The retarding effect of phosphoric acid during CAC hydration

Abstract The hydration of CA-cement under the influence of low concentrations of phosphoric acid was investigated. The research was focused on the developing phase content and phase equilibria by QXRD and pore water analysis. To obtain a quantitative phase content the G-Factor method was employed, which was established and applied in the last years for different cementitious systems. Pore water extraction was enforced through centrifugation of cement paste and by high pressure squeezing of cement stone. Data could be obtained up to 48 h. The overall heat flow during this time was also recorded by heat flow calorimetry. We found strong influence of phosphoric acid on the pore water composition and thus determining the initially and later formed hydrate phases. The theoretical data of oversaturated phases from thermodynamic point of view were compared to the actual phases detected by QXRD.