Experimental study on thermal and mechanical properties of cemented paste backfill with phase change material

The structural safety and thermal properties of cemented paste backfill (CPB) are the key factors to realize geothermal exploitation by using CPB. In this paper, taking the gold tailing-based consolidated backfill body as research object, thermal conductivity, specific heat capacity, density and compressive strength of backfill body were tested by changing the proportioning of backfill materials, the effects of slurry concentration, cement-tailing ratio, phase change material (PCM) addition and other factors on thermal and mechanical properties of backfill body were analyzed. The results show: for backfill body without paraffin, the larger the slurry concentration or cement-tailing ratio, the better the thermal conductivity, specific heat capacity, density and compressive strength. The addition of PCM, paraffin, makes the structure of backfill body lose, and thermal conductivity, density and compressive strength decrease, the average reduction rate is 25.6 %, 12.3 % and 18.7 % respectively, but specific heat capacity increases, the average growth rate is 12.5 %. The increase of specific heat capacity and the existence of phase-change latent heat make backfill body have better heat storage performance. When paraffin is added to backfill body, the larger the cement-tailing ratio, the higher the increase degree of compressive strength with increasing slurry concentration; the higher the slurry concentration, the more obvious the effect of increasing cement-tailing ratio on improvement of compressive strength. Therefore, the weakening of mechanical properties for backfill body caused by the addition of PCM can be improved by increasing slurry concentration or cement-tailing ratio appropriately. The research results provide basic data for the research on thermal and mechanical properties of backfill body with PCM, and also provide theoretical reference for the research on technical system of ore deposit-geothermal collaborative mining, which is mainly based on thermal storage backfill body.