Utilization of by-product in controlled low-strength material for geothermal systems: Engineering performances, environmental impact, and cost analysis

This paper evaluates the feasibility of by-product-based controlled low-strength material (CLSM) as a grout for geothermal systems. Quartz-based mine tailings and pond ash were adopted as filler and fine aggregates, respectively. Settlement, compressive strength, and thermal conductivity, required for grout for geothermal systems were investigated and the leaching behavior of toxic elements from the CLSM was evaluated. In addition, a cost analysis for actual construction sites of the geothermal system was conducted using a design program. The high-workable CLSM with tailings and pond ash satisfied the strength specified in the ACI 229R and its thermal conductivity was higher than that of conventional grout, i.e., bentonite-sand mixture. The CLSM made only with tailings satisfied the 'Treatment Standard for Hazardous Wastes' in the Code of Federal Regulations of US governments (40 CFR 268.40), whereas that with both tailings and pond ash did not. The total construction costs of the geothermal system reduced up to 20.8% when utilizing the by-product-based CLSM compared with conventional grout.