place the joint in a less critical section. The face of the joint shall be trimmed to an approximately vertical face and all loose material shall be removed. 10.4.3 Bonding 10.4.3.1 Use of an adhesive Joints to which an adhesive is applied shall be prepared, and the adhesive applied, in accordance with the manufacturer's recommendations, before the placing of fresh concrete. The engineer may require the contractor to demonstrate that this method achieves the desired level of bonding. 10.4.3.2 Use of a retarder Surfaces of joints that have been treated with a chemical retarder shall be prepared in accordance with the manufacturer's recommendations, before the placing of fresh concrete. 10.4.3.3 Roughening and dampening the surface of the concrete Roughening the surface of the concrete in an acceptable manner shall uniformly expose the aggregate and shall not leave laitance, loosened particles of aggregate or damaged concrete on the surface. The hardened concrete of construction joints and of joints between footings and walls or columns, between the walls or columns and the beams or floors they support, and joints in other elements not mentioned above shall be dampened (but not saturated) immediately before the placing of fresh concrete. The hardened concrete of horizontal construction joints a) in exposed work, or b) in the middle of beams, girders, joists and slabs, or c) in work designed to contain liquids shall be dampened, but not saturated. Before fresh concrete is placed against it (where thorough compaction of the fresh concrete may still result in localized honeycombing), consideration may be given to the application of a concrete layer of thickness approximately 250 mm, and made richer by reducing the amount of coarse aggregate by 25 %. The fresh concrete shall be placed before the intermediate layer of concrete has attained its initial set. 10.4.3.4 Alternative methods to roughen the surface of the concrete Alternatively, mesh or expanded metal stop ends (not extending into the cover zone) may be used, if approved, to provide a rough face to the joint. 10.4.4 Reinforcement All reinforcement shall be continued across construction joints. If a kicker or starter stub is used, it shall be at least 70 mm high and carefully constructed.

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10.4.5 Construction 10.4.5.1 Construction joints shall be formed in accordance with a) the details shown on the drawings, or b) the applicable requirements of the project specification. 10.4.5.2 In the case of an unforeseen joint (see 10.4.2.2), concrete shall be finished off at the place of stoppage in a manner that will least impair the durability, appearance and proper functioning of the concrete. The engineer's instructions shall then be followed. 10.5 Embedded items 10.5.1 General Expansion joint material, waterstops, pipes and conduits, and other embedded items shall be positioned accurately and supported against displacement. Voids shall be filled temporarily with readily removable material to prevent the entry of concrete into the voids. All contractors whose work is related to the concrete (or has to be supported by the concrete) shall be given ample notice and opportunity to introduce or furnish (or both) embedded items before the concrete is placed. 10.5.2 Waterstops The material and design of waterstops and their location in joints shall be as indicated in the contract documents. Each piece of premoulded waterstop shall be of maximum practicable length in order to keep the number of end joints to a minimum. Joints at intersections and at ends of pieces shall be made in the manner most appropriate to the material being used. Joints shall develop effective watertightness fully equal to that of the continuous waterstop material, shall permanently develop at least 50 % of the mechanical strength of the parent section, and shall permanently retain their flexibility. 10.5.3 Pipes and conduits No pipes or conduits, other than shown on the drawings, may be permanently embedded in the concrete without prior approval. 10.6 Concrete for water-retaining structures 10.6.1 Special care shall be taken when concrete for structures intended to retain water is being cast. The details of the drawings shall be followed meticulously, especially regarding the quality of concrete to be used, construction joints, the making good of holes used for formwork fixing purposes, and the grouting of pipes and other accessories. 10.6.2 For purposes of impermeability, the water/binder ratio of the concrete mix shall not be more than 0,5. See clause 6 for durability and the protection of steel. (See also clause 7.) 10.6.3 When so required in terms of the project specification, tests for watertightness shall be carried out to verify that the intended degree of watertightness of the structure has been achieved. Should the degree of watertightness not be approved, an investigation shall be carried out to ascertain what remedial steps are required.

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10.7 Concrete in saturated ground Where concrete is to be placed in saturated ground, shallow drains shall be excavated in the ground, filled with broken stone, and connected to suitably placed sumps. A concrete blinding layer, the top of which will form the foundation level for the structural concrete, shall then be laid. The layout and dimensions of the dry-stone drainage channels and the thickness of the blinding shall be included in the detailed drawings. If this is not the case, or if the engineer considers the project specification inappropriate, the channels and blinding shall be constructed as directed by the engineer. 10.8 Protection and curing of concrete 10.8.1 General 10.8.1.1 Beginning immediately after it has been placed, concrete shall, as far as is practicable, be protected from moisture loss and maintained at a temperature suitable for continued hydration for the period necessary for hydration of the cement and hardening of the concrete. Concrete shall be so protected and cured that it is not exposed to any of the following: a) premature drying out, particularly as a result of solar radiation and wind; b) excessively high or low temperatures; c) erosion by rain and flowing water; d) rapid cooling (during the first few days after placing); e) high internal thermal gradients (see Fulton’s concrete technology); f) frost (see 10.8.3); g) mechanical damage; h) contamination; and i) vibration, movement and impact that could disrupt the concrete and interfere with its bond to the

reinforcement. 10.8.1.2 In the case of concrete surfaces not in contact with forms, one of the following curing procedures shall be adopted as soon as practicable after completion of placement and compaction, subject to the provisions of 10.8.2 and 10.8.3: a) ponding or continuous sprinkling of the exposed surfaces with water, except where the ambient

temperature is below 5 °C; b) covering the concrete with sand, or with mats made of a moisture-retaining material, and keeping

the covering continuously wet except on mass structures where the thermal differential is likely to result in cracking;

c) when steam-curing, ensuring that the temperature in the surrounding environment does not exceed

70 °C. NOTE See Fulton’s concrete technology for further information. d) covering the concrete with waterproof or plastics sheeting firmly anchored at the edges; or

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e) using an approved curing compound, applied in accordance with the manufacturer's recommendations.

NOTE A list of recommended specialist literature on massive concrete is given in annex A. 10.8.1.3 Moisture loss from surfaces placed against wooden forms shall be minimized by keeping the forms wet until they are removed. After form removal, the concrete shall be cured by one of the methods given in 10.8.1.2, for the duration of time prescribed below. Whichever method of curing is adopted, its application shall not cause staining, contamination or marring of the surface of the concrete and the water used shall be in accordance with 4.2. In general, when the development of a given strength or durability is critical to the performance of the concrete during construction or in service, the minimum duration of curing shall be established on the basis of tests of the required properties performed with the concrete mixture in question. When no such test data are available, the minimum curing period shall be as shown in table 4. NOTE Some curing compounds inhibit the bond of finishes, such as toppings, plasters or paints, applied to the hardened concrete. The compound used should therefore be suitable for the intended finish.

Table 4 — Minimum duration of curinga

1 2 3 4 5

Surface concrete temperature

t, °C

Minimum curing period in daysb

Concrete strength developmentc (fcm3/fcm28) = r

Rapid r 0,55

Mediumr 0,5

Slowr 0,45

Very slowr 0,25

25d, e 5 7 10 15

25 > t 15 5 7 10 15

15 > t 5 7 10 15 21

t > 5 10 14 20 30 a Based on 70 % of 28 d strength. b Linear interpolation between values in the rows is acceptable. c The concrete strength development is the ratio of the mean compressive strength after 3 d (fcm3) to the mean

compressive strength after 28 d (fcm28) determined from initial tests or based on known performance of concrete of comparable composition.

d Where the ambient relative humidity is above 85 % this value may be reduced at the discretion of the engineer.e Where the ambient relative humidity is below 85 % this value may need to be increased as directed by the

engineer.

10.8.2 Concreting in hot weather or in windy conditions NOTE See also 7.3.4.2. Protection consists essentially of preventing evaporation from exposed concrete surfaces as soon as concrete has been placed and compacted. A combination of shading the concrete and spraying it or covering it with plastics sheeting may be used. Covers shall be such that they do not mark the surface of the concrete and shall be firmly anchored at the edges to prevent air movement over the concrete. 10.8.3 Concreting in cold weather NOTE See also 7.3.4.1. The temperature of placed concrete shall not be allowed to fall below 5 °C until the concrete has attained a strength of at least 5 MPa. This can be achieved by adequate protection, such as insulation, against temperature loss.

