Study of mix design and performance of alkali-activated concrete with recycled concrete aggregate

Recycled concrete aggregates (RCA) are produced from demolished buildings and old rigid pavements, which are deemed as solid waste, comprising primarily old aggregate and cement mortar. In this study, the use of RCA was introduced in alkali-activated concrete (AAC) to investigate the feasibility of designing the mix proportion of alkali-activated recycled aggregate concrete (AARAC) using a linear fitting formula. A total of 32 mixes, with the amount of cementitious materials varying from 350 kg/m3 to 500 kg/m3 and the sol ratio from 0.43 to 0.55, were prepared for the regression analysis of the relationships between multiple parameters. The tests for water consumption, compressive strength and durability were included. The experimental results indicate that concrete prepared using high-quality RCA exhibited lower water consumption and higher compressive strength. When the natural aggregate (NA) was replaced by the RCA, the compressive strength reached its highest value of 54.0 MPa. Moreover, as the strength grade increased, the chloride penetration resistance, anti-carbonization performance, and freezing resistance of AARAC gradually increased, while the shrinkage decreased. In conclusion, this study provides a new method for the mix design of AARAC, which contributes to the advancement of solid waste management in the construction industry.