Study on the properties variation of recycled concrete paving block containing multiple waste materials

Waste materials are widely used in concrete products, but the properties variation of concrete products containing multiple recycled materials have not been well studied. This research aims to thoroughly investigate the properties, including compressive strength, tensile splitting strength, water absorption, slip resistance and abrasion resistance of concrete paving blocks by replacing the natural aggregates with recycled concrete coarse aggregate (RCCA), crushed glass (CG), recycled concrete fine aggregate (RCFA) and ground granulated blast furnace slag (GGBS). Orthogonal experimental designs were adopted, and microstructure analyses were conducted to reveal the underlying mechanisms. Results demonstrate that RCCA significantly degraded the tensile splitting strength, water absorption, and abrasion resistance of the block containing multiple recycled materials, but CG hardly affected the tested properties. RCFA had an adverse effect on all five blocks’ properties and was proved to have a highly negative impact on blocks’ tensile splitting strength and water absorption. At an optimal replacement level, GGBS was able to improve the compressive strength, tensile splitting strength, and water absorption properties. Furthermore, not only the limit replacement levels of the waste materials in the particular block were investigated, but also two optimal replacement levels for the concrete blocks that contained multiple waste materials were tested and verified successfully: 1. 20 % for RCCA, 0 % for RCFA, and 30 % for GGBS; 2. 20 % for CG, 0 % for RCFA, and 30 % for GGBS. A series of index equations were first derived in this research, which can be used as effective methods to predict the properties of concrete blocks containing multiple waste materials in future studies.