Calcination and reconstruction performances of layered double hydroxides and its inhibition effect to chloride attack in interfacial transition zone of recycled aggregate concrete

Addition of active micro-nanomaterials in recycled aggregate concrete (RAC) is a potential strategy to improve the mechanical properties and durability of RAC. The calcined layered double hydroxides (CLDHs) with special composition, structure and memory effects, exhibit great adsorption and binding capacity to anions. Therefore, the CLDHs were prepared and utilized for inhibiting chloride attack in interfacial transition zone (ITZ) of RAC. The structural transformation characteristics of CLDHs experienced various calcination temperatures were firstly investigated, and the reconstruction performances and Cl - adsorption capacity of CLDHs in solution with different anions, pH and temperature were then explored in detail. The microstructure and chloride erosion resistance property of ITZ in RAC incorporated with CLDHs were further investigated. The results demonstrated that CLDHs exhibited excellent reconstruction performance and Cl - adsorption capacity when LDHs were calcined above 500℃, and the maximum chloride adsorption capacity of the CLDHs was 86.82 mg/g. It was noteworthy that the reconstruction and Cl - adsorption performance of CLDHs will be distinctly suppressed when the pH > 10, in contrast, increasing the ambient temperature promoted the reconstruction and Cl - adsorption performance of CLDHs. Additionally, the width of ITZ in the RAC were significantly reduced and the porosity had decreased by 32.5% with incorporation of 3% CLDHs in RAC. The good filling effect and superior chloride adsorption capacity resulted in the significantly decreased free chloride content in RAC.