硫酸盐侵蚀-干湿循环作用对混凝土力学性能与微结构的影响

Study on the sulfate erosion and dry-wet cycling effects on the mechanical performance and microstructure of concrete

针对黄河流域盐渍土分布地区的混凝土结构在硫酸盐侵蚀作用下的破坏问题,开展硫酸盐侵蚀-干湿循环作用后的物理、力学和微观试验。通过测量不同氯盐侵蚀-干湿循环次数下的试样质量和密度损失率定量表征混凝土结构损伤程度;通过开展单轴压缩试验混凝土力学行为的变化规律进行了研究;最后利用XRD衍射试验和SEM扫描电子显微镜对混凝土的矿物成分与微观结构进行了探测。试验结果表明:在硫酸盐侵蚀-干湿循环作用下,混凝土的结构完整性不断下降,质量和密度损失率呈上升趋势,且上升速率先快后慢;混凝土的强度指标-单轴压缩强度、弹性模量随循环次数增加逐渐衰减,衰减速率先快后慢,而变形性能指标-峰值应变与弹性模量-循环次数的曲线呈反对称分布;依据XRD衍射试验结果,推断硫酸盐溶液对混凝土的腐蚀效应主要是由于水泥水化物与硫酸离子发生了化学反应;由SEM试验观察到水泥水化物在硫酸盐侵蚀-干湿循环次数过程中不断流失,裂隙规模不断扩大。

According to the problem of concrete structure damage under the action of sulfate erosion in the salinized soil distribution area in the Yellow River Basin,the physical,mechanical and microcosmic experiments after the action of sulfate erosion-wet and dry cycle were carried out.The damage degree of concrete structure was quantitative discussed by measuring the sample quality under different salt erosion and dry-wet cycles.Then,the mechanical behavior of salt erosion coupled with dry-wet cycle was studied by unconfined compression test.Finally,XRD diffraction test and SEM scanning electron microscope were used to detect the mineral composition and microstructure of concrete.The results show that the process of sulfate erosion and dry-wet cycle deepens the damage degree of concrete samples continuously.The mass loss rate and density change rate of concrete are increasing due to the gradual peeling and reduction of cement gel.The strength indexes of concrete-uniaxial compressive strength and elastic modulus gradually attenuated with the increase of cycles,and the decay rate was first faster and then slower,while the curve of deformation performance indexes-peak strain and elastic modulus-cycles showed an anti-symmetric distribution.According to the results of XRD diffraction experiments,it is inferred that the corrosion effect of salt solution on concrete is mainly due to the chemical reaction in the cement gel.It was observed by SEM tests that the cement gel of concrete was continuously lost in the process of chemical reaction with ions in salt solution,and the crack scale was continuously enlarged.