Avaliação da autocicatrização autógena de compósitos cimentícios com adições de metacaulim e sílica ativa

Abstract

Constructive elements made using cementitious composites, such as concrete and mortar, are susceptible to the appearance of pathological manifestations, mainly due to the ease with which the material presents cracks, which, in addition to being able to demonstrate structural problems, serves as a gateway for aggressive agents. According to Sitter's "law of five", it is known that the longer it takes to perform an intervention on the element that presents pathologies, the more costly this process becomes, following a ratio of five times for each completed stage of the work. With the aim of minimizing this maintenance cost and aiming at a lower environmental impact, due to the replacement of part of the cement, which is a major emitter of pollutants in the atmosphere, the present work seeks to evaluate the self-healing capacity and recovery of mechanical resistance of cementitious composites that contain addition of metakaolin and silica fume. Three traces of mixtures containing additions were used, one with 10% metakaolin, one with 10% silica fume and the last one with 5% of each addition, all replacing the respective cement mass, in addition to a last reference mixture, to comparison. The self-healing capacity was evaluated 28 days after the composites cracked, which will occurred after the 28 days of submerged curing, required by NBR 13279, with the aid of a crack gauge and computational resources. The recovery of mechanical strength was determined, again, through tests of tensile strength in flexion, also specified by NBR 13279, at 28 days after cracking and exposure of the composites. The two mixes containing silica fume returned the best results, reaching more than 91% of crack closure for exposure to the submerged environment and having recovered, on average, 23.11% of mechanical strength for the mix with just silica fume. It was verified that, alone, the addition of metakaolin is not efficient in any of the evaluated scenarios, either for healing or mechanical recovery, but when combined with the addition of silica, there was a stabilization of the characteristics for the submerged environment and a potentiation of these for exposure to air, which is the most problematic. For the mix containing the two additions, healed outside the submersion tank, there was an average crack closure of 42.79%, more than double that of the second-best mix for the aforementioned exposure, and an average strength recovery of 16.08%.