Impact value test :- The aggregate impact value gives relative measure of the resistance of an aggregate to sudden shock or impact which in some aggregates differs from its resistance to a slow compressive load. With respect to concrete aggregates, toughness is usually considered the resistance of the material to failure by impact. Several attempts to develop a method of test for aggregates impact value have been made. The most successful is the one in which a sample of standard aggregate kept in a mould is subjected to fifteen blows of a metal hammer of weight 14 Kgs falling from a height of 38 cms. The quantity of finer material (passing through 2.36 mm) resulting from pounding will indicate the toughness of the sample of aggregate. The ratio of the weight of the fines (finer than 2.36 mm size) formed to the weight of the total sample taken is expressed as a percentage.
This is known as aggregate impact value. IS 2831970 specifies that aggregate impact value shall not exceed 45 percent by weight for aggregate used for concrete other than wearing surface and 30 percent by weight, for concrete for wearing surfaces, such as run ways, roads and pavements.
