Effect of different gypsums on the workability and mechanical properties of red mud-slag based grouting materials

Grouting technology is widely used in the field of disaster prevention and in the control of underground engineering. Ordinary Portland cement based grouts are the most widely used grouting material at present. But it has the shortcomings of high energy consumption and high engineering cost. The development of a solid waste grouting material has become a current research effort in the field. This study examined the effect of incorporating gypsum dihydrate (NG), flue gas desulfurization (FGD) gypsum, and phosphogypsum (PG) on the workability and mechanical properties of red mud-slag grouting materials with different gypsum contents. Test results indicate that the incorporation of gypsums can decrease the fluidity and shorten the setting time of red mud-slag grouting materials. All of the specimens tested have rheological characteristics which follow the Herschel-Buckley model. All of the different gypsums significantly increased the compressive strength of the grout samples. Analysis of the hydration process, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), infrared spectroscopy (IR), and scanning electron microscopy - energy dispersive spectrometry (SEM-EDS) showed that the increase in the compressive strength was due to the increase in the concentration of Al3+ and Si4+ leached from red mud and slag in the presence of SO42- and the generation of additional C-S-H. Fe3+ was shown to participate in the hydration process of the grout in the presence of SO42-. These results could lead to high-performance, low-cost grouting materials for grouting engineering, and promote the synergistic utilization of slag, red mud, and solid waste gypsum, to protect the ecological environment. (C) 2019 Elsevier Ltd. All rights reserved.