5.12 : Toughness and Hardness of Aggregate

Toughness and hardness are critical properties of aggregate materials used in concrete, particularly on pavement surfaces and industrial flooring subjected to heavy loads. Toughness is defined as the aggregate's resistance to failure by impact and is measured by the aggregate impact value (AIV). For this, the aggregate impact value test is performed, wherein the impact is delivered by a standard hammer, which falls freely under its own weight onto the aggregates. The aggregates fragment in the process, which is quantified in terms of aggregate impact value. The lower the impact value, the tougher the aggregate.

Hardness is defined as the resistance of aggregate to wear. The Los Angeles abrasion test is a method for assessing hardness by simulating attrition and abrasion processes to measure the degradation of the aggregate. In this test, a sample is rotated in a drum with steel balls, which pulverize the aggregate. The results correlate well with actual wear and the compressive strength of concrete made with the tested aggregate, making it a reliable indicator of long-term performance in construction materials.