高掺合料高强混凝土材料耐久性及受弯梁抗冻性研究

发布时间：2018-04-05 13:32

本文选题：粉煤灰　切入点：矿渣　出处：《东北电力大学》2017年硕士论文

【摘要】：高强混凝土因具有强度高,耐久性好,变形小等优点,能适应现代工程结构向着高层、大跨、重载发展,已经也必将得到更广泛的应用。与此同时,混凝土的耐久性危机也日益显现。寒冷地区的海港及海边建筑物,同时经受着冻融和氯盐侵蚀的双重作用,结构表面出现剥落,钢筋锈蚀等情况,严重影响了建筑物的长期使用和安全运行。因此本文从外加掺合料入手,研究掺量对高强混凝土性能的影响以及氯盐环境下高强混凝土受弯梁的冻融损伤情况,为工程应用提供依据。主要研究内容及结论如下:(1)采用粉煤灰和矿渣作为掺合料,以胶凝材料总量的40%和50%取代水泥配制高强混凝土,通过扫描电镜和X射线衍射技术研究了不同龄期时混凝土的水化产物和水化程度,分析了微观结构变化对宏观强度的影响。结果表明,掺加矿物掺合料的混凝土早期强度较低,7d时矿渣已经开始水化,粉煤灰在早期只起到填充作用,但掺合料混凝土后期强度增长迅速,可以达到基准混凝土的2-5倍。复掺粉煤灰和矿渣的混凝土强度高于单掺矿物掺合料的混凝土,微观试验可以看出二者复掺产生的叠加效应能够促进混凝土的二次水化,产生较多水化产物使结构致密。(2)通过快速冻融试验和电通量试验对不同掺量和复掺比下高强混凝土的抗冻性和抗氯离子渗透性能进行研究,并提出运用抗冻耐久性系数与电通量的比值综合评价高强混凝土的耐久性能。结果表明:在掺合料总量不变的情况下,混凝土的抗冻性和抗氯离子渗透性能均随着粉煤灰掺入量的增加和矿渣掺入量的减小而逐渐提升,但掺合料总质量的增加会降低抗氯离子渗透性能;采用抗冻耐久性指数与电通量之比可较好的综合评价高掺合料高强混凝土的耐久性,耐久性较好的适宜配合比为掺合料总量50%,粉煤灰与矿渣掺量比为4:1。(3)对已有的氯离子侵蚀过程仿真的细胞自动机模型进行改进,引入掺合料的影响因素,建立了掺合料混凝土氯离子侵蚀过程模拟的细胞自动机模型,运用Matlab编制的程序对掺合料混凝土的氯离子侵蚀过程进行数值模拟。结果表明:现场暴露实验结果与模拟结果基本一致,运用细胞自动机原理模拟掺合料混凝土中氯离子的扩散是合理且可行的,且模型更适合模拟混凝土在长期龄期作用下氯离子的侵蚀过程。(4)制作高强混凝土受弯梁(120mm×200mm×1200mm)进行氯盐环境下的气冻气融试验,采用无损检测的方法对冻融后受弯梁的损伤层厚度和混凝土的强度进行检测,并测定冻融循环300次后受弯梁的极限承载力。结果表明:受弯梁的冻融破坏主要表现为细小裂纹的出现及发展,冻融循环300次,受弯梁的极限承载力降低,损伤层厚度不断加深,混凝土强度不断降低,并建立了冻融循环次数与受弯梁损伤层厚度和混凝土强度变化间的关系。
[Abstract]:Because of its advantages of high strength, good durability and low deformation, high strength concrete can adapt to the development of modern engineering structures towards tall buildings, long spans and heavy loads, so it will be used more widely.At the same time, the durability crisis of concrete also appears day by day.The seaports and seaside buildings in cold areas are subjected to the double effects of freezing and thawing and chlorine salt erosion, the spalling of the structure surface and the corrosion of steel bars have seriously affected the long-term use and safe operation of the buildings.In this paper, the influence of admixture on the performance of high strength concrete and the freeze-thaw damage of high strength concrete flexural beam under chloride environment are studied in this paper, which provides the basis for engineering application.The main research contents and conclusions are as follows: (1) fly ash and slag are used as admixtures to prepare high strength concrete with 40% and 50% of total cementing material instead of cement.The hydration products and hydration degree of concrete at different ages were studied by means of scanning electron microscope and X-ray diffraction technique. The influence of microstructure change on macroscopic strength was analyzed.The results show that when the early strength of concrete mixed with mineral admixture is lower than 7 days, slag hydration has begun, and fly ash only plays a filling role in the early stage, but the later strength of concrete with mineral admixture increases rapidly, which can be 2-5 times of that of standard concrete.The strength of concrete mixed with fly ash and slag is higher than that of concrete with single mineral admixture. The microcosmic test shows that the superposition effect can promote the secondary hydration of concrete.Through rapid freeze-thaw test and electric flux test, the frost resistance and chloride ion permeation resistance of high strength concrete with different admixture and compound ratio were studied.The ratio of frost durability coefficient and electric flux is used to evaluate the durability of high strength concrete.The results show that the frost resistance and chloride ion permeability of concrete are improved with the increase of fly ash and the decrease of slag content.However, the increase of the total mass of admixtures will reduce the permeability of chloride ions, and the ratio of freezing durability index to electric flux can be used to evaluate the durability of high strength concrete with high admixture.The suitable mix ratio for durability is the total amount of admixture 50 and the ratio of fly ash to slag is 4: 1. 3) the existing cellular automata model of chloride ion erosion simulation is improved, and the influence factors of the admixture are introduced.The cellular automata model of chloride ion erosion process simulation of admixture concrete was established. The process of chloride ion erosion was simulated by Matlab program.The results show that the results of field exposure experiments are in good agreement with the simulation results. It is reasonable and feasible to simulate the chloride ion diffusion in admixture concrete by using the cellular automata principle.The model is more suitable for simulating the chloride erosion process of concrete under long-term age. (4) making high-strength concrete flexural beam (120mm 脳 200mm 脳 1200mm) to conduct air-freeze-gas melting test in chloride environment.The damage layer thickness and concrete strength of freeze-thaw flexural beams were measured by nondestructive testing method, and the ultimate bearing capacity of the beams after 300 freeze-thaw cycles was measured.The results show that the freeze-thaw failure of bending beams is mainly manifested by the appearance and development of small cracks, 300 cycles of freeze-thaw cycles, the reduction of ultimate bearing capacity, the deepening of damage layer thickness, and the decreasing of concrete strength.The relationship between the number of freeze-thaw cycles and the thickness of damaged layer and the strength of concrete is established.
【学位授予单位】：东北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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