【摘要】：高性能混凝土具有強度高、耐久性高、工作性和體積穩(wěn)定性好等綜合優(yōu)勢，在土木工程領(lǐng)域已得到廣泛的研究和應(yīng)用。與普通混凝土相比，高性能混凝土內(nèi)部結(jié)構(gòu)更加致密，滲透性低，脆性更大，當遭受火災(zāi)（高溫）作用時，各項性能劣化更加嚴重，甚至發(fā)生剝落、爆裂，重者使建筑物坍塌，對人民生命、財產(chǎn)造成極大的安全隱患。研究高溫對高性能混凝土性能的影響，揭示其劣化演化規(guī)律，提出科學(xué)合理的改進方法和措施成為業(yè)界人士的關(guān)注重點。 本文優(yōu)選地方原材料，以設(shè)計強度等級為C40的高性能混凝土為研究對象，較為系統(tǒng)地研究了高溫前后混凝土基本物理力學(xué)性能的變化規(guī)律，采用宏觀測試與微觀分析相結(jié)合的方法，定性分析與定量分析并重，從微觀、亞微觀角度，深入探討了混凝土高溫性能劣化的規(guī)律、機理及其影響因素，主要內(nèi)容如下： 一、高性能混凝土的基本性能試驗研究。本文對高性能混凝土基本性能的試驗研究主要包括拌合物坍落度、表觀密度、立方體抗壓強度、劈裂抗拉強度、軸心抗壓強度、彈性模量及抗氯離子滲透性等。結(jié)果表明，配制的混凝土拌合物流動性大，粘聚性好，勻質(zhì)性好，各項基本力學(xué)性能滿足規(guī)范要求，耐久性良好。 二、高性能混凝土的高溫力學(xué)性能試驗研究。主要研究了不同冷卻方式對混凝土立方體抗壓強度、劈裂抗拉強度的影響，分析了混凝土立方體抗壓強度、劈裂抗拉強度、軸心抗壓強度、彈性模量及斷裂性能隨溫度的變化規(guī)律。結(jié)果表明，混凝土各項力學(xué)性能經(jīng)高溫作用后出現(xiàn)不同程度的劣化，噴淋冷卻較自然冷卻對兩種強度的劣化影響更為顯著；對比高溫前后兩種尺寸立方體（邊長為100mm和150mm）抗壓強度和劈裂抗拉強度，高溫后混凝土的尺寸效應(yīng)與常溫下不同；建立了混凝土彈性模量與溫度，以及抗壓強度與彈性模量隨溫度變化的關(guān)系模型；混凝土的起裂韌度隨溫度變化較小，失穩(wěn)韌度總體隨溫度的升高而下降；建立了混凝土劈裂抗拉強度與失穩(wěn)韌度，以及抗壓強度與斷裂能之間的關(guān)系。 三、高性能混凝土的高溫?zé)嵛锢硇阅茉囼炑芯�。從宏觀上觀察了混凝土經(jīng)不同溫度作用后的表觀特征，研究了混凝土表觀密度隨溫度的變化規(guī)律，不同溫度及恒溫時間對混凝土導(dǎo)熱系數(shù)的影響，對比分析了高溫前后混凝土比熱的不同，探討了混凝土及其內(nèi)部各組分在升降溫過程中熱膨脹率的變化。試驗結(jié)果表明，400℃作用后，試件表明出現(xiàn)明顯裂紋；總體上，混凝土表觀密度和導(dǎo)熱系數(shù)均隨溫度升高而下降，但300℃時，不降反增；建立了表觀密度與導(dǎo)熱系數(shù)的關(guān)系；從室溫到565℃，混凝土高溫下的比熱較高溫后的比熱高，且波動大，，DSC曲線上，高溫下混凝土存在兩個明顯的吸熱峰（143℃左右和483℃左右），高溫后無此峰值效應(yīng)；200℃前，混凝土及其各組分的熱膨脹率相差較小，隨著溫度的升高，膨脹率發(fā)生較大變化，其中，硬化漿體膨脹率逐漸減小，砂漿與骨料的體積膨脹率之和與混凝土體積膨脹率不相等；混凝土、骨料及四種硬化漿體的熱膨脹率均隨溫度的降低而減小，冷卻速度不同，膨脹率不同，減水劑減緩了硬化漿體的膨脹率；熱重-差熱曲線表明，混凝土質(zhì)量在100℃、440℃和710℃左右下降最為明顯。 四、高性能混凝土微結(jié)構(gòu)的高溫演化研究。利用壓汞測孔儀、X射線CT掃描儀，對混凝土高溫前后的內(nèi)部微結(jié)構(gòu)進行了定性、定量的分析�；炷恋目偪紫堵孰S溫度升高而增加；不同溫度作用后，混凝土內(nèi)部孔徑分布發(fā)生變化，300℃前，最可幾孔徑主要為毛細孔（孔徑＜50nm），300℃后，更多集中于大孔（孔徑＞50nm）；高溫前后的混凝土孔隙特征具有多重分形特征，轉(zhuǎn)折孔徑在50nm左右，孔徑范圍一定時，孔體積分維數(shù)隨孔隙率增加而減小，大孔對混凝土抗壓強度影響顯著；建立了混凝土立方體抗壓強度與溫度、孔隙率，以及抗壓強度與大孔孔體積分維數(shù)隨溫度變化的關(guān)系及模型；混凝土CT圖像兩個平面（x-y平面、x-z平面）不同代表層所反映的內(nèi)部結(jié)構(gòu)基本相同，高溫作用后，混凝土內(nèi)孔隙數(shù)量增多，孔徑增大，骨料與漿體界面形成微裂縫并進一步擴展至漿體中，與漿體中孔隙連通；二值化圖像中，混凝土各層孔隙率隨溫度升高總體呈增加趨勢，與壓汞法中對應(yīng)孔徑的孔隙率變化規(guī)律基本一致。 本文旨在為高性能混凝土高溫性能的研究奠定較為系統(tǒng)的理論和試驗研究基礎(chǔ)，從宏觀和微觀角度，對后續(xù)有關(guān)高性能混凝土高溫性能的研究提供一定的借鑒和參考。
[Abstract]:The high-performance concrete has the advantages of high strength, high durability, good working ability and volume stability, and has been widely studied and applied in the field of civil engineering. Compared with the common concrete, the high-performance concrete internal structure is more compact, the permeability is low, the brittleness is larger, The property is a great potential safety hazard. The influence of high temperature on the performance of high performance concrete is studied, and the evolution law of its degradation is revealed, and the scientific and reasonable method and measures for improving the performance of the concrete are put forward. In this paper, local raw materials are used to design the high-performance concrete with the strength grade of C40 as the