STRUCTURAL CONCRETE Contents · 1713 Reinforcement - Bar Schedule Dimensions - Cutting and Bending 240 1714 Reinforcement - Fixing 240 1715 Reinforcement - Surface Condition 241

Volume 1 Specification for Road Works

Series 1700 Structural Concrete

STRUCTURAL CONCRETE

Contents

Clause Title Page

1701 Concrete - Classification of Mixes 216

1702 Concrete - Ordinary Structural - Constituent Materials 216

1703 Concrete - Special Structural - Constituent Materials 217

1704 Concrete - General Requirements 218

1705 Concrete - Requirements for Designed Mixes 220

1706 Concrete - Production 221

1707 Concrete - Compliance 222

1708 Concrete - Surface Finish 223

1709 Concrete - Surface Impregnation & Coating 224

1710 Concrete - Construction General 228

1711 Concrete - Grouting of Prestressing Tendons 234

1712 Reinforcement - Materials 240

1713 Reinforcement - Bar Schedule Dimensions - Cutting and Bending 240

1714 Reinforcement - Fixing 240

1715 Reinforcement - Surface Condition 241

1716 Reinforcement - Laps and Joints 241

1717 Reinforcement - Welding 241

1718 Prestressing Tendons - Materials 242

1719 Prestressing Tendons - Handling and Storage 242

1720 Prestressing Tendons - Surface Condition 242

1721 Prestressing Tendons - Straightness 242

1722 Prestressing Tendons - Cutting 243

1723 Prestressing Tendons - Positioning of Tendons, Sheaths and Duct Formers . . 243

1724 Prestressing Tendons - Tensioning 243

1725 Prestressing Tendons - Protection and Bond 245

1726 Stainless Steel Dowels - Materials 245

1727 Inspection and Testing of Structures and Components 245

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Structural Concrete

1701 Concrete - Classification of Mixes

General

1 Unless otherwise described in Appendix 17/4, concrete shall be a designed mix and shall be either ordinary structural concrete or special structural concrete. The mixes for the structural concrete in the Works are given in Appendix 17/1.

Ordinary Structural Concrete

2 Ordinary structural concrete shall contain only materials specified in Clause 1702.

Special Structural Concrete

3 Special structural concrete is concrete containing an admixture or material other than those specified in Clause 1702 or any restriction on the range of material types specified in Clause 1702.

Designed Mix

4 The Contractor shall select the mix proportions and, unless otherwise specified, the workability in order to satisfy the strength and other requirements of the Contract.

1702 Concrete - Ordinary Structural - Constituent Materials

Cement

1 Cement shall comply with one of the following:

(i) IS 1 (Normal and Rapid Hardening Portland Cement);

(ii) BS 12 (White or Coloured Portland cement);

(iii) BS 146 (Portland blastfurnace cements);

(iv) BS 4027 (Sulphate-resisting Portland cement);

(v) BS 6588 (Portland pulverised-fuel ash cement) provided that the PFA complies with (vi) below;

(vi) A mixture of IS 1 or BS 12 (Portland cement) and BS 3892 : Part 1 (pulverised-fuel ash for use in structural concrete) provided that the amount of PFA is not less than 15% nor more than 35% by weight of the total cement. The PFA used shall have a maximum colour index of 7 (Colour comparator disc reference no. 296570) when tested using the Lovibond Colour Comparator system as recommended in BS 3892: Part 1;

(vii) A mixture of IS 1 or BS 12 (Portland cement) and BS 6699 (ground granulated blastfurnace slag for use with Portland cement) provided that the amount of ggbs is not more than 65% by weight of the total cement.

Aggregate

2 Unless otherwise specified or agreed by the Engineer, aggregates shall comply with one of the following Standards, as appropriate:

(i) IS 5 (Aggregates for Concrete);

(ii) BS 1047 : 1983 (Air-cooled blastfurnace slag coarse aggregate for concrete).

The shell content of the aggregates included as calcium carbonate, as determined by the methods in IS 5 : Part 3.3, shall not exceed the following amounts:

Nominal % size (mm)

40 2 20 5 10 15 fine 30

The flakiness index (when determined by the sieve method described in IS 5 : Part 3.2) of the coarse aggregate shall not exceed 35% for 10 mm aggregate nor 30% for 20 mm aggregate. For concrete Grade 40 or higher the ten per cent fines value of the coarse aggregate, determined in accordance with IS 5 : Part 3.9 shall be not less than 100 kN and for other grades not less than 50 kN. The test sample shall be in a soaked condition at the time of test.

Chloride levels of the aggregates shall be determined daily, or as otherwise agreed by the Engineer, in accordance with IS 5 : Part 3.8.

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The drying shrinkage shall not exceed the following values when tested in accordance with BS 812 : Part 120:

Prestressed concrete: 0.045% All other structural concrete: 0.065%

Water

3 If water for the Works is not available from a Public piped supply the Engineers approval shall be obtained regarding the source of supply and manner of its use. When required by the Engineer the Contractor shall arrange for tests of the water to be carried out in accordance with BS 3148. Water from the sea or tidal rivers shall not be used.

1703 Concrete - Special Structural - Constituent Materials

Cement

1 Cement shall comply with sub-Clause 1702.1 or, subject to the approval of the Engineer, with one of the following:

(i) BS 1370 (low heat Portland cement).

(ii) BS 4246 (high slag blastfurnace cement).

(iii) BS 12 (pigmented Portland cement).

(iv) A mixture of IS 1 or BS 12 (Portland cement) and BS 6699 (ground granulated blastfurnace slag (ggbs) for use with Portland cement) provided that the amount of ggbs is not less than 50% nor more than 90% by weight of the total cement.

Admixtures

4 (i) General. The quantity and method of using admixtures shall be in accordance with the manufacturer's recommendations and in all cases shall be subject to the approval of the Engineer. Unless otherwise described in Appendix 17/4 or approved by the Engineer, an admixture shall comply with one of the following Standards:

BS 1014 (Pigments for Portland cement and Portland cement products).

BS 5075 (Concrete admixtures) (except chloride-based admixtures).

In all cases the Contractor shall provide the following information for the Engineer's approval:

(a) the quantity to be used, in ml per kg of cement and ml per cubic metre of concrete for liquid products and in kilograms per 50 kilograms of cement and kilograms per cubic metre of concrete for solid products;

(b) the detrimental effects caused by adding a greater or lesser quantity in kilograms per cubic metre of concrete;

(c) the chemical name(s) of the main active ingredient!s);

(d) whether or not the admixture leads to the entrainment of air.

If required by the Engineer, the Contractor shall demonstrate the action of an admixture by means of trial mixes.

(ii) Calcium chloride. The use of calcium chloride in any form is prohibited.

Aggregate

2 Aggregate shall comply with the requirements of sub-Clause 1702.2. Unless otherwise described in Appendix 17/4 or agreed by the Engineer, lightweight aggregate shall comply with BS 3797.

Water

3 Water shall comply with sub-Clause 1702.3.

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1704 Concrete - General Requirements

Concrete Grade and Class

1 For each grade of concrete the specified characteristic strength in N/mm 2 shall be as given in Table 17/1. The class of concrete shall be defined by its grade followed by the maximum size of aggregate allowed (e.g. 30/20).

Table 17/1: Grades of Concrete

Grade Characteristic Strength

N/mm 2

7.5 7.5 10 10.0 15 15.0 20 20.0 25 25.0

30 30.0 40 40.0 50 50.0 60 60.0

Minimum Cement Content and Maximum Water/Cement Ratio

2 The cement content shall be not less than, and the water/cement ratio shall be not greater than described in Appendix 17/1.

Table 17/2: Maximum Total Chloride

Type or use of concrete

Maximum total chloride content expressed as % of chloride ion by mass of cement (inclusive of ggbs or PFA when these are used as cement)

Prestressed concrete, heat-cured concrete containing embedded metal 0.1

Concrete made with cement complying with BS 4027 0.2

Concrete containing embedded metal and made with cement complying with IS 1, BS 12, BS 146 : Part 2, BS 1370, BS 4246, BS 6588 or

combinations of IS 1 or BS 12 with PFA or ggbs 0.1

NOTE. % chloride ion x 1.648 = % equivalent sodium chloride. % chloride ion x 1.565 = % equivalent anhydrous calcium, chloride

Maximum Cement Content

3 The cement content shall not exceed 500 kg/m' unless otherwise described in Appendix 17/1 or agreed by the Engineer.

Maximum Sulphate Content

5 The total acid-soluble sulphate content of the concrete mix, expressed as SO :„ shall not exceed 4% of the mass of the cement in the mix. The sulphate shall be calculated as the total from the various constituents of the mix.

Maximum Chloride Content

4 The total chloride content of a concrete mix arising from the cement, aggregate and any other source shall not exceed the appropriate limit given in Table 17/2 when determined in accordance with BS 812 : Part 117.

Control of Alkali-Silica Reaction

6 (i) Either sub-clause (ii) or sub-clause (iii) shall be complied with. The Contractor shall indicate to the Engineer which of the procedures he proposes to adopt.

(ii) For protection of the structure by controlling the reactive silica content of the aggregates, the following shall be complied with:

(a) Representative samples of the aggregates to be used shall be subjected to petrographic examination by a competent petrographer approved by the Engineer. The

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(iii)

definition of rock types shall be as per IS 5 : Part 3.14 Description and classification of aggregates.

Where the geological formation of the source material is complex, data from borings may be required to prove the nature of the parent strata.

The petrographer shall produce a report and shall quantify the presence if any of each of the potentially reactive constituents listed in Table 17/3. The report shall state the geological age of any chert discovered. Where the petrographer is evaluating a parent rock or gravel the report shall indicate the percentage of such constituents likely to remain in the aggregates after they have been processed to IS 5.

The Contractor shall then provide the Engineer with a report showing the percentage of the potentially reactive constituents which will occur in the proposed concrete mix as a result of blending the coarse and fine aggregates.

If the content of potentially reactive minerals or rock is above the limits given in the second column in Table 17/3 the aggregates may be acceptable at the Engineer's absolute discretion following further assessment as per sub-clause (ii)(b).

(b) Where the limits of potentially reactive material given in Table 17/3 are exceeded the aggregates may still be acceptable at the Engineer's sole discretion, lb determine acceptability or otherwise of the aggregates the Engineer will require testing in accordance with ASTM C-289-87 and ASTM C-227-87 or as may be otherwise instructed.

For protection of the structure by controlling the alkali content of the cement or concrete, the following subclauses shall be complied with:

(a) (i) The calculated alkali content of the concrete mix shall not exceed 4.0 kg per cubic metre of concrete. If the assessment of the aggregate indicates that the only potentially reactive mineral or rock discovered is microcrystalline or cryptocrys-talline quartz or chalcedony derived from chert which is of carboniferous

Table 17/3: Aggregate Types

Potentially reactive mineral or rock

Acceptable Maximum Content

Opaline silica Crystobalite Tridymite Zero

Microcrystalline and cryptocrystaline quartz, chalcedony 5%

Volcanic glass 5%

Highly strained* quartz 30% or less

If the average undulatory extinction angle obtained from at least 20 separate quartz grains (measured in thin sections under a petrological microscope) is more than 25 degrees, the quartz shall be classified as highly strained.

age or older, the limit may be increased to 4.5 kg per cubic metre.

or (a)(ii) The alkali content of the Portland cement shall not exceed 0.6%.

