Resistance to the alkali-aggregate reaction of sustainable mortars produced with scheelite tailings in replacing natural sand aggregates

This work produced coating mortars with scheelite tailings (ST) in total replacement of natural sand aggregate. The chemical and mineralogical composition of the scheelite tailings was determined by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Mortar samples with a mass proportion of 1:2:9 (cement: lime: sand/scheelite tailings) were prepared with and without the scheelite tailings. The mortars were evaluated by mercury intrusion porosimetry and compressive and flexural strength tests. The resistance to the alkali-aggregate reaction was assessed from the bar expansion test and by scanning electron microscopy (SEM) in the crack and pore regions. The results indicate that until the 22nd day, the scheelite tailings were not reactive; however, in 28 days, the expansion was deleterious. SEM images did not detect the presence of amorphous alkaline gel characteristic of the alkali-aggregate reaction. Therefore, although the mortar with scheelite tailings aggregate has shown the deleterious potential to 28 days, mechanical tests indicate that it has the potential to be used as a coating mortar.

Using SEM and EDS for material’s analysis of the small hydroelectric power plant: case study/ Utilizando MEV e EDS para análise do material de uma pequena central hidrelétrica: estudo de caso

Small Hydroelectric Power Plants (SHPPs) are hydroelectric of reduced size and power, i.e., less than thirteen square kilometres of reservoir area and power less than 30 MW (megawatts). SHPPs account for about 3.7% of all installed capacity of the Brazilian power generation system, which demonstrates their relevance in the national scenario. In addition to this function, SHPPs also influence the socioeconomic development of the region by helping to create direct and indirect jobs. In this context, the goal of this work was the microstructural analysis of the concrete of the dam of SHPP Ponte Queimada, installed in Rio Casca, Minas Gerais, Brazil. Ponte Queimada was built in 1936; over the years it underwent some interventions and, currently, it undergoes a new intervention for maintenance and repairs. By means of visual inspection, the sites for collecting the samples were identified. The samples were analysed regarding the morphology and chemical composition of the concrete using Scanning Electron Microscope (SEM) and energy dispersive spectrometer (EDS). Based on the collected samples, isolated points of occurrence of alkali-aggregate reaction (AAR) were identified. The observed samples, besides possessing chemical elements compatible with manifestations of AAR, also presented shapes that visually resemble to them. It was concluded that the use of SEM is an effective and relatively simple alternative for the identification of pathological manifestations that could compromise the durability of the structures, often allowing the determination of repair measures in anticipation of the prevention of future problems.