Avaliação das propriedades mecânicas e microestrutura de concreto de ultra alto desempenho com adições minerais e resíduos industriais

Abstract

With the increase in the world population, civil construction is the largest consumer of resources, with great environmental impact. One of the ways to reduce this impact is to increase the mechanical strength of the concrete, reducing the resistant sections of the structural parts, dematerializing them from the emanation of greenhouse gases. The use of industrial and pozzolan waste in concrete, in addition to the packaging of particles, are concrete actions that reduce environmental impacts, increasing sustainability. Thus, the general objective of this research was to analyze the microstructure and physical-mechanical properties of ultra high performance concrete (UHPC) with hydrated lime, foundry sand, pozzolanic and inert mineral additions, through the packaging effects of the particles. The specific objectives were: to evaluate the workability of UHPC with rice husk ash (RHA), fly ash (FA), lime CH I, limestone filler (LF), quartz powder and foundry sand, in relation to the reference concrete, with structural white cement, silica fume (SF), quartz powder and sand industrial; study the packaging of particles by the modified Andreassen method; analyze the performance of variables related to the mechanical strength of concrete in wet and thermal cures: axial compression, modulus of elasticity and instrumented breaks; and analyze the microstructure of UHPC mixtures by: X-Ray Diffraction (XRD), Thermogravimetric Analysis (TG/DTG), Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM/EDS). The greatest resistance for all ages was the REF mixture. The efficiency of thermal curing was verified, mainly in early ages, with emphasis on the mixture with 15% partial replacement of cement with rice husk ash (RHA15). For mixtures with mineral additions, the similar behavior was noticeable. This performance confirms that the physical effect was representative, because, even with changes in levels and types of mineral additions, the average clinker intensity did not vary significantly. The elasticity modules showed the same trend of resistance behavior. In instrumented breaks, the stresses were proportional to the specific deformations in almost the entire test. In mixtures with mineral additions (RHA15, FA15, RHA10-FA5 and RHA10-LF5), the deformations were greater, attesting to the less fragile behavior. In XRD, the presence of non-hydrated compounds (alite and belite) was observed due to the low a / mc ratio. In mixtures with the addition of lime there was an increase in the peaks of portlandite and calcite, showing that a portion of the lime did not react with the pozzolana. In TG-DTG, mixtures with mineral additions had higher levels of combined water, calcium hydroxide (CH) and carbonates than REF, attesting that the lime partially reacted with the pozzolan. In FTIR, the REF mixture showed low peaks of portlandite, the opposite behavior of mixtures with mineral additions. In SEM, it was found that mixtures with mineral additions showed higher levels of Ca / Si ratio when compared to the reference concrete.