8/6/2019 5.4.7.2 to 5.4.9.4

1/3

137 SUB HEAD 5.0 : REINFORCED CEMENT CONCRETE WORK

in-Charge. Number of such joints shall be kept to minimum. The joints shall be kept at places where theshear force is the minimum. These shall be straight and shall be at right angles to the direction of mainreinforcement. Construction joints should comply with IS 11817.

5.4.4.2 In case of columns the joints shall be horizontal and 10 to 15 cm below the bottom of the beamrunning into the column head. The portion of the column between the stepping off level and the top ofthe slab shall be concreted with the beam.

5.4.4.3 When stopping the concrete on a vertical plane in slabs and beams, and approved stop board(see Fig. 26C) shall be placed with necessary slots for reinforcement bars or any other obstruction topass the bars freely without bending. The construction joints shall be keyed by providing a triangular ortrapezoidal fillet nailed on the stopboard. Inclined or feather joints shall not be permitted. Any concreteflowing through the joints of stopboard shall be removed soon after the initial set. When concrete isstopped on a horizontal plane, the surface shall be roughened and cleaned after the initial set.

5.4.4.4 When the work has to be resumed, the joint shall be thoroughly cleaned with wire brush andloose particles removed. A coat of neat cement slurry at the rate of 2.75 kg of cement per square metreshall then be applied on the roughened surface before fresh concrete is laid.

5.4.5 Expansion JointsExpansion joints shall be provided as shown in the structural drawings or as indicated in Fig. 5.10 to5.25 or as directed by Engineer-in-Charge, for the purpose of general guidance. However it isrecommended that structures exceeding 45 m in length shall be divided by one or more expansion joints. The filling of these joints with bitumen filler, bitumen felt or any such material and provision ofcopper plate, etc. shall be paid for separately in running metre. The measurement shall be taken twoplaces of decimal stating the depth and width of joint.

5.4.6 CuringAfter the concrete has begun to harden i.e. about 1 to 2 hours after its laying, it shall be protected

from quick drying by covering with moist gunny bags, sand, canvass Hessian or any other materialapproved by the Engineer-in-Charge. After 24 hours of laying of concrete, the surface shall be cured byponding with water for a minimum period of 7 days from the date of placing of concrete in case of OPC

and at least 10 days where mineral admixtures or blended cements are used. The period of curing shallnot be less than 10 days for concrete exposed to dry and hot weather condition.

5.4.7 Finishing5.4.7.1 In case of roof slabs the top surface shall be finished even and smooth with wooden trowel,before the concrete begins to set. Sprinkling of dry cement while finishing shall not be resorted to.

5.4.7.2 Immediately on removal of forms, the R.C.C. work shall be examined by the Engineer-in-Charge,before any defects are made good.

(a) The work that has sagged or contains honey combing to an extent detrimental to structural safetyor architectural concept shall be rejected as given in para 5.4.9.4 for visual inspection test.

(b) Surface defects of minor nature may be accepted. On acceptance of such a work by the

Engineer-in-Charge, the same shall be rectified as follows:1. Surface defects which require repair when forms are removed, usually consist of bulged due

to movement of forms, ridges at form joints, honey-combed areas, damage resulting from thestripping of forms and bolt holes, bulges and ridges are removed by careful chipping ortooling and the surface is then rubbed with a grinding stone. Honey-combed and otherdefective areas must be chipped out, the edges being cut as straight as possible andperpendicularly to the surface, or preferably slightly under cut to provide a key at the edge ofthe patch.

8/6/2019 5.4.7.2 to 5.4.9.4

2/3

CPWD SPECIFICATIONS 2009 138

2. Shallow patches are first treated with a coat of thin grout composed of one part of cementand one part of fine sand and then filled with mortar similar to that used in the concrete. Themortar is placed in layers not more than 10mm thick and each layer is given a scratch finishto secure bond with the succeeding layer. The last layer is finished to match the surroundingconcrete by floating, rubbing or tooling on formed surfaces by pressing the form materialagainst the patch while the mortar is still plastic.

3. Large and deep patches require filling up with concrete held in place by forms. Such patchesare reinforced and carefully dowelled to the hardened concrete.

4. Holes left by bolts are filled with mortar carefully packed into places in small amounts. Themortar is mixed as dry as possible, with just enough water so that it will be tightly compactedwhen forced into place.