(b) (i) The alkali content of the Portland cement shall be taken as the certified average acid soluble alkali content of the cement plus 1.64 times the standard deviation. The certified average acid soluble alkali content shall be the average of the last 25 determinations of alkali content carried out on consecutive daily samples immediately prior to submission. The Contractor shall submit to the Engineer the test certificates furnished by the cement manufacturer. The alkali content of the Portland cement shall be determined in accordance with the method recommended in BS 4550 : Part 2 or by the use of an x-ray fluorescence technique calibrated against that Standard.

(b) (ii) The Contractor shall submit to the Engineer test certificates giving the acid soluble alkali content of any slag or pulverised fuel ash to be used. These shall be determined using an approved method based on BS 4550 : Part 2.

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(b) (iii) The equivalent sodium oxide content of the coarse and fine aggregate shall be calculated from the quantity of chloride ion present, which shall be measured by the method in IS 5 : Part 3.8 : Method of test for chloride salts.

(b) (iv) For the purposes of (iii)(a)(i) the calculated alkali content of the concrete mix shall be determined by summing:

(a) The certified average acid soluble content of the cement plus 1.64 times the standard deviation;

(b) 0.76 times the chloride ion content of the aggregate taken as the percentage by weight (ignore if less than 0.01%);

(c) 50% of the acid soluble Na,0 equivalent of any slag taken as the certified average plus 1.64 times the standard deviation;

(d) 17% of the acid soluble Na,0 equivalent of any PFA taken as the certified average plus 1.64 times the standard deviation; and

(e) the equivalent Na 2 0 contribution of any admixtures.

Any change in the source of material or in mix proportions (except changes in Portland cement content of not more than 20 kg/m : i, of which the Engineer shall be notified) shall be subject to the Engineer's prior approval.

Where Portland cement to IS 1 or BS 12 and pulverised-fuel ash to BS 3892 : Part 1 or Portland cement to IS 1 or BS 12 and ground granulated blastfurnace slag to BS 6699 have been combined by the Contractor then any change in the source material or in the mix proportions (except changes in Portland cement content of not more than 15 kg/m' and changes in pulverised-fuel ash or ground granulated blastfurnace slag of not more than 10 kg/m : l of which the Engineer shall be notified) shall be subject to the Engineer's prior approval.

Trial Mixes

2 The Contractor shall give notice to enable the Engineer to be represented at the making of trial mixes and preliminary testing of the cubes. The Contractor shall prepare trial mixes, using samples of approved material typical of those he proposes to use in the Works, for all grades, to the Engineer's satisfaction before commencement of concreting.

The Contractor shall ascertain the workability of the trial mixes.

Sampling and testing procedures shall comply

with BS 1881.

1705 Concrete - Requirements for Designed Mixes

Suitability of Proposed Mix Proportions

1 The Contractor shall submit for the Engineer's approval, prior to the supply of any designed mix, the following information:

(i) the nature and source of each material;

(ii) either:

(a) appropriate existing data as evidence of satisfactory previous performance for strength, workability and water/ cement ratio; or

(b) full details of tests on trial mixes carried out in accordance with sub-Clause 2 of this Clause;

(iii) the quantities of each material per cubic metre of fully compacted concrete.

The concreting plant and means of transport employed to make the trial mixes and to transport them representative distances shall be similar to the corresponding plant and transport to be used in the Works. A clean dry mixer shall be used and the first batch discarded. Test cubes shall be taken from trial mixes as follows. For each mix a set of six cubes shall be made from each of three consecutive batches. Three from each set of six shall be tested at an age of 28 days and three at an earlier age approved by the Engineer.

The average strength of the nine cubes tested at 28 days shall exceed the specified characteristic strength by 20% or 6 N/mm 2 , whichever is the greater.

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Additional Trial Mixes

3 During production the Contractor shall carry out trial mixes and tests, if required by the Engineer, before substantial changes are made in the materials or in the proportions of the materials to be used, except when adjustments to the mix proportions are carried out in accordance with sub-Clause 1706.4(i).

1706 Concrete - Production

Cement

1 Different cements, pulverised-fuel ash and ggbs shall be stored in separate silos. Alternatively, these materials may be stored in bags in dry weatherproof sheds with raised floors and each consignment shall be kept separate and distinct. Any cement that has become contaminated by damp or other causes shall be removed immediately. Silos for storing pulverised-fuel ash shall be equipped with aerators to ensure free flow within the silo.

The use of cements of the same type from different sources will not normally be permitted. Where permission to use cement from a source other than that used in the original trial mixes is granted, the procedure given in sub-Clause 1705.3 shall be repeated.

Aggregate

2 Fine aggregates and single-sized coarse aggregates shall be used, unless otherwise agreed by the Engineer, and stored in separate hoppers, or different stacks which shall be separated from each other. Relative proportions of coarse aggregates to be used shall be determined on the basis of the trial mixes.

All aggregates shall be kept free from contact with deleterious matter with adequate provision for drainage, and shall be stored and handled so as to avoid segregation.

The overall grading of the aggregates shall be such as to produce concrete of the specified quality that will work readily into position without segregation or excessive bleeding. The overall grading shall be controlled throughout the work so that it conforms closely to that assumed in the selection of the mix proportions. Each delivery shall be inspected and, if required in Appendix 1/5, testing shall be carried out as specified therein.

The Contractor shall provide the Engineer with copies of the results of routine control tests carried out by the aggregate producer.

The quantities of cement, fine aggregate and the various sizes of coarse aggregate shall be measured by weight unless otherwise agreed by the Engineer.

Separate weighing machines shall be used for cementitious materials and aggregates unless otherwise agreed by the Engineer. Alternatively, cementitious materials may be measured by using a whole number of bags in each mix.

The quantity of water adjusted for the free moisture content of the aggregate shall be measured. Any admixture to be added shall be measured and, if solid, shall be measured by weight. Different types of cement shall not be mixed.

The batch weight of aggregate shall be adjusted to allow for the free moisture content of the aggregate being used.

All measuring equipment shall be maintained in a clean and serviceable condition. Its accuracy shall be checked over the range in use when set up at each site, and maintained thereafter.

The accuracy of equipment shall fall within the following limits:

Batching and Mixing

3

Measurement of cementitious materials

Measurement of water

Measurement of aggregate

Measurement of admixture

± 37c of the quantity of cement in each batch

+ 3% of the quantity of water in each batch

± 3% of the total quantity of aggregate in each batch

± 59c of the quantity of admixture in each batch.

The mixer shall comply with BS 1305 where applicable. Care shall be taken to ensure that all constituents are thoroughly mixed and, in particular, any admixtures are uniformly distributed throughout the batch.

The mixing time shall be not less than that recommended by the manufacturer.

Mixers that have been out of use for more than 30 minutes shall be thoroughly cleaned before any fresh concrete is mixed. Unless otherwise agreed by the Engineer, the first batch of concrete through the mixer shall then contain an appropriate additional quantity of cement to be agreed with the Engineer. Mixing plants

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shall be thoroughly cleaned before changing from one type of cement to another.

Control of Strength of Designed Mixes

4 (i) Adjustment to mix proportions. Adjustments to mix proportions shall be made, other than those allowed under sub-Clause 1705.2, subject to the Engineer's approval, in order to minimize the variability of strength and to maintain the characteristic strength.

Table 17/4: Rates of Sampling and Testing

Grade of Sample from one batch selected concrete randomly to represent an

averagevolume of not more than the lesser of:

Greater than 40 10 m1 or 10 batches

30 to 40 20 m* or 20 batches

Less than 30 30 m1 or 30 batches

Ready Mixed Concrete

5 Ready mixed concrete shall comply with this Series (and in particular with sub-Clause 1706.3) and the following special requirements. The concrete shall be carried in purpose-made agitators, operating continuously, or truck mixers. The concrete shall be compacted and in its final position within 2 hours of the introduction of cement to the aggregate, unless a longer time is agreed by the Engineer. The time of such introduction shall be recorded on the delivery note together with the weight of the constituents of each mix.

When concrete is transported in a truck mixer, water shall be added under supervision at the central batching plant. Water shall not be added at the site unless agreed in writing by the Engineer. In no circumstances shall water be added in transit.

1707 Concrete - Compliance

General

1 Sampling and testing of fresh and of hardened concrete shall comply with BS 1881 unless otherwise described in Appendix 17/4.

taken to represent the batches defined in Clause 3.17 of that Standard.

(iii) Special testing. Special testing shall be used if required in Appendix 17/4.

One test cube shall be made from each of two independent representative samples taken from every batch of concrete selected for testing.

The average strength of the two test cubes taken from the same batch of concrete shall exceed the specified characteristic strength by not less than 2.0 N/mm 2 or one-tenth of the specified strength, whichever is the smaller.

If the average strength of the test specimens taken to represent a given batch of concrete fails to meet the appropriate requirement, the whole of that batch of concrete represented by those specimens shall be deemed not to comply with the strength requirements of the Specification. Compliance with the average strength requirement in respect of a given batch of concrete shall not be adduced as evidence of compliance in respect of any other batch.

Strength

2 (i) General. Compliance with the specified characteristic strength shall be based on tests made on cubes at an age of 28 days.

Unless otherwise instructed by the Engineer, the rate of sampling shall be as given in Table 17/4 but not less than one sample shall be taken on each day that concrete of that grade is used.

(ii) Sampling and testing. The procedure for sampling, testing and compliance given in Clause 3.16 of BS 5328 : Part 4 : 1990 shall be used and the results shall be

Workability

3 The workability of the fresh concrete shall be such that the concrete is suitable for the conditions of handling and placing as described in sub-Clause 1710.3 so that after compaction, as described in sub-Clause 1710.3, it surrounds all reinforcement, tendons and ducts and completely fills the formwork. Workability shall be measured for each batch or at such times as directed by the Engineer using tests in accordance with Clause 3.5 of BS 5328 : Part 4. The workability shall be within the limits of the required value given in Clause 3.5 of BS 5328 : Part 4.

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Air Content of Fresh Concrete

4 When air entrainment is required in Appendix 17/1 the average air content of the fresh concrete shall be:

for natural aggregates 10 mm nominal size, 7.5%;



for natural aggregates 40 mm nominal size, 4.5%.

The percentage air content determined from individual samples taken at the point of placing the concrete and representative of any given batch of concrete shall be within ± 2.0% of the specified value. The average percentage air content from any four consecutive determinations from separate batches shall be within ± 1.5% of the specified value.

The air content shall be checked as described in BS 1881 : Part 106 as follows:

(i) for each batch;

(ii) at such times as instructed by the Engineer.

1708 Concrete - Surface Finish

Trial Panels

1 When required in Appendix 17/3 and before commencing concreting, the Contractor shall prepare a trial panel of size and surface finish acceptable to the Engineer.

The panel shall be filled with the proposed concrete mix compacted by the method to be used in the work. As soon as practicable after compaction, the forms shall be removed to enable the Engineer to check the surface finish and compaction achieved.

