Concreto de alta resistência: influência da relação A/C e polímero superabsorvente (SAP) como agente de cura interna

Abstract

High strength concrete has been increasingly used as a solution for the cons- truction of more slender and complex buildings. This concrete has a dense and refined microstructure, which can provide economic and structural advantages. However, it suffers the effect of self-desiccation, a phenomenon responsible for autogenous shrinkage, which can lead to cracking and loss of performance. Autogenous shrinkage occurs in all types of concrete, but it only becomes relevant in concrete with w/c ratios below 0.42. To mitigate this type of shrinkage, it is necessary to use an internal curing method, such as the use of a Superabsorbent Polymer (SAP). This material has shown to be effective in combating autogenous shrinkage, but its addition can reduce the mechanical properties of concrete. Given the above, this work aims to evaluate the influence of the w/c ratio and the addition of an internal curing agent on the physical and mechanical properties of high-strength concrete. In order to do this, two reference mixtures were made with w/c ratios of 0.3 and 0.36, and also two others with addition of polymer for both w/c ratios. The tests carried out were heat release of hydration, free shrinkage, water absorption and void ratio, water absorption by capillary, uniaxial compression and flexural tension. The results show that the polymer was able to significantly minimize the autogenous shrinkage, but reduced the mechanical properties, increased the water absorption, the voids index and the drying shrinkage. On the other hand, the reduction of the w/c ratio provided an improvement in mechanical properties, in the pore structure andreduced the water absorption. Its effect on the autogenous shrinkage proved to be controversial. In this way, it is concluded that the addition of polymer in concrete can fulfill the role of reducing autogenous shrinkage, but generated significant losses in mechanical performance, while the decrease in w/c ratio provided improvements in concrete properties.