Utilization of controlled low strength material (CLSM) as a novel grout for geothermal systems: Laboratory and field experiments

Abstract

Over the past decade, controlled low-strength material (CLSM) has been used extensively as fill material in flowable fills, structural fills, and void fills. However, owing to its good flowability and low shrinkage, CLSM can be considered a heat transfer medium as long as it has sufficiently high thermal conductivity. The main purpose of this study is to evaluate the use of controlled low strength material (CLSM) as a novel grout for geothermal systems by both laboratory and field experiments. Laboratory tests were performed first on various CLSM mixtures to evaluate their performance on general characteristics coupled with thermal conductivity, and the construction cost analysis. As a laboratory test result, all CLSM mixtures satisfied aspects of the abovementioned properties. In addition, in order to prove the proficiency of CLSM based-grout for geothermal systems, a large-scale test was also conducted to verify the workability and heat exchange rate of CLSM based-grout in the field with five boreholes and two control buildings. The workability of CLSM-based grout from the field tests was in the acceptable requirements reported in ACI 229R, (1999). In addition, the heat exchange rate of the proposed CLSM from the field test was found to be better than that of silicate sand and bentonite (i.e., conventional grouts). In conclusion, good workability and sufficient heat exchange rate obtained from the field test strongly reinforced the feasible use of the proposed CLSM as a thermal grout for geothermal systems.