Utilization of marine dredged soil in controlled low-strength material used as a thermal grout in geothermal systems

Abstract

Abstract To date, controlled low-strength material (CLSM) has been used widely 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. In this study, a newly developed CLSM, a blend of natural sand, marine dredged soil (MDS), and binders, was investigated and evaluated for the feasibility of it being used in geothermal systems. In addition to its general properties (flowability, fresh density, and unconfined compressive strength), thermal conductivity (i.e., heat transfer capacity), bleeding rate (i.e., involving volume compensation for boreholes), and environmental impacts (i.e., involving the potential risk of water pollution) were broadly investigated in this study. A bleeding-rate-based volume compensation concept is described for an actual large-scale geothermal system to evaluate total cost. All of the prepared CLSM mixtures performed well in terms of general and environmental characteristics. Moreover, the thermal conductivity of the developed CLSM-based grout was much higher than that of conventional grouts (i.e., bentonite and silicate sand). More importantly, an outstandingly positive effect of MDS was discovered: a sufficient addition of MDS to CLSM-based grout can lead to a considerable decrease in bleeding rate; hence, to only a small volume compensation of required boreholes. Ultimately, the total cost for geothermal construction can be reduced.