In order to meet the strength and durability requirements, the concrete is classified into structural Concrete and Non-Structural Concrete. The use and characteristics are given as follows: -
Non-Structural Concrete: It shall be used as lean, underfloor layers, and hard standings etc. or as described in drawings having compressive strength upto 1500 psi. It is prepared by using cement and other basic ingredients, i.e. Coarse aggregates, Fine aggregates and Water. Frequently used mix proportions are 1:6:12, 1:4:8, 1:3:6 and 1:2:4. The proportions mentioned for non-structural concrete are by volume. A cement bag of 50 kg, forms a unit of 0.035 cum (Gauge box of 30cm x 30cm x 39cm). The engineer in charge shall ensure preparation of the mix proportions or as specified for non-structural elements, based on the availability of local materials.
Structural Concrete: It shall be used in structural members like foundations, columns, lintels, beams and roof slabs etc. The strength of concrete will be specified in terms of minimum 28 days estimated cylindrical strength equal or more than 3000 psi, 3500 psi, 4000 psi, 5000 psi and 6000 psi. For a specified design strength, it is mandatory to get the concrete mix design, prescribing exact quantities of cement, coarse and fine aggregates with their size / gradation, water cement ratio and slump. It is recommended to get the Concrete Mix Design designed from a consultant or engineer in chief's branch (DD&C). In case of Mix Design is prepared by any other private consultant or designer, the use of this concrete will be in accordance with the instructions by the concerned designer and include some or all of the following:-
- Max water cement ratio
- Min cement content
- Air content (if required)
- Slump
- Max size of aggregate
- Min strength
- Other requirements relating to strength, durability, admixtures and special type of cement.
