MS Concrete Works - Method Statement

7/29/2019 MS Concrete Works - Method Statement

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METHOD STATEMENT

CONCRETE WORKS


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SUMMERY CONTENTS

1. Scope of Works 32. Reference Documents 33. Plant Requirements 34. Methodology 4


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1. Scope of Works

This section covers the manufacture, transport, placing and testing ofconcrete, the furnishing and placing of steel reinforcement in concretestructures, supply and erection of all formwork used in the construction ofpermanent work.

2. Reference Documents

Specifications

General Specifications for Road and Bridge works, Republic ofUganda, Volume IIIA: Section 6100

Tender Dossier: Volume IV Section 7.1 (Special Specifications) Manufactured Items: none Inspection, Test and Approval Plan Quality Control Plan: Drainage: Concrete works Contract Drawings

3. Plant Requirements

Tractor & Trailer 7 ton crane truck Water cart 3.5m3 concrete Car mixer Poker vibrators Drive units


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4. Methodology

Before any concrete works can commence, all materials to be used forconcrete as well as the concrete mixed designs needs to be approved bythe Engineer.

The following materials shall comply with the Specifications:

CementOrdinary or rapid hardening Portland cement confirming to requirementsof BS 12

Portland blast furnace cement conforming to requirements of BS 146 Part2Sulphate resisting Portland cement conforming to requirements of BS4027

AggregatesAs per clause 6102.b.i&ii

WaterWater shall be clean and free from detrimental concentration of acids,alkalis, salts, sugar and other organic or chemical substances.

Curing compoundCuring compound shall comply with the requirements of AASTHO M148-60 and shall be clear or pigmented as specified or required by theEngineer. The curing compound shall be the type that can be applied to awet surface without loss of stability or impairment of its water retentionproperties.

The class of concrete to be used in each part of the Works shall be asindicated on the Drawings. All the head-& wing wall structures shall beclass 25/20 MPa concrete.

4.1. FormworkFormwork shall be constructed to attain the required surface textures ofthe structures and be such that it remains rigid and grout tight during theplacing and setting of the concrete. The surface required for the head -&wing wall structures will be a U2 surface finish. Shutter board will be usedas formwork and fixed in perfect alignment and to the true shape anddimensions of the permanent work shown on the drawings. Before eachconcreting operation is commenced, formwork shall be carefully examinedand cleaned out and the concrete contact faces of the formwork shall be


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treated to ensure non-adhesive of the concrete to the form and easyrelease during stripping. By this means, the use of shutter oil will be used.

4.2. ReinforcingReinforcement shall be protected at all times from contamination andcorrosion and shall be stored clear of the ground with adequate support toprevent distortion. When fixing steel, the steel shall be clean and freefrom loose mill scale, loose rust, oil, grease, tar, paint, mud, ice, retarders,concrete droppings and contamination by salts or other deleterious matterand shall be maintained in such condition up to the time of concreting.Reinforcing shall be placed in accordance with the Drawings and shall besupported and maintained in position by provision of wire or clips at itscorrect position. Spacers shall be securely fixed to the reinforcement atthe time of placing concrete. Minimum cover to all reinforcement shall be

40mm, except where otherwise shown on the Drawings, the length of lapjoints shall not be less than 40 times the diameter of the larger bar.

4.3. ConcretingNo concreting shall be commenced until the Engineer has inspected andapproved the placed formwork and reinforcing. SFD Pre-inspectionCheck Sheet shall be completed prior to concreting.

No concrete shall be mixed at an air temperature of less than 17c on a

falling thermometer or 3c on a rising thermometer. Great care shall betaken during hot weather to prevent the cracking or crazing of concrete.

Concrete shall be mixed in a batch type mixer (car mix). Aggregates,sand and cement will be added at the following order water will becontrolled using water gauge, in-situ moister content of sand will bechecked and take into account if necessary, quantities will be controlled byelectronic weighing scale, spot check of the scale will be done beforecasting. Mixing for each batch shall continue until there is uniformdistribution of the materials and uniformity of colour and consistency of theconcrete. Particular care shall be taken to ensure that no residual materialremain in the mixer after depositing each batch of concrete and wash andclean out the mixer drum immediately following the completion of each

concreting operation or when changing a mix using a different type ofcement.

Necessary arrangements shall be made for the sampling and testing offresh and hardened concrete in accordance with the provisions of B.S1881. Slump tests shall be carried out at such times and places as theEngineer may direct and shall be used as a guide to the consistency ofeach class mix.


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Crushing tests shall be carried out on concrete cubes cast in 150mmmoulds prior to the commencement of construction of the works concretetest cubes shall be taken and tested in accordance with the requirementsof the Clause 6106 in the Specifications. In any case shall there not beless than the average rate of one set of cubes per 20 cubic metres ofconcrete.

4.4. Transporting, Placing and Compaction of concrete.Concrete shall be handled from the place of mixing to the place of finaldeposit as rapidly as practicable by the car mix, which will prevent thesegregation or loss of any ingredient. All placing and compaction ofconcrete shall be carried out under the direct supervision of a competentmember of the Contractors staff. Concrete shall be thoroughly compactedby means of a vibrator poker and drive unit, during the operation of placing

and shall be thoroughly worked around the reinforcement and anyembedded fixtures and into corners of formwork and moulds. Concretethat has partially set before final placing shall not be used and shall beremoved from the site.

4.5.Removal of formworkFormwork shall be removed under the personal supervision of acompetent foreman. Great care shall be exercised during the removal ofthe formwork to avoid shocks of reversal of stress in the concrete.Formwork shall remain in place for the appropriate minimum time periodas indicated in Table 6115/1 of the General Specifications, after placing of

the concrete. Surface defects such as small areas of honeycombingcavities, large isolated blowholes, broken corner edges, etc, shall berepaired with mortar consisting of a cement and sand ratio equal to that ofthe concrete being repaired. SFD: Post-concrete Inspection Check Sheetshall be completed after formwork has been removed and concreterepaired.

4.6. Curing of concreteCuring of concrete shall be done by means of a curing compound andplace on the concrete after removal and repairs to the concrete.