JOB PROCEDURE FOR RCC
The purpose of this procedure is to provide methodology for effective survSGSlance of various activities involved in supervision of RCC work at site and to ensure that
- Shuttering is placed as per correct line & level
- Reinforcement is laid on as per approved drawing\BBS\specifications
- Proper procedures are followed for RCC work
- Documents are generated so as to quantify the actual work done.
This procedure covers supervision and record keeping methods for RCC which includes.
- Top & bottom level of RCC.
- Proportioning of concrete mix as per grade of concrete.
- Preparation of pour card and adhering to prescribed quality standards.
- CPWD Specification
- AFC drawing
DETAILED ACTION PLAN:
- Testing of materials; for cement manufacturer test certificate shall be submitted for each batch of cement. In case of MTC correlation is not done, the same shall be tested at approved laboratory. RCC shall be used as per SOR item & AFC drawings.
- Coarse aggregate shall be tested at field laboratory or at approved laboratory, gradation of coarse aggregate shall confirm to IS:383. Crushing value, impact value, abrasion value, flakiness index of coarse aggregate shall be tested at field laboratory or approved laboratory per IS:2386. Frequency of testing shall be as per QAP. (Replace IS: 8112 by IS 1489 where PPC is used installed of OPC)
- Fine aggregate shall be tested at field or at approved laboratory .Gradation of fine aggregates shall confirm to IS:383 & shall be tested at field. Presence of deleterious material shall he tested at laboratory. Frequency of testing shall he as per QAP.
- For reinforcement steel., manufacturer test certificate shall be submitted.
Before establishment of design mix all the materials such as CA, FA cement etc. shall be tested. Design stipulation such as water cement ratio, degree of quality control, minimum cement content, workability etc. shall be considered as stated in contract document. In case of change of design stipulation or change of source of ingredients using for concrete re-design mix will be done.
Trial mix shall be taken at site condition for design mix.
C. Mixing of Concrete:
For weight — batching in plant, the entire ingredient shall be poured by weight. Cement shall be stored in cement through bucket – elevator. Water shall be measured in volume. Admixture shall be measured by weight. During hot/cold weather, the mixing shall be as per IS:7861.
D.Transportation, Placing & Compaction:
Concrete shall be transported from batching plant to pouring location through transit mixers. Concrete shall be poured immediately after its transportation to working site. For concreting in depth chutes shall be used. The vertical fall should not be more than 1.5m height. Immediately after pouring of concrete in the formwork, it shall be compacted by using mechanical vibrating equipment. Immersion type vibrator shall be inserted in vertical position and care should be taken so that it dose not over or under vibrate. At the time of transportation and placing of concrete all the precautionary measure has to be taken to avoid any sort of deterioration in quality. Care shall be taken to ensure adequate vibration, hounding and mounding of Concrete between the succeeding batches. Before placing of concrete the area shall be cleaned properly. Concrete shall be deposited as near as practicable in its final position to avoid re-handling. Concrete shall not be started unless electrical conduits, pipes fixtures etc whenever required are laid before concreting all metal inserts anchor bolts pipe sleeves etc shall be fixed as per relevant drawing and that shall be checked W.R.T. its lines & levels.
Construction joints shall be provided as shown in drawings or as decided by SGS. As far as possible, the number of construction joints has to be minimum. The joint shall be formed 100-150mm below the lowest soft of the beam. The joint in beam & slab shall be vertical with in 1/3rd-1/4th of the span with approved stop board at the time of resume of the next work. The hardened surface shall be cleared off foreign materials, roughened property & wetted by pouring cement slurry or mortar.
Concrete shall be cured by keeping it continuously moist wet for specified period of time to ensure complete hydration of cement & its hardening. Curing shall be started after 8 hrs of placement of concrete in normal weather in hot weather after 4hrs. Exposed surface of concrete shall be maintained continuously in a damp or wet condition for at least for first 7 days after placing concrete. Curing shall be done 10 days for dry /hot weather condition in case of mineral admixture is used curing may be extended to 14 days.
G.Strength Test of Concrete
Samples in the form of 15 cm x I5cm x 15cm cubes shall be taken from fresh
concrete, cured and tested at 7 days & 28 days in accordance with IS:516. Required strength of cubes depending on grade of concrete will be as per IS: 456. The concrete shall be deemed to comply with the strength requirement if satisfies the acceptance criteria as per IS:456.
H.Finishing of Concrete
On removal of form work, all the surface defects observed shall be rectified immediately. The surface of non shuttered faces shall be smoothened with a wooden float to give a finish similar to that of the rubbed down shuttered faces the top faces of the concrete intended to be covered with screed or any other work shall be left with a rough finish.
Forms for concrete shall be of plywood confirming to IS: 6461 or steel & shall give smooth & even surface after removal thereof. Formwork & its support shall maintain their correct position & shall be of correct shape & profile so that the final concrete structure is within the limits of dimensional tolerance specified in IS: 456. The form shall be true, rigid & adequately braced both horizontally & diagonally. The form shall have smooth and even surface & be sufficiently rigid to carry without deformation .The dead weight of green concrete, working load, and wind load & also the side pressure the green concrete form joint shall not permit any leakage. The form shall be strong enough to withstand the effect of vibrations.
Before re-use all form shall be thoroughly scrapped, cleaned, examined & whenever necessary shall be repaired & retreated before re-setting. In the determination of time for removal of form, consideration shall be given to the location & character of structure the weather & other condition including the setting & curing of concrete & material used in the mix. The form shall be removed without shock & method of form removal likely to cause over stressing or damage to concrete shall not be adopted. In normal circumstances form shall he removed below soffits of beams & slabs as per IS: 456.
Staging & scaffolding shall be properly designed & steel tubes will be used. For circular shuttering, care shall be taken so that it is supported properly & diameter has been kept accurately.
Before placing the reinforcement steel, bar bending schedule shall be prepared & got checked by SGS. Reinforcement shall be cut, bend to shape & dimension as shown in BBS/drawings. All reinforcement shall be fixed in the correct position as shown in the drawing & shall be properly supported to ensure that displacement will not occur when the concrete is displaced & completed. Reinforcement bars shall be tied at every intersection. Cover blocks of specified thickness, constructed & cured properly shall be placed in between forms & reinforcement to provide sufficient clearance. In case of overlapping of two bars, lap length shall be provided as mentioned in the drawing. The lap shall he staggered. At any section lap should not be more than 50% of total area. Tolerance of placing of reinforcement shall be as per IS: 456.