Abstract This manuscript evaluates the technical feasibility of reusing coal ash in the formulation design of dense asphalt mixes. Physicochemical and mineralogical properties of fly and bottom ash matrixes prepared with coal ash were analyzed by scanning electron microscopy (SEM), X-Ray diffraction (XRD), semi-quantitative spectrometry by X-Ray fluorescence (XRF) and surface characterization by Nitrogen (N2) adsorption. Filler fractions under 0.075 mm with 6.0% in weight from an entirely gneissic aggregate gradation curve taken as reference were compared to identical mixes prepared with fly and bottom ashes individually and also to a combined sample with 3.0% of each ash type. Tests on compaction ability with gyratory shear press, resistance to action of water and to rutting were carried out to compare mechanical performance. The results indicate that both gneissic and coal ash fillers do not form dipoles of effective electric attractions to bituminous matrixes, resulting in inert and hydrophilic behavior regarding to action of water, respectively. Despite surface and morphologic characteristics underlying the mechanical performance of gneissic fillers, coal ash matrixes have shown, in general, good technical feasibility to be used in asphalt mixes.

O objetivo desta pesquisa é discutir a importância de estudos sobre materiais denominados fíleres de diferentes origens, para utilização na composição de misturas asfálticas, mais especificamente na formulação de mástiques. Os testes laboratoriais foram executados com amostras finamente pulverizadas de rocha calcária e granítica, além do ligante betuminoso classificado como 50/70. As amostras foram avaliadas a partir dos seguintes testes: análise química semi-quantitativa por fluorescência de raio-X, granulometria por emissão de raio laser de baixo ângulo, microscopia eletrônica de varredura, ponto de amolecimento, penetração, adesividade dos sistemas agregado-ligante betuminoso puro e agregado-mástique. Os resultados obtidos enfatizam tendências convergentes, indicando que a comportamento ativo dos fíleres na formulação dos mástiques não está relacionado com o tamanho das partículas, mas sobretudo com a sua forma, textura superficial, área da superfície específica e natureza mineralógica, permitindo que o conceito de atividade dos fíleres possa ser dividido em duas componentes: física (enrijecimento) e química (adesão).

This paper discusses the importance of studies on materials known as fillers from different mineral origins, used in asphalt mixes, specifically in the formulation of mastics. The research was carried out on samples of limestone and granite rock filler and asphalt binder (50/70). The samples were evaluated through semiquantitative chemical analyses by X-ray fluorescence, granulometry by low angle laser emission, scanning electron microscopy, softening point tests, penetration tests, and aggregate-asphalt binder and aggregate-mastic adhesion tests. The results highlighted convergent trends, indicating that the active behavior of the fillers in the mastic formulation is not related to the size of the particles, but rather to their form, surface texture, specific surface area and mineralogical nature, allowing the filler activity concept to be divided into two components: physical (hardening) and chemical (adhesion).