Bulking of sand
Moist sand occupies larger volume if loosely filled in, than dry sand. Due to moisture, thin film of water forms around sand grain which results in increase of volume. This effect of increase in volume (if loosely filled in) due to moisture content is called “Bulking of sand”.
The bulking of sand is largely depends on
1. grain size – Small the grain size, larger will be bulking effect and vise- versa.
2. moisture content – 5 – 8 % moisture can result in 20-35 % increase in volume
Bulking increases with increase in moisture content up to a certain limit and beyond that the further increase in moisture content results in decrease in volume.
Effect of bulking of sand in concrete production :
While batching of aggregates, if weight batching is adopted which is precise and preferred method of batching of aggregate, no effect is taken place due to bulking of sand. However, if batching is done by volume, then less sand than required as per mix design, will be measured. This results in disproportionate and non uniform concrete mixes and may affects the compressive strength of concrete. Therefore it will be necessary to increase the volume of sand by the ‘percentage’ bulking.
How to calculate % bulking
IS: 2386 part 3 provides detail test approach to find out percentage of bulking. Two methods are suggested in this code. Both depend on the fact that the volume of inundated sand is the same as if the sand were dry. In this article, one simple method is described below: