Effects of the Ion Exchange and Adsorption Behavior of Clinoptilolite on Chloride Solidification in Cement Paste

Clinoptilolite has been used in cement-based materials to reduce shrinkage and increase compressive strength, but the ion exchange and ion adsorption behavior of clinoptilolite in cement-based materials have not been studied. In this study, the ion exchange/adsorption behavior of clinoptilolite, and their effects on chloride solidification in cement paste were investigated. Firstly, clinoptilolite particles were immersed in a NaCl solution, the concentration changes of sodium and calcium ions were measured to evaluate the ion adsorption and ion exchange performance of clinoptilolite. Then the pore structure, chemical bonding, and pozzolanic activity of NaCl solution soaked clinoptilolite were investigated. Finally, cement-clinoptilolite-NaCl paste specimens were prepared, the reaction degrees of clinoptilolite/cement, and the solidified chloride contents in the specimens were tested. The results show that, (1) With the increase of environment pH, the sodium ion exchange performance and chloride adsorption property of clinoptilolite decrease. (2) NaCl can improve the pozzolanic activity of clinoptilolite, and improve the reaction degree of clinoptilolite and cement in the paste. (3) When NaCl exists, clinoptilolite improves the content of Friedel's salt in ordinary portland cement (OPC) material but inhibits the production of Friedel's salt in sulphoaluminate cement (SAC) material. (4) Clinoptilolite improves the chloride solidification property of cement paste, especially for SAC materials.