Novel applications of waste foundry sand in conventional and dry-mix concretes

The use of waste materials in the building industry is a major challenge for eco-efficient construction. Brazil generates more than 3 million tons of waste foundry sand (WFS) annually, making it one of the largest industrial wastes produced in the country. This work proposes the use of WFS in two novel ways: in conventional concrete by WFS calcination, and in dry-mix concrete for the production of concrete blocks. For the conventional mixture study, mortars with 0, 50 and 100% replacement of natural sand by WFS and calcined WFS (CFS) were produced. The fresh state properties, volumetric variation, cement hydration and 28-days compressive strength of the mortars were evaluated. For the dry-mix concrete study, compositions with two densities (2.20 and 2.25 g/cm³), three cement contents and 0, 50 and 100% WFS in natural sand replacement were produced in the laboratory. Furthermore, concrete blocks of different strength ranges and 0 and 100% WFS in natural sand replacement were produced in a concrete block manufacturing plant for full-scale testing. The results showed that the use of WFS led to reductions in flowability and compressive strength of the mortars, but did not cause expansion as initially expected. In contrast, the use of up to 100% CFS resulted in mortars with flowability and compressive strength similar to those of the reference. WFS calcination removed the pulverized coal and may have formed pozzolanic phases in the clay material. As a result, the CFS presented performance similar to that of natural sand. In dry-mix concrete, the laboratory results showed that the use of 100% WFS resulted in similar strengths to the reference for concretes of up to 20 MPa. Finally, full-scale tests showed that it was possible to produce concrete blocks with 100% WFS and strengths compatible to the reference.