Effect of HEMC on the early hydration of Portland cement highlighted by isothermal calorimetry

The effects of hydroxyethyl methyl cellulose (HEMC) on the early hydration and main hydrates evolutions of Portland cement were quantitatively investigated by the isothermal calorimetry, setting times, X-ray diffraction analysis, and environmental scanning electron microscope analysis. The results show that HEMC definitely affects the early hydration process of cement paste and retards the beginning of the hydration induction period and acceleration period, but increases the length of these two periods. HEMC decreases the hydration heat evolution rate during the initial reaction period and the acceleration period, but increases the hydration heat evolution rate during the deceleration period. HEMC decreases the hydration heat amount and hydration degree of cement paste at the early hydration time, especially in the first thirty-six hours. There are good positive correlations between the setting time, the length of induction period and the dosages of HEMC. HEMC also delays the formation of the hydrates and affects the morphologies of hydrates. Accordingly, HEMC remarkably retards the cement hydration at the early hydration time, and with its dosage increasing, the retardation effect of HEMC enhances.