Feasibility of recycled aggregates modified with a compound method involving sodium silicate and silane as permeable concrete aggregates

Recycled aggregates (RA) used to prepare pervious concrete solve the problems of poor water permeability and lack of stone in urban pavement and achieve green and sustainable development. However, application of the recycled aggregate is difficult due to its poor performance. Treatment of the RA with sodium silicate and composite silane improves the uniformity of recycled concrete aggregates (RCAs) and recycled brick aggregates (RBAs) and reduces their porosities and pore sizes, thus improving the performance of the recycled aggregates. By using modified RA to prepare pervious concrete, the interfacial transition zones (ITZs) between RBA or RCA and the cement matrix can be improved, the widths of internal cracks and pores can be reduced, and the mechanical properties, durabilities and fatigue properties of permeable concrete (PC) can be improved. Due to the irregular shapes and relatively different RA particles, the connectivity of pores inside the PC is reduced, thus reducing the permeability of the PC. The incorporation of 30%−70% RA may lead to decreases in PC permeability of approximately 10%−25%. On the other hand, modification with sodium silicate and silane does not enhance the permeability of the PC but closes the pores inside the RA, which has an adverse effect on the permeability of the PC.