循环冻融下寒区工程常用保温材料性能变化试验研究

Laboratory tests on impacts of cyclic freeze-thaw on properties of thermal insulation materials used in cold regions engineering

保温材料广泛应用于寒区工程的诸多领域。然而,在服役过程中,保温材料往往会受到浸水、冻融和盐蚀等多场耦合的循环作用,导致其保温、防水和强度等物理力学性能出现不同程度的退化。目前,保温材料的类型非常多,但其性能和耐久性有所不同,因此科学合理地选择保温材料不仅关系到其长期保温效果,同时对于工程构筑物的长期稳定性具有重要的意义。针对循环冻融作用,选取寒区工程中常用的4种保温材料[聚酚醛(FLK)、聚氨酯(PU)、聚苯乙烯挤塑板(XPS)和聚苯乙烯发泡板(EPS)]开展了浸纯水、浸盐水和干燥状态下的室内冻融循环试验,对经历了不同冻融次数的样品进行了表观密度、吸水率、导热系数、压缩强度、弯曲强度和微观结构系列测试。结果表明:浸润作用对保温材料物理力学性质影响显著,亲水性材料FLK的保温和力学性能退化显著,而憎水性材料PU、XPS和EPS变化相对较小。干燥条件下,冻融循环作用对FLK、XPS和EPS吸水率以及FLK的导热系数影响量值可观,但对4种保温材料的压缩和弯曲强度影响不大。浸纯水和盐水条件下,经历30次冻融循环后,FLK的导热系数增加约50%,弯曲强度降低超过0.3%,EPS的压缩强度降低超过10%。浸盐水后保温材料经历冻融循环作用后其物理力学性能退化程度与浸纯水条件下有所不同,该差异值得关注。通过扫描电镜图像能够识别4种保温材料的孔隙尺寸、孔隙致密度和固体颗粒胶结方式,但对经历冻融循环作用后的变化难以识别和量化。基于试验结果,结合寒区交通工程应用场景,分析了4种保温材料的冻融耐久性,以期服务于寒区交通工程保温材料的合理应用。

Thermal insulation materials(TIMs)are widely used in cold regions engineering. During period of use,TIMs usually suffer cyclic multi-fields coupling actions such as moisture intrusion,freeze-thaw and salt erosion,which can cause degradation of their thermal insulation,waterproof and strength performances. At present,there are many kinds of available TIMs in the market,but their thermal and mechanical properties and durability differ considerably. Thus,for different cold regions engineering,a reasonable selection of TIMs does not only affect their insulation performance but also the long-term stability of the engineering infrastructure. With regard to cyclic freeze-thaw(CFT)actions,four kinds of TIMs widely used in cold regions engineering,including FLK FLOLIC FOAM(FLK),polyurethane(PU),polystyrene extruded board(XPS)and polystyrene foamed boards(EPS),were selected to conducted CFT in dry conditions and after immersed in water and salt solution. After experiencing different numbers of CFT,apparent density,water absorption rate,thermal conductivity,compressive strength,bending strength and micro-structure of the four kinds of TIMs were tested following the related specifications. The results showed that,after immersion,the thermal and mechanical performances of hydrophilic FLK degraded considerably,while these of the other three hydrophobic TIMs changed slightly.In dry conditions,the CFTs caused considerable changes in the water absorption rates of FLK,XPS and EPS and the thermal conductivity of FLK. While for specimens immersed in water and salt solution,after 30CFTs,the thermal conductivity and bending strength of FLK increased by 50% and decreased by exceeding 0.3%,respectively,while the compression strength of EPS decreased more than 10%. After the CFTs,there was considerable difference among changes in physical and mechanical properties of the TIMs immersed in water and salt solution. Through scanning electron microscopy images,the cell scale and density and the cementation mode of solids of the TIMs can be observed. However,changes in micro-structure of the TIMs after CFTs cannot be identified. Based on the test results,the frost durability of the four kinds of TIMs were discussed with regard to their application scenery. It is hoped that this study can provided references for application of TIMs in cold regions engineering.