Impact Test on Aggregates Transportation Engineering-I

Impact Test on Aggregates Transportation Engineering-I Aim- To determine aggregate impact value of the given sample of aggregate. To evaluate the toughness of aggregates to break down under application of impact and Aggregates undergo significant wear and tear throughout their life. Aggregates must be hard and tough enough to resist crushing, degradation and disintegration and be able to transmit loads from the pavement surface to the underlying layers and eventually the subgrade. Testing the strength of parent rock alone does not exactly indicate the strength of aggregates in concrete. For this reason assessment of strength of the aggregates are made by using a sample bulk aggregates in standardized manner. The principal mechanical property of aggregate required in any construction is Satisfactory resistance to crushing under the roller during construction Adequate resistance to surface abrasion under traffic Aggregates used in road construction should be strong enough to resist abrasion and crushing and also the impact load. If aggregates are weak, then the stability of pavement structure will be adversely affected. The toughness of aggregate is its ability to resist sudden load acting on it. The movement of vehicles on the road sometimes gives rise to impact loading which results in breaking of aggregates into smaller pieces. Therefore the aggregates should have sufficient toughness to resist their disintegration due to impact. This characteristic of aggregate is measured by impact value test. In this test sample of standard aggregates kept in a mould which is subjected to fifteen blows of metal hammer of weight 14 kgs falling from the height of 38cms. The quantity of finer materials resulting from pounding will indicate the toughness of the sample of aggregates. As per IS 283-1970 Aggregates Impact Value is defined as the ratio of weight of fines formed to weight of total sample taken and is expressed in percentage Aggregates Impact Value gives relative measure of resistance of aggregates to sudden shock or impact, which in some aggregates differs from its resistance to slow compression load. Impact Value should not be less than 45% for aggregates used for concrete other than wearing surface and 30% for concrete used in wearing surface. Table below shows the classification of aggregate with respect to aggregate impact value and limits of aggregate impact value for different types of road construction suggested by Indian Road Congress. Aggregate Impact Value AND Classification less than 20% Exceptionally Strong 10 – 20% Strong 20-30% Satisfactory for road surfacing More than 35% Weak for road surfacing Source:https://ts-nitk.vlabs.ac.in/transportation-engineering/exp/impact-test/