I N S T R U M E N T S
Toughness is the property of a material to resist impact. Due to traffic loads, the road stones are subjectedto the pounding action or impact and there is possibility of stones breaking into smaller pieces. The roadstones should therefore be tough enough to resist fracture under impact. A test designed to evaluate thetoughness of stone i.e., the resistance of the stones to fracture under repeated impacts may be called animpact test for road stones
Impact test may either be carried out on cylindrical stone specimens as in Page Impact test or on stoneaggregates as in Aggregate Impact test. The Page Impact test is not carried out now-a-days and has alsobeen omitted from the revised British Standard for testing mineral aggregates. The aggregate impact testhas been standardized by the British Standard Institution and the Indian Standard Institution.The aggregate impact value indicates a relative measure of the resistance of aggregate to a sudden shockor an impact, which in some aggregates differs from its resistance to a slow compressive load. The methodof test covers the procedure for determining the aggregate impact value of coarse aggregates.
The apparatus consists of an impact testing machine, a cylindrical measure tamping rod, IS sieve balance and oven. (a)Impact testing machine : The machine consists of a metal base with a plane lower surface supported wellon a firm floor, without rocking. A detachable cylindrical steel cup of internal diameter 10.2 cm and depth 5cm is rigidly fastened centrally to the base plate. A metal hammer of weight between 13.5 and 14. Kghaving the lower end cylindrical in shape, 10 cm in diameter and 5 cm long, with 2 mm chamber at thelower edge is capable of sliding freely between vertical guides, and fall concentric over the cup. There is anarrangement for raising the hammer and allowing it to fall freely between vertical guides from a height of 38cm on the test sample in the...