Avaliação da sinergia entre aditivo cristalizante e adições ternárias na autocicatrização de concretos

Abstract

Portland cement concrete is the most widely used construction material due to its high compressive strength and durability. To minimize environmental impacts and enhance existing cements, more studies on supplementary cementitious materials are being developed. The durability of concrete structures is an area that lacks understanding regarding the contribution of these materials. Cracks are pathological manifestations that trigger and accelerate other categories of damage. To cease or mitigate the effects of cracks, materials can be employed that, either spontaneously or stimulated, contribute to self-healing. The general objective of this research is to analyze the influence of crystalline admixture on the behavior of concretes produced with different supplementary cementitious materials (SCMs) concerning the selfhealing capacity of cracks. Limestone filler, metakaolin, and fly ash were used as SCMs, composing ternary additions. The experiments adopted three water-to-cement ratios (0.40, 0.50, and 0.60) with the addition of the crystalline admixture at 0% and 1%. Crack formation occurred at 3 days, and to evaluate self-healing, the following aspects were analyzed: the recovery of strength, establishing a mechanical selfhealing index; the ultrasonic pulse velocity; water absorption; optical microscopy images of cracks; and scanning electron microscopy images. The results show that the use of metakaolin is more efficient than reference mixes in terms of durability, and the crystalline admixture contributed to increased strength and reduced water absorption in most mixes. The use of ultrasonic wave propagation velocity could only be taken as a qualitative evaluation of healing. The analysis of images through optical and scanning electron microscopy contributed to justifying the behaviors observed in the other tests, although it was not possible to obtain data that led to an objective assessment. Through the evaluation conducted, it was possible to observe the contribution of SCMs, with emphasis on the combined use of metakaolin and limestone filler, and the effective contribution of the crystalline admixture.