微胶囊相变材料改良粉质黏土的冻胀特性研究

Study on frost heave of microencapsulated phase change material incorporated silty clay

微胶囊相变材料(microencapsulated phase change material, mPCM)具有出色的储热能力,可以减轻季节冻土在冻结和融化过程中的温度波动。使用扫描电子显微镜、X射线光电子能谱、傅里叶变换红外光谱和热分析等研究手段,全面评估2种分别以硬脂酸丁酯和石蜡为芯材,SiO2为壳材的mPCM(B-PCM, P-PCM)的物化表征,再以兰州地区粉质黏土为研究对象,通过冻融过程和冻胀试验研究4%、8%、10%掺量的mPCM对粉质黏土冻胀特性的影响。试验结果表明:mPCM在相变过程中释放的潜热为土体提供了保温效果,10%添加量的mPCM复合土试样从10℃下降至-10℃所需的时间较于素土试样延长约70%。土体的冻胀变形、冻结深度和含水率变化率随mPCM掺量的提高而降低;B-PCM和P-PCM核壳比的差异导致其冻胀后的水分迁移幅度表现出不同的趋势。总体而言,mPCM对土体的正面影响表现为提升保温性能、抑制冻胀变形等,但其添加量超多8%后会引起土体浅表层的冻胀加剧,这与SiO2壳材的吸水性有关。

Microencapsulated phase change material(mPCM) possess an excellent heat storage capacity, which can mitigate temperature fluctuation of soil during freezing/thawing in seasonal frozen ground. Two types of mPCM with butyl stearate, paraffin as the core material(B-PCM and P-PCM, respectively) and SiO2as shell material are evaluated using Scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infra-red spectroscopy and Thermal analysis, the effects of 4%, 8%, and 10% of mPCM on the frost heave characteristics of the silty clay in Lanzhou are studied through the freeze-thaw process and frost heave tests. The results show that the latent heat released by mPCM in the phase change process provides the soil with a thermal insulation effect, and the elapsed time required for the soil containing mPCM with 10% addition to drop from-10 ℃to 10 ℃ is extended by 71.8%. The frost heave deformation, freezing depth and water content change rate of the soil decrease with the increase of mPCM concentrations;and the differences in core-to-shell ratio between BPCM and P-PCM leads to different trends in the extent of water migration after frost heave. In general, the positive effect of mPCM on the soil is manifested in improving the thermal insulation performance of the soil, inhibiting frost heave deformation, etc. However, adding more than 8% mPCM will increase the frost heave of the superficial layer of the soil, which is related to the water absorption of the SiO2shell material.