Most widely used construction material, Concrete in a homogeneous mixture of cement, sand i.e. fine aggregate, coarse aggregate and water.
Concrete is generally graded according to it’s compressive strength. following figure provides the grade of concrete its compressive strength and approximate mix proportions.
Grade of Concrete is represented as M20, where M stands for Mix and 20 stands for the characteristic strength of concrete in 28 days of curing.
However, these numbers are approximate. the exact Mix design can be done by proper IS method.
Properties of Concrete
Workability – It is ease with which concrete can be mixed, transported and laid in homogeneous state. Workability of concrete depends upon quantity of water, grading of aggregate and percentage of fine materials in the mix. Concrete should have good workability.
Strength – When we talk about strength of concrete, we talk about compressive strength of concrete. Hardened concrete should have high compressive strength to bear heavy loads of the structures. Nowadays, minimum strength of concrete after hardening should be 15 N/mm².
Durability – Concrete must be durable to resist the actions of rain, frost action etc. It is majorly affected by water cement ratio.
Expansion & Shrinkage – Concrete has very low coefficient of thermal expansion, hence if no provisions are made for the expansion, very large forces can be developed. As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material, process gets slowed with time. Concrete should exhibit minimum shrinkage. This property of concrete is mainly guided by water cement ratio
Creep – Creep is permanent movement or deformation of a material in order to relieve stresses within the material. Creep in concrete should be as minimum as possible.
Segregation – It is a case of particle segregation in concrete applications, in which ingredients tend to segregate by virtue of differences in the size, density, shape and other properties of particles of which they are composed.
Tests performed on Concrete
Workability tests – Slump cone test, compaction factor test, Vee-bee consistometer test, flow table test,
Strength tests- compressive strength, flexural strength
We will cover tests on concrete in next article.