Influence of cellulose ethers chemistry and substitution degree on the setting and early-stage hydration of calcium sulphoaluminate cement

Abstract

The setting and hydration process of calcium sulphoaluminate (CSA) cement within 24 h in the presence of five grades of cellulose ethers (CE) that have different chemistry or substitution degrees were studied by the Vicat test, ultrasonic test and isothermal calorimetry. X-ray diffraction (XRD) was further utilized to characterize the mineral phases of hydrates. Test results reveal that hydroxyethyl cellulose (HEC) prolongs the setting time less than hydroxyethyl methyl cellulose (HEMC) or hydroxypropyl methyl cellulose (HPMC). Higher CE dosage causes very limited change to the setting time of the mortar with HEMC/HPMC but narrows their gap with HEC. CE advance the second exothermal peak of CSA cement hydration where HEC works the most while highly-substituted HEMC/HPMC do the least. The trend is more pronounced at high dosage. The total hydration heat and the crystalized phases of hydrates are impacted slightly. CE work similarly in mortar on hydration to that in cement paste, but their effect is greatly weakened. A model is proposed to illustrate the hydration process. CE film is suggested to work as a medium for easier water migration that helps with the acceleration of the cement hydration reaction.