Quality of cement has nothing to do with its color.

It is good to use potable quality of water. It should be free from impurities and harmful ingredients. Seawater isn’t recommended. The water fit for mixing is fit for curing too. Use of minimum quantity of mixing water, consistent with the degree of workability required to enable easy placing and compaction of concrete, is advisable Ensure that water is measured and added Low water to cement ratio is essential for good performance of the structure in the long run.

1:1.5:3, where 1 part of cement is to be mixed with 1.5 parts of sand and 3 parts of coarse aggregates. Water requirement for the mix would be less than 25 liters per bag of cement.

The ways in which concrete maybe spoilt are many, most common of them being: Use of too much or too little water for mixing, or water carelessly added during mixing. Incomplete mixing of aggregate with cement Improper grading of aggregates resulting in segregation or bleeding of concrete. Inadequate compaction of concrete Using concrete which has already begun to set. Placing of concrete on a dry foundation without properly wetting it with water. Use of dirty aggregate or water containing earthy matter, clay or lime. Too much troweling of the concrete surface. Leaving the finished concrete surface exposed to sun and wind during the first ten days after placing without protecting it and keeping it damp by proper methods of curing.

The compressive strength is governed by the following factors: (i)w/c ratio (ii)characteristics of cement (iii)characteristics of aggregates (iv)time of mixing (v)degree of compaction (vi)temperature and period of curing (vii)age of concrete (viii)air entertainment (ix)conditions of testing

Concrete is a mixture of cement, sand, stone aggregates and water.

If a concrete mix is placed in and around a cage of steel rods, it is called Reinforced Cement Concrete (RCC).

Mortar is a mix of cement, sand and water, to be used for brick works/block works and plaster.

Normally the amount of water that is required per bag of cement is 25 -28 liters only.

Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement. Nowadays good quality fly ash is available from Thermal Power Plants, which are processed and used in manufacturing of PPC.

Green concrete has all the three phases – solids, water air. In order to make the concrete impervious & attain its maximum strength it is required to remove the entrapped air from the concrete mass when it is still in plastic state. If the air is not removed completely, the concrete loses strength considerably. It has been that 5% voids reduce the strength by about 30% and 10% voids reduce the strength by over 50%. Compaction eliminates air bubbles and brings enough fine material both to the surface and against the forms to produce the desired finish. One can use such hand tools as steel rods, paddling sticks, or tampers, but mechanical vibrators are best. Any compacting device must reach the bottom of the form and be small enough to pass between reinforcing bars. Since the strength of the concrete member depends on proper reinforcement location, be careful not to displace the reinforcing steel.

The mortar / concrete should be consumed as early as possible after addition of water to it. The hydration of cement starts the moment water is added to it. As the hydration progresses the cement paste starts stiffening and loses its plasticity. The concrete should not be disturbed after this. Normally, this is about 45 –50 minutes.