CEMENT: Cement belongs to the elementary and most vital component of cement concrete. The quality of cement should be fresh while utilizing it for construction work and it should satisfy the standard specifications.
FINE AGGREGATE: Sand is utilized as fine aggregate in cement concrete. Sand particles should comprise of coarse, sharp and angular edges. Size of sand particles should be maintained in such a manner that it can move through 4.75mm sieve. Sand should be clean and does not contain dust and organic matters. Sea sand should not be applied for construction work due to extreme salt contents.
Stone dust is also applied as fine aggregate in cement concrete, but prior to application, check that it adheres to specifications.
COARSE AGGREGATE: Normally, pieces of feverous rocks are applied as coarse aggregates. These stones should be solid, strong, long-lasting and clean. The shapes of aggregates should be cubic or closed to cubic shape. The shape of coarse aggregates should not be laminated and elongated. It should be clean and does not contain from any irrelevant organic matters.
The size of coarse aggregates should satisfy the approved construction work requirements. It should not move through the sieve size of 5mm and coarse aggregates should be graded. Voids should not go beyond 42%.
PROPORTIONING: Based on their fixed ratios, cement, sand and coarse aggregates should be calculated. Prepare a standard measuring box as per the volume of one cement bag. Volume of one cement bag is 1.25 cubic foot.
When, it is required to calculate the ratio of sand, bulking of sand should be taken into consideration. Choose dry sand at the time of making calculation of proportioning. Work out the moisture content in sand and include extra volume of sand. Constantly work out moisture content throughout construction work and include extra volume of sand based on the amount of moisture. It is suggested not to compact coarse aggregates at the time of proportioning.
CONCRETE MIXING: Mixing machine is suitable for large scale construction works whereas hand mixing is chosen since it is cost-effective for smaller concrete works.
CONCRETE CONSISTENCY: Concrete consistency is based on water to cement ratio. Surplus amount of water reduces the strength of concrete and also concrete constituents can be easily detached. The quantity of water given below should be applied against 50kg cement bag.
Concrete Ratio - Amount of Water
1:3:6 - 34 liters
1:2:4 - 30 liters
1:2:3 - 27 liters
1:1:2 - 25 liters
If vibrator is utilized for concrete compaction, then the amount of water should be reduced as per suggestion of engineer in charge.