Caracterização tecnológica de agregados graúdos de algumas regiões do estado do Amazonas, para aplicação em pavimentos rodoviários

Abstract

In paving works, the most applied inputs are aggregates, thus, its demand is high and, consequently, the impact on the environment is also increased due to their extraction and to be in major proportion in terms of mass. The aggregates have significant influence on the mechanical performance and durability of the pavement, once their technical characteristics in disagreement with the project's needs, could adversely affect the structural condition of the pavement. The lack of technical and financial investment in this sector ultimately reduces durability through the design of technically deficient pavements, which provides a high rate of early, frequent and recurring pathologies such as disaggregation, cracking and the permanent deformations. Such conditions, in most cases, occur especially in flexible pavements coated with asphalt concrete (AC), whose lack of control and technological characterization of the aggregate components of this type of pavement, are determining factors. In the state of Amazonas most pavements are covered with AC. In this type of coating, the aggregates are responsible for about 90% of its composition (by mass) and this layer, on the other hand, has the function of protecting the subsequent ones, besides providing quality, safety and good trafficability. Thus, this research aimed the technological and mineralogical characterization of coarse aggregates, geared for use in road pavements. All procedures were based on Brazilian standards (NBR) and guidelines of the National Infrastructure Department (DNIT). The samples are from Barcelos, Presidente Figueiredo, Japurá and Apuí, all municipalities of Amazonas state. The methodology used was laboratory tests, through physical and mechanical characterization, as well as mineralogical appreciation and classification through petrography and X-ray diffraction (XRD). The results of the mineralogical analysis classified the sample BPF-2 as volcanic igneous rock rhyolite, and the samples BBAR, BPF-1 and BPF-3 as plutonic rock syenogranites. Regarding the pebbles, the results classified SXRA as a quartz grain, and finally, SXRJ as a microcrystalline amorphous silica. Also, a chemical composition test was performed by X-ray fluorescence (XRF) resulting in the classification of samples BBAR, BPF-2, BPF-3, SXRA and SXRJ as acid rocks and BPF-1 as intermediate according to the silica content present by mass. The technological characterization was obtained by means of physical and mechanical parameters, with the overall satisfactory results in all gravel samples and in some unsatisfactory pebbles samples. BBAR and BPF-3 showed the best results in all analyzes, while BPF-2 and BPF-1 in the form index test were classified as lamellar and elongated forms. These shapes are distinct from the cubic, which is most desirable for pavement application. In the adhesion parameter with the asphalt binder, only SXRA and SXRJ were classified as unsatisfactory, which means with little or no adherence. This result is justified by the smooth and rounded surface texture of both pebbles, and of course the high silica content (SiO2 ≥ 95%) present in the rocks. Certainly, it is evidenced the application potential of coarse gravel aggregates and a partial restriction, due to negative results regarding the adhesiveness, texture and induced moisture damage (Lottman) of the pebbles of this research.