Plain Concrete - Concrete without reinforcement or very less reinforcement
Reinforcement - Generally Steel Bars
Reinforced Concrete - Combination of Concrete and reinforcement with proper bonding
Clause 1.1.1 of IS 456:2000 For the purpose of this standard, plain concrete structures are those where reinforcement, if provided is ignored for determination of strength of the structure.
Clause 5.6 of IS 456:2000 The reinforcement shall be any of The following:
a) Mild steel and medium tensile steel bars conforming 10 IS 432 (Part I). b) High strength deformed steel bars conforming to IS 1786. c) Hard-drawn steel wire fabric conforming to IS 1566 .
d) Structural steel conforming to Grade A of IS 2062.
CONCRETE MIX PROPORTIONING
9 . CONCRETE MIX PROPORTIONING 9.1 Mix Proportion The mix proportions shall be selected to ensure the workability of the fresh concrete and when concrete is hardened, it shall have the required strength, durability and surface finish. 9.1.1 The determination of the proportions of cement, aggregates and water to attain the required strengths shall be made as follows: a) By designing the concrete mix; such concrete shall be called 'Design mix concrete', or b) 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 cannot 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.
9.2 Design Mix Concrete
9.2.4.2 Assumed standard deviation Where sufficient test results for a particular grade of concrete are not available, the value of standard deviation given in Table 8 may be assumed for design of mix in the first instance. As soon as the results of samples are available, actual calculated standard deviation shall be used and the mix designed properly.
However, when adequate past records for a similar grade exist and justify to the designer a value of standard deviation different from that shown in Table 8, it will be permissible to use that value.
9.3 Nominal Mix Concrete