Specification for P.C.C.

i. Coarse aggregate shall be from hard broken stone of compact basalt or granite or similar stone and shall be free from dust, dirt, oil and other foreign matters.
ii. Size of stone shall be 20 mm and down and all sizes of stones shall be retained in a 5 mm square mesh and well graded.
iii. Size of stone aggregate depends upon the thickness of concrete and nature of work.
i. Fine aggregate shall have coarse sand consisting of hard, sharp and angular grains.
ii. Sand shall be as per the standard specification.
iii. Sand shall be clean and free from dust, dirt, oil and other organic matter.
Cement shall be fresh, not old & as per the standard I.S. specification and shall have required compressive strength and fineness. Water shall be clean water, free from any impurities and free from alkaline and acid matters; water shall be suitable for drinking purpose.
• The proportion of concrete shall be 1:2:4 of cement, sand and course aggregate by volume unless otherwise specified.
• For 7 days, the minimum compressive strength of cement concrete (1:2:4) shall be 14 N/mm2.
• All ingredients shall be dry. Bulking of sand allowance shall be made for wet sand.
• Cement, sand and coarse aggregate shall be taken into the machine mixer in required proportion.
• For concrete of proportion 1:2:4 consist of one bag of cement, two boxes of sand and four boxes of coarse aggregate shall be taken into mixer.
• Mixed concrete shall be discharge on a masonry platform or on a flat iron sheet.
• Hand mixing is allowed for small work only. Mixing of ingredients shall be done on masonry platform or flat iron sheet.
• For concrete of 1:2:4/1:4:8 proportion, one bag of cement, first two boxes of sand shall be mixed dry thoroughly making the material turning up and down by spade and then this homogeneous dry mix shall be placed over a spreaded stack of 4 boxes of coarse aggregate & the complete mixed dry turn up and down with spade at least three times so as to obtain uniform mix. Then water shall be added slowly and gradually and then turning the mix up and down at least three times by spade till to obtain a plastic mix of the required workability and water – cement ratio.
• Water quantity shall be of 25 to 30 liters per bag of cement.
• Form work and centering shall be used as per the standard specifications‟
• Internal surface of formwork shall be applied by oil so as to avoid sticking of concrete during removal of the formwork.
• Concrete shall be laid gently in layers not exceeding 150 mm and compacted with rods & tamping with wooden tampers or with mechanical vibrating machine until a dense concrete is obtained.
• Immersion type vibrators or needle vibrators shall be used for thick concrete or mass concrete. Surface vibrators or form vibrators shall be used for thin concrete. There shall not be over – vibration.
• Concrete shall be laid continuously. If laying of concrete is suspended for rest or on next day the end of concrete shall be slope with an angle of 30 and its surface shall be made rough for proper joining.
• If the concreting work is resumed, the previous sloped portion shall be made rough, clean, watered and a grout of neat cement shall be applied and fresh concrete shall be laid in successive layer in such way that the upper layer shall be laid before the lower layer is set.
• When concrete is on the point of hardening, after and about two hours laying, then it shall be kept wet by covering with wet gummy bags for 24 hours and then cured by flooding with water. Making mud wall 75 mm high or by covering with wet sand continuously for 15 days.
• The measurement shall be taken as per the drawing or as per instruction of the engineer.