The durability of concrete depends on its resistance to deterioration and the environment in which it is placed. The resistance of concrete to weathering, chemical attack, abrasion, frost and fire depends largely upon its quality and constituent materials. Susceptibility to corrosion of the steel is governed by the cover provided and the permeability of concrete. The cube crushing strength alone is not a reliable guide to the quality and durability of concrete;it must also have an adequate cement content and a low water cement ratio. One of the main characteristics influencing the durability of any concrete is its permeability. With strong, dense aggregates, a suitably low permeability is achieved by having a sufficiently low water cement ratio by ensuring as a thorough compaction of the concrete as possible and by ensuring sufficient hydration of cement through proper curing methods. As such, 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. The mix proportions shall be selected to ensure that the workability of the fresh concrete is suitable for the conditions of handling and placing, so that after compaction it surrounds all reinforcements and completely fills the form work. When concrete is hardened, it shall have the required strength, durability and surface finish. The determination of the proportions of cement, aggregates and water to attain the required strength shall be made by designing the concrete mix, such concrete is called Design concrete mix and also by adopting nominal concrete mix, such concrete shall be called Nominal mix concrete. Design mix concrete is preferred to nominal mix. If design mix concrete can't be used for any reason on the work for grades of M-20 or lower, nominal mixes may be used with the permission of engineer -in-charge, which however, is likely to involve a higher cement content. In specifying a particular grade of concrete, the following information shall be included (a) Type of mix, that is, design mix concrete, or nominal mix concrete. (b) Grade designation (c) Type of cement (d) Maximum nominal size of aggregate (e) Minimum cement content (for design mix concrete) (f) Maximum water cement ratio. (g) Workability and (h) Mix proportion (for nominal mix concrete) . In appropriate circumstances, the following additional information may be specified (a) Type of aggregate. (b) Maximum cement content, and (c) Whether an admixture shall or shall not be used and type of admixture and the conditions of use.

Code of practice for plain and reinforced concrete, the Indian standard was adopted by the Indian standards institution on 3 October-1978 after the draft finalized by the Cement and concrete Sectional committee had approval it by the Civil Engineering Division of the Council., thus enlarging the design and scope of use and exercise of the code and also incorporating a number of changes and the additions so required with a view to keeping a breast with the rapid development in the field of concrete technology and also to bring in further clarifications and required modifications in the light of experience gained as per the version of the code to practical situations. In some clauses the code recommends reference to Specialist literature, since the current knowledge on some aspects of design has not yet crystallized for which while the designers are already aware of the need for basing designs on requirements of the adequate strength and the satisfactory serviceability it is too essential to provide for the rationalize approach, taking into account the variations in material strength and loads on the semi probabilistic base has to be introduced to cover the ultimate load based on the working stress method of design. Further the clauses dealing with the sampling and acceptance criteria for concrete have also been revised by elaborating the concepts of statistical quality control and introducing characteristics strength of concrete, to bring it in the line with the latest trends adopted in quality control of the concrete. Information relating to the properties of concrete such as modulus of elasticity, tensile strength, shrinkage, creep and coefficient of thermal expansion has required to be given.