5. Tiered holes extending right through the concrete may be filled with mortar with a pressuregun similar to the gun used for greasing motor cars.

6. Normally, patches appear darker than the surrounding concrete, possibly owing to the

presence on their surface of less cement laitance. Where uniform surface colour is important,this defect shall be remedied by adding 10 to 20 percent of white Portland cement to thepatching mortar, the exact quantity being determined by trial.

7. The same amount of care to cure the materials in the patches should be taken as with thewhole structure. Curing must be started as soon as possible, after the patch is finished toprevent early drying. Damp Hessian may be used but in some locations it may be difficult tohold it in place. A membrane curing compound in these cases will be most convenient.

(c) The exposed surface of R.C.C. work shall be plastered with cement mortar 1:3 (1 cement : 3 finesand) of thickness not exceeding 6 mm to give smooth and even surface true to line and form.Any RCC surface which remains permanently exposed to view in the completed structure, shallbe considered exposed surfaced for the purpose of this specification.

Where such exposed surface exceeding 0.5 sqm in each location is not plastered with cementmortar 1:3 (1 cement : 3 fine sand) 6 mm thick, necessary deduction shall be made for plasteringnot done.

(d) The surface which is to receive plaster or where it is to be joined with brick masonry wall, shallbe properly roughened immediately after the shuttering is removed, taking care to remove thelaitance completely without disturbing the concrete. The roughening shall be done by hacking.Before the surface is plastered, it shall be cleaned and wetted so as to give bond betweenconcrete and plaster.

RCC work shall be done carefully so that the thickness of plaster required for finishing thesurface is not more than 6 mm.

(e) The surface of RCC slab on which the cement concrete or mosaic floor is to be laid shall beroughened with brushes while the concrete is green. This shall be done without disturbing theconcrete.

5.4.8 Strength of ConcreteThe compressive strength on the work tests for different mixed shall be as given in Table 5.5 below:-

8/6/2019 5.4.7.2 to 5.4.9.4

3/3

139 SUB HEAD 5.0 : REINFORCED CEMENT CONCRETE WORK

TABLE 5.5

Compressive Strength in (Kg/ sq cm)Concrete Mix (Nominal Mix onVolume basis)

7 days 28 days

1:1:2 210 315

1:1.5:3 175 2651:2:4 140 210

5.4.9 Testing of Concrete

5.4.9.0 Regular mandatory tests on the workability of the fresh concrete shall be done to achieve thespecified compressive strength of concrete. These will be of two types

(a) Mandatory Lab, Test(b) Mandatory Field TestResults of Mandatory Field Test will prevail over mandatory Lab. Test.

5.4.9.1 Cube Test for Compressive Strength of Concrete - Mandatory Lab Test : Mandatory testsshall be carried out as prescribed in Appendix A of Chapter 5.

5.4.9.2Additional Test: Additional test, if required, shall be carried out as prescribed in Appendix B ofChapter 5.

5.4.9.3 Slump Test : This test shall be carried out as prescribed in sub-head 4 of concrete.

5.4.9.4 Visual Inspection Test : The concrete will be inspected after removal of the form work asdescribed in para 5.4.7.2 The question of carrying out mandatory test or other tests described inAppendix A and B (para 5.4.9.1 and 5.4.9.2) will arise only after satisfactory report of visual inspection.

The concrete is liable to be rejected if:(i) It is porous or honeycombed as per para 5.4.7.2 (a).(ii) Its placing has been interrupted without providing a proper construction joint.

(iii) The reinforcement has been displaced beyond tolerance specified or construction toleranceshave not been met.

However, the hardened concrete may be accepted after carrying out suitable remedial measures tothe satisfaction of the Engineer-in-Charge at the risk and cost of the contractor.

5.4.10 Standard of Acceptance for Nominal Mix

5.4.10.1 Mandatory Lab. Test : For concrete sampled and tested as prescribed in Appendix A ofChapter 5, the following requirement shall apply.

5.4.10.2 Out of six sample cubes, three cubes shall be tested at 7 days and remaining three cubes at 28days.

5.4.10.3 7 days TestsSampling: The average of the strength of three specimen shall be accepted as the compressive

strength of the concrete provided the variation in strength of individual specimen is not more than + 15%of the average. Difference between the maximum and minimum strength should not exceed 30% ofaverage strength of three specimen. If the difference between maximum and minimum strength exceeds30% of the average strength, then 28 days test shall have to be carried out.