Evaluation of laboratory procedures for aggregate polish test

Years of polish value testing at the Texas Department of Transportation have revealed that the test results are highly sensitive not only to aggregate textures, but also to other factors, resulting in large variabilities in test results. For the test results to be purely indicative of aggregate textures, other factors need to be tightly controlled. The primary objectives of the study were to address those factors and to improve the testing procedures to minimize variability. All possible factors were identified and pilot tests were conducted to eliminate factors with nonsignificant effects. Detailed tests were conducted to evaluate the effects of the remaining factors. Among the factors investigated that were found to be significant in this study were curvature of the coupons, the length of the slider contact path, slider rubber characteristics, aggregate particle arrangement, normal slider load, and aggregate selection technique. To minimize the variability, the following emphasis is recommended: (a) measure the coupon curvature before testing, (b) control the length of the slider contact path, (c) maintain the normal slider load between 2500 and 2600 g, and (d) select aggregate particles by splitting, rather than handpicking, for mineralogically heterogeneous aggregates.