Studying properties of pervious concrete containing recycled aggregate loaded with TiO₂/LDHs and its liquid pollutant purification

This paper endows recycled aggregate with photocatalytic properties considering its porous structure. It then prepares recycled-aggregate pervious concrete with photocatalytic-adsorptive synergistic functions to improve reusing construction and demolition waste and reduce the pollution of urban rainwater runoff. To this end, traditional photocatalyst TiO2 is modified by introducing hydrotalcite, layered double hydroxides (LDHs), and the calcined LDHs and TiO2 are mixed to form a composite photocatalytic material, i.e., TiO2/LDHs. Then, we composite different concentrations of TiO2/LDHs with the recycled aggregate by the soaking method to prepare recycled-aggregate pervious concrete. This work studies the effect of TiO2/LDHs on the physical and mechanical properties of recycled-aggregate pervious concrete. The purification performance of the pervious concrete containing TiO2/LDHs-loaded recycled aggregate in the photocatalytic-adsorptive synergistic degradation of liquid pollutants is also measured. In addition, a kinetic model is employed to explore the rate and mechanism of the photocatalytic-adsorptive synergistic degradation. Our findings indicate a significant enhancement in the material properties. Specifically, the addition of TiO2/LDHs led to an approximate reduction of 20% in both porosity and permeability, while concurrently augmenting the compressive strength by nearly 40%. The TL-0.8 specimens have the best physical and mechanical properties: the 28-day compressive strength, permeability coefficient, and porosity reach 27.4 MPa, 1.65 mm/s, and 14.69% respectively. The TL-0.6 specimens have the highest performance in degrading the methylene blue solution, and the degradation rate reaches 65%; the Langmuir pseudo-first-order kinetic model describes the degradation. The TL-0.8 specimens have the highest performance in adsorbing nitrate ions, and the removal rate reaches 56.8%; the adsorption follows the Lagergren pseudo-first-order kinetic model. The mechanism of the photocatalytic-adsorptive synergistic degradation shows that liquid pollutants are first adsorbed onto the surface of the recycled-aggregate pervious concrete, and photocatalytic reactions occur under the action of ultraviolet rays; then, the reaction products are desorbed from the concrete surface or diffuse into its pores, that is, the directional transfer of pollutants, realizing the purification of liquid pollutants.