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10.8.4 Concreting during rainfall Concrete shall not be placed during periods of heavy or prolonged rainfall unless the materials, plant and the concreting operation are all well covered. 10.9 Surface finish of concrete 10.9.1 Upper surfaces of concrete The upper surfaces of concrete shall comply with SANS 10109-2. 10.9.2 Concrete surfaces cast against forms 10.9.2.1 General Surfaces cast against forms may be left as-cast (plain or profiled), or the initial surface may be removed (by tooling or sand-blasting), or the concrete may be covered (by painting or tiling). When the type of external finish is being selected, consideration shall be given to the viewing distance, the weather pattern at the particular location, any impurities in the air and the effect of the shape of the structure upon the flow of water across the surface. 10.9.2.2 As-cast finishes 10.9.2.2.1 Rough form finish No selected form-facing material shall be specified for rough form finish surfaces. Tie holes and defects shall be patched. Fins exceeding 6 mm in height shall be chipped off or rubbed off; otherwise, surfaces shall be left with the texture imparted by the forms. 10.9.2.2.2 Smooth form finish The form-facing material shall be such as to produce a smooth, hard, uniform texture on the concrete. Facing material may be plywood, tempered concrete-form-grade hardboard, metal, plastics, paper, or other acceptable material capable of producing the required finish. Tie holes and defects shall be patched. All fins shall be completely removed. 10.9.2.3 Unspecified finish If the finish is not designated in the project specification, the following finishes shall be used, as applicable: a) rough form finish: for all concrete surfaces not exposed to public view; or b) smooth form finish: for all concrete surfaces exposed to public view. 10.9.3 Repair of surface defects No patching or remedial work shall be undertaken without authorization by the engineer who will, after thorough inspection and investigation of the quality and strength of the defective work, and after due consideration of the possible consequences of such defect, specify the extent and method of repair, or order the demolition and reconstruction of the whole of the defective work to the extent that he/she considers necessary. All repair, remedial and reconstruction work is subject to approval.

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10.10 Records Written records that provide the following information in relation to each part of the works shall be maintained: a) the grade and source of the concrete, and the position of the element in the works; b) the weather; c) the nature of samples taken for test purposes, the dates on which they were taken, and the means

of identification by which the results of tests on such samples may be correlated with the section of work to which they pertain; and

d) the date and starting time of placing the concrete and any unusual delays, the duration and causes.

11 Massive concrete 11.1 General 11.1.1 Concrete is said to be massive when the size and proportions of an element placed in one operation are such that temperature increases (caused by heat of hydration) in the concrete are high enough to result in potentially harmful effects. High temperatures in the concrete can lead to temperature gradients within the concrete. If these gradients are steep enough (i.e. exceeding 20 °C) to cause differential strain that exceeds the concrete's tensile strain capacity of the concrete, the concrete will crack. The critical dimension of an element with regard to heat of hydration is normally the least dimension. Concrete may usually be regarded as massive if the least dimension exceeds 0,5 m to 1,0 m, but the critical value is specific to each situation. 11.1.2 Portions of the structure that are to be treated as massive concrete under the provisions of this clause shall be stated in the project specification. Such massive concrete shall be subject to the provisions of this clause in addition to all other applicable provisions of this part of SANS 10100. 11.2 Construction The construction of massive concrete elements shall be done in such a way that the likelihood of cracking due to thermal effects is minimized. Possible steps include: a) minimizing the binder content; b) maximizing the extender content, for example GGBS or FA, and considering the strength

specification at ages greater than 28 d (see 4.1.2); c) using the largest size coarse aggregate that is practical; d) using aggregates that produce concrete with the lowest possible coefficient of thermal expansion; e) reducing the placing temperature of the concrete; f) installing cooling pipes in the concrete element; g) insulating the placed concrete to minimize internal temperature gradients; and h) using high-strength extended cements like CEM III/B, CEM IV or CEM V.

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The subject of massive concrete is not dealt with in detail in this part of SANS 10100 and reference shall be made to specialist literature (see annex A). 12 Prestressing NOTE See also SANS 10100-1. 12.1 Prestressing tendons NOTE See annex B for information regarding the technical data for prestressed structural elements. 12.1.1 General Prestressing tendons shall comply with specialist documentation. NOTE See also BS 4486 and BS 5896. 12.1.2 Handling and storage All prestressing tendons and sheathing shall be stored clear of the ground and protected from the weather, from surface contamination from other materials, from welding sparks or electric ground currents and physical damage. 12.1.3 Surface condition 12.1.3.1 At the time of incorporation in the structural member, all bonded prestressing tendons and internal and external surfaces of sheathing or ducts shall be free of loose millscale, loose rust, oil, paints, grease, soap or other lubricants (except for the lubricant used in the tensioning process), or other harmful matter. A uniform film of slight rust is not necessarily harmful and may improve the bond. It may, however, also increase the losses due to friction. 12.1.3.2 Cleaning of the tendons may be carried out by wire brushing or by passing the tendons through a pressure box containing carborundum powder. Solvent solutions shall not be used for cleaning without the approval of the engineer. 12.1.4 Straightness 12.1.4.1 Wire Low relaxation and normal relaxation wire shall be in coils of diameter sufficiently large to ensure that the wire plays off reasonably straight. 12.1.4.2 Bars Prestressing bars, as delivered, shall be straight. Any small adjustments necessary for straightness shall be made on site, by hand, under the supervision of the engineer. Bars bent in the threaded portion shall be rejected. Any straightening of bars shall be carried out at ambient temperature. If the ambient temperature is less than 5 °C, any necessary heating shall be by means of steam or hot water to raise the temperature of the bars above 5 °C. 12.1.5 Cutting The following points shall be taken into consideration: a) any special requirements by the supplier of the prestressing system shall be met; b) all cutting to length and trimming of ends shall be by means of either a high-speed abrasive cutting

wheel, guillotine, friction saw or any other mechanical method approved by the engineer; or

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c) in post-tensioning systems, the cutting action as in (a) and (b) above and shall be at least one tendon diameter from the anchor.

12.1.6 Formwork Formwork shall not restrain any elastic shortening, deflection or camber of the structure that results from the application of the prestressing force. Form supports shall not be removed until sufficient prestressing force has been applied to support the self-mass of the element that is being stressed, the formwork and the anticipated construction loads, and shall be done to the engineer's approval. 12.1.7 Sheathing 12.1.7.1 Sheathing for bonded tendons 12.1.7.1.1 Sheathing or duct-formers shall be of a material that will not react with the alkalis in the cement and that is strong enough to retain its shape and resist damage during construction. It shall prevent the intrusion of cement paste from the concrete. Sheathing material left in place shall not cause electrolytic action or deterioration. 12.1.7.1.2 The sheathing shall have an internal cross-sectional area at least twice that of the net steel area of the tendon but may need to be much larger, if a large number of tendons are involved. 12.1.7.1.3 Sheathing shall have injection pipes fitted at each end and vent pipes at all high points except where the curvature is small and the sheathing is relatively level, such as in continuous slabs. Drain holes shall be provided at all low points if the tendon may be subject to freezing after placing and before grouting. 12.1.7.1.4 When preparing the tendons, wires and strands shall be laid out in parallel and maintained in position by metal or PVC spacers before insertion into the sheath. 12.1.7.2 Sheathing for unbonded tendons The sheathing shall have sufficient strength and weather resistance to prevent damage or deterioration during transportation, storage on site and installation. The sheathing shall be a continuous tube and shall continue over the unbonded length of the tendon. In the event of lubricated sheaths the sheathing shall prevent the intrusion of cement paste and loss of lubricant. 12.2 Tensioning 12.2.1 General 12.2.1.1 Tendons may be stressed either by pre-tensioning or by post-tensioning, as agreed with the engineer. In each system, different procedures and types of equipment are used and these govern the method of tensioning and form of anchorage. 12.2.1.2 Where possible, all wires or strands to be stressed in one operation shall be taken from the same batch of prestressing steel. Each tendon shall be tagged with its number and the coil number(s) of the steel used. Tendons shall not be kinked or twisted and individual wires and strands shall be readily identifiable at each end of a member. A strand that has become unravelled shall not be used. 12.2.1.3 Where two or more wires or strands are stressed simultaneously, they shall be parallel and of approximately equal length between anchorage points at the datum of force and extension measurement. The degree of variation in individual extensions shall be small in comparison with the expected extension.

