Materials for Colcrete:

The materials for colcrete are :

(a) Water,

(b) Cement,

(c) Sand,

(d) Coarse aggregate

(e) Admixtures.

Water

Water should have the similar properties as the mixing water for conventional concrete.

Cement

As per IS specifications all cements are suitable for colcrete work.

Sand

The grading of sand should be continuous without gap. It should not have excess of larger, medium and smaller particles as these have predominant effect on the strength of colcrete. The percentage of oversize should be less than 5%. The fineness modulus of sand should not vary more than plus or minus 0.10.

Coarse Aggregate

The size of coarse aggregate should not be less than 40 mm and more than 5 % by weight of the particles smaller than this specified size. The coarse aggregate acceptable for concrete may be used for colcrete.

Admixtures

Admixtures such as surkhi, flyash, pumice, pozzolanas can be incorporated in the mix to substitute cement. On ignition, flyash should not show 8 % loss.

Properties

The below given are the properties of colcrete :

(a) Colcrete has higher strength.

(b) The compressive strength of cube increases with the increase in mixing time. It becomes unworkable after a total mixing time of 90 seconds.

(c) The strength decreases by about 20% when dirty aggregates are used.

(d) The use of extremely coarse sand is not beneficial in colgrout works although compressive strength increases with fineness modulus.

(e) While fineness modulus of sand is between 1.9 to 2.2, bleeding is minimum. It increases both ways with increase or decrease of fineness modulus.

(f) The compressive strength of colcrete decreases by the use of elongated and flat aggregates.

(g) Sand-cement ratio increases with the increase within water-cement ratio. It is more true in case of fine sand than coarse sand.