Control of Colour

2 Each constituent material shall be obtained from a single consistent source. The aggregates shall be free of any impurities that may cause staining. The mix proportions and the grading, particularly of the fine aggregate, shall be maintained constant. The same type of plywood or timber shall be used in formwork throughout similar exposed areas.

Release Agents

3 Release agents for the formwork shall be to the approval of the Engineer and shall enable the formwork to be removed without damage to the


concrete surface. There shall be no adverse residual effect from the release agent on the concrete surface. Where a concrete surface is to be permanently exposed, only one agent shall be used throughout the entire area. Release agents shall be applied evenly and shall not be permitted to come into contact with reinforcement, prestressing tendons and anchorages.

The release agent shall also not leave any residue that is detrimental to the surface impregnation of the concrete.

Where the concrete is to receive an applied finish, or surface impregnation, the release agent shall be compatible.

Surface Finishes for Concrete

4 (i) Formed Surfaces - Classes of Finish

Formwork as described in sub-Clause 1710.2 shall be capable of producing the following finishes where required in the Works:

Class Fl . No extra requirement.

Class F2. The irregularities in the finish shall be no greater than those obtained from the use of wrought thicknessed square edged boards arranged in a uniform pattern. The finish is intended to be left as struck but imperfections such as fins and surface discolouration shall be made good to the approval of the Engineer.

Class F3. The resulting finish shall be smooth and of uniform texture and appearance without discolouration. The formwork lining shall leave no stain on the concrete and shall be so joined and fixed to its backing that it imparts no blemishes. It shall be of the same type and obtained from only one source throughout any one structure. The Contractor shall make good any imperfections in the finish to the approval of the Engineer. Internal ties and embedded metal formwork supports will not be allowed.

Class F4. The requirements for Class F4 are as for Class F3 except that internal ties and embedded metal formwork supports will be permitted. The ties shall be positioned only in rebates or in other positions as described in Appendix 17/3 or as agreed by the Engineer.

Class F5. The resulting finish shall be smooth and of uniform texture. Any blemishes and imperfections, such as discolouration and fins, shall be made

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good to the approval of the Engineer. Provision for the embedment of metal formwork supports in the Permanent Works on a regular spacing, shall be allowed.

Class F6. Bush Hammered Finish.

Class F7. Exposed Aggregate Finish.

Class F8. Board Marked Finish.

Other classes. The finishes shall comply with the specific requirements described in Appendix 17/3.

Permanently exposed concrete surfaces to all Classes of finish other than Fl shall be protected from rust marks and stains of all kinds.

Unless otherwise described in Appendix 17/3, all formwork joints for all classes of finish other than Fl shall form a regular pattern agreed by the Engineer with horizontal and vertical lines continuous throughout each structure and all construction joints shall coincide with these horizontal or vertical lines.

(ii) Unformed Surfaces - Classes of Finish

Class Ul finish. The concrete shall be levelled and screeded to produce a uniform surface to the profile shown on the Drawings. No further work shall be applied to the surface unless it is used as a first stage for another class of finish.

Class U2 finish. After the concrete has hardened sufficiently, the Class Ul finish shall be floated by hand or machine sufficiently only to produce a uniform surface free from screed marks.

Class U3 finish. When the moisture has disappeared and the concrete has hardened sufficiently to prevent laitance from being worked to the surface, a Class Ul finish shall be steel-trowelled under firm pressure to produce a dense, smooth uniform surface free from trowel marks.

Class U4 finish. This finish is for bridge decks that are to receive waterproofing systems. The concrete shall be levelled and screeded to produce a uniform surface. When the concrete has sufficiently hardened and the bleed water evaporated, the surface shall be trowelled to produce a hard dense surface free from screed marks and exposed aggregate. Finally, the surface shall be lightly textured with a wooden float or equivalent.

Alternatively, the concrete shall be levelled, screeded and floated to produce a uniform surface and immediately before

the waterproofing operation this surface shall be water jetted or grit blasted to provide a lightly textured finish.

The finished surface shall not deviate from the required profile by more than 10 mm over a 3 m gauge length or have any abrupt irregularities more than 3 mm.

Notwithstanding the above, it is the contractors responsibility to produce a deck finish appropriate to the deck waterproofing system to be used.

Class U5 finish. This finish is for footbridge surfaces that are to receive either separate or combined systems, or coatings of waterproofing and surfacing materials. The concrete shall be levelled and screeded to produce a uniform finish. When the concrete has sufficiently hardened to prevent laitance being worked to the surface it shall be floated to produce a surface free from screed marks and exposed aggregate. Finally, the surface shall be textured as agreed by the Engineer to suit the requirements of the particular waterproofing and surfacing system. The accuracy of the finished surface shall be such that it does not deviate from the required profile by more than 5 mm over a 3 m gauge length or have any abrupt irregularities.

Class U6 finish. Bush Hammered Finish.

Class U7 finish. Exposed Aggregate Finish.

Other classes. The finishes shall comply with the specific requirements described in Appendix 17/3.

1709 Concrete - Surface Impregnation and Coating

General

1 (i) Impregnation and/or coatings shall be applied to those surfaces described in Appendix 17/2 in accordance with the manufacturer's instructions unless otherwise agreed by the Engineer.

(ii) Testing of performance of Silane or Siloxane shall be carried out in accordance with the German Department of Transport's document "Technical Test standards for Surface Protection Systems" TP OS, 1990 Edition, referred to hereafter as "TP OS"

("Technische Priifvorschriften fur Oberflachenschutzsysteme").

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Impregnation with Silane or Siloxane

2 (i) Silane can be used alone or with a coating, Siloxane is always used with a coating. Such materials are to be used as described in Appendix 17/2.

(ii) Following evaporation the minimum active material content in the treated substrates must be > 5% when treated in accordance with Section 2.2 of TP OS.

(iii) Reaction products must not contain hazardous materials referred to in EC Directives 88/379 and 67/548 or in any additions to these documents current at the time of tendering.

(iv) For mortar samples tested in the untreated and treated condition in accordance with Section 6.12 of TP OS the ratio:

Water absorption when treated with hydrophobic material divided by Water absorption when untreated shall be less than 0.3.

that delivery complies with sub-Clause 2.1(i) of this Clause. Material shall not be used in the works until this certificate of compliance has been accepted by the Engineer.

(iii) The material shall be stored in a dry frost free environment protected from direct heat.

(iv) The containers shall remain sealed until their contents are required for use. The contents of any opened container shall be used within 48 hours or disposed of safely in accordance with the manufacturer's instructions.

Equipment for Silane Application

4 A continuously circulating pumped system with a nozzle pressure of 0.06-0.07 N/mm- shall be used to apply the material. Water shall be prevented from entering any part of the equipment.

(v) If equal approved water based or solvent free impregnation materials are available these shall be used.

(vi) The Engineer may accept materials offering a performance in respect of the protection of concrete and long term durability equivalent to that of monomeric alkyl (isobutyl) trialkoxy silane and siloxane. The assessment of the durability of an alternative impregnating material will be based on the provision of evidence that it has in practice provided an effective water repellant but vapour permeable layer at the concrete surface for a period of not less than 15 years after application. The Engineer's decision on suitability of alternative materials shall be final.

Silane

3 (i) Where the material used for impregnation is Silane based it shall be monomeric alkyl (isobutyl) trialkoxy silane with a minimum active content of 95% delivered to the site in sealed containers. The 5% fraction shall not contain hydrocarbon solvents. In respect of specific gravity and refractive index, the material shall comply with the values stated in the manufacturer's product specification.

(ii) The Contractor shall provide with each delivery a certificate that the material in

Surface Condition for Silane Application

5 (i) Areas to be treated shall be protected from adverse effects of the weather and shall be surface dry for a minimum of 24 hours before application commences. Artificial drying of surfaces shall not be permitted.

(ii) Surfaces shall be free from loose or deleterious matter and residues of curing membranes and release agents. The Contractor shall demonstrate to the Engineer that harmful residual effects from the application of curing membranes are not present before impregnation commences. Surfaces of old structures shall be hand brushed with a stiff bristle brush to remove surface deposits. In addition, when a surface coating is to be applied after application of Silane, concrete surfaces shall be water jetted at a pressure of 180-200 bar to remove loose matter, laitance etc.

(iii) Where water jetting is used as a means of surface preparation, surfaces must be allowed to dry for at least two days (at 15°C) before application begins.

(iv) Where a surface coating is to be applied after application of Silane, all pores and blowholes in concrete surfaces to be coated shall he repaired before treatment with Silane as specified in 1709.13.

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(v) Where a subsequent coating is not to be applied after application of Silane, blowholes etc. shall be repaired to the satisfaction of the Engineer prior to application of Silane.

Application of Silane

6 (i) Impregnation shall be carried out as a series of continuous operations in a sequence agreed by the Engineer.

(ii) Impregnation shall be earned out not less than 28 days after the concrete has been placed and not less than 14 days after concrete repairs have been completed.

(iii) The material shall be applied by continuous spray technique giving saturation flooding, working from the lowest level upwards. Two applications shall be made each at a coverage of 300 ml/m*, with an interval between each of at least six hours.

(iv) Impregnation shall not be carried out in the following conditions:

(a) when the shade temperature is below 5°C;

(b) when the temperature of the concrete surface is greater than 25°C.

(v) Elastomeric bearings, painted steel surfaces, exposed bituminous materials and joint sealants adjacent to members to be impregnated shall be masked off. All masking shall be removed following completion of the impregnation process.

(vi) Members shall be protected from rain and traffic spray during application and for at least six hours after completion.

Siloxane

7 (i) Where the material used for impregnation is siloxane-based it shall be siloxane with high alkali resistance satisfying the requirements of Section 6.12 of TP OS. The active content and material composition must meet the overall requirements laid down in 1709.2. The materials shall comply with the values stated in the manufacturer's product specification and technical data sheets and shall be delivered to the site in sealed containers.

(ii) The Contractor shall provide with each delivery a certificate that the material in that delivery complies with 1709.7(i)

above. Material shall not be used in the works until this certificate of compliance has been accepted by the Engineer.

(iii) The material shall be stored in a dry frost free environment protected from direct heat.

(iv) The containers shall remain sealed until their contents are required for use. The content of any opened container shall be used within 4 weeks or disposed of safely in accordance with the manufacturer's instructions.

Equipment for Siloxane Application

8 A continuously circulating pumped system with a nozzle pressure of 0.06-0.07 N/mm- may be used to apply the material. Water shall be prevented from entering any part of the equipment. Application by brush or roller is also suitable.

Surface Condition for Siloxane Application

9 (i) Areas to be treated shall, where necessary, be protected from adverse effects of the weather and shall be surface dry for a minimum of 24 hours before application commences. Artificial drying of surfaces shall not be permitted.

(ii) Surfaces shall be free from loose or deleterious matter and residues of curing membranes and release agents. The Contractor shall demonstrate to the Engineer that harmful residual effects from the application of curing membranes are not present before impregnation commences. In addition, where a surface coating is to be applied after application of Siloxane, concrete surfaces shall be water jetted at a pressure of 180-200 bar to remove loose matter, laitence etc .

