Evaluation of polishing and degradation resistance of natural aggregates and steel slag using the aggregate image measurement system

Aggregate resistance to polishing and degradation can be related to the change in some of those aggregates particles' characteristics. Polishing resistance can be related to the loss of surface texture, and it can affect asphalt pavements' microtexture, influencing its skid resistance. Degradation resistance is related to the loss of angularity and to the aggregates' breakage. It affects pavement distresses' resistance and aggregate gradation. The methodologies used to evaluate these characteristics produce results that are mostly not representative. This paper aims to present a digital image processing (DIP) technique to evaluate aggregates' resistance to polishing and degradation, along with the use of the Los Angeles abrasion equipment. The aggregate image measurement system was used to analyse the aggregates mainly not only with respect to angularity and surface texture, but also with respect to sphericity and flatness/elongation particle percentage, before and after the polishing and the degradation processes. Three natural aggregates (granite, gneiss and phonolite) collected from Brazilian quarries, and one by-product (steel slag) were evaluated. The findings from this study can be used to rank aggregates with respect to their shape properties. With the results obtained for the steel slag, it can be concluded that this material was the most resistant to polishing when compared with the natural aggregates.