本文選題：混凝土 + 尺寸效應(yīng)　； 參考：《燕山大學(xué)》2014年博士論文

【摘要】：混凝土是由水泥砂漿和石子等粗骨料組成的非均勻、各向異性的工程復(fù)合材料。由于其成本低廉，便于運(yùn)輸、施工和容易澆筑成任何形狀，又具有良好的抗凍性、耐腐蝕性和較強(qiáng)的抗壓強(qiáng)度，所以混凝土材料被廣泛的應(yīng)用在工業(yè)和民用等建筑中。但是，在一些重大的事故如地震中房屋的倒塌、一些堤壩的過(guò)早破壞等事件中，人們發(fā)現(xiàn)除去個(gè)別因施工質(zhì)量等因素外，混凝土材料均沒(méi)有達(dá)到設(shè)計(jì)時(shí)的強(qiáng)度就已發(fā)生破壞。后來(lái)經(jīng)過(guò)研究發(fā)現(xiàn)，之所以混凝土結(jié)構(gòu)的構(gòu)筑物遠(yuǎn)低于設(shè)計(jì)值便發(fā)生災(zāi)變破壞，是因?yàn)槿藗儧](méi)有考慮尺寸效應(yīng)的影響。 以往各國(guó)學(xué)者對(duì)混凝土的各種尺寸效應(yīng)研究了很多，本文主要從混凝土試件的不同表面狀態(tài)、不同骨料粒徑這兩種尺寸效應(yīng)來(lái)研究它們對(duì)混凝土試件破壞的影響。本文研究手段主要是借助試驗(yàn)的方法。不同表面狀態(tài)的試件分為澆筑表面的試件和切割表面的試件，澆筑表面試件為在試模里直接澆筑形成，試件外層主要為砂漿層。切割表面試件為由一大塊混凝土試件切割而成，試件外層露出很多粗骨料。不同骨料粒徑的試件為混凝土試件中骨料粒徑分別為5-10mm、5-15mm、5-20mm。 先對(duì)不同的試件進(jìn)行了靜壓試驗(yàn)，對(duì)靜壓試驗(yàn)后試件的強(qiáng)度值、應(yīng)變值進(jìn)行了對(duì)比，并計(jì)算出了各個(gè)試件的吸收能。通過(guò)這些數(shù)值的對(duì)比，發(fā)現(xiàn)澆筑表面的試件無(wú)論是在強(qiáng)度值、應(yīng)變值還是在吸收能上均大于切割表面狀態(tài)的試件。不同表面狀態(tài)下不同骨料粒徑的試件在這三個(gè)參數(shù)的對(duì)比上也得到了一致的規(guī)律，，即最大骨料粒徑較小的試件均大于最大骨料粒徑較大的試件。接下來(lái)用白光散斑法分析了試件表面變形場(chǎng)的不同。文中用應(yīng)變場(chǎng)漲落來(lái)定量分析混凝土試件應(yīng)變場(chǎng)的局部化程度。試驗(yàn)后對(duì)比發(fā)現(xiàn)，不同的表面狀態(tài)和不同的骨料粒徑對(duì)試驗(yàn)后試件的應(yīng)變漲落有著明顯的影響，試件的局部化程度也不同，最終試件發(fā)生破壞的方式也不同。 又對(duì)不同種類的試件進(jìn)行了疲勞加載的試驗(yàn)。試驗(yàn)采集中分別借助了白光散斑法、超聲法、聲發(fā)射和低場(chǎng)核磁共振掃描的方法。通過(guò)白光散斑法的采集計(jì)算，得到了不同試件加載過(guò)程中的應(yīng)變場(chǎng)。通過(guò)對(duì)比發(fā)現(xiàn)，這兩種尺寸效應(yīng)對(duì)混凝土試件的位移場(chǎng)及應(yīng)變場(chǎng)的演化、剪切應(yīng)變場(chǎng)的演化也有明顯的影響，不同試件會(huì)有不同的破壞。用超聲波法對(duì)疲勞后的試件進(jìn)行了內(nèi)部探傷，發(fā)現(xiàn)試件表面狀態(tài)不同，骨料粒徑不同，試件內(nèi)部的損傷量是不一樣的，即尺寸效應(yīng)對(duì)試件的內(nèi)部損傷產(chǎn)生了不同的影響。 用聲發(fā)射法分別對(duì)靜壓加載和疲勞加載的試件進(jìn)行了采集。試驗(yàn)發(fā)現(xiàn)在這兩種加載形式下，得到了與前述試驗(yàn)方法大致相同的尺寸效應(yīng)影響試件破壞的規(guī)律。 為了進(jìn)一步分析不同試件內(nèi)部的孔隙破壞情況，對(duì)疲勞后的試件進(jìn)行了核磁掃描。通過(guò)核磁掃描后分析得到的T2譜圖、孔徑分布圖、孔隙度以及成像圖等，發(fā)現(xiàn)不同骨料大小以及不同表面狀態(tài)的試件疲勞后，內(nèi)部所表現(xiàn)出的孔隙破壞特征與之前所用試驗(yàn)方法總結(jié)得到的規(guī)律一致。這也進(jìn)一步驗(yàn)證了本文總結(jié)的兩種尺寸效應(yīng)對(duì)混凝土災(zāi)變破壞影響規(guī)律的準(zhǔn)確性。
[Abstract]:Concrete is an uneven, anisotropic engineering composite made of coarse aggregate such as cement mortar and stone. Because of its low cost, easy transportation, construction and easy pouring into any shape, it has good frost resistance, corrosion resistance and strong compressive strength. The concrete material is widely used in industry and civil and so on. However, in some major accidents, such as the collapse of the buildings in the earthquake, and the premature destruction of some dikes and dams, it is found that the strength of the concrete material has not been destroyed when the quality of the concrete is not reached to the design, and it is found that the construction of the concrete structure is far lower than that of the concrete. The design value will suffer catastrophic damage because people do not consider the effect of size effect.
In the past, many scholars have studied various size effects of concrete. This paper mainly studies the effect of the two size effects of different surface state of concrete specimen and different aggregate size on concrete specimen damage. The main method of this paper is to use the method of experiment. The test parts of different surface states are divided into pouring table. The test parts of the surface and the cutting surface are tested directly in the test die. The outer layer of the specimen is mainly the mortar layer. The cutting surface specimen is cut by a large concrete specimen, and the outer layer of the specimen shows a lot of coarse aggregate. The size of the specimen with different aggregate size is 5-10mm, 5-15mm, 5, respectively. -20mm.