(hi) If water jetting is used as a means of surface preparation, the surface must be allowed to dry for at least two days (at 15°C) before application commences.

(iv) Where, in Appendix 17/2, the specification calls for a surface coating to be applied after application of Siloxane, all pores and boreholes in the concrete surfaces to be subsequently coated shall be repaired prior to application of Siloxane as specified in 1709.13.

(v) Where subsequent coating is not to be applied after application of Siloxane,

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blowholes etc. shall be repaired to the satisfaction of the Engineer prior to application of Siloxane.

Application of Siloxane

10

(ii)

(iii)

(iv)

(v)

(vi)

Coating

11 (i)

Impregnation shall be carried out as a series of continuous operations in a sequence agreed by the Engineer.

Impregnation shall be carried out not less than 28 days after the concrete has been placed, and not less than 14 days after concrete repairs have been completed.

The material shall be applied using equipment described in 1709.8 giving saturation flooding, working from the lowest level upwards. Two application, shall be made, each at a coverage of 250 ml/m2 with an interval between each of at least 4 hours.

Impregnation shall not be canned out in the following conditions:


(b) when the temperature of the concrete surface is greater than 25°C.

Elastomeric bearings, painted steel surfaces, exposed bituminous materials and joint sealants adjacent to members to be impregnated shall be masked off. All masking shall he removed following completion of the impregnation process.

Members shall be protected from rain and traffic spray during application and for at least six hours after completion.

Only coating systems having a current Irish Agrement Board Roads and Bridges Certificate shall be used. Coating materials shall form part of a coating system consisting of the following components:

(a) Cementitious fillers to close any pores, voids or holes to be applied after substrate preparation.

(b) Coating materials.

Materials shall be based on acrylates, diluted in suitable solvents or shall be water based.

The coating shall consist of a primer and two pigmented top coats.

The coating system shall form a continuous film to protect the concrete surfaces.

All parts of the coating system, fillers and coatings must be part of a system and be compatible with each other and with the substrate. Where surface impregnation precedes coating, all parts of the coating system shall be compatible with impregnation material.

(ii) The following performance requirements of the coating must be met:

(a) The diffusion resistance against carbon dioxide uCO. must be > 2.0 x 106;

(b) The water vapour diffusion resistance must be < 15 x 10';

(c) The water absorption coefficient W24 of a standard prism (according to DIN 52617) coated with the coating must be < 3.0 x 10 1 kg/m 2 h"s;

(d) The adhesive bonding strength (mean value) of the coating system must be greater than 1 N/mm 2.

(iii) The materials shall comply with the values stated in the manufacturers product specification and technical data sheets and shall be delivered to the site in unopened containers.

The Contractor shall provide with each delivery a certificate showing that the material in that delivery complies with paragraphs (i) and (ii) of this Section. Material shall not be used in the works until this certificate of compliance has been accepted by the Engineer.

(iv) The material shall be stored in a dry frost free environment protected from direct heat.

(v) The container shall remain unopened until the contents are required for use. The content of any opened container shall be used within 48 hours or disposed of safely in accordance with the manufacturer's instructions.

Equipment for Coating Application

12 Equipment used shall be strictly in accordance with manufacturer's instructions and in accordance with the product specification and technical data sheets on the products supplied by the manufacturer.

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Surface Condition and Repairs prior to Coating Application

13 (i) Areas to be treated shall be protected from adverse effects of the weather and shall be surface dry. Surface conditions shall be strictly in accordance with the product specification and technical data sheets on the products supplied by the manufacturer.

(ii) Surfaces which have recently been prepared and treated with silane or siloxane need only be free from loose dirt. Surfaces which have had no previous preparation shall be cleaned by water jetting at a pressure of 180-200 bar.

(iii) Any necessary concrete repair work must be carried out after surface preparation, using cementitious concrete repair systems suitable for bridge and structural repairs.

(iv) Pores and blow holes shall be closed with a proprietary cementitious fine filler which is part of the coating system. Prior to the application, the concrete substrate should be damp but not saturated with water. The scratch coat shall be allowed to cure for at least two days before any surface impregnation or coating is applied.

(v) The coating system shall be carried out as a series of continuous operations in a sequence agreed by the Engineer.

If necessary, test sample areas shall be carried out to determine colour, coverage rates and coating system finishes.

(vi) Coating systems shall be applied not less than 21 days after the concrete has been placed and not less than 14 days after concrete repairs have been completed.

(vii) Coating systems shall not be carried out in the following conditions:


(b) when the surface temperature of the concrete is greater than 25°C.

(viii) Elastomeric bearings, painted steel surfaces, exposed bituminous materials and joint sealants adjacent to members to be coated shall be masked off. All masking shall be removed following completion of the coating process.

(ix) Members shall be protected from rain and traffic spray during application and for at least six hours after completion.

Application of Coating

14 (i) Where surface impregnation prior to coating has been carried out, surfaces shall not be coated until after the minimum waiting time stated in the technical product data sheets has elapsed.

(ii) A primer coat, based on acrylate resin, shall be applied to the surface by brush, roller or airless spray at a rate of 150-200 gms/m 2.

(iii) After the minimum waiting time stated on manufacturer's written instructions, a first sealer coat, consisting of an acrylate based resin, shall be applied to the surface generally by brush, roller or airless spray at a rate of 200-230 gms/m-.

(iv) After the minimum waiting time stated in manufacturer's written instructions, a second sealer coat, consisting of an acrylate based resin, shall be applied to the surfaces generally by means of brush, roller or airless spray at a rate of 200-230 gms/m-.

1710 Concrete - Construction General

Construction Joints

1 The position of construction joints shall be as shown on the Drawings and/or agreed with the Engineer before the concrete is placed. When concrete is placed in vertical members, walls, columns and the like, the lifts of concrete shall finish level or, in sloping members, at right angles to the axis of the members, and the joint lines shall match features of the finished work, if possible, or be formed by grout checks. Kickers, if required, shall be constructed integrally with the lift of concrete below. They shall be at least 100 mm high and they shall be provided in all locations shown on the drawings and at all locations where in the Engineer's opinion the specified quality of concrete or finish requires their use.

Concreting shall be carried out continuously up to construction joints.

When the concrete is self-supporting but still sufficiently green, the formwork shall be removed, as necessary to expose the

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construction joint, subject to the requirements of sub-Clause 5 of this Clause. The concrete surface shall be sprayed with a fine spray of water or brushed with a stiff brush, just sufficiently to remove the outer mortar skin and expose the larger aggregate without disturbing it. Alternatively, where this preparation proves impracticable, the hardened surface skin and laitance shall be removed by grit blasting or a needle gun. Hardened surfaces shall not be hacked.

Retarding agents shall not be used unless approved by the Engineer.

Immediately before any fresh concrete is placed against the joint, the surface shall be cleaned, dampened and coated with a neat cement/water slurry, the surface shall be free of standing water.

Formwork

2 (i) Design and construction. The formwork shall be sufficiently rigid and tight to prevent loss of grout or mortar from the concrete at all stages and for the appropriate method of placing and compacting.

The formwork shall be so arranged as to be readily dismantled and removed from the cast concrete without shock, disturbance or damage. Where necessary, the formwork shall be so arranged that the soffit form, properly supported on props only, can be retained in position for such period as may be required by maturing conditions as described in sub-Clause 1710.4(h). If the component is to be prestressed whilst still resting on the soffit form, provision shall be made to allow for elastic deformation and any variation in weight distribution.

Where it is intended to re-use formwork it shall be thoroughly cleaned and made good to the approval of the Engineer.

Internal metal ties which require to be withdrawn through hardened concrete shall not be used where either face is permanently exposed. Where internal ties arc left in, they shall be provided with a mortar cover approved by the Engineer of at least 40 mm or the nominal cover to the reinforcement, whichever is the greater.

(ii) Cleaning and treatment of forms. The faces of the forms in contact with the

concrete shall be clean and treated with a suitable release agent, where applicable as described in sub-Clause 1708.3.

Immediately before concreting, all forms shall be thoroughly cleaned out.

(iii) Projecting reinforcement and fixing devices. Where holes are needed in forms to accommodate projecting reinforcement or fixing devices, care shall be taken to prevent loss of grout when concreting or damage when striking forms.

(iv) Permanent formwork shall comply with Appendix 17/4.

(v) Control. The design, detailing, construction and use of Temporary Works is the sole responsibility of the Contractor, who shall take into account the recommendations of BS 5975 Code of Practice for Falsework as well as "Formwork" - a joint report of the Concrete Society and the Institution of Structural Engineers 1986. All design and detailing of temporary works shall be carried out under the control of a competent Temporary Works Designer and construction and use shall be under the direct control of a competent Falsework Co-ordinator. The Contractor shall submit details of his proposals for the design, detailing, construction and use of all temporary works to the Engineer well in advance of commencement of temporary works.

(vi) Void Formers. Void formers shall be made of either Standard Duty (SD) expanded polystyrene to BS 3837, of cardboard or other suitable material approved by the Engineer. They shall be of adequate strength to resist deformation due to loads resulting from movement of personnel or concreting operations. The maximum moisture absorption of polystyrene shall be 4% by volume and the external faces of cardboard void formers shall be sealed to prevent moisture absorption from the wet concrete. Details of proposed void formers and of the proposed method of location and anchorage shall be submitted to the Engineer well in advance of ordering.

Transporting, Placing and Compacting

3 Concrete shall be so transported and placed that contamination, segregation or loss of the constituent materials does not occur.

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Concrete shall not be placed in any part of the Works until the Engineer's approval has been given. If concreting is not started within 24 hours of approval being given, approval shall again be obtained from the Engineer. Concreting shall then proceed continuously over the area between construction joints.

Concrete, when deposited, shall have a temperature of not less than 5°C and not more than 30°C. Fresh concrete shall not be placed against in situ concrete that has been in position for more than 30 minutes unless a construction joint is formed as described in sub-Clause 1 of this Clause.

Concrete shall not be dropped into place from a height exceeding 2 metres unless prior approval has been given by the Engineer.

When trunking or chutes are used they shall be kept clean.

Concrete shall not be pumped or discharged through items containing aluminium alloys.

Concrete shall not be placed in flowing water. Underwater concrete shall be placed in position by tremies or by pipelines.

Concreting operations shall not be permitted to displace reinforcement, tendon ducts, tendon anchorages or formwork, or to damage the faces of formwork. Competent steel fixers and formwork carpenters shall be in constant attendance during concreting operations.

Concrete shall be thoroughly compacted by vibration, unless otherwise agreed by the Engineer, during the operation of placing, and thoroughly worked around the reinforcement, tendons or duct formers, around embedded fixtures and into corners of the formwork to form a solid mass free from voids. When vibrators are used to compact the concrete, vibration shall be applied continuously during the placing of each batch of concrete until the expulsion of air has practically ceased and in a manner that does not promote segregation of the ingredients.

All necessary compaction shall be completed within 30 minutes of discharge from the mixer or agitator unless otherwise agreed by the Engineer.

Particular care shall be taken when concreting bridge decks of substantial thickness to avoid layering of concrete, and the whole thickness shall be placed in one pass. In deck slabs where void formers are used, adequate means to prevent flotation shall be employed and care


taken to ensure adequate compaction of the concrete placed beneath the void formers.

