Cellulose ethers such as hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) are common admixtures in factory made mortars. Nevertheless, their use principally remains empirical, and no cement–admixture interaction mechanism has ever been rigorously demonstrated. The main issue of this publication deals with the control of secondary effects generated by these admixtures such as the retardation of cement hydration. In this frame, a study of the impact of HEMC and HPMC molecule parameters on the modification of cement hydration was carried out. Minor influence of the molecular weight and of the hydroxypropyl or the hydroxyethyl group content was observed. On the contrary, the results emphasize that the methoxyl group content appears as the key parameter of the hydration delay mechanism.
The different studies in water and limewater media are coherent. However, the lime media emphasizes enhanced tendencies. Whatever the hydration kinetics conditions (water or lime solution), the results allow to demonstrate that the methoxyl content is the key parameter concerning the portlandite precipitation delay induced by HPMCs and HEMCs. On the contrary, the molecular weight and the hydroxypropyl content seem to have a lower impact on admixed cement hydration process. Furthermore, these results let us to think that HPMCs and HEMCs with a well known methoxyl content could enable to control hydration delay for applications in the building industry.
Link: https://www.sciencedirect.com/science/article/abs/pii/S0008884605001912