A CONDUCTION CALORIMETRIC STUDY OF EARLY HYDRATION OF ORDINARY PORTLAND-CEMENT HIGH-ALUMINA CEMENT PASTES

Conduction calorimetry was applied to an investigation of the early hy dration of ordinary Portland cement (OPC)/high alumina cement (HAC) pa stes. Three different rate of heat-evolution profiles were observed, d epending on the HAC/OPC ratio. Relevant processes affecting heat devel opment include ettringite formation, HAC and OPC hydration. Results fr om SEM examination and X-ray diffraction studies are also presented. A n acceleration of OPC hydration was observed in pastes containing less than 12.5% HAC. A similar acceleration effect on HAC hydration was al so obtained with the addition of OPC. A large amount of ettringite was formed and OPC hydration delayed in the pastes containing 15%-30% HAC . The latter could be one of the factors attributed to poor strength d evelopment in these HAC/OPC systems. Early hydration mechanisms of OPC /HAC systems are also discussed.