A sufficient number of vibrators in serviceable condition shall be on site to ensure that spare equipment is always available in the event of breakdowns.

Vibration shall not be applied by way of the reinforcement. Where vibrators of the immersion type are used, contact with reinforcement and all inserts shall be avoided as far as is practicable.

Concrete shall not be subjected to disturbance between 4 hours and 24 hours after compaction except with the agreement of the Engineer. Re-compaction of the upper layers of deep lifts to prevent or close settlement cracking shall be subject to the approval of the Engineer. Whenever vibration has to be applied externally, the design of formwork and disposition of vibrators shall ensure efficient compaction and the avoidance of surface blemishes.

There shall be no excess water on the top surface on completion of compaction.

Striking of Formwork

4 The Engineer shall be informed in advance when the contractor intends to strike any formwork.

(i) General. Formwork shall be removed in a manner not to damage the concrete, and at times to suit the requirements for its curing and to prevent restraint that may arise from elastic shortening, shrinkage or creep.

(ii) Striking period. Where the concrete compressive strength is confirmed by tests on concrete cubes stored under conditions approved by the Engineer that simulate the field conditions, formwork supporting concrete in bending may be struck when the cube strength is 10 N/mm 2 or three times the stress to which it will be subjected, whichever is the greater. (For prestressed concrete the requirements of sub-Clause 1724.4 also apply)

For ordinary structural concrete made with Portland cement (PC) only, in the absence of control cubes, the period before striking shall be in accordance with the minimum periods given in Table 17/5, unless otherwise instructed by the Engineer.

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Table 17/5: Minimum Period Before Striking Formwork (PC Concrete)

Minimum Period Before Striking

Surface temperature of concrete:

16°C 7°C t°C (any temperature between 3°C and 25°C)

Vertical formwork to columns, walls and large beams

12 hours 18 hours 3 0 0 hours

t + 10

Soffit formwork to slabs 100

4 days 6 days ~ ^ days

Props to slabs 250

10 days 15 days days t + 10

Soffit formwork to beams 230

9 days 14 days ~ ^ days

Props to beams 360

14 days 21 days r* days

Curing of Concrete

5 (i) Curing methods. Immediately after compaction and thereafter for the curing time, except where elevated temperature curing is used, concrete shall be protected against harmful effects of weather, including rain, rapid temperature changes, frost, and from drying out. The method of curing shall provide a suitable environment for the concrete to mature and prevent harmful loss of moisture.

The curing time shall be the number of days given in Table 17/6 unless the average surface temperature of the concrete during the required number of days falls below 10°C, in which case the period of curing shall be extended until the maturity of the concrete reaches the value given in the table.

Details of all curing liquids, compounds, membranes and methods to be used, and subsequent removal, where necessary, shall be subject to the agreement of the Engineer. Where the Contractor proposes to use a curing liquid, compound or membrane on surfaces on which a waterproofing system is to be laid, it shall be completely removable or compatible with the system.

Where the Contractor proposes the use of a curing liquid, compound or membrane on surfaces scheduled in Appendix 17/2, it shall be of a film type that fully degrades by exposure to ultra-violet light without leaving any residue that is detrimental to the surface impregnation of the concrete.

(ii) Accelerated curing. Elevated-temperature curing as described below may be used only with Portland cement or sulphate-resisting Portland cement.

(a) The formwork may be generally heated to no more than 20°C prior to the placing of concrete.

(b) Once placing is complete the concrete shall be left for 4 hours without additional heating. The concrete temperature can then be raised at a maximum rate of 10°C per Y>. hour.

(c) The concrete temperature shall at no time exceed 70°C.

(d) The rate of subsequent cooling shall not exceed the rate of heating.

(e) Cubes shall be cured under identical conditions to those which the concrete is subjected to, and in a manner to be approved by the Engineer.

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Table 17/6: Normal Curing Periods for Different Types of Cement

Conditions under which concrete is maturing

Number of days (where the average surface temperature of the concrete exceeds 10°C during the whole period)

Equivalent maturity (degree hours) calculated as the age of the concrete in hours multiplied by the number of degrees Celsius by which the average surface temperature of the concrete exceeds -10°C

Conditions under which concrete is maturing

Other SRPC PC Other* SRPC PC

1. Hot weather or drying winds

7 4 3 3500 2000 1500

2. Conditions not covered by 1

4 3 2 2000 1500 1000

NOTE. Other* includes all permitted cements except PC and SRPC. PC = Portland cement. SRPC = Sulfate-resisting Portland cement.

The use of accelerated curing methods for concrete containing other types of cement or any admixture shall be subject to the Engineers approval.

Cold Weather Work

6 Concrete shall not be placed while the air temperature is below 2°C measured on a rising thermometer or below 4°C measured on a falling thermometer unless the following requirements are met:

(i) The aggregates and water used in the mix shall be free from snow, ice and frost;

(ii) The surface temperature of the concrete at the time of placing shall be at least 5°C and shall not exceed 30°C;

(iii) The surface temperature of the concrete shall be maintained at not less than 5°C until the concrete reaches a strength of 5 N/mm- as determined by tests on cubes that were cured under identical conditions to the structural concrete, in a manner approved by the Engineer;

(iv) Before placing concrete, the formwork, reinforcement, prestressing steel and any surface with which the fresh concrete will be in contact shall be free from snow, ice and frost;

(v) Cement shall not be allowed to come into contact with water at a temperature greater than 60°C.

Hot Weather Work

7 During hot weather the Contractor shall ensure that the constituent materials of the concrete are sufficiently cool to prevent the concrete from stiffening in the interval between its discharge from the mixer and compaction in its final position.

Cement shall not be allowed to come into contact with water at a temperature greater than 60°C.

Precast Concrete Construction

8 (i) Manufacture off the Site. When the method of manufacture has been approved, no changes shall be made without the consent of the Engineer.

The Contractor shall inform the Engineer in advance of the date of commencement of manufacture and casting of each type of member.

A copy of all 28-day cube test results relating to the work shall be sent to the Engineer as soon as they become available.

For all prestressed members , the Contractor shall send to the Engineer not more than 7 days after the transfer of stress, a certificate showing the force and extension in the tendons after they were anchored, the strength and age of test cubes cast as described in sub-Clause 1724.4(iv) and the minimum age in hours of the concrete at the time the stress was applied to the member.

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For all prestressed pretensioned members, the length, cross-section dimensions and straightness of precast concrete shall be measured at 28 ± 2 days after casting or as otherwise agreed with the Engineer. Unless otherwise stated, and notwithstanding the requirements of (iv) below, the allowable dimensional variations shall not exceed the following:

Length Variation

Up to 3 m ± 6 mm

3 to 4.5 m ± 9 mm

4.5 to 6 m ± 1 2 mm

Additional for every subsequent 6 m ±6 mm

Cross section (each direction)

Up to 500 mm ± 6 mm

500 to 750 mm ± 9 mm

Additional for every subsequent 250 mm ± 3 mm

Straightness or bow (deviation from intended line)

Up to 3 m

3 to 6 m

6 to 12 m

Additional for every subsequent 6 m

± 6 mm

± 9 mm

±12 mm

± 6 mm

The above allowable dimensional variations have not been taken into account in the bar schedules (Clause 1713 refers).

Where the Engineer requires tests to be carried out, no members to which the tests relate shall be dispatched to the Site until the tests have been satisfactorily completed.

All members shall be indelibly marked to show the member mark as shown on the Drawings, the production line on which they were manufactured, the date on which the concrete was cast and, if they are of symmetrical section, the face that will be uppermost when the member is in its correct position in the Works. The markings shall be so located that they are not exposed to view when the member is in its permanent position.

Unless otherwise specified, the vibrated top surface of precast concrete members

which will subsequently receive in situ concrete shall be further prepared by one of the following methods as shown on the Drawings:

Class 1 surface preparation,

The surface finish shall be in accordance with sub-Clause 1 of this Clause.

Class 2 surface preparation,

The hardened surface shall be jetted with air or water to remove laitance and all loose material and no further roughening shall then be carried out (rough as cast).

(ii) Storage. When members are stored, they shall be firmly supported only at the points described in Appendix 17/4. The accumulation of trapped water and deleterious matter in the units shall be prevented. Care shall be taken to avoid rust staining and efflorescence.

When a stack is several units high, packings shall be vertically above each other to prevent additional bending stresses in any unit. Where disfigurement would be detrimental, packing pieces shall not discolour or otherwise permanently damage the units.

(iii) Handling and transport. Members shall be lifted or supported only at points described in Appendix 17/4 or otherwise agreed by the Engineer and shall be handled and placed without impact.

(iv) Assembly and erection. In a composite slab bridge where precast beams are laid side by side with minimal gaps to form a deck:

(a) the difference in soffit level between adjacent units before the in situ concrete is placed shall nowhere exceed 5 mm for units up to 5 m in length or 10 mm for longer units;

(b) the width of the deck soffit shall be within + 25 mm of that shown on the Drawings;

(c) in adjacent spans, the continuity of line of the outside beams shall be maintained;

(d) the width of the gap between individual beams shall not exceed twice the nominal gap shown on the Drawings;

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Volume 1 Specification for- Road Works

(e) the alignment of transverse holes shall permit the reinforcement or prestressing tendons to be placed without distortion.

The in situ concrete in composite slab bridges shall be placed in such a sequence that the advancing edge of the freshly deposited concrete over the full width of the deck, between longitudinal construction joints, is approximately parallel to the deck supports. Precast beams shall be prevented from moving laterally during the placing of the in situ concrete.

The method of assembly and erection shall comply with any particular requirements in Appendix 17/4.

(v) Forming structural connections. No structural connections shall be made until the Engineer's approval has been given.

Unless otherwise agreed by the Engineer, the composition and water/cement ratio of the in situ concrete or mortar used in any connection and in the packing of joints shall be in accordance with the assembly instructions.

Levelling devices shall only be released or removed with the Engineer's approval.

(vi) Protection. At all stages of construction, precast concrete units and other concrete associated therewith shall be properly protected to prevent damage to permanently exposed concrete surfaces, especially arrises and decorative features.

Tolerances

9 The finished structure and all its parts shall be constructed to the lines, levels and location shown on the Drawings, subject to the following tolerances unless otherwise specified.

(i) Horizontal deviation from intended position ± 25 mm

(ii) Deviation from intended level ± 10 mm

(iii) Deviation from vei'tical or near-vertical plane (plumbness) 2 mm per m with a maximum of 25 mm for heights in excess of 12.5 m.


1711 Concrete - Grouting of Prestressing Tendons

General

1 The Contractor shall undertake grouting trials, when required in Appendix 17/4, in accordance with the details described therein. The trials are required to demonstrate that the grouting methods and procedures proposed by the Contractor will ensure that grout completely fills the ducts and surrounds the prestressing steel.

The Contractor shall submit, at least 4 weeks before onsite trials, a detailed method statement covering proposed materials, duct, anchorage and vent arrangements, personnel, equipment, grouting procedures and quality control for the approval of the Engineer.

