DETAIL AND GENERAL SPECIFICATION FOR THE PLAIN CEMENT CONCRETE (PCC) WORK IN ISOLATED COLUMN FOOTING

 

GENERAL SPECIFICATION

• In plain cement concrete coarse aggregate should be hard durable and free from impurities.
• Fine aggregate should contain sharp, angular grain.
• Cement should be fresh Portland cement.
• Mixing should be done by hand mixing or by machine mixing.
• Laying and compaction should be done before setting of concrete i.e. within 30 min.
• Curing should be done for minimum 14 days. 

 

 

DETAIL SPECIFICATION          

MATERIALS

Coarse aggregate:

·         Aggregates shall comply with the requirements of IS 383.

·         It shall be crushed or broken from hard stone from the approved quarry.

• It shall be hard, strong, dense and durable, clean and free from soft friable, thin, flat, elongated or laminated, flaky pieces and shall be roughly cubical in shape.
• It shall be clean and free from dirt and any other foreign matter.
• Coarse aggregate may be graveled, may either be river bed shingle or pit graveled. It shall be sound, hard, clean suitably graded in size.
• This shall be free from flat particles of shale, powdered clay, slate, loam and other impurities.
• Gravel shall have to be washed if it contains soil materials adhering to it.
• Unless specially mentioned the size of the coarse aggregate shall be 20 mm graded down and shall be retained in 5mm square mesh so that the voids do not exceed 42%.

 

Fine aggregate:

• Aggregate most of which passes 4.75mm IS sieve is known as fine aggregate. Sand as fine aggregate shall be coarse, consisting of sharp, angular grains and be of standard specification.
• Crushed dust stone may also be used as fine aggregate.

Cement:

• Cements shall be phrased as Portland cement and confirmed to the ISI specification. 
• It should have required compressive and tensile strength and fineness.

Water:

• Water used shall be clean and reasonably free from injurious quantities of deleterious materials such as oils, acids, alkalis, salts and vegetable growth.
• Generally potable water shall be used.
• The pH value of the water should not be less than 6.
• The maximum permissible limits for solids shall be as per IS 456:2000 Clause 5.4, Page No 15.

 

PROPORTION

• Proportioning of cement, sand and coarse aggregate shall be 1:2:4 or as specified.

• Coarse aggregate and sand shall be measured by measuring box of 30cmx30cmx38cm of suitable size equivalent to one bag cement of 1/30 m³or 0.035 m³.
• Cement shall be measured by bag weighing 50kg.
• Sand shall be measured on the basis of its dry volume.
• While measuring the aggregate sacking, ramming or hammering shall not be done.
• If damp sand is used compensation shall be made by adding additional sand to the extent required for the bulking of damp sand.

 

MIXING

Hand mixing:

• Hand mixing by batches shall be permitted on small works.
• The mixing shall be done on a clean water tight masonry or concrete slab or steel plate platform.
• Measured quantity of sand shall be sprayed evenly. The cement shall be dumped on the sand and distributed evenly. The sand and cement shall be mixed thoroughly with spade turning the mixture over and over again until its even colour throughout and free from streaks. The measured quantity of coarse aggregate shall be sprayed out and the sand cement mixture shall be sprayed on its top.
• This shall be mixed at least three times by shoveling and turning over by twist from centre to side then back to the centre and again to the sides.
• A hollow shall be made in the middle of the mixed pile.
• Three quarters of the total quantity of water required shall be added while the material is turned in toward the centre with spades.
• The remaining water shall be added by water can fitted with rose head slowly turning the whole mixtures over and over untill a uniform colour and consistency is obtained throughout the pile.

    Machine Mixing:

• Measured quantity of dry coarse aggregate, fine aggregate and cement shall be placed in the hopper respectively.
• The dry materials shall be mixed in the mixing drum for at least four turns of the drum after which correct quantity of water shall be added gradually while the drum is in motion.
• The total quantity of water for the mixing shall be introduced before 25% of the mixing time has elapsed and shall be regulated to achieve the specific water cement ratio.
• The mixing shall be thorough to have a plastic mix of uniform colour.

 

 

MIXING TIME:

• The materials shall be mixed in a drum for a period of not less than 2 min and until a uniform colour and consistency obtained.
• The time shall be counted from the moment all the materials have been put into the drum.

CONSISTENCY

• The quantity of water to be used for each mix of 50kg cement to give the required consistency shall be as follows

                        Not more than 34 lit – 1:3:6 mix

                        Not more than 30lit – 1:2:4 mix

                        Not more than 27lit – 1:1 ½:3 mix

                        Not more than 25lit – 1:1:2 mix

• The quantity of water shall be regulated by carrying out regular slump test.

LAYING

• The entire concrete used in the work shall be laid gently in layers not exceeding 15cm and shall be thoroughly vibrated by means of mechanical vibrators till a dense concrete is obtained.
• Hand compaction shall be done with the help of punning rods and tamping rods and tamping with the wooden tampers so that concrete is thoroughly compacted and completely walked into the corners of the form work.
• The layers of concrete shall be so placed that the bottom layer does not finally sit before the top layer is placed.
• Compaction shall be completed before the initial setting starts that is within thirty minutes of addition of water to the dry mixture.

PROTECTION AND CURING

• Freshly laid concrete shall be protected from rain by suitable covering
• After the concrete as begun to harden, that is about one to two hours after its laying it shall be protected with moist gunny bags, sand or any other materials against quick drying.
• After 24hrs of lying of concrete the surface shall be cured by flooding with water of about 25mm depth or by covering with weight absorbent materials .Curing shall be done for a minimum period of 14 days.

FORMWORK

• If centering and shuttering are required to be done for this work.
• This shall be done in accordance with the specifications for form work under R.C.C