【摘要】：目前,國內(nèi)外關于混凝土耐久性的研究成果顯著,但在混凝土結(jié)構(gòu)的安全檢測與評價方面仍有待改進。無損檢測技術(shù)作為一種經(jīng)濟、合理、簡捷、高效的檢測手段,經(jīng)常應用于混凝土檢測中。通過對凍融循環(huán)作用下的混凝土應力波傳播特性進行研究,可為混凝土的耐久性研究提供參考,同時對水利工程的安全與運行具有十分重要的現(xiàn)實意義。本文通過室內(nèi)凍融試驗,對凍融循環(huán)作用下的混凝土彈性波波速、動彈性模量等進行測試,研究不同水灰比、引氣劑摻量、凍融次數(shù)對彈性波波速、動彈性模量的影響規(guī)律,分析彈性波波速與動彈性模量之間的關系,建立混凝土凍融損傷模型。本文的主要研究內(nèi)容及結(jié)論如下:1)采用沖擊彈性波無損檢測技術(shù)對凍融循環(huán)作用下混凝土試件的彈性波傳播特性進行研究,分析不同水灰比、引氣劑摻量及凍融循環(huán)次數(shù)時的混凝土試件的彈性波傳播規(guī)律。試驗結(jié)果表明:在未添加引氣劑的試件中,隨著凍融次數(shù)的增加,試件的彈性波波速都會減小;試件的水灰比越小,彈性波波速越大;水灰比越大,彈性波波速的下降速度越快。添加引氣劑對混凝土試件的彈性波波速產(chǎn)生一定的影響,會使其彈性波波速減少,不過引氣劑的添加也會讓彈性波波速的衰減過程更為平緩,衰減幅度變小。2)通過對凍融循環(huán)作用后的混凝土試件的動彈性模量進行測試,研究水灰比、引氣劑摻量以及凍融循環(huán)次數(shù)等因素對混凝土動彈模的影響規(guī)律。試驗結(jié)果表明:隨著凍融次數(shù)的增加,試件的動彈性模量均在減少;添加引氣劑在一定程度上會引起混凝土試件動彈性模量的減少,但添加引氣劑的混凝土試件的動彈性模量的衰減幅度較小,比未添加引氣劑的混凝土試件的表現(xiàn)更為穩(wěn)定。3)通過分析凍融循環(huán)作用下混凝土動彈性模量與彈性波傳播特性參數(shù)之間的聯(lián)系,建立凍融循環(huán)作用下的混凝土耐久性檢測模型,為混凝土的凍融研究提供新的檢測方法。對試驗中的8組試件的彈性波波速與動彈性模量進行函數(shù)擬合,發(fā)現(xiàn)冪函數(shù)擬合效果較好。分別以動彈性模量、彈性波波速為損傷因子確定混凝土凍融損傷度,分析混凝土凍融破壞程度。4)利用相對動彈性模量以及質(zhì)量損失率作為混凝土是否發(fā)生破壞的判斷依據(jù),結(jié)合試驗成果分析混凝土的凍融破壞情況。
[Abstract]:At present, the research results of concrete durability at home and abroad are remarkable, but the safety detection and evaluation of concrete structures still need to be improved. As an economical, reasonable, simple and efficient testing method, nondestructive testing technology is often used in concrete testing. By studying the propagation characteristics of concrete stress wave under the action of freeze-thaw cycle, this paper can provide a reference for the study of concrete durability, and also has a very important practical significance for the safety and operation of water conservancy projects. In this paper, the elastic wave velocity and dynamic elastic modulus of concrete subjected to freeze-thaw cycle are tested through indoor freezing and thawing tests. The effects of different water / cement ratio, air entraining agent content and freeze-thaw times on the elastic wave velocity and dynamic elastic modulus are studied. The relationship between elastic wave velocity and dynamic elastic modulus is analyzed, and the damage model of concrete freeze-thaw is established. The main contents and conclusions of this paper are as follows: 1) the elastic wave propagation characteristics of concrete specimens subjected to freeze-thaw cycles are studied by using impact elastic wave nondestructive testing technique, and different water-cement ratios are analyzed. The elastic wave propagation law of concrete specimen with air entraining agent and freeze-thaw cycle times. The results show that the elastic wave velocity decreases with the increase of freeze-thaw times, and the smaller the water-cement ratio, the greater the elastic wave velocity. The larger the water-cement ratio, the faster the velocity of elastic wave decreases. The addition of air entraining agent has a certain effect on the elastic wave velocity of concrete specimen, which will reduce the elastic wave velocity, but the air entraining agent will also make the attenuation process of elastic wave velocity more smooth. The attenuation amplitude becomes smaller. 2) by measuring the dynamic elastic modulus of concrete specimens after freeze-thaw cycle, the effects of water / cement ratio, air entraining agent content and freeze-thaw cycle times on the dynamic elastic modulus of concrete are studied. The results show that with the increase of freeze-thaw times, the dynamic elastic modulus of the specimens decreases. The addition of air entraining agent can reduce the dynamic elastic modulus of concrete specimen to some extent, but the attenuation range of dynamic elastic modulus of concrete specimen with air entraining agent is smaller. The performance of concrete specimens without air entraining agent is more stable. 3) the relationship between the dynamic elastic modulus of concrete under freeze-thaw cycle and the parameters of elastic wave propagation characteristics is analyzed. The durability detection model of concrete under freeze-thaw cycle is established, which provides a new testing method for freeze-thaw research of concrete. The elastic wave velocity and dynamic elastic modulus of 8 groups of specimens were fitted by function, and it was found that the power function fitted well. The damage degree of concrete is determined by dynamic elastic modulus and elastic wave velocity. 4) the relative dynamic elastic modulus and mass loss rate are used as the basis for judging whether the concrete is damaged or not. The freeze-thaw failure of concrete is analyzed based on the test results.
【學位授予單位】：重慶交通大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TU528

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