5.12 : קשיחות וקשיות של אגרגט

To ensure the durability of a concrete airport runway, the aggregates within the concrete require sufficient toughness to withstand impact forces and hardness to resist wear.

The toughness of aggregates is tested on aggregates passing a half-inch sieve and retained on a three-eighths-inch sieve.

The aggregates are weighed and filled in a cup by tamping with a rod. 

These aggregates are subjected to impact loads by allowing a standard hammer to fall freely under its weight from a specific height.

After 15 blows, the fraction of aggregates passing a No. 8 ASTM sieve is weighed, and the aggregate impact value, indicating the toughness of aggregates, is calculated.

To determine hardness, aggregates of the required mass and size distribution, along with steel balls, are placed inside the drum of the Los Angeles abrasion testing machine.

The drum is then rotated a specific number of times, and the aggregates undergo wearing in the process.

Afterward, the aggregates from the drum are sieved through the No. 12 ASTM sieve, the fraction passing the sieve is weighed, and the Los Angeles abrasion value is calculated.