高温作用后砂岩-混凝土黏结界面拉伸力学特性研究

Study on tensile mechanical properties of sandstone-concrete bonding interface after high-temperature treatment

热灾害频发对地下工程的安全性提出了挑战,尤其围岩-衬砌黏结界面作为地应力传递的“纽带”,对支护结构的稳定至关重要。文章对不同界面粗糙度的砂岩-混凝土组合圆盘开展25~800℃高温处理后的劈裂试验,结合单一材料性能、界面黏结机理和组合圆盘的破裂演化过程,分析了粗糙程度、温度效应对界面拉伸强度和劈裂模式的影响。结果表明:组成围岩-衬砌结构的混凝土和砂岩的物理力学性能均随温度的升高出现一定程度的劣化,且前者受热损伤程度远大于后者。高温作用下,热裂隙并不局限于界面过渡区,而是主要汇集在砂岩和混凝土结构内部;同时,组合体的拉伸强度基本介于两种材料强度之间,说明岩-混凝土黏结界面未必是组合结构的薄弱面。存在以JRC=5.86的阈值粗糙度,砂岩-混凝土组合试样的拉伸强度以此为界先降低而后增强,这种强度变化趋势在25~400℃温度范围内相当显著(降幅介于49.11%~59.31%,增幅达56.13%~69.79%),而600℃和800℃加热后强度变化基本趋于平缓(降低24.09%~28.85%,无明显回升)。破裂演化过程表明,随着加热温度的提高,组合试样的劈裂模式由端部压剪破坏向中部拉伸破坏过渡;增大界面粗糙度使得界面从端部单点起裂向多点复合断裂转变。

Heat-calamities threaten the safety of underground engineering.As the link of in-situ stress transmission,the rock-lining interface is critical to the stability of the support structure.Splitting tests were conducted on sandstone-concrete discs with different joint roughness coefficients subjected to a heated temperature ranging from 25 to 800℃.Combined with properties of a single medium,the bonding mechanism and failure evolution of composites,the effects of roughness and temperature on the strength characteristics and failure mode of bonding interfaces are analyzed.The thermal physical and mechanical properties of concrete and sandstone deteriorate to a certain extent,and the thermal damage degree of the former is much greater than that of the latter.Because of heated treatments,the thermal cracks don’t gather in the transition zone of sandstone-concrete interface,but in the interior of sandstone and concrete.The tensile strength of composites ranges between those of the two media,indicating that the bonding interface may not be the weak link of overall structures.With the threshold roughness of 5.86,the tensile strength decrease first and then increase,which is quite significant in the temperature range of 25~400℃(reduce by 49.11%~59.31%,and then rise by 56.13%~69.79%).Nevertheless,the strength variation would tend to be gentle after treatment at 600 and 800℃(reduce by 24.09%~28.85%,and no rise).The failure evolution process shows that the splitting mode transitions from end shear-compression failure to the middle tensile failure with the increase of heat temperature.Increasing the interfacial roughness will make the failure mode change from single-point mode to multi-point mixed mode.