research object, and the change rule of the basic physical and mechanical properties of the concrete before and after the high temperature is systematically studied, and the combination of the macro-test and the micro-analysis is adopted. The law, the qualitative analysis and the quantitative analysis are given, and the law, the mechanism and the influencing factors of the degradation of the high-temperature performance of the concrete are discussed in detail from the micro and the sub-micro-angles. The main contents are as follows: Next: Basic performance test of high-performance concrete The experimental research on the basic properties of high-performance concrete mainly includes the falling of the mixture, the apparent density, the cube compressive strength, the splitting tensile strength, the axial compression strength, the elastic modulus and the chloride ion permeability. The results show that the prepared concrete mixture has large fluidity, good adhesion, good homogeneity, and the basic mechanical properties meet the requirements of the specification. high-temperature mechanical property of high-performance concrete The effects of different cooling methods on the compressive strength and the splitting tensile strength of the concrete cube were studied. The compressive strength, the splitting tensile strength, the axial compressive strength, the elastic modulus and the fracture property of the concrete cube were analyzed. The results show that the mechanical properties of the concrete are deteriorated to a certain extent after high temperature, and the effect of spraying and cooling on the degradation of the two kinds of strength is more significant; the compressive strength and the splitting strength of the two size cubes (the side length is 100 mm and 150 mm) before and after the high temperature are compared. The tensile strength of the concrete and the effect of the concrete after high temperature are different from the normal temperature. The relationship between the elastic modulus and the temperature of the concrete and the change of the compressive strength and the elastic modulus with the temperature is established. The tensile strength and the fracture toughness of the concrete are established, and the compressive strength and the fracture energy are established. The relationship between high-temperature and high-performance concrete The effect of apparent density of concrete on the thermal conductivity of concrete was studied from the macroscopic view of the apparent characteristics of concrete after different temperature, and the effect of different temperature and constant temperature on the thermal conductivity of concrete was studied. The specific heat of the condensed soil is different, and the concrete and its components are discussed in the process of raising and lowering temperature The experimental results show that after 400 鈩

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