Home | | Highway Engineering | Highway Construction: Specific Gravity and water absorption

# Highway Construction: Specific Gravity and water absorption

The specific gravity and water absorption of aggregates are important properties that are required for the design of concrete and bituminous mixes.

Specific Gravity and water absorption

The specific gravity and water absorption of aggregates are important properties that are required for the design of concrete and bituminous mixes. The specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. Because the aggregates may contain water-permeable voids, so two measures of specific gravity of aggregates are used:

apparent specific gravity and bulk specific gravity.

Apparent  Specific         Gravity,      Gapp   ,  is  computed    on  the  basis  of  the  net  volume  of aggregates        i.e    the volume excluding water-permeable voids.Thus

where, MD is the dry mass of the aggregate, VN is the net volume of the aggregates excluding the volume of the absorbed matter, W is the density of water.

Bulk Specific Gravity, Gbulk , is computed on the basis of the total volume of aggregates including water permeable voids. Thus

where, VB is the total volume of the aggregates including the volume of absorbed water.

Water absorption, The difference between the apparent and bulk specific gravities is nothing but the water-permeable voids of the aggregates. We can measure the volume of such voids by weighing the aggregates

dry and in a saturated, surface dry condition, with all permeable voids filled with water. The difference of the above two is MW . MW is the weight of dry aggregates minus weight of aggregates saturated surface dry condition. Thus

The specific gravity of aggregates normally used in road construction ranges from about 2.5 to 2.9. Water absorption values ranges from 0.1 to about 2.0 percent for aggregates normally used in road surfacing.

Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail
Civil : Highway Planning and Alignment : Highway Construction Materials And Practice : Highway Construction: Specific Gravity and water absorption |