Total recycling of low-quality urban-fringe construction and demolition waste towards the development of sustainable cement-free pervious concrete: The proof of concept

This work presents a proof-of-concept study of recycling low-quality urban-fringe construction and demolition waste for the development of sustainable cement-free pervious concrete. Waste was in-situ collected from a local construction site of urban-fringe in Hangzhou, China, and elaborately analyzed for quality assessment. Ground brick powder was activated by alkali activators at different (Al+Si)/Na ratios to find the optimal mix ratio. Macro waste solids and alkali-activated recycled brick powder were used as the aggregate and binding material, respectively, to achieve total recycling of the waste. The effects of binder-to-aggregate ratio on the engineering performances and multi-scale structures of the cement-free recycled waste pervious concrete were explored. Results showed that the optimized alkali-activated recycled brick powder paste had high compressive strength up to 50 MPa. The cement-free recycled waste previous concrete showed relatively low compressive strength but high water permeability. Microstructural mechanisms in the aspects of pores, skeletons, and matrix-aggregate interactions were discussed. The replacement of cement by alkali-activated brick powder showed substantial economic and environmental benefits. The findings of this work would provide a promising route towards solving the large-scale construction and demolition waste in China.