混凝土在硫酸盐侵蚀和干湿循环共同作用下耐久性研究

发布时间：2018-01-26 11:46

本文关键词： 混凝土耐久性干湿循环硫酸盐侵蚀损伤演化方程　出处：《西安建筑科技大学》2013年硕士论文　论文类型：学位论文

【摘要】：混凝土的硫酸盐侵蚀是一个很常见的耐久性问题，且造成的损失很严重。国内外学者已经进行了大量研究。但由于考虑的因素、遵循的标准不同，相互之间有比较大的差异性，可以说目前对混凝土硫酸盐侵蚀的研究是非常混乱的。硫酸盐和干湿循环共同作用时对混凝土造成的损伤比两种条件单独作用时更大，且实际环境中的腐蚀都不是单一因素作用，研究两种因素共同作用的情况将更有实际意义。本文采用的试验制度是先将混凝土试块浸泡7d，然后自然晾置8d，试验共计360d。每隔30d对试块进行以下指标的测试：1）抗压强度；2）质量损失；3）动弹性模量；4）混凝土损伤层厚度和损伤层超声波速。最后使用扫描电子显微镜观察腐蚀产物的生成情况。试验考察了水胶比、Na2SO4溶液浓度和矿物掺合料的影响，结合宏观试验和电镜扫描结果对混凝土的损伤机理进行了分析，建立了基于动弹模量Ed的损伤演化方程。综合分析结果，将混凝土在干湿循环和硫酸盐侵蚀共同作用下的腐蚀过程分为四个阶段：第一个阶段是硫酸盐物理结晶的膨胀应力起主要作用，，混凝土内部有少量裂缝产生，密实性有所下降，造成混凝土的动弹模量降低。由于混凝土的水化作用，混凝土的强度有所增加；第二个阶段化学腐蚀不断加重，腐蚀产物增多，部分地填充了混凝土的孔隙，延缓混凝土密实性的降低，这一阶段混凝土的质量和强度都开始下降，而动弹模量降低得比之前慢；第三阶段是由于物理、化学作用的加剧致使各个性能指标的退化，混凝土的质量、动弹模量和抗压强度都出现下降；第四阶段是加速劣化阶段，混凝土试块表层剥蚀和脱落，边角出现大量裂缝，这个阶段内混凝土的各个指标均加速降低。本文第五章从损伤层厚度的角度对混凝土的损伤情况进行了分析。根据超声波在混凝土中的传播速度计算混凝土的损伤层厚度。损伤层厚度的变化和宏观试验结果大体相符合，损伤层厚度的变化基本上可以反映混凝土的损伤情况。
[Abstract]:Sulfate erosion of concrete is a very common durability problem, and the loss caused by it is very serious. Many domestic and foreign scholars have done a lot of research. However, due to the factors considered, the standard is different. There are great differences between each other. It can be said that the present study on sulfate erosion of concrete is very confusing. The damage to concrete caused by the combined action of sulfate and dry and wet cycle is greater than that of the two conditions alone. And the corrosion in the actual environment is not a single factor, so it will be more meaningful to study the interaction of the two factors. The test system adopted in this paper is to soak the concrete test block for 7 days, then set it naturally for 8 days, for a total of 360 days. The compressive strength of the test piece is tested on the following indexes: 1) every 30 days; 2) quality loss; 3) dynamic elastic modulus; 4) thickness of concrete damage layer and ultrasonic velocity of damage layer. Finally, the formation of corrosion products was observed by scanning electron microscope (SEM). The water-binder ratio was investigated experimentally. The damage mechanism of concrete was analyzed by Na2SO4 solution concentration and mineral admixture. The damage evolution equation based on dynamic modulus Ed was established. The results show that the corrosion process of concrete under the combined action of wet and dry cycle and sulfate erosion is divided into four stages: the first stage is the expansion stress of sulfate physical crystallization. There are a few cracks in the concrete and the compactness decreases, which results in the decrease of the dynamic modulus of the concrete. The strength of the concrete increases due to the hydration of the concrete. In the second stage, the chemical corrosion becomes more and more serious, and the corrosion products increase, partly filling the pores of the concrete, delaying the reduction of the compactness of the concrete, and the quality and strength of the concrete begin to decline in this stage. However, the dynamic modulus decreased more slowly than before. The third stage is the deterioration of each performance index due to the aggravation of physical and chemical action, and the decrease of concrete quality, dynamic modulus and compressive strength. In the 4th stage, the accelerated deterioration stage, the surface erosion and shedding of the concrete test block, and a large number of cracks appear in the edge corner, and each index of the concrete is accelerated to decrease in this stage. In chapter 5th, the damage of concrete is analyzed from the point of view of the thickness of damage layer. According to the velocity of ultrasonic wave propagation in concrete, the thickness of damage layer of concrete is calculated. The results were consistent. The change of damage layer thickness can basically reflect the damage of concrete.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528.0

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