Mapping of the alkali reactive potencial of the sands in Rio Grande do Sul

Abstract

There are several deterioration processes that interfere in the performance and durability of a concrete, among these processes is the alkali-aggregate (RAA) reaction. RAA is a general term used to describe the chemical reaction that takes place internally in concrete structures, between the alkali hydroxides present in the cement and reactive mineral phases present in the aggregates. As a result of the reaction, a silica-alkaline gel is formed which, in the presence of moisture, absorbs water, being able to expand inside the concrete mass, which can cause expansion and, consequently, internal and external cracking in the concrete structures. Preventive measures for the occurrence of RAA have been known for a long time and routinely applied only in hydroelectric plant structures. Knowing that any structure subject to intense humidity can develop the RAA, prevention is also necessary in residential buildings, for example, in places where the concrete is exposed to moisture, in order to ensure structures that are more durable and therefore more sustainable , since the generation of waste due to the need for constant maintenance or demolition goes against the pillars of sustainability in construction. In this context, the first step in the process of preventing the occurrence of RAA is to know the reactive potential of the aggregates, because knowing this parameter it is possible to use cementitious materials adequate to the inhibition of the reaction. The objective of this study was to evaluate the alkali-reactive potential of eight sand samples coming from the raw materials for the production of concrete in Rio Grande do Sul. The study was carried out based on the accelerated method of mortar bars, according to ABNT NBR 15577-4 (2018) and in the evaluation of the mineralogical characteristics of the aggregates through the petrographic analysis. The results indicated a high deleterious potential of the samples evaluated. It was found that 7 of a total of 8 samples analyzed were classified as potentially reactive. The percentage variation between the sample from highest to least expansion was 93.44% (0.61% -0.04% respectively), potentially only the sand sample from the city of Osório / RS.