Potential Alkali-Reactivity of a Granodiorite. Expansion in Concrete Produced with Recycled Concrete Aggregate

The main source of crushed stone for concrete in Montevideo, Uruguay, is the granodiorite quarry. The aim was to evaluate the potential reactivity of this crushed stone and determine the expansion of concrete produced with recycled concrete aggregate (RCA), including the granodiorite. The concrete prisms from the accelerated expansion test were crushed once the evaluation in granodiorite was completed. Then the crushed concrete was used as coarse aggregate (at 25% and 75% replacement of non-reactive coarse aggregate) to evaluate the expansion in prisms kept at 60 ℃ and 95% RH for 13 weeks (accelerated methodology) and in prisms kept at 38 ℃ and 95% RH for 40 weeks (traditional methodology). Petrographic analysis of the granodiorite rock showed the presence of microcrystalline quartz as a reactive constituent. In accordance with the expansion in the concrete prism test using the traditional methodology, four samples exhibited reactivity while one did not. However, according to the accelerated methodology with an expansion limit of 0.08%, only two samples displayed reactivity. The concrete containing RCA exhibited greater expansion compared to the reference concrete (which employed non-reactive aggregate) but remained within acceptable limits. The results indicate that the use of RCA derived from concrete containing the studied granodiorite crushed stone resulted in a similar expansion compared to the original concrete. This suggests that the potential reactivity of the granodiorite coarse aggregate persists, even after it has previously undergone a reactive process within concrete.