Concrete produced with recycled concrete aggregate exposed to treatment methods

Some techniques, such as removing the adhered mortar particles and surface modification of recycled aggregates, have been investigated in an attempt to improve their quality. This study intends to evaluate the performance of concrete containing recycled concrete aggregate (RCA) subjected to Portland cement treatment and grinding, as partial replacement of coarse crushed aggregates at 20 % and 50 %. It became evident that using RCA in the mix of new concrete has a negative impact on its properties. However, it was found that the use of treatments such as mechanical grinding and a two-stage mixing approach (TSMA) with 25 % Portland cement in the mix were viable technical alternatives for improving these aggregates. The test results indicated that, due to the efficiency of the grinding treatment (T1), the CRCA50-G mix presented a higher compressive strength than CRCA20-G and, when treatment TSMA (T2) was used, both the CRCA20-G-TS25 and CRCA50-G-TS25 mixes outperformed the conventionally mixed concrete, resulting from a superposition of effects. The splitting tensile strength results were satisfactory when replacing up to 50 % and the use of treatment T2 in concrete with varying RCA did not present a significant effect on this property. The two-stage mixing method applied together with grinding aid in the densification of the porous microstructure, which improved concrete resistance against carbon dioxide diffusion and chloride ingress, beyond improvements in water absorption by capillarity, which enabled greater use of RCA. It was concluded that the use of treatments like these improves the mechanical properties and durability of concrete produced by RCA, mainly when these treatments are used simultaneously. In general, using a properly prepared RCA can be produced concrete with physical and mechanical properties besides performance characteristics.