Assesment of the potential reactivity of rocks used as aggregates in civil construction in the Rio Grande do Sul state

Abstract

The alkali-aggregate reaction (AAR) is one of the possible causes for reduction of the durability and deterioration of concrete structures, being a matter of integrity and safety concern in concrete structures worldwide. In recent years cases confirmed in Brazil have affected structures such as foundations of residential buildings, bridges, dams, among others. The AAR process develops from the combination of agents such as alkalis present in Portland cement and reactive aggregates, with the constant presence of moisture, and as a result a hygroscopic gel is developed around the aggregate, resulting in expansion and cracking of the concrete, with possible bleeding of the gel, turning into irreversible damages. The present study aims to present a petrographical characterization of four types of rocks used in civil construction in the state of Rio Grande do Sul, as well as to verify the potential reactivity of these rocks by the accelerated bar method. Two aggregates were identified as volcanic rocks and the other two were identified as being sub-volcanic igneous and plutonic igneous origin, respectively. While volcanic rocks showed a deleterious effect in alkali-aggregate reactivity, the other two rocks showed innocuous behavior, with potential to be used as aggregates in civil works, without being necessary any addition of mitigating materials, since their expansion levels are in compliance with the criteria established in the Brazilian standards.