FUNCTIONS OF INGREDIENTS OF MORTAR | CEMENTING MATERIALS | FINE AGGREGATES | WATER

FUNCTIONS OF INGREDIENTS OF MORTAR

As discussed earlier, the ingredients of mortar are:

1. Binding or cementing materials, viz., cement or lime

2. Fine aggregates, viz., sand, surkhi, cinder, etc.

3. Water

 

FUNCTIONS OF CEMENTING MATERIALS

The primary requirement of cementing materials is to provide strength and durability to the structure.

For cement mortar mostly Ordinary Portland Cement is used. However, for special types of works other cement may be used appropriately to the work. Cement performs the following functions when used in cement mortar:

(i) Primarily, it fills the voids formed by fine aggregates and thereby makes the mortar impermeable.

(ii) It binds the fine aggregates into a solid mass with time on adding water to the mix.

(iii) It imparts strength after setting and hardening.

 

For lime mortar, different types of lime are used, viz., eminently hydraulic, semi-hydraulic and fat limes. For preparing lime mortar, the lime should be slaked before mixing it with the fine aggregate. However, the strength of lime mortar is less than that of cement mortar. Lime performs the following functions when used in lime mortar:

(i) It binds the fine aggregates into a solid mass. However, it takes more time to set.

(ii) It imparts adequate strength to the lime mortar on setting and hardening.

 

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:

(i) It reduces the shrinkage of the binding material and thereby prevents the formation of cracks.

(ii) It provides high resistance to the mortar to withstand compressive forces.

(iii) It divides the paste of the binding material and spreads to provide more surface contact area.

(iv) It makes the fat lime porous to assist in setting and hardening.

(v) 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 gener- ally 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.

 

FUNCTIONS OF WATER

The quality of water required for mortar has been discussed earlier. Water plays a significant role in the formation of mortar. It helps in mixing, transporting and in the proper laying of the mortar. As a matter of fact, the quality and quantity of water contribute to the strength of the mortar. Water plays the following roles in mortar:

(i) It wets the surface of the aggregates to provide better bonding.

(ii) It helps in the spreading of the cementing material over the surface of the fine aggregate.

(iii) By acting as a lubricant for the aggregate, the mortar is made workable.

(iv) It causes hydration of cement and lime because of which setting and hardening of cement mortar and lime mortar take place.

SOURCE: BUILDING CONSTRUCTION MATERIALS AND TECHNIQUES | P. PURUSHOTHAMA RAJ

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