预湿对塑钢纤维轻骨料混凝土抗冻性及微观结构影响研究

发布时间：2018-03-15 10:18

本文选题：预湿　切入点：轻骨料混凝土　出处：《内蒙古科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：轻骨料混凝土作为一种新型建筑材料，具有轻质、高耐久性、经济性突出等诸多优点，然而它存在的一些缺陷：弹性模量小、易产生脆性破坏、工作性与可泵送性难于控制等，严重制约着轻骨料混凝土在土木工程中广泛应用。现有研究表明掺入适量塑钢纤维对轻骨料混凝土的抗折、抗裂及韧性等性能均有不同程度的改善作用。目前工程中普遍通过对陶粒预湿处理1h的方式来改善轻骨料混凝土工作性能，而陶粒饱水状态还会对轻骨料混凝土的强度以及耐久性等产生一定影响。因此需要在综合考虑轻骨料混凝土各方面宏观性能的基础上，来确定陶粒的合理预湿时间。本文选用两种高强陶粒：粉煤灰陶粒和页岩陶粒，分别在四种不同预湿时间下研究陶粒饱水状态对轻骨料混凝土宏观上工作性、强度、抗冻性以及微观上轻骨料－浆体界面过渡区等影响规律，据此来确定陶粒最佳预湿时间，研究结果表明：随着轻骨料吸水率增加，混凝土坍落度经时损失呈减小趋势，尤其在加压预湿处理情况下损失数值最小，表现出较好工作性。塑钢纤维的掺入使轻骨料混凝土受压破坏形态具有一定塑性。7d、14d时，混凝土强度随着陶粒吸水率增加而减小，并且各组试件强度相差较大。但28d、56d时，混凝土强度与陶粒饱水状态关系不大，而主要与轻骨料自身强度有关。轻骨料混凝土的抗冻性随着陶粒吸水率提高而降低，常压预湿处理的陶粒其混凝土抗冻等级大于F300，而加压预湿处理的陶粒其混凝土抗冻等级则没能达到F300，即陶粒加压预湿时混凝土抗冻性严重被削弱。粉煤灰陶粒使用前常压预湿1h即可。而页岩陶粒预湿时间可以根据需求而改变：当注重抗冻性时，常压预湿0.25h～3h；当对工作性要求较高时，，常压预湿3h～6h。加压预湿处理的陶粒其混凝土3d时界面过渡区中存在大量Ca(OH)2晶体，而常压预湿处理情况下很少发现。7d时轻骨料－水泥浆体界面过渡区成为了一个较为密实的整体。28d时常压预湿处理的陶粒其混凝土界面过渡区较为平整、密实，整体性强；而加压预处理的陶粒其混凝土界面区结构相对多孔、疏松、整体性较差。
[Abstract]:As a new type of building material, lightweight aggregate concrete has many advantages, such as light weight, high durability, outstanding economy and so on. However, it has some defects, such as small elastic modulus, easy to produce brittle failure, difficult to control workability and pump ability, etc. The extensive application of lightweight aggregate concrete in civil engineering is seriously restricted. Existing studies show that appropriate amount of plasticized steel fiber can resist the bending of lightweight aggregate concrete. The properties of crack resistance and toughness have been improved to some extent. At present, the work performance of lightweight aggregate concrete is generally improved by pre-wetting ceramsite for 1 hour. The saturated state of ceramsite will also have a certain effect on the strength and durability of lightweight aggregate concrete. Therefore, it is necessary to determine the reasonable prewetting time of ceramic particle on the basis of considering all aspects of macroscopic properties of lightweight aggregate concrete. In this paper, two kinds of high strength ceramsite, fly ash ceramsite and shale ceramsite, were used to study the macroscopic workability and strength of lightweight aggregate concrete under four different prewetting times. According to the influence of freezing resistance and transition zone between lightweight aggregate and slurry on microstructure, the optimum prewetting time of ceramsite is determined. The results show that:. With the increase of water absorption of lightweight aggregate, the slump loss of concrete decreases, especially in the case of pressure-pre-wetting treatment. The strength of the concrete decreases with the increase of the water absorption rate of ceramsite, and the strength of the specimens varies greatly with the increase of the water absorption rate of ceramsite, but at 28 days or 56 days, the strength of the concrete decreases with the increase of the water absorption rate of ceramsite, but at 28 days or 56 days, the strength of the concrete decreases with the increase of the water absorption rate of ceramsite. The strength of concrete is not related to the saturated state of ceramsite, but mainly to the strength of lightweight aggregate. The frost resistance grade of concrete treated by atmospheric prewetting treatment is greater than that of F300, but the frost resistance grade of concrete treated by pressurized prewetting treatment does not reach F300, that is to say, the frost resistance of concrete is seriously weakened when ceramsite is prewetted under pressure. The prehumidification time of shale ceramsite can be changed according to the demand: when it pays attention to frost resistance, it is 0.25h / h for 3 h, and 3h / h when the requirement of workability is higher, while the prewetting time of shale pellet can be changed according to the demand before using fly ash ceramsite at atmospheric pressure for 1h. The prehumidification time of shale ceramsite can be changed according to the demand. There are a large number of Ca(OH)2 crystals in the transition zone of concrete interface after 3 days of pressure-pre-wetting treatment. However, under the condition of atmospheric prewetting treatment, it is seldom found that the transition zone between lightweight aggregate and cement paste becomes a relatively dense interfacial transition zone between lightweight aggregate and cement paste under normal pressure prewetting treatment at 0.28 d. The transition zone of concrete interface is relatively smooth, dense and strong integrity. However, the structure of concrete interface is relatively porous, loose and poor integrity.
【学位授予单位】：内蒙古科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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