温度和应力下能源桩桩身加筋混凝土变形性质试验研究

能源桩是将地埋管换热器置于建筑桩基础中来实现地下换热的一种新型的地源热泵技术。然而，不同季节运行条件下，冷热变化导致的能源桩桩身混凝土的膨胀和收缩会影响能源桩的持续使用甚至危及建筑的安全。因此，寻找到一种温度和轴向应力作用下变形性能较好的桩身混凝土对能源桩技术安全使用和推广至关重要。探讨了桩身素混凝土和掺入不同含 量的钢纤维，聚丙烯纤维桩身加筋混凝土在温度和应力下的变形特性。导热系数测试表明，钢纤维的掺入能提高能源桩桩身混凝土的导热系数，聚丙烯纤维的掺入降低了能源桩桩身混凝土的导热系数。钢纤维掺入量为1.3%时，导热系数最大，为2.44 W/(m·K)；热力学梯级加温试验表明，能源桩桩身混凝土掺入钢纤维，聚丙烯纤维均能有效减小应变，钢纤维最大应变减少量为62.43%，聚丙烯纤维最大应变减少量为61.11%；热力学全过程试验表明，钢纤维能有效减少制冷收缩应变，全过程中应变最小。综合对比3种能源桩桩身混凝土热物性参数及温度和应力作用下变形特性可知，钢纤维加筋混凝土更适合作为能源桩桩身材料。

Experimental study of deformation properties of reinforced concrete in energy piles under temperature and stress

The energy pile is a new type of ground source heat pump technology that places the ground heat exchanger in the building pile foundation to achieve underground heat exchange. However, the expansion and shrinkage of plie materials threat the long-term running and the building safety because that the energy piles often operate in cooling and heating thermal loads at different seasons. Grouting materials with proper thermal-mechanical characteristics are crucial for the safe use and widespread of the energy piles. This paper aims to investigate thermal-mechanical behaviours of concrete piles mixed with different contents of polypropylene fibre and steel fibre. The results show that thermal conductivity increased when adding steel fibre into concrete but decreased when adding polypropylene fibre. The maximum thermal conductivity was measured to be 2.44 W/(m·K) for the concrete mixed with 1.3% steel fibre. The thermodynamic step heating test showed the strain of the concrete reinforced both by steel fibre and polypropylene fibre was effectively reduced. The reductions of concrete reinforced by steel fibre and polypropylene fibre were about 62.43% and 61.11%, respectively. Furthermore, heating expansion and cooling shrinkage strain of concrete reinforced by steel fibre were both reduced during the heating and cooling load testing cycles, and the strain was the minimum in the whole process. Compared with three different types of concrete, steel fibre reinforced concrete is suggested as a suitable material for the grouting of energy piles.