Title: Effect of Welan Gum-High-Range Water Reducer Combinations on Rheology of Cement Grout
Author(s): K. H. Khayat and A. Yahia
Publication: Materials Journal
Appears on pages(s): 365-372
Keywords: bleeding (concrete); cement grout; high-range water reducer;
polysaccharide; rheology-modifying admixture; setting time; stability;
viscosity; viscosity-modifying admixture; washout; welan gum;
Polysaccharides are high-molecular weight, water-soluble organic polymers which can be used to reduce water dilution, bleeding, segregation, and sedimentation in cement-based systems. The effects of combined additions of welan gum and naphthalene-based high-range water reducer on the rheological properties of cement grouts are investigated. Grouts with dosages of rheology-modifying admixture varying from 0 to 0.075 percent by mass of cement were prepared. For each group of grout, the concentration of high-range water reducer was varied to obtain four mixtures of various fluidity levels. Measured properties included apparent viscosities at different shear rates and estimates of plastic viscosity and yield value. Other measurements of consistency included the ease of spread and flow of grout evaluated using the mini-slump and Marsh cone tests, respectively. The grout stability was evaluated by measuring its resistance to water dilution when cast in water as well as its ability to retain water when subjected to sustained pressure (forced bleeding). Initial setting times were determined for selected mixtures. In all, a total of 27 grout mixtures were evaluated. Test results show that the increase in the dosage of rheology-modifying admixture increases significantly the yield value and plastic and apparent viscosities of cement grouts. Combined with an adequate dosage of high-range water reducer, losses in fluidity are regained without significant reduction in stability. With the increase in high-range water reducer dosage, the apparent viscosity at low rates of shear decreases more dramatically than that at high rates of shear due to the pseudo-plastic behavior of such grouts. The combined use of proper dosages of rheology-modifying admixture and high-range water reducer is shown to clearly contribute to securing high- performance cement grout that is highly fluid, yet cohesive enough to reduce water dilution and enhance water retention. For equal fluidity level, greater stability is obtained with mixtures containing high contents of viscosity modifying admixture. The initial setting time is shown to be delayed by the incorporation of high-range water reducer and rheology-modifying admixture with the latter additive exhibiting a greater influence on retardation of setting.