SAND

SAND

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Sand is the chief material used as a fine aggregate. It Is re­quired in mortar or concrete for economy and to prevent the excessive cracking. Mortar made without sand would be, expensive.

The word "sand" is applied to any finely divided material which will not injuriously affect the cement or lime and. which is not subject to disintegration or decay. Sand is almost the only material which is suffi­ciently cheap and which will futfil theso requirements.

The strength of the structure te to a considerable extent de­pendent on the Qualities ot the sand. There have been many failures of structures due to the use of poor sand.

The sand should be clean The presence of dirt reduces the

strength of mortar and concrete . ₄

The proportion of voids is higher In a send in which particles are of uniform size than fn one wtitch containsjj variety of particles size. Tbe greater the proportion of voids, the greater the amount ol ce­menting material Is needed to bind the sand grains together Sand con­taining a large proportion of very fine particles Is not suitable, as an ex­cessive amount J water is required to make the mortar workable, and this reduces its strength and increases shrinkage.

A suitably graded sand consists ot particles varying In S120 from coarse to fine. The best results are obtained with a sand having a grad­ual gradation of particle size from coarse to fine.

A mixture of coarse and tine grains is very satisfactory, as it makes a denser and stronger concrete with a less amount of cement then when only Hne grained sand is used.

Tests have shown that the shape of the particles is not very im­portant

lne following sattus are used fw mortars: pit or quarry sand, rivei sand and sea sand.