Insight into multi-ionic adsorption behavior of recycled cement paste exposed to chloride solutions
Lei Xu, Xiaochuan Hu, Q. Y. Yang, Bo Ran, Kefei Li, Junjie Wang, Xin Zhang
Abstract
The multi-ionic adsorption behavior of recycled cement paste (RCP) exposed to NaCl and CaCl 2 solutions is investigated in this study by comparing with that of the ordinary cement paste (OCP). The adsorption of Na + , K + , Ca 2+ , and Cl - in RCP and OCP are quantified by ICP-OES and potentiometric titration. RCP has larger adsorption capacity for Na + , K + , and Cl - compared to OCP, which is attributed to a lager specific surface area of RCP. For the multi-ion adsorption of OCP and RCP in both NaCl and CaCl 2 solutions, the adsorption amount of minor cation ions are found to be influenced by the concentration of primary cation ion, reflecting a competitive adsorption among cation ions. Besides, the maximum Na + adsorption amount is proportional to the product of the specific surface area and the percentage of the silanol groups in CSH measured by 29 Si NMR spectroscopy . Additionally, molecular dynamics simulation is conducted to investigate the Na + and Cl - adsorption behavior of CSH in OCP and RCP at a molecular level. The simulation results confirm the higher adsorption capacity of OCP than RCP.