本文選題：PVA纖維混凝土　切入點(diǎn)：凍融循環(huán)　出處：《湖北工業(yè)大學(xué)》2017年碩士論文

【摘要】：在嚴(yán)寒地區(qū),由于氣溫正負(fù)不斷交替,混凝土材料內(nèi)部往往會(huì)遭受一定程度上的凍融損傷。這種損傷對(duì)混凝土結(jié)構(gòu)的力學(xué)性能、滲透性能以及安全運(yùn)行都很不利,嚴(yán)重影響其耐久性,導(dǎo)致許多構(gòu)筑物常常提前發(fā)生失效破壞。研究表明,凍融導(dǎo)致混凝土耐久性降低而破壞主要體現(xiàn)在其加劇了混凝土內(nèi)部原始微裂縫的生長并誘發(fā)了新裂縫的出現(xiàn)和發(fā)展。在混凝土中摻加PVA纖維能夠有效提高其自身的阻裂能力,隨著我國經(jīng)濟(jì)和技術(shù)的向前發(fā)展,新型綠色建筑材料PVA纖維以其高抗拉強(qiáng)度、高彈性模量、耐酸堿等特點(diǎn)獲得廣大學(xué)者的重視,其應(yīng)用也逐漸得到推廣,但對(duì)PVA纖維混凝土的研究目前仍處于初級(jí)階段,而且多集中在物理力學(xué)方面,針對(duì)其耐久性的研究鮮有報(bào)道。因而,開展對(duì)PVA纖維混凝土凍融損傷試驗(yàn)的研究存在重要的意義。本文將凍融循環(huán)試驗(yàn)、宏觀力學(xué)試驗(yàn)和氯離子滲透試驗(yàn)相結(jié)合,以纖維摻量和凍融循環(huán)次數(shù)為考察因素,對(duì)PVA纖維混凝土的凍融損傷展開研究,以便為其今后在實(shí)際應(yīng)用中提供參考。論文主要研究工作和得出的結(jié)論如下:(1)采用快速凍融法,對(duì)普通混凝土和體積摻量依次為0.05%、0.1%、0.2%的PVA纖維混凝土經(jīng)凍融循環(huán)作用后的表觀形態(tài)、質(zhì)量損失率、相對(duì)動(dòng)彈性模量進(jìn)行比較研究。結(jié)果表明:PVA纖維的摻入能夠增強(qiáng)混凝土的抗凍融剝蝕能力,明顯減緩經(jīng)凍融循環(huán)作用后質(zhì)量和相對(duì)動(dòng)彈性模量的下降速度,提高混凝土的抗凍耐久性能,且體積摻量為0.1%的PVA纖維混凝土呈現(xiàn)出的抗凍融能力最強(qiáng)。(2)對(duì)凍融前后PVA纖維混凝土的抗壓強(qiáng)度和三點(diǎn)彎折強(qiáng)度進(jìn)行分析,研究凍融損傷對(duì)PVA纖維混凝土力學(xué)性能的影響。結(jié)果表明:凍融循環(huán)次數(shù)越高,抗壓以及抗折強(qiáng)度的衰減幅度越大。摻入PVA纖維能夠有效抑制混凝土內(nèi)部因凍融產(chǎn)生裂縫的發(fā)展,減緩混凝土抗壓強(qiáng)度和抗折強(qiáng)度的衰減速率。值得注意的是,PVA纖維對(duì)凍融損傷過程中抗折強(qiáng)度的補(bǔ)強(qiáng)作用較大。(3)開展經(jīng)不同凍融循環(huán)次數(shù)作用后PVA纖維混凝土的氯離子侵蝕試驗(yàn),研究凍融損傷對(duì)氯離子擴(kuò)散性能的影響。試驗(yàn)結(jié)果表明:凍融循環(huán)對(duì)PVA纖維混凝土氯離子擴(kuò)散速度的影響較之于普通混凝土要小;混凝土凍融損傷程度越高,氯離子擴(kuò)散系數(shù)越大,其抵抗氯離子侵蝕能力也就越弱。(4)從宏觀損傷理論出發(fā),基于Weibull分布的概率密度函數(shù)和損傷變量之間的關(guān)系,對(duì)試驗(yàn)數(shù)據(jù)進(jìn)行擬合,估計(jì)模型參數(shù),建立了不同體積摻量PVA纖維混凝土凍融隨機(jī)損傷演化方程;通過回歸分析,建立了氯離子擴(kuò)散系數(shù)與凍融循環(huán)次數(shù)的關(guān)系,進(jìn)而推導(dǎo)得出了損傷因子與氯離子擴(kuò)散系數(shù)的數(shù)學(xué)關(guān)系表達(dá)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.
【學(xué)位授予單位】：湖北工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TU528.572

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