HPMC and HEMC influence on cement hydration

Abstract

International audienceCellulose 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

HEC influence on cement hydration measured by conductometry

“…Actually, using range of wellcharacterized hydroxypropylmethyl cellulose (HPMC) and hydroxyethylmethyl cellulose (HEMC) with different investigation tools to follow cement hydration, different studies [2,3] come to similar results: the degree of substitution (DS) is the key parameter which influences the hydration delay.…”

“…Finally, hydration kinetics observed by synchrotron XRD allowed to conclude that the lower the DS, the stronger the delay of C 2 S/C 3 S hydration. The molecular parameters which mainly influence the retarding effect of HPMCs and HEMCs were also identified by Pourchez et al [3]. The impact of the weightaverage molecular weight (M w ) was determined thanks to cellulose ether samples having identical chemical structure and differing only by their molecular weights.…”

“…Moreover, HECs are also frequently introduced in dry-set mortar production in South America [1,4,5]. Using the same experimental procedures as the previous paper [3], the impact on hydration retardation of the HEC molecular parameters is examined.…”

Influence of hydroxypropylguars on rheological behavior of cement-based mortars

“…Indeed, a certain amount of water is lost due to cement hydration and mortar drying. Moreover, a non-negligible amount of polymer may be trapped into the mortar paste during hydration [57] and/or irreversibly adsorbed onto cement phases [48]. Therefore it is impossible to estimate the real concentration of polymer in solution without its measurement.…”

“…The sample thus exhibits higher viscosity at low shear rate and higher yield stress. Moreover, polysaccharides such as HPG and HPMC are able to adsorb on cement grains [29,48]. Since polysaccharides exhibit long chains, the same molecule can adsorb on separate cement particles and draw them together.…”