DOS & DONTS OF QUALITY CONCRETE, REINFORCEMENT AND RCC IN MAJOR PROJECTS

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CONTENTS

Setting out of Building Excavation Concreting Cement Aggregates Form Work Reinforcement Concrete Work

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Testing Building Bricks Cement Coarse Aggregate MS & TOR Steel Concrete

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Setting Out of Buildings. Check Orientation according to site condition. Mark all buildings according to plans on gound before starting excavation. Ensure that plinth level, length of wall and right angles/diagonals are checked. Dont overlook underground cables, sewage/water mains, electric/telephone wire coming in the way of siting of bldgs. Dont provide high plinths and consider stepping foundations where necessary

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Excavation.

Ensure that safe bearing capacity is checked before commencement of the work. (IS : 1904) Ensure that refilling of trenches done in layers of not exceeding 15 cm with available means as specified, adequately watered and consolidated. Ensure safety precautions while excavating in soft soils or in case of deep excavations. (IS : 5121 1979 and IS : 3764 1966). Ensure that foundation shall be laid and on original GL.

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Ensure in RCC footing, the thickness at the edge shall not be less than 150mm for footing on soils and not less than 300mm above the top of piles for fasting in piles. (IS : 456 2000 clause 34.1.2). Ensure min depth of foundation as per subsoil investigation report.Only approved earth must be used in filling under foundation, plinth and floors. Avoid silt and expensive soil for filling Do not lay foundation till hard soil/moorum/rocks is met with.

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Do not over look the measures for anti termite soil treatment. (IS : 6313 (Pt III 1981).

NB.The chemicals are banned vide E-in-Cs Branch letter No(a)Aldrin EC(b)Heptachlor EC( c)Chlordane ECOnly chloropyrophos EC 20% is to be used.

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QUALITYCONCRETING

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Cement. Accept from main producers Ensure proper dunnage for storing cement. It shall be stored in water proof sheds. Ensure that stocks are consumed reasonably/ quickly so that the stock remains as fresh as possible. (FIFO). Cement over 6 months be tested for its strength, setting time etc before use. Do not stack more than 12 bags high to avoid humping under pressure. Use cement batching always by weight (mass).

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Aggregates. Aggregate shall comply with requirements of IS : 383. Preference should be given to natural aggregate (IS : 456-2000 clause 5.3) Test for alkaline aggregate reaction is must (8.2.5.4). Test for deleterious content of sand is must. Use the sand washed condition. Use of too fine sand should be avoided. FM below 0.6 is dangerous.Ensure grading of coarse and fine aggregate as (well graded). 20mm aggregate is suitable for this zone.

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The grading of coarse and fine aggregate should be checked frequently as possible (10.2.1). Mica content of fine sand should not be overlooked. Excess of 6% may not be allowed (SP-23-1982). Coarse and fine aggregate shall be batched separately. IS : 456 2000 Clause 5.3.4) Determine MC in both FA & CA as frequently as possible as per IS : 2386 (Pt 3). Allow proper allowances for variation in masses of aggregate due to MC.

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Form Work.(IS : 14687- latest) Remember : Good finishing practices are essential for durable concreteUse steel shuttering/plywood shuttering/timber shuttering. In case of timber shuttering see that the joints are neat and if possible tongued and grooved to avoid any loss of slurry from the concrete. (11.1 IS : 456 2000). Ensure adequate supports/bracings to withstand concrete tamping/vibration pressure.

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Provide proper wedges while using oil on steel plate, ensure no spillage are the reinforcement Do not allow rickety formwork or yielding supports like cracked ballies bamboos. Failure of auditorium at Dehradun (during ) being completed by NBCC was due to failure of form works. It should be rigid and of adequate strength. The face of form work in contact with concrete shall be cleaned and treated with form release agent like oil, soap solution, water wash. Ensure thin quoting of release agents to form works without coating reinforcement avoid .spillage etc while coating (IS : 456 2000, Clause 11.2) .

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Do not allow very old formworks/shuttering. Ensure removal of rubbish, chippings, shavings, saw dust from the interior of the forms. (IS : 456 2000, Clause 11.2) Do not remove form work untill concrete has hardened for specified days. (Recommended stripping time) (IS : 456 2000, clause 11.3.1) The number of props left under shall be spaced adequately to safely carry the full dead load of concrete and live load likely to occur during curing or further construction.