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12.2.2 Safety precautions A tendon, when tensioned, contains a considerable amount of stored energy, which, in the event of failure of a tendon, anchorage or jack, may be released violently. All possible precautions shall be taken (both during and after tensioning) to safeguard persons from injury and to safeguard equipment from damage that may be caused by the sudden release of this energy. 12.2.3 Tensioning apparatus 12.2.3.1 The means of attachment of the tendon to the jack or tensioning device shall be safe and secure. 12.2.3.2 The tensioning apparatus shall be such that the total force can be applied in stages and no dangerous secondary stresses are induced in the tendons, anchorage or concrete. 12.2.3.3 The force in the tendons during tensioning shall be measured by direct-reading load cells or obtained indirectly from gauges of minimum diameter 150 mm fitted into the hydraulic systems to determine the pressure in the jacks. When pressure gauges are used, they shall be calibrated together with the jack to allow for jack friction. Facilities shall be provided for the measurement of the extension of the tendon and of any movement of the tendon in the anchorage devices. The force measuring device shall be calibrated to an accuracy of ± 2 % (or better) and checked at intervals not greater than six months. Elongation of the tendon shall be measured to an accuracy of at least 2 % or 2 mm, whichever is the more accurate. 12.2.4 Pre-tensioning 12.2.4.1 General Where pre-tensioning methods are used, positive means shall be used to maintain the full force during the period between tensioning and transfer. The force shall be transferred slowly to minimize shock, which would adversely affect the transmission length. 12.2.4.2 Straight tendons 12.2.4.2.1 In the long-line method of pre-tensioning, sufficient locator plates shall be distributed along the length of the bed to ensure that the wires or strands are maintained in their proper position during concreting. Where a number of units are made in line, they shall be free to slide in the direction of their length and thus permit transfer of the prestressing force to the concrete along the whole line. 12.2.4.2.2 In the individual mould system, the moulds shall be made sufficiently rigid to accommodate the reaction to the prestressing force without distortion. 12.2.4.3 Deflected tendons 12.2.4.3.1 Where practical, the mechanisms for holding down or holding up of tendons shall be such that the part in contact with the tendon is free to move in the line of the tendon in order to eliminate frictional losses. If, however, a system is used that develops a frictional force, this force shall be determined by testing, and due allowance made to the applied force. 12.2.4.3.2 For a single tendon, the deflector in contact with the tendon shall have a radius of at least five times the tendon diameter for wire, or 10 times the tendon diameter for a strand, and the total angle of deflection shall not exceed 15°. 12.2.4.3.3 The transfer of the prestressing force to the concrete in conjunction with the release of hold-down and hold-up forces shall be so effected that any tensile stresses in the concrete that result during the process, do not exceed the permissible limits.

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12.2.5 Post-tensioning 12.2.5.1 Arrangement of tendons 12.2.5.1.1 Where wires, bars or strands in a tendon are not stressed simultaneously, rigid spacers shall be made so that they are not displaced during the successive tensioning operations. 12.2.5.1.2 Tendons, whether in anchorages or elsewhere, shall be so aligned that they do not pass round sharp bends or corners likely to provoke rupture when the tendons are under stress. 12.2.5.2 Anchorages 12.2.5.2.1 The adequate performance of anchorages shall be demonstrated before prestressing. NOTE Suitable tests for checking prestressing tendon anchorage performance are described in BS 4447 and in the FIP recommendation for acceptance and application of post-tensioning systems. 12.2.5.2.2 The anchorage system in general comprises the anchorage itself and the arrangement of tendons and reinforcement designed to act with the anchorage. The form of anchorage system shall be such as to facilitate the even distribution of stress in the concrete through the length of the member and shall be capable of maintaining the prestressing force under sustained and fluctuating load and under the effect of shock. 12.2.5.2.3 Split-wedge-and-barrel type anchors shall be of such material and construction that a) under the forces imposed during the tensioning operation, the strain in the barrel does not allow

such movement of the wedges that the wedges reach the limit of their travel before sufficient lateral force is developed to grip the tendon, and

b) the wedges do not cause an excessive force in the tendon at or before the limit of travel. 12.2.5.2.4 If a proprietary form of anchorage is used, the anchoring procedure shall be strictly in accordance with the manufacturer's instructions and recommendations. 12.2.5.2.5 Before the tensioning operation all bearing surfaces of the anchorages, of whatever form, shall be cleaned. 12.2.5.2.6 Any allowance for draw-in of the tendon during anchoring shall be in accordance with the engineer's instructions, and the actual slip occurring shall be recorded for each individual anchorage. 12.2.5.2.7 After the tendons have been anchored, the force exerted by the tensioning apparatus shall be gradually and steadily decreased in such a way that shock to the tendon or the anchorage is avoided. 12.2.5.2.8 Provision shall be made for the protection of the anchorage against corrosion. 12.2.5.2.9 Intermediate anchorages, if bearing against hardened concrete at a construction joint, shall effectively transfer the prestressing force to the hardened concrete and shall have adequate protection against corrosion. 12.2.5.3 Deflected tendons 12.2.5.3.1 Where practicable, a deflector in contact with a tendon shall have a radius of at least 50 times the diameter of the tendon, and the total angle of deflection shall not exceed 15°. 12.2.5.3.2 Where the radius of the deflector is less than 50 times the diameter of the tendon or the angle of deflection exceeds 15°, the loss of strength of the tendon shall be determined by testing, and due allowance made.

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12.3 Positioning of tendons and sheathing 12.3.1 The tendons and sheathing shall be accurately located and maintained in the position, both vertically and horizontally, shown on the drawings. Unless otherwise shown on the drawings, the permitted tolerance in the location of the tendon or sheathing shall be as given in table 5.

Table 5 — Permitted tolerance in location of tendons and sheathing

Dimensions in millimetres

1 2 3 4

Depth of member d

Vertical tolerance Width of beam

W Horizontal tolerance

d < 200 200 ≤ d ≤ 1 000

d >1 000

± d/40 ± 5

± 10

W < 200 200 ≤ W ≤ 1 000

W >1 000 (incl. slabs)

± 5 ± 10 ± 30

12.3.2 The method of supporting and fixing the tendons (or the sheathing) in position shall be such that they will not be displaced by heavy or prolonged vibration, by pressure of the wet concrete, by workmen or by construction traffic. These supports shall not unnecessarily increase the friction when they are being tensioned. 12.3.3 Sheathing shall retain its correct cross section and profile and shall be handled carefully to avoid damage. 12.3.4 Joints in sheathing shall be securely taped and water-tested to prevent penetration of the sheath by concrete or cement paste, and the ends of sheaths shall be sealed and protected after the stressing and grouting operations. Joints in adjacent sheathing shall be staggered at least 300 mm. 12.3.5 As damage might occur during the concreting operation, and if the tendon is to be inserted later, the sheath shall be water tested before the concreting operation to ensure a clear passage for the tendon. 12.4 Tensioning procedure 12.4.1 All tendons shall be free to move in the ducts before being tensioned. Tensioning shall be carried out by experienced operators under competent supervision. The stress in the tendons shall increase at a gradual and steady rate. Tensioning shall not be carried out at a temperature below 0 °C without the approval of the engineer. 12.4.2 The supervisor in charge of stressing shall be provided with particulars of the required tendon force and expected extensions. During stressing, allowance shall be made for the friction in the jack and in the anchorage, although allowance for the former is not necessary when load cells are used. 12.4.3 Stressing shall be continued in stages until the required tendon force is reached. The measured extension shall allow for any draw-in of the tendon occurring at the non-jacking end, but measurement shall not begin until any slack in the tendon has been taken up. A comparison between the measured extension and the expected extension provides a check on the accuracy of the assumptions made for the frictional losses at the design stage. If the difference exceeds 5 %, corrective action shall be taken, but only with prior approval by the engineer. Full records shall be kept of all tensioning operations, including the measured extensions, pressure-gauge readings or load-cell readings, and the amount of draw-in at each anchorage.