Grout Materials

2 The properties of the grout, made with the materials and using the plant and personnel proposed for use on site, shall be assessed for suitability for the intended purpose sufficiently in advance of grouting operations to enable adjustments to be made in use of materials or plant or personnel. All retrials shall be at the Contractor's expense.

The materials assessment shall consist of the preparation of the grout, made with the materials and using the plant and personnel proposed for use on site, and the testing of it in accordance with sub-Clause 9 of this Clause. The preparation shall be carried out under conditions of temperature expected on site. If grouting operations are likely to cover different seasons, the assessment shall include the range of expected temperatures.

The sources of materials and procedures approved as a result of satisfactory trials shall not be departed from without the written approval of the Engineer.

Unless otherwise instructed or agreed by the Engineer as a result of grouting trials, the grout shall consist only of Portland cement complying with IS 1, admixtures complying with sub-Clause 10 of this Clause and water complying with BS 3148.

The age, chemical composition, fineness and temperature of the cement shall be subject to close control.

The materials used shall be such that the chloride ion content of the grout shall not exceed 0.1% chlorides by mass of the cement.

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Ducts

3 The system of ducts, duct connectors, grouting connections, vents, vent connections, drains, transitions to anchorages and caps for anchorages shall form a complete air-and water-tight encapsulation for the tendons. Ducts shall be of an electrically non conductive, corrosion resistant durable material such as high density polyethylene or polypropylene. Unless otherwise permitted by the Engineer, all fittings, including couplers and integral vent connections, shall be part of a single integrated system. The system shall be fully compatible with the prestressing anchorages. The encapsulation shall be pressure tested to 0.1 N/mm 2 before concreting to demonstrate that the system is undamaged and has been correctly assembled. As a minimum, the test shall equal the results of experimental testing carried out by the manufacturer on proven systems.

The Contractor shall provide evidence of testing that the encapsulation remains intact after tensioning of the tendons and also that the wall thickness of ducts after tensioning is not less than 1.5 mm.

The Contractor shall provide evidence of testing to demonstrate that the duct will develop full bond strength over a minimum of 40 duct diameters.

Air vents of at least 25 mm internal diameter shall be provided at the anchorages and in the ducts at troughs and crests and 400 mm beyond each intermediate crest in the direction of grout flow, and elsewhere as required by the Engineer. The maximum spacing of vents shall be 15 m. The vent size and spacing may be varied if trials demonstrate the suitability of alternatives. The vents shall be rigidly connected to the ducts, and holes in the ducts shall be of the same diameter as the vents and be formed before pressure testing. All ducts shall be kept free from standing water at all times and shall be thoroughly clean before grouting. All anchorages shall be sealed by caps and fitted with grouting connections and vents. Sealing of anchorages shall permit the flow of grout through the anchor head.

Air vents on each tendon shall be identified by labelling and shall be protected against damage at all times.

Air vents at high points shall extend to a minimum of 500 mm above the highest point on the duct profile.


Grouting Equipment

4 Grouting equipment shall consist of a mixer, a storage reservoir and a pump with all the necessary connection hoses, valves, measuring devices for water, cement and admixtures and testing equipment.

The mixing equipment shall be capable of producing a grout of homogeneous consistency and shall be capable of providing a continuous supply to the injection equipment.

The capacity of the equipment shall be such that the duct can be filled and vented without interruption and at the required rate of injection.

The injection equipment shall be capable of continuous operation with little variation of pressure and shall include a system for recirculating the grout while actual grouting is not in progress.

The equipment shall have a constant delivery pressure of less than 1 N/mm 2; it shall be equipped with a pressure gauge and shall prevent pressures above 2 N/mm 2 . All piping to the grout pump shall have a minimum number of bends, valves and changes in diameter and shall incorporate a sampling Tee with stop cock.

The equipment shall be capable of maintaining pressure on completely grouted ducts and shall be fitted with a valve that can be locked off without loss of pressure in the duct.

During the grouting operation the Contractor shall provide adequate flushing out plant to facilitate complete removal of the grout in the event of a breakdown of the grouting equipment or other disruption before the grouting operation has been completed and shall demonstrate that this equipment is in full working order.

All equipment shall be kept free from build-up of adhering materials by washing as required.

Batching and Mixing of Grout

5 All materials shall be batched by mass except the mixing water and liquid admixtures which may be batched by mass or volume. The accuracy of batching shall be:

± 2% for cement and admixtures; ± 1% for mixing water.

The mixing water shall include the water content of liquid admixtures.

Depending upon environmental or material influence (e.g. temperature, configuration of

March 2000 235



the tendon and properties of the cement used), the w/c ratio shall be kept as low as possible, having regard to the required plastic properties of the grout.

The maximum w/c ratio shall be 0.40. The material shall be mixed in a colloidal mixer to produce a homogeneous grout and shall be kept in slow continuous agitation until pumped into the duct. Water shall be added to the mixer first, followed by the cement and admixtures. The batch quantities of cement and admixture may be added as a whole or in part in sequence until the total quantities are added. The minimum mixing time determined from grouting trials shall be adhered to.

The temperature of freshly mixed grout shall be between 5°C and 25°C.

Injecting Grout

6 Grouting operations shall be carried out by operatives with appropriate knowledge, training and proven experience in carrying out similar operations and be approved by the Engineer.

A check shall be made to ensure the ducts, vents, inlets and outlets are capable of accepting injection of the grout. This shall be done by blowing through the system with dry, oil free air and proving each vent in turn.

Where there is water in the duct, it shall be removed. Outlets at the lowest points and dry, oil-free compressed air may be used for this purpose.

Grouting of the ducts shall be carried out within 28 days of installation of the tendon or as soon as practicable thereafter, in which case additional measures shall be taken to avoid corrosion of the prestressing steel. The Engineer's written agreement to commence shall be obtained. Injection shall be continuous, and it shall be slow enough to avoid producing segregation of the grout. Unless otherwise agreed by the Engineer, grout injection shall be at the i-ate of between 5 and 10 metres of duct per minute. The method of injecting grout shall ensure complete filling of the ducts and complete surrounding of the steel. Grout shall be allowed to flow from each vent and the free end of the duct until its consistency is equivalent to that of the grout injected. Following this, a further 5 litres at each vent shall be vented into a clean receptacle, tested in accordance with sub-Clause 8 and 9 of this Clause and then discarded. The opening shall be firmly closed. All vents shall be closed in a similar manner one after another in the direction of the flow

except that at intermediate crests the vents 400 mm downstream shall be closed before their associated crest vent.

A pressure of 0.5 N/mm 2 shall be maintained for at least one minute. The injection tubes shall then be sealed off under pressure.

Grout vents at high points shall be reopened 10 minutes after completion of grouting and any escape of air, water or grout recorded and reported immediately to the Engineer.

The filled ducts shall not be subjected to shock or vibration within 24 hours of grouting.

Not less than 48 hours after grouting, the level of grout in the injection and the vent tubes shall be inspected and topped up as necessary with freshly mixed grout.

No less than 48 hours after grouting, the end caps at anchorages shall be removed and a photographic record taken, clearly identified.

If, in the opinion of the Engineer, there is cause for doubt that the ducts are completely filled with grout, the Engineer may require non destructive testing to be carried out.

The Contractor shall keep full records of grouting for each duct. Copies of these records shall be supplied to the Engineer within 24 hours of grouting.

Grout vents shall be positively sealed to be waterproof on completion of grouting so as to maintain the encapsulation to the tendons by a means separate from the deck waterproofing membrane.

Grouting during Cold Weather

7 When the ambient temperature may be expected to fall below 5°C, accurate temperature records shall be kept covering maximum and minimum air temperatures, and temperatures of the structures adjacent to the ducts to be grouted. Materials in which frost or ice is present shall not be used, and the ducts and equipment shall be completely free of frost and ice.

Grout shall not be placed when the temperature of the structure adjacent to the ducts is below 5°C, or is likely to fall below 5°C during the following 48 hours, unless the member is heated so as to maintain the temperature of the placed grout. Methods of heating shall be to the approval of the Engineer.

Ducts shall not be warmed with steam.

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Properties

8 (i) Fluidity The fluidity of the grouting during the injection period shall be high enough for it to be pumped effectively and adequately to fill the duct, but low enough to expel the air and any water in the sheath. When tested by the method given in sub-Clause 9 of this Clause, the grouts shall have the values given in Table 17/7.

(ii) Bleeding The bleeding of the grout shall be sufficiently low to prevent excessive segregation and settlement of the grout materials. When tested by the method given in sub-Clause 9 of this Clause, the bleeding shall be less than 2% of the initial volume of the grout and the average of four successive results shall be less than 1%. The water shall be reabsorbed by the grout during the 24 hours after mixing.

(iii) Volume Change The volume change assessed may be either an increase or decrease. When tested in accordance with the method given in sub-Clause 9 of this Clause, the volume change of the grout shall be within the range - 1 % to +5%. For grouts with expanding agents there shall be no decrease in volume.

(iv) Strength The compressive strength of 100 mm cubes made of the grout shall exceed 27 N/mm-at 7 days. Cubes shall be made, cured and tested in accordance with BS 1881.

(v) Sieve Test The grout shall contain no lumps. This shall be verified by checking the sieving medium on the fluidity test cone.

Table 17/7: Fluidity Test Requirements Cone test

Immediately 30 Min. after Mixing* At Duct after Mixing at the end of the Outlet

Injection Period

Time (s) Time (s) Time (s)

< 25(50) < 25(50) >10

Mixing time shall be measured from the time when all of the materials are in the mixer.

Note: For grouts prepared in some mixers which have a high shear mixing action, the upper limits given in Table 17/7 may be Increased to 50 seconds. The mixer and these limits shall be subject to the approval of the Engineer.


The Testing of Grout

9 (i) General Conditions Testing shall comprise suitability testing of the materials assessment, and acceptance testing of the grouting trials and actual works operations.

Suitability testing shall wherever possible be carried out in the conditions of temperature and humidity expected on site but in the absence of these data the conditions of temperature and relative humidity at test shall be as follows:

Temperature 20°C ± 2°C Relative Humidity > 65 ' <.

Variations in temperature and humidity on site are likely to cause variations in the test results and shall be reported.

The temperature of the freshly mixed grout shall be given in all test reports.

(ii) Fluidity Test (a) Principle

The fluidity of the grout, expressed in seconds, is a measure of time necessary for a stated quantity of grout to pass through the orifice of the cone, under stated conditions.

(b) Apparatus The following apparatus is required for the test:

1. Modified Marsh Funnel Viscometer: It shall be robust and manufactured from materials not reactive with any materials specified. It shall consist of an inverted frustrum of a cone with the following internal dimensions in mm. Height; 280 ± 10, upper diameter; 152 ± 3, bottom diameter 10 ± 0.1. A 10 mm (± 0.1) pipe with a tap shall be fitted at the lower cone orifice and shall project a total of 60 mm ± 3 mm.

2. Sieving Medium: The sieving medium aperture shall be 1.5 mm and the sieving medium shall be fitted to the top (wide) end of funnel and be removable.

