Research on rheology performance and sealing effect of alkali-activated GGBS paste used for tunnel leakage plugging

This paper investigated rheological behavior and leakage plugging effect of alkali-activated slag (AAS) with the aim of promoting plugging application of slag resources. A series of laboratory tests were carried out to study effects of different activator concentrations (i.e. 1, 2, and 3 mol/L) and temperatures (i.e. 20, 30, and 40 degrees C) on time-dependent rheological properties (i.e. yield stress, apparent viscosity, and thixotropy) of AAS paste, which was made from ground granulated blast furnace slag (GGBS) and sodium hydroxide activator. The temporal variations in hydration process of AAS paste were examined and analyzed using X-ray diffraction (XRD) and scanning electron microscope (SEM). Moreover, the plugging effect of AAS paste was investigated by tunnel leakage plugging test. The test results indicate that the shearing behavior of AAS paste could reasonably be described by Bingham plastic model. There was a great increase in yield stress, apparent viscosity, and thixotropy of AAS paste with an increase in activator concentration and temperature. The increase in those rheological properties were mainly attributed to the rapid formation of C-S-H gels and aluminum hydroxide magnesium at a higher concentration level and temperature. In addition, a power function was proposed to fit the time-dependent apparent viscosity, which enabled the explicit quantification of activation energy, i.e. the minimum energy required to initiate the hydration of AAS paste. In leakage plugging test, the characteristic of decreasing with the increase of exciter concentration and temperature was seen in both the point of water pressure and the time required to reach 0.5 MPa sealing water pressure.