Viscosity-enhancing admixtures for cement-based materials — An overview

Influence of hydroxypropylguars on rheological behavior of cement-based mortars

“…Moreover, admixed mortars with HPG 5 exhibit a more shear-thinning behavior (lower fluidity index) than mortars admixed with other HPG, whatever the dosage. As suggested by Khayat [7], polysaccharides enhance the shear thinning behavior of cementitious materials by making the pore solution (which is Newtonian in the absence of admixture) shear-thinning. Indeed, polymers exist in solution in coil form.…”

“…Since polysaccharides exhibit long chains, the same molecule can adsorb on separate cement particles and draw them together. This phenomenon is known as polymer bridging flocculation [49][50][51] and induces a rise in yield stress [7,13,16].…”

“…According to many authors, incorporation of polysaccharide leads to an increase in apparent viscosity of cement-based materials because of an increase in the pore solution viscosity [7,10,12,13]. Fig.…”

“…The incorporation of VEA in shotcrete or render mortar is also very useful to ensure sagging resistance for thick application on vertical support, and allows sufficient fluidity for normal pumpability [10,[14][15][16][17] by supplying shear thinning rheological behavior. Thus polysaccharides provide high yield stress and apparent viscosity at low shear rate but low resistance to flow at high shear rate [7].…”

“…Natural polysaccharides or their derivatives are well-known to act as viscosity-enhancing admixtures (VEA) by modifying the rheological behavior of cementitious materials [7].…”