3. Stopwatch: The stopwatch shall be accurate to 0.2 seconds in 60 seconds and shall show time to 0.1 seconds.

4. Graduated cylinder of minimum 1 litre capacity.

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(c) Test Procedure Mount the cone with its axis vertical and its largest diameter uppermost. Fix the sieving medium to the top (wide) end of funnel. During the test, prevent the cone from vibrating. Place the cylinder under the cone outlet. All surfaces of the cone shall be clean and shall be dampened so that the surfaces are moist but without free water. Close the lower cone orifice.

Pour the grout through the sieving medium to fill the conical section of the cone. Pouring shall be sufficiently slow to prevent the built up of air in the grout in the cone. Open the lower cone orifice and, at the same time, start the stopwatch. Measure the time taken to the nearest 0.2s to fill the cylinder to 1 litre. The presence of lumps on the sieving medium shall be reported. For suitability testing, three tests shall be carried out, the first immediately after the grout is mixed and the remaining two tests 30 minutes after the grout is mixed. The grout shall be kept agitated while awaiting testing.

(d) Reporting of Results Report the time to the nearest 0.5s. Report also the presence of lumps.

Report the result as the average of the times determined to the nearest 0.5s of the second and third tests, separately from the result of the first test.

For acceptance testing, the test shall be performed on grout from each anchorage outlet and from the mixer at the start and end of grouting of each duct.

(iii) Bleeding Test (a) Principle

The test consists of measuring the quantity of water remaining on the surface of the grout which has been allowed to stand protected from evaporation.

(b) Apparatus A transparent cylinder 50 mm internal diameter and 200 mm in height, graduated in mm.


(c) Test Procedure Place the cylinder on a surface free from shocks or vibration. The grout used should be from the same batch as that used for the fluidity test.

Pour grout into the cylinder to a height of approximately 150 mm and seal the cylinder to prevent evaporation. Note the height to the top of the grout (h), ignoring the meniscus. After 3 hours, measure the depth of water on top of the grout (h,). After 24 hours, check whether the water has been reabsorbed. The test is carried out on one sample of grout.

(d) Reporting of Results Bleeding at the end of 3 hours is given by

— x l 0 0 ( % ) h

where h, is the height in mm of water on the surface of the grout after 3 hours and h is the initial height in mm of grout.

The report shall state the range of air temperatures and the grout temperature at the time of test, the bleeding at 3 hours and whether the water has been reabsorbed after 24 hours. For Acceptance testing, a minimum of two tests per day shall be performed.

(iv) Volume Change Test (a) Principle

The volume change is measured as a percentage of the volume of grout between the start and the end of the test. The test measures mainly the volume change caused by segregation or expansion. The volume change test may be a continuation of the bleeding test.

(b) Apparatus A transparent cylinder 50 mm internal diameter and 200 mm in height, graduated in mm.

(c) Test Procedure Place the cylinder on a surface free from shocks or vibration. Fill it with grout to approximately 150 mm and seal the cylinder to prevent evaporation. Note the height to the top of the grout (h) ignoring the

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meniscus. Twenty four hours after filling the cylinder measure the height of the grout in the cylinder (h2).

(d) Reporting of Results Volume change at the end of 24 hours is given by:

h , - h — x 100(%)

h

where h is the initial height in mm of grout and h, is the height in mm of grout after 24 hours.

The report shall state the range of air temperatures during the test and the volume change.

For acceptance testing, the test shall be performed twice each day.

Admixtures

10 (i) General Admixtures shall be used to achieve a low water/cement ratio and impart good fluidity, minimum bleed and volume stability or expansion to the grout to comply with sub-Clause 8 of this Clause. They should be added on site during the mixing process and used in accordance with the manufacturers recommendations.

(ii) Types Admixtures are divided into two types expanding and non-expanding.

Expanding grout admixtures are supplied as powders which expand to ensure there is no decrease in the volume of grout at the end of the hardening period. Non-expanding grout admixtures are supplied in liquid or powder form.

Both types of grout admixture may also permit a reduction in water/cement ratio, improve fluidity, reduce bleeding and retard the set of the grout.

Admixtures may be used singly or in combination to obtain the required grout performance. Admixtures used in combination shall be checked for compatibility.

(iii) Chemical Composition Admixtures shall not contain substances in quantities which will adversely affect the grout or the corrosion protection of the prestressing steel. Thiocyanate, nitrates, formate and sulphides shall not be used in admixtures.

(iv) Material Requirements The admixture shall not segregate and shall be uniform in colour. The composition shall not change and the manufacturer shall operate an appropriate certified quality management scheme listed in Appendix 1 / 24. Where appropriate, admixtures shall comply with BS 5075 : Parts 1 to 3. Other admixtures shall be permitted provided they satisfy sections 6, 7.1 and 7.3 of BS 5075 : Part 1 and full account is taken of their effects on the finished product and their fitness for purpose. Data on their suitability, including previous experience with such materials, shall be made available and records of the details and performance of such materials shall be maintained.

(v) Corrosion Grout admixtures shall not cause the grout to promote corrosion of the prestressing steel by rusting, pitting, stress corrosion or hydrogen embrittlement.

<vi) Dosage The optimum dosage of the admixture shall be determined by trial mixes with the cement to be used in the grout. This dosage shall be expressed as per cent by mass of the cement. It shall be within the range recommended by the supplier and shall not exceed 5% by mass of the cement.

The method of measuring dosage and checking weights of prepacked dry materials shall be agreed with the Engineer.

Grouting Trials

11 At least 56 days before the planned commencement of fixing ducts for prestressing for the permanent works, the Contractor shall carry out full scale grouting trials as shown on the contract drawings. The trial shall incorporate all relevant details of ducts, vents, duct supports, prestressing anchorages, prestressing strands, grout inlets and outlets.

The tendons shall be sufficiently tensioned such that the strands within the duct take up a representative alignment. All methods and materials are to be those proposed for the permanent works and shall have been submitted to the Engineer as part of the detailed method statement required in sub-Clause 1 of this Clause.

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Grouting and testing shall be carried out in accordance with the Specification.

After 3 days the Contractor shall carefully cut and expose cross sections and longitudinal sections of the duct and anchorages where directed by the Engineer to demonstrate that the duct is fully grouted.

A report shall be prepared by the Contractor giving full details of the trial, testing results and photographs of the cut sections.

Prestressing for the permanent works will not be permitted without the written approval of the Engineer of the grouting procedures and formal acceptance of the results of the grouting trial.

Protection of Tendons

12 (i) The prestressing tendons shall be protected by cement grout within a pressure tested completely sealed encapsulation.

(ii) Metal parts of anchorages shall be electrically bonded to the adjacent reinforcement at each end of the tendon. Electrical continuity of the structure over the length of the tendon shall be tested.

Supervision of Prestressing Operations

13 Prestressing and grouting operations shall be under the charge of a Supervisor with appropriate knowledge, training and experience in carrying out similar operations. That person shall be present during all procedures and shall be responsible for all safety precautions relating to the operations.

The appointment of the responsible person shall be subject to the approval of the Engineer.

1712 Reinforcement - Materials

Hot Rolled and Cold Worked Bars

1 Hot rolled and cold worked steel bars shall comply with BS 4449 except that no bar shall contain a flash weld.

Hard Drawn Steel Wire

2 Hard drawn mild steel wire shall comply with BS 4482.

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Steel Fabric

3 Steel fabric reinforcement shall comply with BS 4483 and shall be delivered to the Site in flat mats or pre-bent.

Bond Strength

4 The classification of deformed bars as Type 1 or 2 for bond strength shall be in accordance with BS 4449. The type of deformed bar shall be as described in Appendix 17/4.

1713 Reinforcement - Bar Schedule Dimensions - Cutting and Bending

1 The bar schedules are based on the dimensions of the concrete and the nominal cover to the reinforcement shown on the Drawings. The reinforcement shall be cut and bent within the tolerances given in BS 4466 but this shall not relieve the Contractor of his responsibility for the correct fit of the reinforcement and the achievement of the required cover as described in Clause 1714.

Bending at temperatures below 5°C or in excess of 100°C may only be carried out with the Engineer's approval and under his supervision.

Any reinforcement bar that has already been bent shall not be rebent at the location of the original bend without the Engineer's agreement.

1714 Reinforcement - Fixing

1 Reinforcement shall be secured against displacement. Unless specified otherwise, the actual concrete cover shall be not less than the required nominal cover minus 5 mm.

The cover to a bar in an outer layer of reinforcement shall not exceed the nominal cover shown on the Drawings by more than 49c of the overall dimension of the member, measured in the same direction, or by more than 20 mm, whichever is the lesser. Bars in inner layers shall be located as shown on the Drawings; they shall be in close contact with the bars of the outer layer, unless otherwise indicated. Welding of reinforcing bars for fixing purposes shall be in accordance with Clause 1717.

Cover blocks shall be of comparable strength,

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durability and appearance to the surrounding concrete. They shall match the mix proportions of the adjacent material so far as is practicable. They shall ensure that the reinforcement is correctly positioned and shall be as small as possible consistent with their purpose, of a shape acceptable to the Engineer and designed so that they will not overturn or be displaced when the concrete is placed.

Wire cast in the block for the purpose of tying it to the reinforcement shall be as described below. Stainless steel tying wire shall be used in cover blocks to exposed surfaces.

Other types of cover blocks may be used only with the approval of the Engineer. Pieces of wood, metal, tile or porous material shall not be used as cover blocks.

Projecting ends of ties or clips shall not encroach into the concrete cover. Tying wires shall be:

(i) 1.6 mm diameter soft annealed iron wire for unexposed surfaces;

(ii) 1.2 mm diameter stainless steel wire for exposed surfaces, throughout bridge decks and for other locations described in Appendix 17/4.

The Contractor shall provide access to enable the Engineer to carry out a cover measurement survey of all reinforced concrete surfaces within the 24-hour period following the removal of formwork, unless otherwise agreed with the Engineer.

1715 Reinforcement - Surface Condition

1 Immediately before concrete is placed around it, reinforcement shall be free from mud, oil, paint, retarder, release agent, loose rust, loose mill scale, snow, ice, grease or any other substance that can be shown to have an adverse chemical effect on the steel or concrete, or to reduce the bond.

1716 Reinforcement - Laps and Joints

1 Laps and joints shall be made only where shown on the Drawings or agreed by the Engineer.


2 Where jointed reinforcing bars are required the Contractor shall demonstrate to the approval of the Engineer that the fatigue life, durability and other properties of the coupled bar are adequate. The Contractor shall make available to the Engineer independent test evidence which confirms that the coupled bars satisfy the following criteria:

(a) When a test is made on a representative gauge length assembly comprising reinforcement of the size, grade and profile to be used and a coupler of the precise type to be used, the permanent elongation after loading to 0.6f v shall not exceed 0.1 mm.

(b) The design strength of the coupled bar shall exceed the specified characteristic strength by the percentage specified in BS 4449.

1717 Reinforcement - Welding

General

1 Welded reinforcement, other than steel fabric reinforcement, shall not be incorporated in the Permanent Works without the written approval of the Engineer. The Contractor shall demonstrate to the approval of the Engineer that at each location the fatigue life, durability and other properties of the member are not adversely affected by the proposal.

