Interaction between zeolite and sulfate, and its influences on cement hydration

Zeolite internal curing has been proven to be effective in reducing shrinkage of cement-based materials, but the sulfate erosion resistance of materials internally cured by zeolite is unclear. In this study, the interaction between zeolite and sulfate, and its effects on cement hydration were experimentally investigated. Firstly, the effects of sulfate on pore structure characteristics and pozzolanic activity of zeolite were studied, then sulfate ion adsorption and sodium ion exchange property of zeolite were tested. Finally, cement paste specimens with zeolite and sulfate were prepared, cement hydration degree, zeolite pozzolanic reaction degree, hydration product characteristics, and compressive strength of the specimens were studied. The test results show that, 1) Sodium sulfate can increase the pore content and pozzolanic activity of zeolite; 2) Zeolite particles can adsorb sulfate ions, sodium ions can exchange calcium ions in zeolite, alkaline environment inhibits the ion exchange process but promotes the ion adsorption process; 3) Sulfate-zeolite addition increases the hydration degree of cement, the pozzolanic reaction degree of zeolite, and the compressive strength of cement paste; 4) Sulfate erosion increases the porosity of Ordinary Portland cement (OPC) materials and reduces the porosity of Sulphoaluminate cement (SAC) materials, zeolite has an inhibitory effect on the influence of sulfate on pore structure.