Thermal Conductivity of Controlled Low Strength Material (CLSM) Made with Excavated Soil and Coal Ash

This paper focused on the quantitative evaluation of thermal conductivity of CLSM made with excavated soil and coal ash for a possible use as thermal grout for borehole heat exchangers. In a preliminary study, control mixtures were produced with Portland cement or cementless binder, Class F fly ash, and ponded ash. Then, for other mixtures, excavated soil substituted for ponded ash in amounts of 10, 20, 30, and 40% by weight. A series of laboratory tests including bleeding, flowability, initial setting time, and unconfined compressive strength were carried out in accordance with applicable ASTM Standard. Afterward, thermal conductivity was measured by using thermal needle probe, conforming ASTM D 5334 to verify the feasibiliy as thermal grout for borehole heat exchangers. The test results presented herein showed that the engineering properties of CLSM with excavated soil, possibly up to 30%, satisfied the specifications of ACI 229R. Moreover, an increase of excavated soil amount in CLSM could lead an improvement in thermal conductivity.