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12.4.4 Where a large number of tendons or tendon elements are being tensioned and the full force cannot be achieved in an element because of breakage, slippage or blockage of a sheath, and if the replacement of that element is not practicable, the engineer may have to determine whether a change in the stress levels is still within the relevant limit state requirements. 12.4.5 In the case of curved tendons, or tendons made up of a number of constituent elements, or tendons loaded in stages, the engineer shall specify the order of loading and the magnitude of the force for each component of the tendon. 12.4.6 Tensioned tendons, anchorages and sheathing forms shall be effectively protected from corrosion during the period between stressing and covering with grout, concrete or other permanent protection. Ducts shall be plugged at their ends and at their vents. 12.5 Grouting of prestressing tendons 12.5.1 General 12.5.1.1 The two main objectives when the sheathing of post-tensioned concrete elements is grouted are as follows: a) to protect the prestressing tendons from corrosion, and b) to provide a bond between the prestressing tendons and the concrete element in order to control the

spacing of cracks at serviceability loads and to increase the ultimate moment of resistance of the element.

12.5.1.2 Both of the objectives in 12.5.1.1 make it essential to ensure that the whole of the void space within the ducts is filled. The success of this operation will be dependent on the production of a grout mix that has the desired properties, together with efficient equipment for its injection, and proper workmanship and careful supervision on site. 12.5.1.3 The required properties of a satisfactory grout for the injection of sheathing in a post-tensioned member are good fluidity and low sedimentation or bleeding in the plastic state, and durability and density with low shrinkage in the hardened state in order that the grout will bond with the steel and the sides of the duct and provide protection for the prestressing tendon. The methods to be adopted shall be such that they can be effectively and reasonably easily carried out on site and shall be agreed with the engineer. 12.5.1.4 Grouting trials shall be undertaken when required by the engineer. 12.5.2 Grouting equipment 12.5.2.1 A high-pressure water supply of sufficient volume shall be provided before grouting starts. Sheathing shall be cleaned of dirt and other foreign matter by thorough flushing with water immediately before grouting. 12.5.2.2 The mixing equipment shall be of a type that is capable of producing a grout of colloidal consistence by means of high local turbulence while imparting only a slow motion to the body of the grout. 12.5.2.3 The injection equipment shall be capable of continuous operation with little variation of pressure and shall include a system for agitating the grout while actual grouting is not in progress. Compressed air shall not be used to agitate or inject the grout.

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12.5.2.4 Normally, equipment should have a delivery pressure of 1 MPa. Piping to the grout pump shall have a minimum of bends, valves and changes in diameter, and connections shall be air-tight. All baffles to the pump shall be fitted with sieve strainers of aperture size 3 mm. All equipment, especially piping, shall be thoroughly flushed with clean water after every series of operations and more frequently if necessary. Intervals between washings shall not exceed 3 h. 12.5.3 Materials 12.5.3.1 General All materials shall be measured by mass. 12.5.3.2 Cement Only CEM I 42,5N or CEM II 42,5N or higher and that has been stored on site for less than one month, shall be used. The temperature of the cementitious binder shall be less than 45 °C. Alternatively, approved cementitious grouts may be used with the approval of the engineer. 12.5.3.3 Sand Sand shall only be used when the diameter of the duct exceeds 150 mm. Sand shall be of particle size not exceeding 0,6 mm. The mix proportions shall be agreed with the engineer. 12.5.3.4 Admixtures Admixtures shall only be used when tests have shown that their use improves the properties of the grout. Admixtures shall not contain nitrates, sulfides or sulfates. Chlorides shall be limited to 500 mg/L. When aluminium powder is used, the total expansion shall not exceed 6 % by volume. 12.5.4 Ducts 12.5.4.1 Air vents of diameter at least 10 mm shall be provided at any crests present in the sheathing profile, since it is important that the whole volume of the sheathing be filled with grout. Horizontal sheathing of length not exceeding 30 m shall be grouted from one end, without intermediate vents. 12.5.4.2 Threaded entries to the duct or anchorage to permit the use of a screwed connector from the grout pump may be used with advantage. 12.5.4.3 Before the concrete is placed, sheaths shall be inspected for continuity, correct alignment, secure fixing, dents, splits and holes, and any defects shall be rectified. Particular attention shall be paid to joints between ducts and anchorages and joints between adjacent precast units. 12.5.4.4 Sheaths shall be kept dry before grouting to prevent corrosion of the tendon, possible frost damage or excess water, but they may be flushed with water immediately before grouting. If the tendon is to remain unstressed for more than 28 d from the time of tendon placement, temporary corrosion protection shall be provided. Vertical ducts shall be sealed at all times before grouting, to prevent the ingress of rain and debris. 12.5.5 Mixing 12.5.5.1 The water/cement ratio of the mix shall not be more than 0,43 by mass. The quantity of sand or filler used shall not exceed 30 % of the mass of the cement. 12.5.5.2 Water shall be added to the mixer first, then two-thirds of the cement. When these are thoroughly mixed, any admixture or sand and the remainder of the cement shall be added. Mixing shall continue for not less than 2 min and not more than 5 min, until a uniform consistence is obtained. Mixing by hand is not permissible.

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12.5.6 Strength of grout The compressive strength of 100 mm cubes of grout, made in conditions similar to those of the injected grout and cured in a moist atmosphere for the first 24 h and thereafter in water at 22 °C to 25 °C, shall exceed 20 MPa at 7 d. 12.5.7 Injection of grout 12.5.7.1 Grout shall be used within 60 min of mixing unless it contains a retarder. Grout that has partially set shall be discarded. Injection shall be continuous and slow enough (6 m/min to 12 m/min) to avoid segregation of the grout. The method of injecting grout shall be such as to ensure complete filling of the sheaths and complete surrounding of the steel. The volume of the spaces to be filled by the injected grout shall be compared with the quantity of grout injected. Grout shall be allowed to flow from the free end of a sheath until its consistence is equivalent to that of the grout injected. The opening shall then be firmly closed. Any vents shall be similarly closed, one after another, in the direction of the flow. 12.5.7.2 Grouting shall be carried out as soon as is practicable but not later than 7 d after the tendons have been stressed. 12.5.7.3 Vertical and inclined ducts shall be grouted from the lowest point, the maximum length grouted in one operation being 50 m. 12.5.7.4 In the event of a blockage or an interruption of grouting, all grout shall be flushed from the sheath with water. 12.5.8 Grouting during cold weather 12.5.8.1 When the weather is cold, accurate records shall be kept of maximum and minimum air temperatures, and the temperatures of the members to be grouted. Any materials in which snow, frost or ice is present shall not be used. The ducts and equipment shall be completely free from frost and ice. 12.5.8.2 Unless the member is so heated as to maintain the temperature of the placed grout above 5 °C for at least 48 h, no grout shall be placed when the temperature of the member is below 5 °C or is likely to fall below 5 °C during the following 48 h. 12.5.8.3 Unless accompanied by general external heating of the member or structure, sheaths shall not be warmed with steam. 12.5.8.4 The grout materials shall be warmed within the limits recommended for concrete (see 7.3.4). 12.5.9 Protection and bonding of prestressing tendons 12.5.9.1 General It is essential to protect prestressing tendons from both mechanical damage and corrosion. Protection may also be required against fire damage. 12.5.9.2 Protection and bonding of internal tendons Internal tendons may be protected and bonded to the element by either cement grout or sand cement grout in accordance with 12.5.3 and 12.5.5. Alternatively, the tendons may be protected by other materials based on bitumen, epoxy resins, rubber and the like, provided that the effects on bonding and on fire resistance are investigated.

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12.5.9.3 Protection and bonding of external tendons 12.5.9.3.1 A tendon is considered to be external when, after stressing and incorporation in the work but before protection, it is outside the structure. This does not apply, for example, to a floor comprising a series of precast beams that are themselves stressed with external tendons and subsequently so concreted or grouted that the prestressing tendons are finally contained in that filling together with adequate cover. 12.5.9.3.2 Protection of external prestressing tendons against mechanical damage and corrosion shall generally be provided by an encasement of dense concrete or dense mortar of adequate thickness. It may also be provided by other materials hard enough and stable enough for the particular environment. 12.5.9.3.3 When the type and quality of the material to be used for the encasement are being determined, full consideration shall be given to the differential movement between the structure and the applied protection that arises from changes of load and stress, creep, relaxation, drying shrinkage, humidity and temperature. If the applied protection is dense concrete or dense mortar, and investigations show the possibility of undesirable cracking, a primary corrosion protection that will be unimpaired by differential movement shall be used. 12.5.9.3.4 If external prestressing tendons are to be bonded to the structure, this shall be achieved by suitable reinforcement of the concrete encasement to the structure.

