Study of the mechanism of inhibiting alkali-aggregate reaction and self-healing in concrete materials

Abstract

Concrete is one of the most widely used materials in the world; however, several pathological manifestations can be associated with the design, execution, and selection of its constituent materials. Cracks, one of these pathological manifestations, are caused by the alkali-aggregate reaction (AAR). This is a chemical phenomenon in which silica, which is present in aggregate, reacts with alkali ions of the cement paste to produce an expansive silica-alkali gel. Herein, the clogging mechanism of the pathological cracks, which form during AAR, was investigated using a reference mortar trace, in order to select innocuous and reactive aggregates. Expansion in the mortar mix was examined using these two types of aggregates: (i) a potentially reactive aggregate, which can promote the formation of pathological cracks during AAR, and (ii) an innocuous aggregate to establish a reference trace without any expansive reaction. Subsequently, a concrete mix was characterized and reactivities of its constituents evaluated. In addition, fine and coarse granulometry analyses were performed. The concrete mix was dosed with the mortar mix, which comprised potentially reactive aggregate, and the bars were molded for the expansion tests. The crystalline mineral additive was added in these concretes to observe the clogging of the cracks. Comparative evaluation of the concrete mix, with and without reactive aggregate, suggested the occurrence of clogging because of the autogenous healing caused by chemical reactions, resulting in a reduction in the expansion of the concrete bars, with crystalline additive, at day 56.