Properties study of artificial aggregate with high-content recycled concrete powder

Abstract

With the need for urban development, there is a trend towards constructing large-span and super high-rise buildings. People have placed higher performance requirements on building materials. Therefore, the development of high-strength materials has become one of the current research focuses. Recycled concrete powder (RCP) is the residual powder generated while crushing waste concrete into a recycled aggregate. In order to achieve the low energy consumption resource utilization of RCP solid waste, a large amount of RCP with slag (a by-product of the blast furnace ironmaking process) addition was activated under an alkaline environment to prepare a cementitious material. The effects of RCP/Slag, liquid-solid ratio, Na2O content, and Na2SiO3 modulus on the setting time, compressive strength, and microstructure of alkali-activated high-content RCP-slag cementitious materials (AARCPS) were determined. The results showed that AARCPS had good compressive strength and microstructure; as the RCP content increased, the setting time of the cementitious material gradually prolonged. Based on the research of AARCPS, the mixing ratio was improved, and alkali-activated high-content RCP-slag aggregates (AARCPSA) were prepared. The results showed that with the increase in RCP content, the material fast setting speed and the sticky surface of material balls phenomenon during the aggregate preparation process was improved, and increasing the RCP content from 0% to 50% increased the ball-forming rate by about 14.36%. AARCPSA has good early strength performance, with the compressive strength at 3d reaching 75.18%–90.15% of that at 28d and the compressive strength at 7d reaching 93.85%–99.51% at 28d. The maximum compressive strength at 28d was 8.2 MPa. Increasing the slag and Na2O content in AARCPSA increased aggregate strength and density and decreased water absorption. The increase in RCP content and the decrease in Na2O content increased the peak strain of single particle compression of the aggregate and improved the deformation performance of the aggregate.