Abstract
In this paper, the effect of HPMC (hydroxypropyl methyl cellulose ether) on the cement mortar water retention (WR) and composition was studied. The relationship between the plastic viscosity and water retention of cement mortar was revealed. The results showed that HPMC formed a colloidal film with a 3D network structure in water, which changed the ability of water to migrate. The HPMC colloid adsorbed on the surface of cement and sand particles and played a bridging role due to the influence of the spatial network structure of the thin film. Fine particles formed a grid-like distribution, and the hydration products formed a unique fibrous tree-like structure. A positive correlation was observed between the plastic viscosity and the water holding capacity of cement mortar. Finally, the mechanism responsible for the improved water retention of cement mortar by HPMC was analyzed using the changing water migration capacity, migration channels, and mortar cohesion.
Highlights
Cellulose ethers (CEs) are used to improve the workability of cement mortars while maintaining the water holding capacity and fluidity [1,2]
The results showed that the adsorption capacity of CE on the surface of cement particles was related to the molar degree of substitution (MS) and degree of substitution (DS)
The water holding capacity of mortar reflects the ability of fresh mortar to hold water under an retention rate increased greatly with the HPMC content and reached 92.1% at 0.10% HPMC
Summary
Cellulose ethers (CEs) are used to improve the workability of cement mortars while maintaining the water holding capacity and fluidity [1,2]. HPMC is the most widely-used CE [3]. High water retention improves the cement hydration and limits the absorption of the mixing water by a substrate and provides good mechanical and adhesive properties to the mortar [4,5]. Cellulose ethers thicken cement slurries, and their water retention is usually attributed to increased slurry viscosity. Desbrieres et al [6] showed that polymers increase the water retention of cement-based pastes by increasing the viscosity, which reduces filtration loss. Anionic polymers can adsorb on the surface of cement particles, block cake pores, and act bridges between cement particles. Marlieres [7] et al
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