Influence of cellulose ethers molecular parameters on hydration kinetics of Portland cement at early ages

Cellulose ethers (CEs) are excellent thickening and water retention agents for dry-mixed mortars, but they commonly retard cement hydration. Isothermal calorimetry is conducted to investigate the influence of molecular parameters of CEs on hydration kinetics of Portland cement at early ages. The retardation effect of CEs with different molecular parameters is different, the lower the molecular weight of CEs or the hydroxyethyl content in HEMCs (hydroxyethyl methyl celluloses) or methyl content in HPMCs (hydroxypropyl methyl celluloses) and HEMCs is, the stronger the retardation ability is. The major retardation mechanism is the adsorption between CEs molecule and hydration products, which acts between the OH groups of CE molecules and metal hydroxide on hydration products. Main chains of CE molecules and side chains of substituent groups have the steric hindrance effect on the OH groups at CE molecules, which play an important role on the retardation ability of CEs, the smaller the steric hindrance to OH groups is, the stronger the adsorption ability of CEs is. (C) 2012 Elsevier Ltd. All rights reserved.