Linglin Xu

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

Abstract 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.

Effect of calcium aluminate cement variety on the hydration of Portland cement in blended system

Two kinds of CACs with different monocalcium aluminate (CA) contents were used in the PC/CAC (PAC) mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confirming that the CA phase in CAC plays an important role in the delay of PC hydration.