The Reason For Running The Abrasion Test

Abrasion resistance can be defined as the ability of a surface to resist being worn away by rubbing or friction . It is very important in construction of floors, roads, or pavements. Abrasion resistance is particularly dependent on good curing but also relies upon other factors including materials and surface finishing, aggregate hardness, mix proportions, aggregate/paste bond, and placing and compaction. The reason for running the abrasion test in four parts is to give a better average loss figure for the paddle. Experience has shown that the first single interval of 15 minutes with 400 grams of material tends to give unduly high abrasive losses; this is explained by the lack of hardening on the paddle surface initially. This might not be observable in the normal Nickel-Zinc-Moly steel used as standard paddle but in the case of manganese steel paddles this is particularly noticeable. The average velocity of the paddle at the mid point of its exposed area is 1200 fpm. The exposed area is exactly 2 sq. in, 1 in of the 3 in length being inserted in the shaft hub and locked in place by the setscrew. As the rock falls away from the drum, it has nearly zero velocity, and the paddle striking against it with a velocity of 1200 fpm produces a true impact blow. This not only reduces the material but also results in the rapid abrasion of the paddle necessary to make rapid tests. It has been found that this apparatus will reduce 400 grams of even hard material and that it is not effective to any great extent abrasively after a 15-minute interval. Another reason for the continuously reduced wear rate is that the shape of the paddle is changed. The originally sharp edge of the paddle is quickly worn off. As it becomes more and more rounded off, the weight loss per minute is reduced.