Influence of MgAl-LDHs/TiO2 composites on the mechanical and photocatalytic properties of cement pastes and recycled aggregates

To study the effects of MgAl-LDHs/TiO2 on the properties of cement paste and recycled aggregates, MgAl-LDO (MgAl-LDHs calcined products) and TiO2 were mixed during the reconstruction of MgAl-LDHs laminates based on the memory effects of layered double hydroxides (LDHs), and then MgAl-LDHs/TiO2 was synthesized. The performance changes were characterized with hydration heat tests, the microscopic morphologies of the hydration products, and the physical and mechanical properties of the cement paste. The effect of the MgAl-LDHs/TiO2 on the multi-interfacial transition zone (ITZ, the interface between the old paste and new paste) of the recycled aggregates was characterised with the micromorphology, meso-mechanical properties, and element diffusion behaviour. The photocatalytic activity of MgAl-LDHs/TiO2 loaded on recycled aggregate was evaluated with the degradation of methylene blue under sunlight. The results showed that the addition of MgAl-LDHs/TiO2 promoted the initial hydration of ordinary Portland cement (OPC) and induced and promoted the growth and formation of crystalline cement hydration products. The initial setting time and final setting time were shortened, and the compressive strength of the hardened paste was improved when MgAl-LDHs/TiO2 was added to the cement paste. The MgAl-LDHs/TiO2 compacted the recycled aggregates and improved the structural properties of the ITZ. The MgAl-LDHs/TiO2 altered diffusion within the ITZ. The total efficiency for the degradation of methylene blue by the 5-10 mm MgAl-LDHs/TiO2 loaded on recycled aggregate reached 82.2% after 80 min under simulated sunlight.