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Reinforcement.(Reinforcement shall be bent and fixed in accordance with procedure specified in IS : 2502 (12.1).

Accept the reinforcement from the main producer only SAIL/TISCO etc, All reinforcement shall be free from loose mill scales, loose rust and coats of paints, oil, mud or any other substances which may destroy or reduce the bond (IS : 456 2000 Clause 5.6.1). When reinforcement is left exposed for future construction, it should be adequately protected from corrosion and weathering action.

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Congestion of steel should be avoided at intersections. Ensure hooked and bent bars have adequate concrete cover. Ensure splicing in reinforcing bars are of correct dimensions and away from maximum stress and properly staggered . Check that cranking is at correct position. Provide skin/side face reinforcement for Beam 750mm (without torsion) Beam 450 mm (with torsion) Storage of steel shall be as per IS : 4082 (5.7)

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Do not use too many small lengths. Do not allow different types of metal within the concrete mass to avoid bimetal corrosion. (IS : 456 2000 Clause 12.6) Crossing bars should not be tack-welded. Ensure bar bending schedules to be prepared. (Clause 12.1 ISO 4066 1977 for detailing). Ensure that bar supports and cover blocks are placed to maintain correct and bottom side cover.

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Ensure high chairs and stools on to support supper reinforcement mats at the correct level (SP 23 clause 2.5). Ensure that positioning of down take pipes (inlets/outlets) sleeves, pipes and electrical conduits alongwith reinforcement. Avoid rough handling, shock loading and dropping from height of reinforcement. No welding should be allowed for splicing spacers ; cover blocks should be of concrete of same strength or PVC (12.3.1)

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Ensure special ductility detailing for earthquake resistant buildings (IS : 4326 1976)

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Concrete Work.

Ensure to give adequate notice to the contractor prior to start any important operation for concreting. (IS : 456 2000 Clause 13.6) Batching for concrete should be allowed by mass only for cement and aggregates. Water shall be weighed or measured by volume in a calibrated tank. (IS : 456-2000, Clause 10.2). Weigh batching machine is a mandatory requirement. Ensure deep containers for transportation of concrete during hot weather. (IS : 456 2000, Clause 13.1.1) Allow only mechanical mixer for quality concreting. The mixer should comply with IS : 1791 & IS : 12119. The mixer shall be fitted with water measuring devices (IS : 456 02 Clause 10.3). Ensure time for mixing 11/2 to 2 min to obtain mass of concrete uniform in colour and consistency. Flat slabsor pavements thickness not exceeding 200mm depth screed vibrators (IS : 2500 1968). Be careful to avoid displacement of reinforcement or movement of formwork. Ensure concreting in one operation between the expansion joints and construction joints without any break at the dummy joints (pavement). Ensure proper placing of PVC/MS conduits for internal electrification on roof before concreting.

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Ensure that concrete is placed and compacted before initial set. Use vibrators for all RCC and pavement slabs and other important works. Ensure concrete cubes are made and tested as specified. Ensure proper curing.Do not allow concreting unless you have been satisfied regarding positioning of reinforcement, spacers, soundness of formwork and all aspects.

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Do not allow excessive vibration. Do not allow over trowelling/floating. Do not expose fresh concreting to scorching sun, rain or frost. Avoid concreting in such conditions if unavoidable, precautions enumerated in SP : 25-1984 should be adopted. Ensure that measuring guage boxes are of correct sizes and actually used for measuring aggregate. Ensure that sand and aggregate conforms to grading specified.

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Ensure that slump test is carried out at regular intervals. Check proportion of silt in sand. Ensure proper water cement ratio. Ensure that curing of the concrete is done for specified number of days. Ensure immediate inspection of site after stripping the form works for any defective works. Ensure that where foundations are stepped the overlap is more than thickness of concrete layer.

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Concrete mix should be workable mix. Ensure concreting for fire resistant structure as per IS : 1642. Dont allow concrete to be compacted in layer exceeding what thickness is stipulated in specification. Dont allow ramming/vibration of concrete once the concrete has set. Dont allow concreting in severe weather. If unavoidable precautions as per IS : 7861 should be followed. Dont allow concrete to be thrown from a height. (permissible free fall 1.5m as per IS : 456-2000)

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Dont do excessive vibration. Otherwise segregation starts. Do not allow any rubbish particularly chippings shavings and sawdust in the interior of the forms Do not allow construction joints by free flow of concrete. It should be true vertical. Ensure all Quality Assurance Measures incorporated in IS : 456-2000.

