Functions of Various Ingredients

Cement is a binding material. It hydrates and binds aggregates after addition of water and the surrounding surfaces such as bricks and stone. Richer mix (with more cement) gives more strength generally. Setting time begin after 30 minutes and ends after 6 hours. Therefore concrete should be laid in its mould before 30 minutes of mixing of water and it should not be subjected to any external forces until final setting takes place.

Coarse aggregate consists of crushed stones. This should be well graded and the stones should be of igneous origin. They should be, sharp, clean, angular and hard. They provide mass to the concrete and prevent shrinkage of cement. Fine aggregate consists of river sand. It prevents cement from shrinkage. It gains mobility enters the voids in coarse aggregates When surrounded by cement and binding of ingredients occur. As it fills the voids it adds density to concrete. Denser the concrete higher is its strength.

Water which is used for making concrete should be clean. This activates the hydration of cement and then forms plastic mass. Becomes of hard mass, it sets completely concrete. Water gives workability to concrete which means water enables to mix the concrete with easy and place it in final position. More water better workability. While excess water reduces the strength of concrete. With water cement ratio given figure shows the variation of strength of concrete. Cement ratio of 0.4 to 0.45 is used to achieve required workability and at the same time good strength water, in case of machine mixing and for hand mixing water cement ratio of 0.5 to 0.6 is used.

           Variation of strength of concrete with w/c ratio