Influence of Recrystallized Silica Aggregates on Alkali-Silica Reactivity

Abstract

The potential reactivity of aggregates and the influence of recrystallized silica was studied using several test methods—namely, oxide composition analysis, accelerated mortar-bar testing (AMBT), accelerated concrete microbar testing (ACMT) and analysis of microscopic characteristics using a digital stereo microscope and a scanning electron microscope (SEM). Three different types of greywacke aggregate from the same source were investigated; greywacke aggregate (GRA), moderate quartz greywacke aggregate (MGA) and recrystallized aggregate (REA). The results indicated that all studied aggregates were quite similar in oxide composition. Thin-section analysis indicated that GRA and MGA were coarse-grained greywacke composed of quartz feldspar rock fragments. However, REA was high weathering chlorite with a matrix of re-crystallized quartz and rock fragments altered by tectonic forces. The findings indicated that the recrystallized aggregates increased the alkali silica reaction risk and may be considered as having a more deleterious effect than the other aggregates. The largest expansion was observed from both the AMBT and AMCT methods. The results from stereomicroscopy of concrete thin-section analysis and the SEM study confirmed this finding.