Workability and Environmental Evaluation of Using Sunflower Stalk Ash as an Alkali Activator with Blast Furnace Slag and Black Rice Hull Ash to Prepare Geopolymer Grouts

To solve the problem of environmental pollution from stockpiling of solid waste and to achieve safe and efficient underground engineering, an environment-friendly waste-based ternary geopolymer grout was developed using blast furnace slag, sunflower stalk ash, and black rice hull ash. KOH-activated grouts were used as the controls. The applicability of grouts with different sunflower stalk ash additions was also investigated. The results showed that the 28-day compressive strength of sunflower stalk ash-activated grout reached 24.31 MPa, which exceeded that of the control group by 163.7%. Potassium and calcium salts, such as fairchildite and magnesium potassium silicate, in sunflower stalk ash promoted the formation of C(K)–A–S–H and C–S–H gels. The carbon emissions calculated from global warming potential in the life cycle assessment of the sunflower stalk ash system were 83.5% lower than those of KOH. The leaching results showed that the concentration of all heavy metals dropped below 0.02 mg/L after 28 days of solidification. The immobilization efficiencies of Cr, Pb, and Zn exceeded 98.65%, indicating the considerable immobilization ability of the sunflower stalk ash-activated grout and that it can be used safely in further applications. These findings provide support for the development of environmentally friendly alkali activator and the preparation of high performance engineering materials.