Influência do aditivo cristalizante na autocicatrização de barras de argamassa afetadas pela reação álcali-agregado

Abstract

This study aims to verify the influence of a crystallizing additive on mortar mixes produced with aggregates previously characterized as potentially reactive for CPV-ARI Portland cement against alkali-aggregate reaction (AAR), analyzing the effectiveness of this additive in the self-healing of microcracks caused by AAR through tests of water absorption by capillarity, bending tensile and axial compression. The mortars were produced using Portland cement CPV-ARI with the addition of 2% of crystallizing additive, two reactive aggregates from the region of Alegrete-RS and Quara´ı-RS and a non-reactive aggregate (sand from IPT), to serve as a reference. Three mixtures were produced with a standard mix defined by the NBR 15577-4 standard and mortar bars were molded in 2 different models of molds. Model-I was used for the RAA tests and model-II for mechanical and durability tests. After producing the mixtures, all mortars were immersed in a basic NaOH solution at 80 0C for 30 days (model I samples) and 28 days (model II samples). During the immersion period, the model I mortar bars were monitored for their length to determine the expansions by RAA. Model II mortar bars remained immersed in solution for 28 days to induce microcracking in the specimens. After this process, they were removed from the solution, cooled to room temperature and divided into two batches. The first batch was tested from the age of 28 days (water absorption by capillarity, bending tensile and axial compression). The second batch was conditioned in submerged curing for 32 days, until it reached the age of 60 days, to optimize the action of the crystallizing additive, and subsequently underwent the same control tests as the first batch. The results of the accelerated AAR test showed little difference in relation to the results of Dutra (2018), indicating little influence of the crystallizing additive on the expansion of the specimens by AAR. Regarding the mechanical and durability properties, an improvement of some properties was observed and the maintenance of others with the use of the crystallizing additive. The results of the capillary water absorption tests showed that all mixtures showed improvements in this property at greater ages. With regard to the bending tensile tests, a trend of resistance constancy over time was observed, demonstrating a low effectiveness of the crystallizing additive to improve this property. For the axial compression tests, there was an increase in the resistance of the specimens produced with reactives aggregates. For the mortars of reference aggregate, resistance was maintained. In general, it is concluded that for the materials and techniques applied in this study, the crystallizing additive showed promise in self-healing in mortars damaged by the Alkali-Aggregate Reaction. Keywords: Crystallizing admixture. Self-healing. Crack sealing.