Estudo da zona de transição de concretos preparados com metacaulim através de análise nanomecânica

Abstract

The use of pozzolanic materials in concrete results in several beneficial effects in the fresh and hardened state. As one of these alternatives, metakaulin is considered a highly effective material for improving concrete in several properties. Within the context of technological advances in concretes, nanotechnology has been a prominent element in recent research, it has progressively changed the science and engineering of materials, especially in terms of understanding its properties through nanoscience techniques. The nanoindentation technique, capable of obtaining hardness values and elasticity modulus on a nanometric scale of different phases, using significantly small loads, is a viable alternative for specific studies in the concrete interfacial zone transition. Therefore, the objective of this work is to analyze the properties of the interfacial zone transition of concretes prepared with metakaolin using the technique of nanoindentation and SEM / EDS. The following independent variables were adopted: different cement consumptions and the mixing ratio of the other concrete constituents (mixtures); replacement content of cement by metakaolin (%); and healing time (days). The following response variables were adopted: resistance to axial compression; interfacial zone transition thickness; hardness and elasticity modulus; and formation of high and low density C-S-H in the transition zone. Four horizontal profiles were used in each sample, with a total length of 120 µm and spaced vertically by 20 µm, that is, 9 points horizontally spaced by 15 µm and 4 vertically spaced by 20 µm, totaling 36 indentations per sample. The same samples prepared and subjected to nanodarkness tests were used to investigate their IZT using SEM / EDS techniques. The incorporation of metakaolin made it possible to optimize the concretes with Portland cement at the macro, micro and nanostructural level, correlating the improvements in mechanical resistance to axial compression with the decrease in the thickness of the interfacial zone transition of the produced concrete. The percentage of CSH frequency in the cementitious matrix can be increased with the incorporation of MK, as well as the reduction of porosity and CH content in concretes; the decrease in IZT is a direct consequence of these reported effects, however, this beneficial effect of MK in IZT is more pronounced in concretes that are poorer in cement consumption.