砂浆在冻融早期的空间损伤演化机理

Evolution mechanism of spatial damage of mortar in the early freeze-thaw stage

关键词:  冻融早期  空间特征  FBG测试  局部应变  损伤发展

Key words:  early freeze-thaw stage  spatial characteristic  FBG test  local strain  damage development

摘要:

受温度与水分传递方向的影响,砂浆在冻融早期的损伤发展呈现出空间特征。然而,现有冻融损伤监测方法多聚焦于试件整体的平均性能,忽略了局部损伤演化的差异性。为定量评估空间位置对砂浆冻融早期损伤的影响,并深入揭示其演化机制,本文提出一种基于布拉格光纤光栅传感器的实时、原位应变监测方法,并测试了冻融早期砂浆内部不同空间位置的应变。结果表明,在冻融早期阶段,砂浆上层区域应变幅值高于中层；随着冻融循环次数的增加,峰值应变持续上升,残余应变出现；微观形貌分析结果验证了以残余应变判断冻融损伤空间差异的可靠性。基于此,本文进一步构建了考虑空间位置的早期冻融损伤发展模型。由宏观性能测试与局部应变对比分析结果可知,砂浆在冻融早期的损伤以表层开裂为主,虽然该现象对宏观性能弱化的影响较小,但能够为环境水分进入砂浆内部提供新的传输通道,进一步加剧冻融损伤的演化。

Abstract:

Affected by the direction of temperature and moisture transfer, the damage development of mortar in the early freeze-thaw (F-T) stage exhibits spatial characteristics. However, existing F-T damage monitoring methods mostly focus on the overall average performance of specimens, ignoring the differences in local damage evolution. To quantitatively evaluate the influence of spatial position on the early F-T damage of mortar and further reveal its evolution mechanism, this paper proposed a real-time and in-situ strain monitoring method based on fiber bragg grating sensors and tested the strain at different spatial positions inside mortar during the early F-T stage. Results show that the strain amplitude in the upper layer of mortar is higher than that in the middle layer during the early F-T stage; with the increase of F-T cycles, the peak strain continues to rise, and residual strain appears; micro-morphology analysis results verify the reliability of using residual strain to judge the spatial difference of F-T damage. Based on this, this paper further established an early F-T damage evolution model considering spatial position. The comparative analysis results of macroscopic performance tests and local strain show that the damage of mortar in the early F-T stage is dominated by surface cracking. Although this phenomenon has little effect on the degradation of macroscopic performance, it can provide new transmission channels for environmental moisture to enter the interior of mortar, further aggravating the evolution of F-T damage.