Alkali-reactivity of Pernambuco east shear zone coarse concrete aggregates: An experimental discussion

Abstract

Being the fifth largest country globally, Brazil has a wide variety of rocks used in concrete production. Due to their mineralogical characteristics, many Brazilian rocks present reactive alkali potential, mainly due to the strong presence of silica and/or silicates in their composition. Alkali silica reaction (ASR) was firstly public in Brazil in 1963 in the Jupiá dam. Since then, several ASR events have been reported, namely in Dam and electric power plants, which represent a concern, mainly due to those infrastructures' social, economic, and environmental impact. Even though the selection of the raw materials should consider the aggregate quality and adequacy for a certain application, it mostly depends on the local availability due to economic reasons. Thus, an effective way to evaluate ASR susceptibility on concrete aggregates and predict or prevent the in situ behaviour of the final concrete product properties is crucial. This is particularly important when aggregates sources are Shear Zones, such as Pernambuco East Shear Zone. International standards suggested evaluating aggregate susceptibility prone to ASR through petrographic analysis of aggregates in addition to expansion tests at mortar and/or concrete levels. Concrete prism tests (CPT) are considered the most reliable method for ASR potentially of concrete aggregates; however, CPT are very time consuming, and results might be available after one year. Thus, Brazilian Association for Standardisation suggested a new accelerated concrete test based on RILEM recommendation AAR-4.1, the NBR 15577-7.This work evaluated the behaviour of the coarse aggregate obtained from ZCPE, to prone ASR among different testing conditions proposed by most widespread international standards, namely, petrographic examination, ASTM C 1260, RILEM AAR-4.1, ASSTHO T 380 and NBR 15577-7. Then results were compared and discussed the applicability of the new national standard NBR 15577-7. According to petrographic examination, the coarse aggregate from Pernambuco East Shear Zone was potentially reactive. Expansion tests at mortar and concrete levels corroborated such results, and coarse aggregate was classified as potentially reactive among all standards followed. Thus, it can be concluded that the new NBR 15577-7 outputs similar results compared to other international standards and seems to be a faster way (20 weeks/140 days) to access the ASR potential of reactive aggregates.