13 Precast concrete 13.1 General Precast units, whether of plain, reinforced or prestressed concrete, shall have been designed in accordance with the provisions of SANS 10100-1 and the quality and workmanship shall be in accordance with the applicable provisions of this part of SANS 10100. 13.2 Permissible deviations 13.2.1 For permissible deviations, see SANS 10155. Allowances for construction inaccuracies are given in SANS 10100-1. 13.2.2 While dimensional variations are inevitable, precast concrete units can be manufactured to comparatively small permissible deviations. Manufacturing to such fine tolerances, however, will materially increase the cost of the units. 13.2.3 Permissible deviations shall only be specified for those dimensional characteristics that are important to the correct assembly, performance and appearance of the structure, and shall be as large as is practicable. The permissible deviations for other dimensional characteristics shall be left to the discretion of the manufacturer, but shall be reasonable for the conditions of production and use. The manufacturer shall, when so requested, make these permissible deviations known. 13.2.4 The permissible deviations for the units shall be consistent with any variation in the position of the adjoining elements in the building. 13.2.5 The permissible deviations are a general guide. In exceptional cases, it may be possible to reduce certain permissible deviations even further by means of specially designed moulds, but such reductions shall be made with considerable caution.

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13.2.6 It is strongly recommended that the manufacturer's advice be obtained at the early design stages when very small permissible deviations are likely to be required, since those that can be achieved in practice depend on a number of factors, including the following: a) the shape of the unit, particularly since this affects the stiffness of the mould; b) the mould materials and the method of assembly; c) the number of castings from each mould; and d) the position and shape of any projections through the moulded faces. 13.2.7 For irregular, curved or specially shaped units, the necessary dimensions and permissible deviations shall be clearly defined in the project specification and shown on the drawings. 13.2.8 Particular attention is drawn to the fact that deviations can be cumulative, i.e. adjoining edges of two floor panels nominally at the same level can differ by the sum of the positive deviations on bow and thickness on one unit, and the same negative deviations on the next unit. 13.2.9 Where appropriate, permissible deviations shall be given as both plus and minus values on a specific dimension, rather than as a deviation from a maximum or minimum value. Working drawings to be used by the manufacturer shall give the dimensions and permissible deviations as required. 13.3 Prestressed units 13.3.1 When permissible deviations for prestressed units are being specified, the creep, shrinkage and elastic shortening of the concrete, the eccentricity of the steel and other significant factors shall be taken into account. 13.3.2 At a given age, and by the use of factors appropriate to that age applied to the method recommended in SANS 10100-1, a camber can be predicted. This predicted camber, the age and other controlling conditions (for example when supported at the ends and subjected to self-mass only) shall be stated on the drawings or in the project specification. The actual camber shall not exceed the predicted camber by more than 50 %. 13.3.3 Where variation in camber between closely associated units (for example floor panels laid side by side and practically touching, and receiving plaster or topping, or both) is critical, it shall not exceed 6 mm for units of up to 4,5 m in length, or 9 mm for longer units. 13.3.4 Where variation in camber is not critical (for example in the case of closely associated units that have a false ceiling and thick top screed, or units not closely associated with one another), variations in camber in excess of those stated above may be acceptable to the engineer, and shall be judged in relation to the conditions the units have to fulfil. 13.4 Handling and erection of precast concrete units 13.4.1 Lifting equipment Lifting equipment shall comply with safety regulations. The method of support during lifting and placing shall be in accordance with approved procedures. 13.4.2 Handling and transportation 13.4.2.1 Precast units shall be designed to resist, without permanent damage, all stresses induced by handling, storage and transport. The minimum age for handling and transporting shall be specified by the engineer or designer, and is related to the concrete strength, the type of unit and other factors.

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13.4.2.2 The position of lifting and supporting points, the method of lifting, and the type of equipment and transport to be used shall be as specified by the engineer or as agreed by him/her, and shall be practical and safe to use, and such that no damage is likely to result from the lifting equipment. 13.4.2.3 Units shall be marked with indelible identity, location and orientation marks, as and where necessary. 13.4.2.4 The engineer shall, in all cases, specify the points of support during storage, and shall ensure that these are so chosen as to prevent unacceptable permanent distortion of the units. Resilient supporting arrangements that permit small settlements without inducing stresses in the units are preferred. The engineer shall also ensure that, when a stack is several units high, the units are vertically above one another to prevent bending stresses in any unit. Where disfigurement would be detrimental, packing pieces shall not discolour or otherwise permanently damage the units. 13.4.2.5 Trapped water and dirt shall not be allowed to accumulate in the units. NOTE The freezing of trapped water can cause severe damage. 13.4.2.6 Where necessary, precautions shall be taken to prevent projecting reinforcement from causing rust stains, and to minimize efflorescence. 13.4.2.7 During transportation, the following additional factors shall be considered: a) overloading of the transporting vehicle; b) centrifugal force resulting from cornering; c) oscillation (a slim unit might flex (vertically or horizontally) sufficiently to cause damage); and d) the possibility of damage due to chafing. 13.4.3 Assembly and erection The method of assembly and erection specified as part of the design shall be strictly adhered to on site. Immediately when a unit is in position and before the lifting equipment is removed, temporary supports or temporary connections shall be provided between units, as necessary. The final structural connections shall be completed as soon as is practicable. 13.4.4 Temporary supports during construction 13.4.4.1 When temporary supports are being provided, all construction loads (including wind) likely to be encountered during the completion of joints between any combination of precast units and in-situ concrete structural elements shall be taken into account. Temporary supports (when relevant) shall take movements into account, including those caused by shrinkage of concrete and any post-tensioning. In addition, the arrangement and design of temporary supports shall be such that, if a unit breaks or accidentally strikes against another during erection, the temporary supports of adjacent units will be sufficient to prevent any local collapse from becoming progressive. 13.4.4.2 The supports shall be arranged in a manner that will permit the proper finishing and curing of any in-situ concrete, mortar or grout. Temporary supports shall not be removed or released until the required strength is attained in the in-situ portion of a construction. NOTE Attention is directed to the requirements of various acts and regulations that govern temporary works, stagings, scaffolding and lifting equipment.

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13.4.5 Forming structural connections 13.4.5.1 General requirements 13.4.5.1.1 The precast units shall be inspected to ensure that the design requirements of the structural connection are met. 13.4.5.1.2 The precast units shall be free from irregularities of such size and shape as to lead to damaging stress concentrations. When reliance is placed on bond between the precast units and in-situ concretes, the contact surface of the precast unit shall have been suitably prepared in accordance with SANS 10100-1. If frictional resistance is assumed to have developed at a bearing, the construction shall be such that this resistance can be realized. Particular attention shall be given to checking the accurate location of reinforcement and any structural steel sections in the ends of precast units and to the introduction of any additional reinforcement needed to complete a connection. 13.4.5.2 Packing requirements 13.4.5.2.1 General The packing of joints shall be carried out in accordance with assembly instructions. 13.4.5.2.2 Concrete or mortar packing The following points shall be taken into consideration: a) when joints between units, particularly the horizontal joints between successive vertical lifts, are

load-bearing and are to be packed with mortar or concrete, tests shall be carried out to prove that the material is suitable for the purpose and that the proposed method of filling results in a solid joint;

b) the composition and water/cement ratio of the in-situ concrete or mortar used in any connection

shall be as specified by the engineer; and c) care shall be taken to ensure that in-situ material is thoroughly compacted. The use of an expanding

agent may be considered advantageous. 13.4.5.2.3 Other packing materials The following points shall be taken into consideration: a) packing materials other than grout, mortar or concrete (for example resinous adhesives, lead and

bituminous compounds) may be used, provided that they fulfil all the necessary requirements and are compatible in all respects with the concrete components being joined together;

b) the manufacturer's recommendations for the methods of application shall be strictly followed; and c) levelling devices, such as nuts and wedges, that have no load-bearing function in the completed

structure, shall be slackened, released or removed, as necessary. 13.4.5.3 Fixing by welding Where precast units are fixed by welding, it shall be noted that the expansion of cast-in plates may cause cracking of the precast section. Heat may be reduced by the use of a) low-heat welding rods of small size,

