Compressive strength of concrete is affected very prominently by the strength of aggregate, its moisture content, grading, surface texture and the maximum aggregate size. For the making of high strength concrete, aggregates like quartzite, trap rock or felsite are required that are very strong. There are various weak aggregates like marble, sandstone and metamorphic rocks. These aggregates are used where normal concrete strength is required.
If a normal strength concrete is made by using high strength aggregates than incase if concrete get fails then it is due to cracking in the mortar and with a little failure of aggregates. If mortar cracking starts because of aggregates failure, then it leads to the sudden failure of concrete. This type of case occurs most probably for a high strength concrete and a very rare chance in lightweight concrete.
If aggregates are crushed and angular, then the bond between the aggregates and the cement paste will be stronger. This is because of the rough surface of crushed aggregates and also a well graded aggregate results in concrete that will be less porous. Lessen value of porosity leads to stronger bond. It enhances the concrete workability and in returns it provides a good concrete finishability.
As the aggregate size increases i.e., maximum aggregate size, then it gradually decreases the concrete strength. There are many aggregates that start a reaction with the alkali (Alkali is the component of cement). This lead to a long term expansion of the concrete and that expansion destroy the concrete structures.
Aggregates cover almost 60 – 80% of the concrete. It is the major component of concrete. The remaining 20% is covered by water cement admixtures etc.
Aggregates are used almost in every sort of construction projects. For example construction of buildings, roads, for road stabilization, road covering, in road base, asphaltic concrete aggregates, in construction of different construction products like concrete blocks, bricks, in railway tracks etc.