Verônica Teixeira Franco Castelo Branco

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.

The influence of stone crushing processes on aggregate shape properties

Aggregate shape properties have a direct influence on the behaviour of pavement materials. The crushing process is the main factor responsible for generating these shape properties; however, there has hardly been any effort directed toward optimising the performance of pavement materials by altering the crushing techniques to produce aggregate particles with desired shape properties. The aim of this research is to analyse how the crushing process influences aggregate shape properties. Form, angularity and surface texture of five coarse and five fine aggregates, from three different quarries, were evaluated by means of digital image processing and were categorised by two different classification systems. The jaw crusher produced coarse aggregates with a better combination of sphericity and angularity during the first crushing stage. Fine aggregates produced by cone crushers in the final crushing stages were more elongated, but had a greater angularity than fine aggregates produced by the primary jaw crusher.