Flash Butt Welding

2 Flash butt welding shall only be carried out with the combination of flashing, heating, upsetting and annealing approved by the Engineer and subject to the satisfactory performance of trial joints. Only those machines that automatically control this cycle of operations shall be used.

Manual Metal-arc Welding

3 Metal-arc welding shall be carried out in accordance with BS 7123 and the recommendations of the reinforcement manufacturer, subject to the approval of the Engineer and the satisfactory performance of trial joints.

Other Methods

4 Other methods of welding may be used subject to the approval of the Engineer and the satisfactory performance of trial joints.

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Strength of Structural Welded Joints

5 The strength of all structural welded joints shall be assessed following tests on trial joints to establish the minimum specified mechanical properties of the joint.

1718 Prestressing Tendons -Materials

General

1 Post-tensioning work shall be carried out using a single proprietary system throughout.

Steel Wire

2 Steel wire shall comply with BS 5896 : 1980.

Cold Worked High Tensile Alloy Bar

3 Cold worked high tensile alloy steel bars for prestressed concrete shall comply with BS 4486.

Stress-relieved Seven-wire Strand

4 Stress-relieved seven-wire strand shall comply with BS 5896 : 1980 or have properties that are not inferior.

Sampling and Testing

5 When it is proposed to use super strand complying with BS 5896 : 1980 Table 6, or other than the lowest strength 3, 4, 5, 6 or 7 mm diameter wires complying with BS 5896 : 1980 Tables 4 or 5 the following shall apply:

(i) A sample shall be taken from each reel of material proposed for use in the Works in the presence of the Engineer.

(ii) A reel shall only be accepted if both the breaking load and the 0.1% proof load of the sample exceeds the specified characteristic loads given in Tables 4 or 6. In the case of Table 5, this requirement shall apply to the breaking load and the load at 1% elongation.

6 Where scheduled in Appendix 1/5, the Contractor shall arrange for samples of the steel intended for use in the Works to be tested at a testing laboratory approved by the Engineer.


1719 Prestressing Tendons -Handling and Storage

1 Tendons shall be installed in ducts before concreting unless otherwise approved by the Engineer. Care shall be taken to avoid mechanically damaging, work-hardening or heating prestressing tendons while handling. All prestressing tendons shall be stored clear of the ground and protected from the weather, from splashes from any other materials, and from splashes from the cutting operation of an oxy-acetylene torch, or arc-welding processes in the vicinity.

In no circumstances shall prestressing tendons after manufacture be subjected to any welding operation, or heat treatment or metallic coating such as galvanizing.

1720 Prestressing Tendons -Surface Condition

1 Prestressing tendons and internal and external surfaces of sheaths or ducts shall be clean and free from pitting, at the time of incorporation in the work. Slight rusting is acceptable.

1721 Prestressing Tendons -Straightness

Wire

1 Unless otherwise agreed by the Engineer, low relaxation and normal relaxation wire shall be in coils of sufficiently large diameter to ensure that the wire pays off straight.

Strand

2 Prestressing strand, however manufactured, shall be in coils of sufficiently large diameter to ensure that the strand pays off straight.

Bars

3 Prestressing bars, as delivered, shall be straight. Any small adjustments for straightness that are necessary on Site shall be made 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 cold but at a temperature of not less than 5°C. Any necessary heating shall be by means of steam or hot water.

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1722 Prestressing Tendons -Cutting

1 All cutting of wire, strand or bar shall be carried out using a high-speed abrasive cutting wheel or friction saw at not less than three diameters from the anchor, or any other mechanical method approved by the Engineer. An oxy-acetylene cutting flame may be used for cutting tendons between beams on long line prestressing beds.

1723 Prestressing Tendons -Positioning of Tendons, Sheaths and Duct Formers

1 Tendons, sheaths and duct formers shall be accurately located and maintained in position both vertically and horizontally as shown on the Drawings. Unless otherwise described in Appendix 17/4 the tolerance in the location of the centre line of sheath or duct shall be ± 5 mm.

Where tendons are described in the Contract as debonded from the concrete, they shall be covered with sleeves approved by the Engineer. The ends of the sleeves shall be taped to the tendon to prevent the ingress of grout.

Joints in sheaths shall be securely taped to prevent penetration of the duct by concrete or laitance, and ends of ducts shall be sealed and protected after the stressing and grouting operations. Joints in adjacent sheaths shall be spaced at least 300 mm apart.

1724 Prestressing Tendons -Tensioning

General

1 All wires, strands or bars stressed in one operation shall be taken, where possible, from the same parcel. Each cable shall be tagged with its number from which the coil numbers of the steel used can be identified. Cables shall not be kinked or twisted. Individual wires and strands for which extensions are to be measured shall be readily identifiable at each end of the member. No strand that has become unravelled shall be used.

Tensioning shall be carried out only in the presence of the Engineer unless he gives written permission to the contrary.

Tensioning Apparatus

2 The tensioning apparatus shall meet the following general requirements:

(i) The means of attachment of the tendon to the jack or tensioning device shall be safe and secure.

(ii) Where two or more wires or strands are stressed simultaneously, they shall be approximately of equal length between anchorage points at the datum of load and extension measurement. The degree of variation shall be small compared with the expected extension.

(iii) The tensioning apparatus shall be such that a controlled total force is imposed gradually and no dangerous secondary stresses are induced in the tendons, anchorage or concrete.

(iv) The force in the tendons during tensioning shall be measured by direct-reading load cells or obtained indirectly from gauges fitted in the hydraulic system to determine the pressure in the jacks. Facilities shall be provided for the measurement of the extension of the tendon and of any movement of the tendon in the gripping devices. The load measuring device shall be calibrated to an accuracy within ± 2% and checked at intervals to the approval of the Engineer Elongation of the tendon shall be measured to an accuracy within 2% or 2 mm, whichever is the more accurate.

(v) The tensioning equipment shall be calibrated before the tensioning operation and at intervals approved by the Engineer.

Pretensioning

3 Where pretensioning methods are used, the tension shall be fully maintained by some positive means during the period between tensioning and transfer. The transfer of stress shall take place slowly to minimize shock.

(i) Straight tendons. In the long-line method of pretensioning, sufficient locator plates shall be distributed throughout 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.

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In the individual mould system, the moulds shall be sufficiently rigid to provide the reaction to the prestressing force without distortion.

(ii) Deflected tendons. Where possible, the mechanisms for holding down or holding up tendons shall ensure that the part in contact with the tendon is free to move in the line of the tendon so that frictional losses are nullified. If, however, a system is used that develops a frictional force, this force shall be determined by test and due allowance made as agreed by the Engineer.

For single tendons, the deflector in contact with the tendon shall have a radius of not less than 5 times the tendon diameter for wire or 10 times the tendon diameter for strand, and the total angle of deflection shall not exceed 15°.

The transfer of the prestressing force to the concrete shall be effected in conjunction with the release of hold-down and hold-up forces as approved by the Engineer.

Unless otherwise described in Appendix 17/4, concrete shall not be stressed until it has reached at least the age at which 2 test cubes taken from it attain the specified transfer strength. The test cubes shall be made and tested as described in BS 1881 : Part 108 and BS 1881 : Part 116 respectively. They shall be cured in similar conditions to the concrete to which they relate in a manner approved by the Engineer. The Contractor shall cast and test sufficient cubes to demonstrate that the required strength of the concrete at transfer has been reached.

Post-tensioning

4 (i) Arrangement of tendons. Where wires, strands or bars in a tendon are not stressed simultaneously, the use of spacers shall be in accordance with the recommendations of the system manufacturer.

(ii) Anchorages. Anchorages shall be tested in accordance with BS 4447.

For each anchorage system used in the Works, the characteristic value for anchorage efficiency shall be not less than 90%.

Proprietary anchorages shall be handled and used strictly in accordance with the manufacturer's instructions and recommendations.


(iii) Deflected tendons. The deflector in contact with the tendon shall have a radius of not less than 50 times the diameter of the tendon, and the total angle of deflection shall not exceed 15° unless otherwise agreed by the Engineer.

(iv) Tensioning procedure. Before tensioning, the Contractor shall demonstrate that all tendons are free to move in the ducts unless the geometry of the ducts makes this impracticable as agreed by the Engineer. Tensioning shall be carried out in such a manner that the stress in the tendons increases at a gradual and steady rate. Tensioning shall not be carried out at a temperature below 0°C without the approval of the Engineer.

Unless otherwise described in Appendix 17/4, concrete shall not be stressed until it has reached at least the age at which 2 test cubes taken from it attain the specified transfer strength. The test cubes shall be made and tested as described in BS 1881 : Part 108 and BS 1881 : Part 116 respectively. They shall be cured in similar conditions to the concrete to which they relate in a manner approved by the Engineer. The Contractor shall cast and test sufficient cubes to demonstrate that the required strength of the concrete at transfer has been reached.

The Contractor shall ensure that those carrying out the stressing are provided with particulars of the required tendon loads, order of stressing and extensions. Allowance shall be made during stressing for the friction in the jack and in the anchorage, although the former is not necessary when using load cells.

Any allowance for draw-in of the tendon during anchoring shall be in accordance with the Engineer's instructions.

Stressing shall continue until the required extension and tendon load are reached or are approved by the Engineer.

The extension shall allow for any draw-in of the tendon occurring at a non-jacking end, but measurement shall not commence until any slack in the tendon has been taken up. The average difference between the computed and measured elongations shall not exceed ± 5% for all tendons in one deck while the difference allowed for any individual tendon shall be ± 15% unless otherwise approved by the Engineer.

Immediately after anchoring, the forces in the prestressing tendons shall not exceed 70% of

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their characteristic strength. During stressing the value may exceed 70% of their characteristic strength, with the approval of the Engineer, but shall not exceed 80%.

After the tendons have been anchored, the force exerted by the tensioning apparatus shall be decreased gradually and steadily so as to avoid shock to the tendon or the anchorage. Full records shall be kept of all tensioning operations, including the measured extensions, pressure-gauge or load-cell readings, and the amount of draw-in at each anchorage. Copies of these records shall be supplied to the Engineer within 24 hours of each tensioning operation.

Unless otherwise agreed by the Engineer tendons shall not be cut less than 3 days after grouting.

1725 Prestressing Tendons -Protection and Bond

1 The prestressing tendons including their anchorages shall be protected in their permanent positions from both mechanical damage and corrosion as described in Appendix

1726 Stainless Steel Dowels -Materials

1 Dowels shall be made from Type 304 S 31 or 316 S 33 and Grade 250 or 460 steel bars complying with BS 6744.

1727 Inspection and Testing of Structures and Components

General

1 Inspection and testing of structures and components shall be carried out as described in Appendix 17/4.

Records of such tests shall be retained by the Contractor on site. These records shall show the location in the works to which these tests relate. The records shall also show the location in the works to which each day's output of concrete relates.

17/4.

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Volume 1 Series 1700 Specification for Road Works Structural Concrete

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Documents

STRUCTURAL CONCRETE Contents · 1713 Reinforcement - Bar Schedule Dimensions - Cutting and Bending 240 1714 Reinforcement - Fixing 240 1715 Reinforcement - Surface Condition 241