Functions of Fine Aggregates

The fine aggregate mainly used is sand. The required properties of good sand were discussed earlier. Sand plays the following functions in mortar:

1. It reduces the shrinkage of the binding material and thereby prevents the formation of cracks.
2. It provides high resistance to the mortar to withstand compressive forces.
3. It divides the paste of the binding material and spreads to provide more surface contact area.
4. It makes the fat lime porous to assist in setting and hardening.
5. It provides any proportion of the mortar.

Surkhi is another form of fine aggregate, which is usually prepared by powdering slightly unburnt bricks. It should be free from admixtures of any foreign materials. Surkhi is generally used with sand. If used on its own, it causes the mortar to disintegrate. When used in combination with sand, it performs all the functions as that of sand. In addition, it provides strength and improves hydraulic properties of the mortar.

Sometimes ash or cinder is provided as fine aggregate in lime mortar. It provides strength and improves hydraulic properties. It acts as an adulterant and hence increases the volume.