循环冲击作用下冻融混凝土-砂岩组合体力学特性试验与分析

Test and analysis of mechanical properties of freeze-thaw damaged concrete-sandstone composite under cyclic impact

  • 摘要: 以寒区隧道开挖过程中衬砌结构承受循环动力扰动和冻融循环为工程背景,开展了冻融后混凝土-砂岩组合体的循环冲击压缩试验,结合NMR和SEM测试手段,研究了砂岩层厚度比和冻融循环次数对混凝土-砂岩组合体孔径分布、应力波波形、峰值应力、变形破坏特征和微观形貌的影响,基于纵波波速的变化定义了能够综合考虑冻融和循环冲击的复合损伤变量。结果表明,随着砂岩层厚度比的增加,组合体试样微孔数量减少、中孔数量显著上升,试样抗循环冲击次数逐渐增多,峰值应力增大。循环冲击次数的增加会导致组合体试样峰值应力和割线模量降低、峰值应变增大。随着冻融循环次数的增加,组合体试样破坏形态由单一主裂纹逐渐演化为多裂纹,砂岩层和混凝土层内部损伤加剧,混凝土层的微裂纹和孔洞的数量与尺寸明显高于砂岩层,且砂岩层内出现明显的沿晶裂纹和穿晶裂纹,但两者的界面未出现明显破坏。混凝土、砂岩、混凝土-砂岩组合体试样的损伤阈值均随冻融循环次数的增加逐渐增大。

     

    Abstract: Based on the engineering background of lining structure subjected to cyclic dynamic disturbance and freeze-thaw (F-T) cycle during tunnel excavation in cold area, the cyclic impact compression tests of F-T damaged concrete-sandstone combination were carried out. The effects of rock layer thickness ratio and F-T cycles on the pore size distribution, stress wave shape, peak stress, deformation and failure characteristics and micro-morphology of composite were studied. In addition, a composite damage variable, which could consider the effects of F-T cycle and cyclic impact, was defined based on the variation of longitudinal wave velocity in the present study. Results showed that with the increase of rock layer thickness ratio, the number of micropores decreased while the number of medium pores increased significantly, meanwhile, both the number of anti-cyclic impact times and the peak stress increased gradually. With the increase of cyclic impact times, both theincrease of F-T cycles, the failure mode of the composite specimen gradually evolved from single main crack to multiple cracks, the internal damage of rock and concrete layers was intensified, and both the number and size of micro-cracks and pores in concrete layer were obviously higher than that in rock layer. Obvious intergranular cracks and transgranular cracks were observed in rock layers, however, no obvious damage occurred at the interface of the above two materials. The damage thresholds of concrete, sandstone and concrete-sandstone composite specimens increased gradually with the increase of F-T cycles.

     

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