The static pressure test of different specimens is carried out first. The strength value and strain value of the specimens after the static pressure test are compared, and the absorption energy of each specimen is calculated. Through the comparison of these numerical values, it is found that the specimen on the surface of the pouring is in the strength value, the strain value or the specimen in the absorption energy which is larger than the cutting surface. In the contrast of the three parameters, the specimens with different aggregate sizes are also consistent, that is, the specimen with the smaller size of the largest aggregate is larger than the larger size of the aggregate. Then the difference of the surface deformation field of the specimen is analyzed by the white light speckle method. The quantitative analysis of the concrete specimen by the strain field fluctuation is used in this paper. The degree of localization of strain field. After the experiment, it is found that different surface state and different aggregate size have obvious influence on the strain fluctuation of the test specimen, the degree of localization of the specimen is different, and the way of final specimen damage is also different.
The tests of fatigue loading of different kinds of specimens were carried out. In the test collection, the methods of white light speckle, ultrasonic, acoustic emission and low field magnetic resonance were used respectively. The strain field in the loading process of different specimens was obtained by the acquisition and calculation of white light speckle method. Through comparison, these two kinds of size effects were found to be concrete. The evolution of the displacement field and strain field, the evolution of the shear strain field also have obvious influence, the different specimens will have different damage. The internal test of the specimen after fatigue is carried out by ultrasonic method. It is found that the surface state of the specimen is different, the size of the aggregate is different, and the damage amount inside the specimen is different, that is, the size effect is inside the specimen. The damage of the Ministry has had a different effect.
The specimens of static pressure loading and fatigue loading are collected by acoustic emission method. It is found that under these two kinds of loading forms, the law of damage of the specimen with the same size effect as the experimental method is obtained.
In order to further analyze the void damage in different specimens, the specimens after fatigue were scanned by NMR. The T2 spectra, pore size distribution, porosity and imaging of the specimens were analyzed after the NMR scanning, and the characteristics of the internal pore damage were found after the fatigue of the specimens with different aggregate size and different surface states. It is consistent with the rules obtained by the previous method, which further validates the accuracy of the effect of the two size effects on the damage of the concrete.

【學(xué)位授予單位】：燕山大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU528

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