Avaliação das relações entre propriedades de agregados minerais com base nas características do processo de britagem e da rocha de origem

Abstract

The mineral aggregate, as it is the predominant component in different composites used in Civil Engineering, is significantly responsible for the behavior of these materials. The shape properties of the particles attract increasing attention over the years, with the development of modern methods for their characterization, based on Digital Image Processing (DIP). These properties are influenced by the rock characteristics and by the crushing process used in the material processing. These factors, however, are not always used in order to obtain the most appropriate aggregate for each intended application. The present work seeks to investigate the relations between the aggregate’s shape properties, the crushing process that generated it, the rock characteristics and its resistance to degradation. For this purpose, aggregates generated by different crushing processes and from different rocks were compared on the basis of the petrographic, mineralogical and morphological characteristics (form, angularity and surface texture), and each material was submitted to mechanical degradation tests (Treton and Micro-Deval), being evaluated its tendency to breakage, abrasion and polishing. From the obtained results, diagrams that summarize the main findings and that may help the production process and selection of aggregates were constructed. Some of the main conclusions of the study were: cone crusher with controlled interparticular crushing proved to be more suitable to generate coarse aggregates with higher sphericity and lower angularity, which may provide better workability to the composite; while the vertical shaft impact crusher raised the particles angularity, ensuring their interlocking, a desirable feature in some applications, such as asphalt mixtures. The biotite content in aggregates of granite / gneiss indicated, to some extent, to provide a greater resistance when the particles were submitted to breakage, higher mass losses and lower surface roughness losses when the particles were subjected to wear. Aggregates from phonolitic rock, in comparison to those of granitic / gneiss origin, have lower losses in mass and in angularity with wear, but greater losses in surface roughness. For fine aggregate, the phonolithic rock presented lower elongation and lower angularity, whereas granite / gnaiss rocks formed particles with higher angularity.