Potential reactivity of granitic rocks. Petrographic characterization vs accelerated expansion tests

Abstract

ResumoSeveral cases of alkali-silica reaction involving granitic aggregates have been diagnosed in damaged concrete structures in Portugal. Nonetheless, this kind of rock is usually regarded as slow/late reactive or even non-reactive to alkalis. Granitic rocks are widely exploited in Northern and Central Portugal, representing almost half of the produced aggregates in this country. Project IMPROVE rose from the need to accurately diagnose the potential reactivity of granites to alkalis. The study involved about forty granites collected from different regions in Portugal, from which the results of eight samples are being presented in this paper. The tests carried out include the petrographic analyses of the aggregates and mortar and concrete expansion tests. It was concluded that the content of microcrystalline quartz correlates better with the results of AAR-4.1 than with the other expansion tests.Keywords: alkali-silica reaction; granites; petrography; expansion tests; performance.Diversos casos de reação álcalis-sílica têm sido diagnosticados em estruturas de concreto nas quais foram utilizadas rochas graníticas. No entanto, este tipo de rocha é geralmente considerado como inócuo ou de reactividade pouco provável aos álcalis. As rochas graníticas são amplamente exploradas no norte e centro de Portugal, representando quase metade da produção total de agregados no país. O Projeto IMPROVE surgiu da necessidade de diagnosticar corretamente a potencial reatividade aos álcalis de granitos. No âmbito desse projeto foram estudadas diversas amostras colhidas em diferentes regiões de Portugal, apresentando-se neste artigo os resultados de oito destas. Os ensaios realizados incluem a caracterização petrográfica dos agregados e ensaios de expansão de barra de argamassa e prisma de concreto. Concluiu-se que o conteúdo em quartzo microcristalino se correlaciona melhor com os resultados do ensaio em prisma de concreto RILEM AAR-4.1 do que com os outros ensaios de expansão.Palavras-chave: reação álcalis-sílica, granito, petrografia, ensaios de expansão, desempenho.

Petrographic Evaluation of Aggregate from Igneous Rocks: Alkali–Silica Reaction Potential

“…However, the relationship was the exponential function and was not so statistically significant (R 2 = 0.72) as in the conducted research. The expansion increased with the increase in total strained and microcrystalline quartz content, while the results obtained by Ramos et al [39] performed on the granitic specimens led to the conclusion that the ASTM C1260 mortar bar test demonstrated a weak association with the petrographic characterization of the aggregate.…”