Foundry Sand Waste and Residual Aggregate Evaluated as Pozzolans for Concrete

This research is about the utilization of two solid wastes in concrete: foundry sand from the steel smelting process and residual aggregate powder from the asphalt mix production. The solid wastes were added to concrete in contents of 0.0, 5.0, 10, 15, and 20 wt% with respect to cement, and tested in concrete with a design resistance of 280 kgf/cm 2 (27.5 MPa). The effects of these wastes in concrete were compared with commercially available metakaolin, a typical admixture added to concrete, in contents of 0.0, 5.0, 10, 15, and 20 wt% replacing cement content. For all samples, the resistant activity index was evaluated at 28 days. Slump test, air content, density, and compressive strength tests were conducted. The materials’ microstructures were evaluated with SEM and XRD after 270 days, in samples immersed in water. Results show that both by-products have pozzolanic activity, classified as N-type pozzolans. Besides, concrete with the residual aggregate powder gave a strength of 541 kgf/cm 2 (53.1 MPa), which corresponds to sample M4 (concrete containing 15% residual aggregate powder), consistent with 93% improvement with respect to the strength resistance. Furthermore, concrete with the foundry sand powder gave a strength of 561 kgf/cm 2 (55 MPa), consistent with 100% improvement with respect to the strength resistance, which corresponds to M15 (concrete containing 20% foundry sand). Concrete with the metakaolin powder presented a strength of 609 kgf/cm 2 (59.7 MPa), which corresponds to M9 (concrete containing 15% metakaolin), consistent with 116% improvement with respect to the strength resistance. The concrete developed with the by-products can be produced at lower costs than traditional admixtures, which guarantees the feasibility of the environmental solution.