Influence of polycarboxylate superplasticizer on chloride binding in cement paste

This paper aims to study the influence of polycarboxylate superplasticizer on chloride binding in cement paste. The equilibrium isotherms, kinetics and thermodynamics of chloride ions binding in cement with different contents of polycarboxylate superplasticizer were thoroughly examined. It has been found that all of the equilibrium isotherms data can be well fitted by the Langmuir isotherm and Freundlich isotherm. However, the amount of chloride equilibrium binding is decreased with the increase of polycarboxylate superplasticizer content. The kinetic data in the initial 24 h is well described by pseudo-first-order kinetic model and pseudo-second-order model is well suitable to describe the long-period adsorption kinetics data. The rate of chloride binding within 24 h is decreased with the increase of polycarboxylate superplasticizer content. The negative value of free energy, enthalpy and entropy of chloride binding are increased with the content of polycarboxylate superplasticizer, and the process of chloride binding in cement paste is spontaneous and exothermic. Based on the above results, the 'electrical double layer' model is used to describe the influence of polycarboxylate superplasticizer on chloride binding in cement paste.