Study on the Mechanical Properties and Microstructure of Soil Stabilized with Alkali-Activated Slag–Steel Slag–Silica Fume

ABSTRACT In order to solve the problem of low comprehensive utilization rate of industrial solid waste, this article focuses on the three problems of slag, which are steel slag, reuse of silica fume, and the strength enhancement and microscopic mechanism of slag-steel slag-silica fume composite material; analyzes the macro strength of the mixture under different curing ages from the two indexes of unconfined compressive strength and splitting tensile strength; and conducts microscopic tests such as X-ray diffraction, scanning electron microscopy, and Fourier transform infrared. The internal mechanism of hydration product formation and strength change of slag and steel wollastonite cementitious material under the excitation of sodium hydroxide and sodium silicate mixed solution as alkali activator was discussed. The strength results show that when the optimum mixture ratio of slag: steel slag: silica fume is 6:3:1, the modulus of lye is 1.2, the content of lye is 6 %, and the compressive strength of slag-steel slag-silica fume base polymer reaches 2.44 MPa under the standard curing condition of 28 day. The results show that the hydration products of geopolymer mainly consist of calcium-silicate-hydrate (C-S-H) gel and a small amount of ettringite (AFt) crystal. The addition of slag reduces the calcium/silicon ratio and increases the aluminum/silicon ratio, which makes the gel polymerization degree increase. C-S-H gel can be formed by the reaction of calcium hydroxide and silicon dioxide produced by steel slag hydration. Silica fume can provide highly reactive silicon for the system, and its seed effect and pozzolanic effect can accelerate the hydration process of the system.