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b) intermittent welds, and c) smaller welds. Plates shall not be less than 10 mm thick. Welding should preferably not be done where connections are galvanized, unless steps are taken to reinstate the zinc layer, for example with zinc-rich epoxy paint. Where galvanizing is used, consideration shall be given to using a chromate passivator in the concrete, to prevent interaction of the zinc with the alkali in the cement. Welding shall not be done near prestressing cables or anchorages. 13.4.6 Protection At all stages, and until completion of the work, precast concrete units and any other concrete associated with them shall be properly protected. The degree and extent of the protection to be provided shall be sufficient for the surface finish and profile being protected, the position and importance of the units being borne in mind. This is particularly important in the case of permanently exposed concrete surfaces, especially arrises and decorative features. The protection can be provided by timber strips, hessian, etc., but shall be such as will not damage, mark or otherwise disfigure the concrete.

14 Testing and acceptance of concrete 14.1 General Concrete materials and operations shall, as the work progresses, be tested and inspected in accordance with the methods referred to in the project specification or in accordance with such other methods as specified by the engineer. Failure to detect any defective work or material shall not in any way prevent later rejection when such defect is discovered nor shall it obligate the engineer to final acceptance. Site testing shall be carried out by a competent technician or by a person deemed by the engineer to be sufficiently experienced. Laboratory testing shall be carried out by an approved laboratory. 14.2 Testing services 14.2.1 Basic site testing services The following testing services shall be performed: a) reviewing or testing (or both) the contractor's proposed materials for compliance with the relevant

specification (see clause 4); b) collecting samples of materials at plants or stockpiles during the course of the work and testing them

for compliance with the relevant specification (see clause 4); c) during construction, conducting strength tests of the concrete in accordance with 14.3 (see

clause 4); d) monitoring mix characteristics such as the water/cement ratio and cement content where these have

been specified (see clause 6); and e) monitoring in-situ cover to reinforcement.

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14.2.2 Testing services required by the engineer for compliance verification The following services shall be performed when so required by the engineer: a) reviewing or testing (or both) the contractor's proposed mix design; b) inspecting concrete batching, mixing and delivery operations to the extent deemed necessary by the

engineer; c) sampling concrete at the point of placement, and carrying out the required tests; d) reviewing the manufacturer's report for each shipment of cementitious binder, reinforcing steel and

prestressing tendons, or conducting laboratory tests or spot checks of the materials as received (or both), for compliance with relevant specifications; and

e) other testing as required by the work specification. 14.2.3 Additional services when required The following services shall be performed, when necessary: a) additional testing and inspecting when changes in materials or proportions are proposed by the

contractor; and b) additional testing of materials or concrete occasioned by their failure by test or inspection to comply

with specification requirements. 14.2.4 Test reports Concrete test reports shall include the exact location in the work where the batch of concrete represented by a test was placed. Reports of strength tests shall include detailed information on storage and curing of specimens before testing, as well as the test facility and the technician and shall be signed by the approved signatory. 14.2.5 Responsibilities and duties of the contractor 14.2.5.1 The contractor shall submit to the engineer his/her proposals for the concrete materials and the concrete mix designs. These shall include the results of the tests performed on the materials and the tests to establish the mix designs (see clauses 4 and 6). No concrete shall be placed in the works until the contractor has received the approval of the engineer. 14.2.5.2 To facilitate testing and inspection, the contractor shall ensure that the following test equipment, in good condition, is available: a) slump test apparatus as specified in SANS 5862-1 or flow test apparatus as specified in

SANS 5862-2 (or both); b) moulds for compressive strength testing in accordance with the requirements of SANS 5863, and in

sufficient quantity to permit the frequency of sampling and testing in terms of 14.3; c) apparatus for curing strength specimens as specified in SANS 5861-3; and d) any other test equipment specified.

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14.3 Strength tests of concrete during construction 14.3.1 General procedures 14.3.1.1 During the time when concrete of a particular grade is being placed, samples shall be taken in accordance with SANS 5861-2 and in accordance with a predetermined programme. The programme shall be worked out taking the following into account: a) each sample (one sample being sufficient for three cubes for each testing age) shall be taken from a

different batch of concrete chosen on a random basis. The numbers of batches to be selected as the test batches shall be determined before the start of concrete placement;

b) at least one sample shall be taken from each day's placing and from at least every 50 m3 of

concrete of each grade placed; and c) the frequency of sampling shall be determined by the importance of the work, for example a critical

part of the structure may require that additional samples be taken. 14.3.1.2 The slump of the concrete sample shall be determined in accordance with SANS 5862-1 for each strength test and whenever the consistence of the concrete appears to vary. 14.3.1.3 The cubes shall be cast and cured in accordance with SANS 5861-3. Cubes cured on site shall be cured in water at a temperature between 22 °C and 25 °C. 14.3.1.4 The cubes shall be tested in accordance with SANS 5863 to obtain valid test results. Three cubes shall be tested for acceptance at the age specified, which is usually 28 d. For prestressed concrete, sets of three cubes shall be tested at 3 d. Sets of three cubes may be tested at other ages for information. 14.3.2 Evaluation of strength test results Test results for test cubes shall be evaluated separately for each grade of concrete. Such evaluation is only valid if tests have been conducted in accordance with the procedures specified in 14.3.1. 14.3.3 Acceptance criteria for strength test results 14.3.3.1 For site mixed concrete the strength test results shall meet the following criteria: a) no individual valid test result shall be more than 3 MPa below the specified characteristic strength; b) the mean of the first three valid results shall exceed the specified characteristic strength by at least

2 MPa; and c) the mean of any group of four consecutive and overlapping valid results shall exceed the specified

characteristic strength by at least 3 MPa. 14.3.3.2 If the test results fail to meet the acceptance criteria given in 14.3.3.1, the following apply: a) the mix design shall be adjusted to ensure compliance with the acceptance criteria, due cognizance

being taken of available 7 d/projected 28 d cube results; b) in relation to the part of the structure in which concrete represented by the test results has been

used, 1) an assessment of the stress level in the structure shall be carried out; or 2) tests shall be carried out in accordance with 14.4 or clause 15 (or both);

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c) if the acceptance criterion given in 14.3.3.1(a) is not met, the amount of concrete represented by the test shall be limited to the lesser of 50 m3 and that represented by the actual testing frequency; and

d) if the acceptance criterion given in 14.3.3.1(b) is not met, it shall be assumed that the concrete

represented by the test includes the batches represented by the first and the last samples, together with all intervening batches.

14.3.3.3 Should a concreting operation of the same concrete mix be of such magnitude or the sampling of such frequency that 30 or more valid test results have become available within three months, the contractor may choose to have results assessed statistically. It shall be noted that the engineer may, when considering a request for the statistical assessment of the results on the current project, accept evidence of test results from other recent projects undertaken by the contractor and where he/she is satisfied that the workmanship, equipment and materials used are substantially similar. In such a case, the mean of overlapping sets of 30 valid test results for a specific grade of concrete shall exceed the specified strength by at least 1,64 times the standard deviation, and no individual result shall fall below the value specified in 14.3.3.1(a). In the event of strength failure, 14.3.3.2 shall apply. 14.3.3.4 If the compressive strength meets the above criteria but the mean compressive strength of any grade of concrete is less than the specified characteristic strength, steps shall be taken to increase the mean compressive strength to comply with the requirements of table 6. However, the concrete already cast need not be tested as in 14.3.3.2.