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TESTINGS

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BUILDING BRICKS Test to be done Compressive Strength Water absorption Efflorescence Warpage Dimensions Shape and texture

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Basis of Testing IS : 3495 1976 (Part I to IV) IS : 1077 1986 IS : 5454 1978 Sampling Sampling may be done while bricks are in motion or when they are stacked. In both the cases a sample of 50 bricks should be taken from every consignment of 50,000 bricks or part thereof. Samples should be stored in dry place till tests are carried out. Minimum number of bricks required for testing is 20.

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CEMENT Test to be Performed Fineness Soundness Setting Time Compressive and tensile strength Chemical Requirements Drying shrinkage for PPC

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Basis of Testing IS : 269 1976 for OPC IS : 8112 1976 for High strength IS : 1489 1976 for PPC Sampling

A fair average sample should be obtained from a mixture of approximately equal portions taken from 12 different bags. Final sample should not weigh less than 10 kgs

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COARSE& FINE AGGREGATE Tests to be Performed Sieve analysis Specific gravity, density, voids, moisture content/absorption and bulking Organic impurities Flankiness Index Elongation Index Aggregate impact value Aggregate crushing value Aggregate abrasion value Soundness of aggregate

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Basis of Testing and Sampling IS : 2386 1963 (Part I to VIII) IS : 383 - 1970 IS : 5640 1970 IS : 2430 - 1986 Sampling The sampling is to be carried out as per IS : 2430 for each lot of 15m3 or part thereof. Material of each nominal size should be separately sampled. The weight of sample to be sent should be as follows :-

Max size present Size of Sample in kg(i) Coarse aggregate 63 cm100 Kg (ii) 40mm and below 50 Kg

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Aggregate should be packed in double gunny bags to prevent loss in transit. The size of aggregates should be prominently marked on gunny bags.

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MILD STEEL & MEDIUM TENSILE STEEL Tests to be Performed Tolerance in dimension weight Tensile test Reverse bend test Basis of Tests IS : 432 1982 226 - 1975 IS : 1786 1985 (for Deformed bars) IS : 4905 1968

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Sampling For tensile test, one test piece should be selected for every 40 tonne and for cold bend test one piece should be selected for every 20 tonne. A separate test is to be carried out for each diameter or for thickness of bar. Length of specimen for each test should not be less than 1.5m

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CONCRETE Tests to be Performed Workability Compressing Strength Core strength (where required) Flexure strength (where required) Basis of Tests IS : 1199 - 1959 IS : 516 1959 IS : 456 2000

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Frequency of sampling. Workability to be tested for each batch of concrete as per IS : 456 2000 Compressive strength by casting 3 cube samples for 7 days and 28 days, be tested in accordance with IS : 456 2000 Flexure strength by costing 3 beams samples for 7 days and 28 days be tested.

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GENERAL

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Some important points are mentioned below :- Study carefully all drawings, specifications, SSR and contract conditions. Always have copies of above mentioned documents readily available for consultation. Get conversant with all the relevant TDs of the Zone Do not hesitate to point out any mistake in drawings, specifications or contract documents. In case of doubt , get clarification from your superior officer.

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Keep samples of all materials to be incorporated in works for ready comparison with approved samples kept in GEs sample room. Ensure deployment of qualified site engineer by the contractor. Ensure better co-ordination between E/M and B/R activities of the project. For RCC framed, construction of panel walls & partition wall should be proceeded with from top down ward

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For RCC frame structures, the drgs/provisions of ductility provisions should be well understood. Do not adopt a very fast pace of construction to avoid cracking.Ensure that essential field testing equipment such as plumb bob, measuring tape, spirit level, compass, leveling instrument etc are in good condition readily available. Ensure all the tests specified in Contract Agreement of the Zone as per Appx D .

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Ensure that all work site documents like works Diary, site instruction book, stage - passing register, measure- ment book, testing register, steel acceptance register, sample passing register etc are properly filled regularly or periodically. See that contractors work is properly organized and executed with efficient manner. A proper job-oriented CPM analysis chart should be prepared with the help of contractor and work executed accordingly. Ensure STEs/TEs obsns are replied and recoveries/ rectifications effected promptly Ensure users participation since inception of the project.

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THANK YOU

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