冻融循环作用下PVA纤维混凝土的损伤试验研究

发布时间：2018-04-05 14:08

本文选题：PVA纤维混凝土　切入点：冻融循环　出处：《湖北工业大学》2017年硕士论文

【摘要】：在严寒地区,由于气温正负不断交替,混凝土材料内部往往会遭受一定程度上的冻融损伤。这种损伤对混凝土结构的力学性能、渗透性能以及安全运行都很不利,严重影响其耐久性,导致许多构筑物常常提前发生失效破坏。研究表明,冻融导致混凝土耐久性降低而破坏主要体现在其加剧了混凝土内部原始微裂缝的生长并诱发了新裂缝的出现和发展。在混凝土中掺加PVA纤维能够有效提高其自身的阻裂能力,随着我国经济和技术的向前发展,新型绿色建筑材料PVA纤维以其高抗拉强度、高弹性模量、耐酸碱等特点获得广大学者的重视,其应用也逐渐得到推广,但对PVA纤维混凝土的研究目前仍处于初级阶段,而且多集中在物理力学方面,针对其耐久性的研究鲜有报道。因而,开展对PVA纤维混凝土冻融损伤试验的研究存在重要的意义。本文将冻融循环试验、宏观力学试验和氯离子渗透试验相结合,以纤维掺量和冻融循环次数为考察因素,对PVA纤维混凝土的冻融损伤展开研究,以便为其今后在实际应用中提供参考。论文主要研究工作和得出的结论如下:(1)采用快速冻融法,对普通混凝土和体积掺量依次为0.05%、0.1%、0.2%的PVA纤维混凝土经冻融循环作用后的表观形态、质量损失率、相对动弹性模量进行比较研究。结果表明:PVA纤维的掺入能够增强混凝土的抗冻融剥蚀能力,明显减缓经冻融循环作用后质量和相对动弹性模量的下降速度,提高混凝土的抗冻耐久性能,且体积掺量为0.1%的PVA纤维混凝土呈现出的抗冻融能力最强。(2)对冻融前后PVA纤维混凝土的抗压强度和三点弯折强度进行分析,研究冻融损伤对PVA纤维混凝土力学性能的影响。结果表明:冻融循环次数越高,抗压以及抗折强度的衰减幅度越大。掺入PVA纤维能够有效抑制混凝土内部因冻融产生裂缝的发展,减缓混凝土抗压强度和抗折强度的衰减速率。值得注意的是,PVA纤维对冻融损伤过程中抗折强度的补强作用较大。(3)开展经不同冻融循环次数作用后PVA纤维混凝土的氯离子侵蚀试验,研究冻融损伤对氯离子扩散性能的影响。试验结果表明:冻融循环对PVA纤维混凝土氯离子扩散速度的影响较之于普通混凝土要小;混凝土冻融损伤程度越高,氯离子扩散系数越大,其抵抗氯离子侵蚀能力也就越弱。(4)从宏观损伤理论出发,基于Weibull分布的概率密度函数和损伤变量之间的关系,对试验数据进行拟合,估计模型参数,建立了不同体积掺量PVA纤维混凝土冻融随机损伤演化方程;通过回归分析,建立了氯离子扩散系数与冻融循环次数的关系,进而推导得出了损伤因子与氯离子扩散系数的数学关系表达式。
[Abstract]:In cold regions, due to the continuous alternation of positive and negative temperatures, concrete materials are often damaged by freezing and thawing to some extent.This kind of damage is unfavorable to the mechanical properties, permeability and safe operation of concrete structures, which seriously affects the durability of concrete structures and results in the failure of many structures in advance.The results show that freeze-thaw results in the decrease of durability and the failure of concrete is mainly due to the growth of original micro-cracks in concrete and the emergence and development of new cracks.With the development of economy and technology in our country, the new green building material PVA fiber has high tensile strength and high elastic modulus.The characteristics of acid and alkali resistance have been paid attention to by many scholars and their application has been popularized gradually. However, the research on PVA fiber reinforced concrete is still in the primary stage, and it is mostly focused on physical mechanics. The research on its durability is seldom reported.Therefore, it is of great significance to study the freezing and thawing damage test of PVA fiber concrete.In this paper, the freeze-thaw damage of PVA fiber concrete is studied by combining freeze-thaw test, macroscopic mechanical test and chloride ion permeation test, taking fiber content and freeze-thaw cycle times as the investigation factors.In order to provide reference for its practical application in the future.The main research work and conclusions are as follows: (1) using rapid freeze-thaw method, the apparent morphology and mass loss rate of ordinary concrete and PVA fiber concrete with volume volume of 0.05% 0.2wt% are obtained by freeze-thaw cycle.The relative dynamic modulus of elasticity is compared.The results show that the addition of w / PVA fiber can enhance the anti-freezing and thawing denudation ability of concrete, obviously slow down the decreasing speed of mass and relative dynamic elastic modulus after freeze-thaw cycle, and improve the frost resistance and durability of concrete.The compressive strength and three-point bending strength of PVA fiber concrete before and after freeze-thaw were analyzed, and the effect of freeze-thaw damage on mechanical properties of PVA fiber concrete was studied.The results show that the higher the number of freeze-thaw cycles, the greater the attenuation range of compressive strength and flexural strength.The addition of PVA fiber can effectively inhibit the development of cracks in concrete due to freeze-thaw and slow down the attenuation rate of compressive strength and flexural strength of concrete.It is worth noting that the reinforcing effect of PVA fiber on the flexural strength during freeze-thaw damage is great.) the chloride ion erosion test of PVA fiber concrete after different freeze-thaw cycles is carried out to study the effect of freezing and thawing damage on chloride diffusion property.The results show that the effect of freeze-thaw cycle on the chloride diffusion rate of PVA fiber concrete is smaller than that of ordinary concrete, and the higher the damage degree of concrete is, the greater the chloride diffusion coefficient is.Based on the macroscopic damage theory and the relation between the probability density function of Weibull distribution and damage variables, the experimental data are fitted to estimate the model parameters.The stochastic damage evolution equation of PVA fiber concrete with different volume content was established, and the relationship between chloride diffusion coefficient and freeze-thaw cycle times was established by regression analysis.The mathematical expression between the damage factor and the chloride diffusion coefficient is derived.
【学位授予单位】：湖北工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528.572

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