The Influence of Crushed Sand Particle Shape in Alkali-Aggregate Reaction

摘要

The increasing demand for fine aggregate in the civil construction industry and the depletion of natural sand, calls for new options of aggregate to be used in concrete and mortar. A material that has been shown as a viable alternative to replace partially or completely natural aggregate is the crushed sand. This material is the reject of aggregate plants, with a particle size less than 4.8mm. Several studies have proved its technical viability; this crushed sand has provided quality concrete and also an increase in compressive strength. However, the crushed sand has been used without an investigation of concrete durability, such as the alkali-aggregate reaction (AAR). The AAR is a chemical process in which some mineralogical constituents of the aggregates, in particular the silica, react with alkali hydroxides, mainly from the cement. This reaction generates products that are expansive in the presence of moisture, and consequently can cause cracks and displacements in the concrete. This study aimed to evaluate the capability of reactive aggregates from crushed basalt with different particle shape, and also investigate the mitigation of this reaction using cement with different pozzolan contents. This study was conducted using the Accelerated Mortar Bar method, using four cement types and five different aggregate shapes. The results showed that the basalt crushed sand have a predisposition to generate deleterious expansions, when associated with cement without or with low content of pozzolan. On the other hand, cements which contain a higher content of pozzolan, about 40%, were effective in controlling the expansion. It was observed that the aggregate particle shape has significant influence on expansion caused by AAR.