Table 6 ― Required mean compressive strength

1 2

Number of tests Required mean compressive strength

4 Specified characteristic strength + 3 MPa

5 Specified characteristic strength + 4,5 MPa




14.3.3.5 Should the strength of the concrete be unsatisfactory, an investigation shall be done in accordance with 14.4 on that part of the structure in which concrete represented by the result has been used. NOTE 1 Acceptance criteria for ready-mix concrete should be in accordance with SANS 878. NOTE 2 The specified strength referred to below is the characteristic strength shown on the drawings or otherwise specified. 14.4 Strength tests of concrete in place NOTE For load tests, see clause 15. 14.4.1 Non-destructive testing Testing by a rebound hammer or other non-destructive device may be permitted by the engineer to determine relative strengths at various locations in the structure as an aid in evaluating the strength of concrete in place or for selecting areas to be cored. Such tests, unless properly calibrated and correlated with other test data, shall not be used as a basis for acceptance or rejection.

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14.4.2 Core tests Where so required, drilled cores shall be obtained and tested in accordance with SANS 5865. Cores shall be drilled and tested when the age of the concrete is as close as possible to the age for strength acceptance according to cubes. At least three representative cores shall be taken from each member or predetermined volume of concrete in locations that are considered potentially deficient. The location of cores shall be determined by the engineer to cause the least impairment to the strength of the structure. The lesser of the top 300 mm and top 20 % of the depth of the concrete member shall not be used for core testing unless unavoidable (for example thin slabs). If, before testing, one or more of the cores show evidence of having been damaged subsequent to or during removal from the structure, it shall be replaced with a new core. If a core contains reinforcing steel, the measured compressive strength of the core shall be corrected in accordance with SANS 5865. Core holes shall be filled with low-slump concrete or mortar. 14.4.3 Acceptance of concrete on the basis of core strengths 14.4.3.1 Provided the cores are tested within 60 d after casting, if the mean core strength is at least 80 % of the specified strength (see 14.3.3), and if no single core strength is less than 70 % of the specified strength, the concrete shall be accepted from a structural capacity point of view. 14.4.3.2 If the concrete in a certain area fails to comply with 14.4.3.1 because a single core result falls below 70 % of the specified strength, a further set of three cores may be taken from the same area to determine the extent of deficient concrete. If the new set of three cores complies with the requirements of 14.4.3.1, the area represented by this second set of cores shall be considered acceptable. If the new set of cores fails to comply with the requirements of 14.4.3.1, 14.4.3.3 applies. 14.4.3.3 If the core strength does not meet the acceptance criteria of 14.4.3.1 or 14.4.3.2, the following shall be considered in relation to the deficient part of the structure: a) strength requirements for the member(s); b) performance of a full-scale load test as in clause 15; c) strengthening the deficient part of the structure; and d) removal and replacement of the deficient part of the structure.

15 Load tests 15.1 Individual precast units 15.1.1 General The load tests described in this clause are intended as checks on the quality of the units, and shall not be used as a substitute for normal design procedures. Where units require special testing, such special testing procedures shall be in accordance with the project specification. Test loads shall be applied and removed incrementally.

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15.1.2 Non-destructive tests 15.1.2.1 Support the unit at its designed points of support and load it for 5 min with a load equal to the sum of the nominal self-mass plus 1,25 times the nominal imposed load. Record the deflection. Ensure that the maximum deflection measured after application of the load is in accordance with the requirements defined by the engineer. 15.1.2.2 Measure the recovery 5 min after the removal of the applied load and then reimpose the load. Ensure that the recovery after the second loading is not less than that after the first loading and not less than 90 % of the deflection recorded during the second loading. At no time during the test shall the unit show any sign of weakness or faulty construction as defined by the engineer in the light of a reasonable interpretation of the relevant data. 15.1.3 Destructive tests Support the unit at its designed points of support and load it. The unit shall not fail at its ultimate load within 15 min of the time when the test load (see 15.2.3) becomes operative. Regard a deflection exceeding 1/40 of the span as failure of the unit. 15.1.4 Special tests In the case of very large units or units not readily amenable to the above tests, such as columns, the precast parts of composite beams, and units designed for continuity of fixity, special testing arrangements shall be agreed upon before such units are cast. 15.2 Structures and parts of structures 15.2.1 General The tests described in this clause are intended as a check on structures other than those covered by 15.1, where there is doubt regarding serviceability or strength. Test loads shall be applied and removed incrementally. 15.2.2 Age at test 15.2.2.1 Carry out the test as soon as possible after expiry of the 28 d from the time of placing the concrete. The test may be carried out earlier, if the test is for any reason other than uncertainty in respect of the quality of the concrete in the structure, and provided that the concrete has already reached its specified strength. 15.2.2.2 When testing prestressed concrete, make allowance for the effect of prestress being above its final value at the time of testing. 15.2.3 Test loads 15.2.3.1 The test loads to be applied for the limit states of deflection and for local damage are the appropriate loads, i.e. the self-mass plus the nominal imposed load. When the ultimate limit state is being considered, ensure that the test load, maintained for a period of 24 h, is the greater of a) the sum of the self-weight plus 1,25 times the nominal imposed load, or b) 1,25 times the sum of the self-weight plus the nominal imposed load. If any of the final self-weight loads is not in position on the structure, add compensating loads as necessary.

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15.2.3.2 Where only part of a structure is to be tested, special precautions may be necessary to ensure that all the elements actually under test are subjected to the full test load, with proper allowance being made for load sharing between elements. 15.2.4 Measurements during the tests Examine the structure before loading, and record the location and width of any cracks present. Take measurements of deflection and crack width as follows: a) immediately after the application of load; b) in the case of the 24 h sustained load test, at the end of the 24 h period of loading; c) after removal of the load; and d) after a 24 h recovery period. Record the ambient temperature and weather conditions during the test. 15.2.5 Assessment of results 15.2.5.1 In assessing the serviceability of a structure or part of a structure after a loading test, consider the possible effects of variation in ambient temperature and humidity during the period of the test. 15.2.5.2 The following criteria shall apply: a) in the case of reinforced concrete structures and class 3 prestressed concrete structures (see

SANS 10100-1), the maximum width of any crack measured immediately on application of the test load for local damage shall not exceed two-thirds of the value for the limit-state requirement (see SANS 10100-1). In the case of class 1 and class 2 prestressed concrete structures, no visible cracks shall have occurred under the test load for local damage;

b) in the case of elements spanning between two supports, the deflection measured immediately after

application of the test load for deflection shall not exceed 1/500 of the effective span. Agreement on limits shall be reached before cantilevered portions of structures are tested;

c) if the maximum deflection, in millimetres, occurring during a period of 24 h under load test, does not

exceed 40 L2/h (where L is the effective span, in metres, and h is the overall depth of construction, in millimetres), the recovery need not be measured, and the criteria given in (d) and (e) below will not apply;

d) if, within 24 h of the removal of the test load calculated in accordance with 15.2.3 for the ultimate

limit state, a reinforced concrete structure or class 3 prestressed concrete structure does not show a recovery of at least 75 % of the maximum deflection occurring during the 24 h under load, repeat the loading. Consider the structure to have failed the test if the recovery after the second loading is less than 75 % of the maximum deflection shown during the second loading; and

e) if, within 24 h of the removal of the test load calculated in accordance with 15.2.3 for the ultimate

limit state, a class 1 or class 2 prestressed concrete structure does not show a recovery of at least 85 % of the maximum deflection occurring during the 24 h under load, repeat the loading. Consider the structure to have failed the test if the recovery after the second loading is less than 85 % of the maximum deflection occurring during the second loading.

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16 Procedure in the event of failure Concrete work judged (by structural analysis or by results of a test) to be inadequate shall be replaced or shall be strengthened by additional construction or other means approved by the engineer. The procedure shall apply to a) each section that failed or contains concrete that failed, as relevant, and b) any other section, irrespective of strength, the functional purpose of which is affected by the section

or concrete referred to in (a) above.

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Annex A (informative)

Recommended specialist literature on massive concrete BAMFORTH, PB. Mass concrete. Concrete Society Digest, 1984, No. 2. Cooling and insulating systems for mass concrete. American Concrete Institute (ACI). Revised edition. Detroit. Committee Report 207.4R-93.

