Concrete Component Under Sulfate Containing Environment.

Concrete is influenced by internal and external sulfate ion. The product from a chemical reaction of sulfate ion and cement components can result in volume expansion or strength loss. The change of cement component and composition would affect directly on its quality deterioration. To figure out a change of hydrated matrix in Portland Cement in sulfate solution, the thermodynamic model was developed as a function of concentration of sulfate ion and redox potentials. Not only the composition of the phase assemblage of Ordinary Portland Cement and the solutions surrounding the cement material, but also the mixed forms of several admixture and the Portland Cement were determined. The thermodynamic database of the initial, intermediate and final form of the cement material was gathered from reference and was modified for this modeling program. Redox potential didn't have any influence on amount of Ettringite and Thaumisite when the concentration of sulfate ion was lower than specific concentration. According to the change of redox potential, Fly Ash added cement had lower gypsum than Ordinary Portland Cement while the highest ettringite and thaumasite concentration within the admixture added cement. SiO₂ added cement precipitated the least amount of gypsum, thaumasite and ettringite.