Addition of alkaline solutions and fibers for the reinforcement of kaolinite-containing granite residual soil

Abstract

Granite residual soil (GRS) contains a large amount of kaolinite, which is highly hydrophilic and thus easily disintegrated by water. These characteristics may cause severe landslides and debris flows in some hillslopes composed of GRS. This paper describes an investigation of possible solutions to this problem: the addition of fiber and/or alkaline solutions to GRS to reinforce GRS. The effects of the silica-to‑sodium oxide (SiO2-to-Na2O) molar ratios of alkaline solutions on the static mechanical properties of reinforced GRS and the effects of fiber type on the impact resistance of reinforced GRS are discussed. The reinforcement mechanism, characterized by a combination of techniques, namely X-ray powder diffraction, Fourier-transform infrared spectroscopy, microcomputed tomography, and scanning electron microscopy, is also discussed. Static load test results indicated that the alkaline solution–reinforced GRS with a SiO2-to-Na2O molar ratio of 0.5 exhibited the highest compressive strength (4550 kPa), which is attributable to this reinforced GRS having the lowest porosity (2.3%). The alkaline solution reacted with GRS to form cementitious materials, thereby improving the compressive strength of GRS. Drop weight impact testing showed that fiber-reinforced GRS had dynamic mechanical properties superior to those of pristine GRS, and that in combination with a given alkaline solution, glass fibers reinforced GRS more effectively than basalt fibers. This is because the silicon atoms on the surface of glass fibers participated in the reaction with the alkaline solution, thus forming more cementitious materials. These materials were evenly distributed on the surface of the glass fibers, and thus particles of glass fiber–reinforced GRS were more closely bound to each other than particles of basalt fiber–reinforced GRS particles. These findings suggest that waste GRS, once appropriately reinforced, could be used for the construction of high-strength foundations and embankments.