Analytical models for estimating yield stress of high-performance pseudoplastic grout

The yield stress of cement grout is commonly determined by extrapolating the shear stress- shear rate flow curve to a zero shear rate using an analytical model. High-performance structural cement grouts, made with relatively low water-to-cementitious materials ratio (W/CM) incorporating various supplementary CMs and theology-modifying admixtures (RMAs), can exhibit theological behavior different than that of conventional grout. Such mixtures can exhibit high pseudoplastic sheer thinning characteristics. Therefore, the degree of error in estimating the yield value of high-performance grouts can be greater than for conventional ones. In this paper, yield stresses of cement grouts made with 0%, 0.03%, 0.05%, and 0.075% of welan gum RMA, by mass of binder, and various high-range water-reducer (HRWR) concentrations were evaluated. Mixtures with different replacement values of silica fume and blast furnace slag were also investigated. All grouts had a constant W/CM of 0.40. Yield stress values obtained using various theological models are compared. The results showed that, depending on the adopted analytical model, the deducted yield stress can be quite different. A new method to estimate yield stress of highperformance, pseudoplastic grout is proposed and shown to result in lower yield stress estimates than the other models. For mixtures made with 100% cement, the estimated values of yield stress given by the proposed model are found to be close to those estimated using the De Kee model. (C) 2001 Elsevier Science Ltd. All rights reserved.