EFFECT OF WELAN GUM HIGH-RANGE WATER REDUCER COMBINATIONS ON RHEOLOGYOF CEMENT GROUT

Polysaccharides are high-molecular weight, water-soluble organic polym ers which can be used to reduce water dilution, bleeding, segregation, and sedimentation in cement-based systems. Such rheology-modifying ad mixtures increase the pseudo-plastic and thixotropic behavior of cemen t grout and are often used in conjunction with high-range water reduce rs that are added to compensate for some of the increase in flow resis tance. The effects of combined additions of welan gum a commonly used rheology modifier and naphthalene-based high-range water reducer on th e rheological properties of cement grouts are investigated for mixture s made with 0.40 water-to-cement ratios. Grouts with dosages of rheolo gy-modifying admixture varying from 0 to 0.075 percent by mass of ceme nt were prepared. For each group of grout, the concentration of high-r ange water reducer was varied to obtain four mixtures of various fluid ity levels. Measured properties included apparent viscosities at diffe rent 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, respect ively. The grout stability was evaluated by measuring its resistance t o water dilution when cast in water as well as its ability to retain w ater when subjected to sustained pressure (forced bleeding). Initial s etting 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 Wi th the increase in high-range water reducer dosage, the apparent visco sity at low rates of shear decreases more dramatically than that at hi gh rates of shear due to the pseudo-plastic behavior of such grouts. T he combined use of proper dosages of theology-modifying admixture and high-range water reducer is shown to clearly contribute to securing hi gh-performance cement grout that is highly fluid, yet cohesive enough to reduce water dilution and enhance water retention. For equal fluidi ty level greater stability is obtained with mixtures containing high c ontents of viscosity modifying admixture. The initial setting time is shown to be delayed by the incorporation of high-range water reducer a nd rheology-modifying admixture with the latter additive exhibiting a greater influence on retardation of setting.