Effect of degree of saturation on thermal conductivity of CLSM used for a horizontal ground coupled heat pump system

The aim of this paper is to investigate the effect of degree of saturation on thermal conductivity of coal ash based CLSM for an use as backfill material of a Horizontal Ground Coupled Heat Pump system (HGCHP). Initially, a family of coal ash based CLSM mixtures with a variable range of water to binder (W/B) and water to solid (W/S) ratios, different kinds of binders (e.g., cement and Cementless Binder (CB)) were systematically tested in accordance with applicable ASTM Standards to determine general properties of CLSM including bleeding, flowability, fresh unit weight, initial setting time, and unconfined compressive strength. Subsequently, thermal conductivity was measured by using thermal needle probe conforming ASTM D 5334 at various degrees of saturation of CLSM specimens. As a result, the general engineering properties of coal ash based CLSM satisfied the specification of ACI 229R. In addition, a sensitive relationship between degree of saturation and thermal conductivity of prepared CLSM mixtures was achieved, the higher the degree of saturation, the higher the thermal conductivity. This finding is very important when determining a proper thermal conductivity with respect to various degrees of saturation to play a significant role in achieving optimum performance and full potential toward the use of the given CLSM mixtures as a backfill for trenches of HGCHP. Finally, a thermal conductivity prediction equation was proposed as a function of degree of saturation, thermal conductivity under fully saturated and dry states.