大流动性混凝土均匀性控制与抗裂技术研究

发布时间：2018-05-28 11:44

本文选题：大流动性混凝土 + 抗裂辅料　；参考：《东南大学》2017年硕士论文

【摘要】：随着中国经济的快速发展,政府在基建类项目上大力投资,因此对混凝土需求量逐年增大。现代高性能混凝土提高流动性以便于泵送施工,但大流动性混凝土的开裂问题一直困扰着工程技术人员。人们试图通过增加配筋和降低混凝土收缩来减小混凝土开裂倾向,但收效甚微,大流动性混凝土均匀性差和易开裂的问题仍没有得到很好的解决。均匀性主要是骨料在混凝土中均匀分布的程度,它是影响混凝土抗裂性能的重要因素,本文研究了大流动性混凝土均匀性的检测和表征方法,提出采用混凝土离析率、内外混凝土密度差和内外混凝土粗骨料质量差来表征新拌混凝土均匀性,采用超声波声速表征硬化混凝土均匀性,还可以采用图像处理法精确描述和研究混凝土内部结构的均匀性。影响混凝土均匀性的因素包括原材料质量,如砂石级配;混凝土配比参数,如水胶比、砂率和减水剂掺量;混凝土和易性,如流动性、保水性和粘聚性;还有施工控制和振动时间。而关键因素则是混凝土流动性和振动时间。均匀性差的混凝土局部表现出砂浆或净浆的特点,其抗压强度降低、收缩增大,抗裂性能明显下降。本文提出用混凝土超声波声速的不均匀度大小来判断混凝土的不均匀性,不均匀度越小,混凝土的均匀性越好,混凝土干燥收缩率越低,抗裂性能和抗氯离子渗透性能增强。混凝土均匀性影响因素较多,流动性、砂率、水胶比、振动时间对混凝土均匀性的影响各不相同;在不改变其它条件的前提下,根据混凝土均匀性表征结果,研究混凝土均匀性对其强度和耐久性能的影响。通过改善混凝土和易性来提升混凝土均匀性,改善混凝土和易性主要从两个方面实施,一方面控制原材料质量与优化混凝土配合比参数;另一方面,在混凝土施工过程中,要严格控制配料的准确性、搅拌均匀性和成型的密实性,特别是控制好混凝土的流动性和振捣时间。本文分析了大面积混凝土易开裂的原因,使用研制的抗裂辅料掺入混凝土表层,通过改善混凝土表层均匀性可以显著提高混凝土表层抗裂性能,针对不同强度等级的混凝土选用相应的抗裂辅料,可使其抗塑性开裂性能提升95%。对低水胶比高自收缩的高强混凝土,采用掺轻质粒内养护技术,内养护效果明显,提高了混凝土的强度,降低了混凝土的收缩,提高了混凝土抗裂性能和抗硫酸盐侵蚀能力。
[Abstract]:With the rapid development of China's economy, the government has invested heavily in infrastructure projects, so the demand for concrete is increasing year by year. Modern high performance concrete (HPC) improves fluidity in order to facilitate pumping construction, but the cracking problem of high fluidity concrete has been puzzling engineers and technicians. People try to reduce the cracking tendency of concrete by increasing reinforcement and reducing concrete shrinkage, but there is little effect. The problems of poor uniformity and easy cracking of large fluidity concrete have not been solved well. Homogeneity is mainly the degree of uniform distribution of aggregate in concrete. It is an important factor that affects the crack resistance of concrete. In this paper, the detection and characterization method of homogeneity of high fluidity concrete is studied, and the segregation rate of concrete is proposed. The uniformity of freshly mixed concrete is characterized by the density difference of inner and outer concrete and the quality difference of coarse aggregate of inner and outer concrete, and the uniformity of hardened concrete is characterized by ultrasonic sound velocity. Image processing method can also be used to accurately describe and study the homogeneity of concrete internal structure. Factors affecting the homogeneity of concrete include raw material quality, such as gradation of sand and stone; concrete proportioning parameters, such as water-binder ratio, sand ratio and water reducer content; concrete and easiness, such as fluidity, water retention and agglomeration; There is also construction control and vibration time. The key factors are concrete fluidity and vibration time. The concrete with poor homogeneity shows the characteristics of mortar or mortar, its compressive strength decreases, its shrinkage increases, and its crack resistance decreases obviously. In this paper, it is proposed that the unevenness of ultrasonic velocity of concrete be used to judge the inhomogeneity of concrete. The smaller the unevenness of concrete is, the better the uniformity of concrete is, the lower the drying shrinkage of concrete is, the stronger the crack resistance and chloride ion permeability are. There are many factors affecting the homogeneity of concrete, such as fluidity, sand ratio, water / binder ratio, vibration time and so on. The influence of the uniformity of concrete on its strength and durability was studied. To improve the uniformity of concrete through improving concrete and easiness, the improvement of concrete and ease is mainly carried out from two aspects: on the one hand, controlling the quality of raw materials and optimizing the parameters of concrete mix ratio; on the other hand, in the process of concrete construction, It is necessary to strictly control the accuracy of ingredients, mixing uniformity and compactness, especially the fluidity and vibrational time of concrete. In this paper, the causes of cracking in large area concrete are analyzed. The crack resistance of concrete surface can be improved by adding the crack resistant adjuncts to the surface layer of concrete by improving the uniformity of the surface layer of concrete. The crack resistance of concrete with different strength grades can be improved by 95% by selecting corresponding crack resistant adjuncts. For high strength concrete with low water-binder ratio and high autogenous shrinkage, the effect of internal curing is obvious, the strength of concrete is improved, the shrinkage of concrete is reduced, and the crack resistance and sulfate corrosion resistance of concrete are improved.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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