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The thermal conductivity of cementitious grouts was investigated in order to determine suitability of these materials for grouting vertical boreholes used with geothermal heat pump systems. In addition, other relevant physical and mechanical properties were determined. Emphasis was placed on evaluation of cement-sand grouts to take advantage of ready availability, simplicity, low cost, widespread use for other applications and good thermal properties. Different sand gradations were tested to determine effects on thermal conductivity and compatibility with pumpability requirements. The roles of mix variables such as water/cement ratio and sand/cement ratio were measured. Superplasticizer was used to improve flow characteristics and supplementary cementing materials (fly ash and ground granulated blast furnace slag) were used to improve durability. The compatibility of optimizing thermal conductivity with other property criteria was investigated. The cement-sand grouts were tested for rheological characteristics, bleeding, permeability, bond to HDPE pipe, shrinkage, coefficient of thermal expansion, exotherm, durability and environmental impact. Comparisons were made with conventional neat cement grout to quantity the benefit of adding sand to the grout formulations. It was found that the thermal conductivities of the cement-sand grouts ranged from 1.731 to 2.644 W/m.K (1.000 to 1.528 Btu/hr.ft.(degree)F), depending on sand/cement ratio and sand type. This compares with 0.803 to 0.868 W/m.K for neat cement grouts, 0.75 to 0.80 W/m.K for conventional high-solids bentonite grout and 1.,46 W/m.K for thermally enhanced bentonite. The thermal conductivity of neat cement and bentonitic grouts decreases significantly under drying conditions. The reduction in conductivity of cement-sand grouts depends on mix proportions and is typically 5--11% for the mixes of interest.
The thermal conductivity of cementitious grouts was investigated in order to determine suitability of these materials for grouting vertical boreholes used with geothermal heat pump systems. In addition, other relevant physical and mechanical properties were determined. Emphasis was placed on evaluation of cement-sand grouts to take advantage of ready availability, simplicity, low cost, widespread use for other applications and good thermal properties. Different sand gradations were tested to determine effects on thermal conductivity and compatibility with pumpability requirements. The roles of mix variables such as water/cement ratio and sand/cement ratio were measured. Superplasticizer was used to improve flow characteristics and supplementary cementing materials (fly ash and ground granulated blast furnace slag) were used to improve durability. The compatibility of optimizing thermal conductivity with other property criteria was investigated. The cement-sand grouts were tested for rheological characteristics, bleeding, permeability, bond to HDPE pipe, shrinkage, coefficient of thermal expansion, exotherm, durability and environmental impact. Comparisons were made with conventional neat cement grout to quantity the benefit of adding sand to the grout formulations. It was found that the thermal conductivities of the cement-sand grouts ranged from 1.731 to 2.644 W/m.K (1.000 to 1.528 Btu/hr.ft.(degree)F), depending on sand/cement ratio and sand type. This compares with 0.803 to 0.868 W/m.K for neat cement grouts, 0.75 to 0.80 W/m.K for conventional high-solids bentonite grout and 1.,46 W/m.K for thermally enhanced bentonite. The thermal conductivity of neat cement and bentonitic grouts decreases significantly under drying conditions. The reduction in conductivity of cement-sand grouts depends on mix proportions and is typically 5--11% for the mixes of interest.
Thermal conductivity of cementitious grouts for geothermal heat pumps. progress report fy 1997
by Allan (Autor:in)
1997
58 pages
Report
Keine Angabe
Englisch
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