Degree of cement hydration can be characterized by hydration parameters including activation energy (E-a) and hydration curve parameters (ultimate hydration degree alpha(u), hydration shape parameter beta, and hydration time parameter tau). These parameters are affected by material compositions including chemical and mineral admixtures. In this study, isothermal calorimetry, tests were performed at different ambient temperatures with cement mortar mixtures with different amounts of water reducers and fly ashes. Hydration model was used to back-calculate hydration parameters using the measured heat generation-time relationship. Results showed that the activation energy E-a generally increases with increasing water reducer dosage and fly ash replacement. Hydration curve parameter alpha(u) seems to decreases, while tau generally increases with increasing water reducer dosage and fly ash replacement, and beta seems to increase with increasing water reducer dosage. As a result, the simulated temperature developments in the early-age concrete pavement showed that increased water reducer dosage and fly ash replacement results in decreased pavement temperature, thus reduced thermally-induced stress. (C) 2009 Elsevier B.V. All rights reserved.