DURABILITY OF CONCRETE DEPENDS UPON THE QUALITY OF CONSTITUENT MATERIALS, AND WORKABILITY ON THE WATER CEMENT RATIO FOR WHICH SLUMP TEST AND COMPACTION FACTOR TEST ARE ASCERTAINED.

According to the purpose for which the concrete is required, the mix may contain cement from one of the following groups like all kinds of ordinary portland cement, Portland blast furnace cement, pozzolanic cement and sand Portland cement, high alumina cement , expanding cement and non shrinking cement, super sulphate cement or slag sulphate cement. Various groups and corporate companies are preparing all types of cement so required for the use based on the workability where concrete mix proportions chosen should be such that the concrete is of adequate workability for the placing conditions of the concrete and can be properly compacted with the means available for which the workability is measured by two methods -- (1) Slump test (2) Compaction factor test. The durability of concrete depends on the resistance to deterioration and the environment in which it is placed. The resistance of concrete to weathering, chemical attack, abrasion, frost and fire depends upon quality of constituent materials. One of the main characteristics influencing the durability of concrete is its permeability. With strong, dense aggregates, a suitability low permeability is achieved by having a sufficiently low water cement ratio by ensuring as thorough compaction of the concrete as possible, and by ensuring sufficient hydration of cement through proper curing methods. Therefore for given aggregates, the cement content should be sufficient to provide adequate workability with a low water cement ratio, so that concrete can be completely compacted with the means available. For complete hydration of a given amount of cement, an amount of water equal to about 25 percent of the cement by weight, is needed for chemical reaction. An additional 10to 15 percent water is added to provide mobility for the water in the cement paste during the hydration process so that it can reach the cement particles. This makes for a total minimum water cement ratio of 0.35 to 0.40 by weight.