Effects of Calcium Sulfate on Performances of CSA Clinker-Premixed Cl− System: Chloride Binding Analysis

Abstract

Calcium sulfoaluminate cement (CSA) has excellent chloride (Cl−) binding capacity, which is significantly influenced by the existence of calcium sulfate within mixes. However, impacts of dosage and type of the calcium sulfate on the binding performances and mechanisms are still unclear. In the paper, these impacts in CSA clinker-premixed Cl− system were thoroughly explored with experimental studies, including parameters of fresh properties, hardened properties, and mineralogy aspects. Results showed that calcium sulfate accelerated CSA hydration, reduced the setting time, and sharply decreased Cl− binding due to promoting formation of ettringite (AFt). The stability of Friedel’s or Kuzel’s salts formed by binding of monosulphoaluminate (AFm) and Cl− was worse than that of AFt. Compressive strength reduced slightly with calcium sulfate increasing. Compared with anhydrite, dihydrate gypsum reduced shrinkage, improving volume stability.