The strength of concrete is basically referred to compressive strength and it depends upon three factors.
i- Paste Strength
ii- Interfacial Bonding
iii- Aggregate Strength
i. Paste strength:
It is mainly due to the binding properties of cement that the ingredients are compacted together. If the paste has higher binding strength, higher will be strength of concrete.
ii. Interfacial bonding:
Interfacial bonding is very necessary regarding the strength. Clay hampers the bonding between paste and aggregate. The aggregate should be washed for a better bonding between paste and aggregate.
iii. Aggregate strength:
It is mainly the aggregate that provide strength to concrete especially coarse aggregates which act just like bones in the body. Rough and angular aggregate provides better bonding and high strength.
Factors affecting Strength of concrete:
Following are the factors that affect the strength of concrete:
a. Water-Cement ratio
b. Type of cementing material
c. Amount of cementing material
d. Type of aggregate
e. Air content
a. Water-Cement ratio:
It is water cement ratio that basically governs the property of strength. Lesser the water cement ratio, greater will be strength.
b. Type of cement:
Type of cement affect the hydration process and therefore strength of concrete.
Amount of cementing material: it is the paste that holds or binds all the ingredients. Thus greater amount of cementing material greater will be strength.
c. Type of Aggregate:
Rough and angular aggregates is preferable as they provide greater bonding.
Chemical admixtures like plasticizers reduce the water cement ratio and increase the strength of concrete at same water cement ratio. Mineral admixtures affect the strength at later stage and increase the strength by increasing the amount of cementing material.