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Annex B (informative)

Technical data for prestressed

structural elements

B.1 Data for pre-tensioned elements The following technical data in respect of pre-tensioned structural elements should be given on the construction drawings: a) Tendon alignment: A diagrammatic layout showing the centroid of each tendon or group of tendons

in both the horizontal and vertical planes, together with the ordinates and offset dimensions. b) Tendons: The number of tendons on which the design is based, designated by the number and

nominal diameter of the bars, wires or strands and the type of prestressing steel, expressed in that order, for example 15 mm × 12,5 mm 7-Hi strand.

c) Tensioning force: The required tensioning force and the corresponding stress level in the

prestressing steel, for each tendon or group of tendons. The forces should be given in kilonewtons (kN) and the stress levels should be expressed as a percentage of the characteristic strength, the 0,2 % proof stress or the yield stress of the prestressing steel, as relevant. The required prestressing force can also be given at salient locations along a member with a tolerance range specified for each.

d) Prestressing losses in tendons: The losses allowed for in the design should be given as follows: 1) elastic deformation of concrete: the "elastic factor", which, when multiplied by the mean

compressive stress in the concrete adjacent to the tendon, will give the loss due to elastic deformation of the concrete;

2) creep of concrete: the "creep factor", which, when multiplied by the mean compressive stress in

the concrete adjacent to the tendon, will give the loss due to the creep of the concrete; 3) shrinkage of concrete: the stress loss, in megapascals (MPa), due to shrinkage of the concrete;

and 4) relaxation of prestressing steel: the stress loss, in megapascals (MPa), at a stress level of 70 % of

the characteristic strength of the prestressing steel due to relaxation of the prestressing steel. e) Bursting reinforcement: for the prestressing system on which the design is based. f) Precamber: at intervals not exceeding 0,25 times the span length. B.2 Data for post-tensioned elements The following technical data in respect of post-tensioned elements should be given on the construction drawings in the format of either a detailed design based on the particular system, or salient requirements for prestressing force and centroid of tendons with the drawings and calculations that comply with the requirements: a) Tendon alignment: A diagrammatic layout showing the centroid of the tendons in both the

horizontal and vertical planes, together with the ordinates, offset dimensions and curve equations of the centroid of the tendons.

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b) Tendon system: The tendon system on which the design is based, designated by the number and nominal diameter of the bars, wires or strands per tendon and the type of prestressing steel, expressed in that order, for example 12 mm × 12,7 mm 7-Hi strand.

c) Tensioning force: The initial jacking force and the effective force at the life anchorage(s) after

transfer, as well as the corresponding stress level in the prestressing steel, for each tendon or group of tendons. The forces should be given in meganewtons (MN) and the stress levels shall be expressed as a percentage of the characteristic strength, the 0,2 % proof stress or the yield stress of the prestressing steel, as relevant.

d) Draw-in or intended release: of the tendons or group of tendons, in millimetres (mm). e) Prestressing losses in tendons: 1) friction loss: the formula used to determine the tendon/duct friction loss together with the values

adopted for the friction coefficient (u) due to curvature and the wobble factor (k) due to unintentional variation from the specified alignment;

2) elastic deformation of concrete: the "elastic factor", which, when multiplied by the mean

compressive stress in the concrete section, will give the loss due to elastic deformation of the concrete;

3) creep of concrete: the "creep factor", which, when multiplied by the compressive stress in the

concrete adjacent to the tendon, will give the loss due to the creep of the concrete; 4) shrinkage of concrete: the stress loss, in megapascals (MPa), due to shrinkage of the concrete;

and 5) relaxation of prestressing steel: the stress loss, in megapascals (MPa), at a stress level of 70 %

of the characteristic strength of the prestressing steel due to relaxation of the prestressing steel. f) Anchorages: The positions where loop type or fan type dead end anchorages may be used. g) Concrete cover: The minimum depth of concrete over the outside of the surface of the sheath or

tendon support (or both). h) Tensioning of tendons: The following tensioning requirements are allowed for in the design: 1) the minimum concrete strength required for initial tensioning; 2) the requirements for partial tensioning or tensioning at a specific stage; 3) the overall sequence of tensioning; and 4) the precamber at intervals not exceeding 0,25 times the span length.

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Bibliography ALEXANDER, MG., et al. Concrete durability index testing manual. Research Monograph no. 4, Departments of Civil Engineering, University of Cape Town and University of the Witwatersrand, March 1999. ASTM C 232, Standard test methods for bleeding of concrete. BS 1881-130, Testing concrete – Part 130: Method for temperature-matched curing of concrete specimens. BS 4486, Specification for hot rolled and hot rolled and processed high tensile alloy steel bars for the prestressing of concrete. BS EN 12504-3, Testing concrete structures – Part 3: Determination of pull-out force. BS EN 13391, Mechanical tests for post-tensioning systems. BUNGEY, JH., MILLARD, SG. and GRANTHAM, MG. Testing of concrete structures. 4th ed. London: Taylor & Francis, 2006. Calcium carbonate-saturated pH value. Cement and Concrete Institute, C&CI TM 9.201. Calcium hardness. Cement and Concrete Institute, C&CI TM 216. Commentary on SANS 1083, Cement and Concrete Institute. 1994. Early age strength assessment of concrete on site. British Cement Association. Crowthorne, BCA, 2000. Best Practice Guides for In-situ Concrete Framed Buildings. Formwork striking times – Criteria, prediction and method of assessment. CIRIA Report 136, 1995. Guide to curing concrete. American Concrete Institute (ACI), 2001, Committee Report 308R. Harrison, T.A. CIRIA Report 136, Formwork striking times: criteria, prediction and methods of assessment. London: Thomas Telford, 1995. Hobb’s’ minimum requirements for durable concrete. 8th ed. BCA, 1998. MACKECHNIE, JR. Predictions of reinforced concrete durability in the marine environment. PhD Thesis, University of Cape Town, 1995. NEWMAN, J. and CHOO, BS. Advanced concrete technology: concrete properties. Oxford: Elsevier, 2003, p. 4/13–4/22. Recommendation for acceptance and application of post-tensioning systems. Federation Internationale de la Precontrainte. Slough: FIP, 1981. SANS 5860, Concrete tests – Dimensions, tolerances and uses of cast test specimens. SANS 9001/ISO 9001, Quality management systems – Requirements. SANS 10160 (all parts), Basis of structural design and actions for buildings and industrial structures.

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SABS – Standards Division The objective of the SABS Standards Division is to develop, promote and maintain South African National Standards. This objective is incorporated in the Standards Act, 2008 (Act No. 8 of 2008). Amendments and Revisions South African National Standards are updated by amendment or revision. Users of South African National Standards should ensure that they possess the latest amendments or editions. The SABS continuously strives to improve the quality of its products and services and would therefore be grateful if anyone finding an inaccuracy or ambiguity while using this standard would inform the secretary of the technical committee responsible, the identity of which can be found in the foreword. The SABS offers an individual notification service, which ensures that subscribers automatically receive notification regarding amendments and revisions to South African National Standards. Tel: +27 (0) 12 428 6883 Fax: +27 (0) 12 428 6928 E-mail: [email protected] Buying Standards Contact the Sales Office for South African and international standards, which are available in both electronic and hard copy format. Tel: +27 (0) 12 428 6883 Fax: +27 (0) 12 428 6928 E-mail: [email protected] South African National Standards are also available online from the SABS website http://www.sabs.co.za Information on Standards The Standards Information Centre provides a wide range of standards-related information on both national and international standards. The Centre also offers an individual updating service called INFOPLUS, which ensures that subscribers automatically receive notification regarding amendments to, and revisions of, international standards. Tel: +27 (0) 12 428 7911 / 0861 27 7227 Fax: +27 (0) 12 428 6928 E-mail: [email protected] Copyright The copyright in a South African National Standard or any other publication published by the SABS Standards Division vests in the SABS or, in the case of a South African National Standard based on an international standard, in the organization from which the SABS adopted the standard under licence or membership agreement. In the latter case, the SABS has the obligation to protect such copyright. Unless exemption has been granted, no extract may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior written permission from the SABS Standards Division. This does not preclude the free use, in the course of implementing the standard, of necessary details such as symbols, and size, type or grade designations. If these details are to be used for any purpose other than implementation, prior written permission must be obtained. Details and advice can be obtained from the Manager – Standards Sales and Information Services. Tel: +27 (0) 12 428 6883 Fax: +27 (0) 12 428 6928 E-mail: [email protected]

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