Experiment design to evaluate interaction of high-range water-reducer and antiwashout admixture in high-performance cement grout

The injection of cement grout in water-saturated medium and the sealing of anchorages require the use of grout with high resistance to water dilution to enhance in-situ performance. This can be achieved by reducing the WIC and incorporating an antiwashout admixture (AWA) to enhance the stability. Such admixture can increase the viscosity and yield stress and necessitate higher dosage of high-range water-reducer (HRWR) to maintain the desired fluidity. Cement-based grouts with 0.30 to 0.50 W/C and different combinations of AWA and HRWR were evaluated. The study was undertaken to highlight the influence of WIC and dosage of chemical admixtures on fluidity, washout resistance, and residual compressive strength (RCS) of the underwater-cast grout. Statistical models established using a statistical design of experiments indicate that the W/C has greater effect on changes in minislump flow washout, and RCS than the concentrations of HRWR and AWA. On the other hand, for mixtures prepared with a fixed W/C of 0.40, the models show that measured responses are highly affected by the dosages and interaction of both admixtures. Trade-off between fluidity and washout resistance and means to optimize mixture proportioning to enhance the resistance to water dilution without adversely affecting fluidity are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.