粉煤灰轻骨料混凝土抗硫酸盐腐蚀及微结构特征研究

发布时间：2018-10-21 10:32

【摘要】：轻骨料混凝土在满足强度要求的同时,既能减轻自重,有效增加桥梁跨径,缩小构件尺寸,减少桥墩数量,又能提高基体抗腐蚀性能,节约基础处理费用等,这一特性将为其在桥梁、高层建筑中的拓展应用提供理论基础,具有重要的应用价值和现实意义。本文以粉煤灰等量取代水泥,制备了用于大跨度桥梁和高层建筑的粉煤灰轻骨料混凝土,并通过系统试验,对轻骨料混凝土进行了早期力学和抗硫酸腐蚀等方面的综合研究。其中包括粉煤灰轻骨料混凝土配合比、拌合物性能以及早期力学性能等。在力学试验基础上,研究了硫酸盐溶液干湿循环,对粉煤灰轻骨料混凝土抗压强度腐蚀影响；与此同时,引入了工业CT试验和压汞试验,对硫酸盐腐蚀后结构内部细观裂纹扩展规律和孔隙变化作出了系统评价,总结了其相关影响因素。主要研究成果如下：(1)在配合比试验基础上,研究了粉煤灰等级、粗细骨料类型以及粗骨料预湿时间对轻骨料混凝土工作性能影响。结果表明,随粉煤灰细度的增加,轻骨料混凝土工作性能明显提高；相比于破碎型轻骨料混凝土,在相同配合比条件下,圆球型轻骨料混凝土流动性较好,但保水性有所降低,有离析现象产生；在相同水胶比条件下,砂细度模数在2.4～2.8区间时,轻骨料混凝土基本性能将达到最优值。(2)不同细度等级、不同掺量粉煤灰等量取代水泥,并研究了其对轻骨料混凝土力学性能影响。结果表明,由于粉煤灰早期活性较低,轻骨料混凝土3d抗压强度均低于基准样,粉煤灰细度越高,轻骨料混凝土强度上升越快,超过28d抗压强度影响较小。(3)用一级粉煤灰等体积取代30%普通砂,与此同时,用超细粉煤灰或者硅灰等量取代水泥,研究其对轻骨料混凝土抗硫酸盐腐蚀性能影响。结果表明,Na2S04溶液浓度在0-10%范围内,粉煤灰轻骨料混凝土抗压强度在干湿循环20次时达到最高值,超过20次后强度下降较快：在于湿循环条件下,矿物掺合料能在一定程度上提高了轻骨料混凝土抗蚀性,同时,还增强了轻骨料与砂浆界面粘结性能,优化了浆-骨界面过渡区,延缓了SO42-对结构基体的进一步侵蚀。(4)在制备粉煤灰轻骨料混凝土基础上,引入压汞试验,研究了矿物掺合料对轻骨料混凝土内部孔隙影响。结果表明,矿物掺合料使轻骨料混凝土内部孔径明显减小,50～100 nn孔径体积分数明显增多。掺超细粉煤灰或者硅灰后,轻骨料混凝土100nm孔径体积分数分别为普通混凝土的1.39,1.46倍。(5)用破碎型和圆球型页岩陶粒,在制备两种不同轻骨料混凝土基础上,引用工业CT试验,研究了干湿循环作用下,硫酸盐溶液对轻骨料混凝土断面CT数、裂纹扩展及演变规律影响。结果表明,在浓度为5%的Na2SO4溶液作用下,干湿循环50次后,轻骨料混凝土破坏面主要表现为贯穿骨料破坏；由轻骨料混凝土断面CT数-应力关系曲线可知,试样从微裂纹产生到整体破坏大体可分为四个阶段：压密、裂纹萌生发展、裂纹扩展贯通和破坏。
[Abstract]:While the lightweight aggregate concrete meets the strength requirement, the lightweight aggregate concrete can reduce the dead weight, effectively increase the span of the bridge, reduce the size of the member, reduce the number of piers, improve the corrosion resistance of the base body, save the foundation treatment cost and the like, The development and application of high-rise buildings provide theoretical foundation, which has important application value and practical significance. In this paper, fly ash lightweight aggregate concrete for large-span bridges and high-rise buildings is prepared by replacing cement with equal amount of fly ash, and comprehensive research on early mechanical and anti-sulfuric acid corrosion of lightweight aggregate concrete is carried out through systematic test. including fly ash lightweight aggregate concrete mix ratio, mix property and early mechanical properties, etc. On the basis of mechanics experiment, the effects of dry and wet cycle of sulfate solution on compressive strength of fly ash lightweight aggregate concrete were studied. In this paper, a systematic evaluation of meso-crack propagation rule and pore variation in the structure of sulfate corrosion has been made, and its related factors are summarized. The main research results are as follows: (1) On the basis of the matching ratio test, the influence of fly ash grade, coarse aggregate type and coarse aggregate pre-wet time on the working performance of lightweight aggregate concrete is studied. The results show that, with the increase of fineness of fly ash, the workability of lightweight aggregate concrete is obviously improved. Compared with the broken lightweight aggregate concrete, the fluidity of the spherical lightweight aggregate concrete is better than that of the broken lightweight aggregate concrete, but the water retention is reduced and the segregation phenomenon is generated. Under the same water-cement ratio, the basic properties of lightweight aggregate concrete will reach the optimum value when the fineness modulus of sand is in the range of 2. 4 ~ 2. 8. (2) Different fineness grades, different amounts of fly ash were substituted for cement, and the mechanical properties of lightweight aggregate concrete were studied. The results show that the compressive strength of lightweight aggregate concrete 3d is lower than that of reference sample, the higher the fineness of fly ash is, the higher the strength of lightweight aggregate concrete rises, and the impact on compressive strength exceeds 28d. (3) replacing 30% of common sand by volume of primary fly ash, meanwhile, replacing cement with ultra-fine coal ash or silicon ash to study its effect on sulfate corrosion resistance of lightweight aggregate concrete. The results show that in the range of 0-10% of Na2S04 solution, the compressive strength of fly ash lightweight aggregate concrete reaches its highest value in 20 times of dry and wet cycle, and the decrease of strength after 20 times is faster: under wet cycle condition, mineral admixture can improve the corrosion resistance of lightweight aggregate concrete to a certain extent. meanwhile, the bonding property between the light aggregate and the mortar interface is enhanced, the transition area of the slurry-bone interface is optimized, and further erosion of the slurry-to-structure matrix is delayed. (4) On the basis of preparing lightweight aggregate concrete with fly ash, mercury pressure mercury test was introduced to study the influence of mineral admixtures on the internal pores of lightweight aggregate concrete. The results show that the pore size of lightweight aggregate concrete is obviously reduced, and the pore volume fraction of 50 ~ 100 parts is obviously increased. The pore volume fraction of lightweight aggregate concrete at 100nm is 1.39, 1.46 times that of ordinary concrete after ultrafine coal ash or silica fume is added. (5) Based on the preparation of two kinds of lightweight aggregate concrete, the influence of sulfate solution on CT number, crack propagation and evolution of lightweight aggregate concrete under wet and wet cycle was studied. The results show that, under the action of Na2SO4 solution with concentration of 5%, after 50 times of dry and wet circulation, the damage surface of light aggregate concrete is mainly caused by the destruction of aggregate, and the CT number-stress relation curve of lightweight aggregate concrete section can be seen. It can be divided into four stages: pressure density, crack initiation development, crack propagation penetration and destruction.
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

【参考文献】