Ultrasonic assessment and finite element modelling of thermo-mechanical damage in mortar

ABSTRACT Experiments were conducted to evaluate degradation of mechanical properties in mortar specimens subjected to thermal and mechanical loading. Ultrasonic pulse velocity was used to assess changes in the microstructure of the specimens due to thermal and mechanical loads applied separately. Both longitudinal and transverse waves were used. At first the specimens were tested in the undamaged stage, and then they were also tested after their exposure to a non-uniform thermal load only, finally, mechanical loading was applied until peak load. A finite element model was used in the dynamic simulation of pulses propagation. Results showed that mortar mix with a larger proportion of coarser aggregates is more sensitive to mechanical loading after exposure to heat than mortar with lesser and smaller aggregate contents. Mortar mix design with less and finer aggregate did not show a reduction in the pulse velocity as intense as the mortar with more coarse aggregate, which indicates a less severe diffuse microcracking.

摘要 本研究开展实验以评估受热与力学荷载作用后砂浆试件的力学性能退化情况。采用超声波脉冲速度（Ultrasonic pulse velocity）法，分别针对单独施加热荷载与单独施加力学荷载的工况，评估试件微观结构的变化，测试过程中同时使用纵波与横波。实验流程为：首先对未受损伤的原始试件进行测试，随后对仅承受非均匀热荷载的试件开展检测，最后对试件施加力学荷载直至达到峰值荷载。本研究采用有限元模型（finite element model）对脉冲传播过程进行动力学模拟。实验结果表明，相较于粗骨料占比更低、粒径更小的砂浆配合比，粗骨料占比更高的砂浆配合比在受热后对力学荷载更为敏感。采用少而细骨料的砂浆配合比，其脉冲速度衰减幅度不及粗骨料占比更高的砂浆，这表明前者的弥散微裂纹发育程度更轻。