Cellulose ethers and yield stress of cement pastes

We study in this paper the physical and chemical phenomena at the origin of the influence of cellulose ethers on flow onset of cement pastes. We first show that cellulose ether adsorption seems to slow down the nucleation of calcium silicates at the surface of the cement grains in the tens of minutes following mixing. We moreover suggest that the measured collapse of the van der Waals attractive interaction network upon the addition of cellulose ethers finds its origin in repulsive steric forces generated by adsorbed cellulose ether molecules. Finally, we measure the formation of a new interaction network in the system. From dimensional inter-particle force analysis, we suggest that this network finds its origin in the bridging of cement grains by adsorbed ether molecules. Flow onset occurs then through a desorption process, the energy of which can be assessed via adsorption isotherm measurements.