高温对C40高性能混凝土物理力学性能的影响

发布时间：2019-06-15 05:25

【摘要】：高性能混凝土具有强度高、耐久性高、工作性和体积稳定性好等综合优势，在土木工程领域已得到广泛的研究和应用。与普通混凝土相比，高性能混凝土内部结构更加致密，渗透性低，脆性更大，当遭受火灾（高温）作用时，各项性能劣化更加严重，甚至发生剥落、爆裂，重者使建筑物坍塌，对人民生命、财产造成极大的安全隐患。研究高温对高性能混凝土性能的影响，揭示其劣化演化规律，提出科学合理的改进方法和措施成为业界人士的关注重点。 本文优选地方原材料，以设计强度等级为C40的高性能混凝土为研究对象，较为系统地研究了高温前后混凝土基本物理力学性能的变化规律，采用宏观测试与微观分析相结合的方法，定性分析与定量分析并重，从微观、亚微观角度，深入探讨了混凝土高温性能劣化的规律、机理及其影响因素，主要内容如下： 一、高性能混凝土的基本性能试验研究。本文对高性能混凝土基本性能的试验研究主要包括拌合物坍落度、表观密度、立方体抗压强度、劈裂抗拉强度、轴心抗压强度、弹性模量及抗氯离子渗透性等。结果表明，配制的混凝土拌合物流动性大，粘聚性好，匀质性好，各项基本力学性能满足规范要求，耐久性良好。 二、高性能混凝土的高温力学性能试验研究。主要研究了不同冷却方式对混凝土立方体抗压强度、劈裂抗拉强度的影响，分析了混凝土立方体抗压强度、劈裂抗拉强度、轴心抗压强度、弹性模量及断裂性能随温度的变化规律。结果表明，混凝土各项力学性能经高温作用后出现不同程度的劣化，喷淋冷却较自然冷却对两种强度的劣化影响更为显著；对比高温前后两种尺寸立方体（边长为100mm和150mm）抗压强度和劈裂抗拉强度，高温后混凝土的尺寸效应与常温下不同；建立了混凝土弹性模量与温度，以及抗压强度与弹性模量随温度变化的关系模型；混凝土的起裂韧度随温度变化较小，失稳韧度总体随温度的升高而下降；建立了混凝土劈裂抗拉强度与失稳韧度，以及抗压强度与断裂能之间的关系。 三、高性能混凝土的高温热物理性能试验研究。从宏观上观察了混凝土经不同温度作用后的表观特征，研究了混凝土表观密度随温度的变化规律，不同温度及恒温时间对混凝土导热系数的影响，对比分析了高温前后混凝土比热的不同，探讨了混凝土及其内部各组分在升降温过程中热膨胀率的变化。试验结果表明，400℃作用后，试件表明出现明显裂纹；总体上，混凝土表观密度和导热系数均随温度升高而下降，但300℃时，不降反增；建立了表观密度与导热系数的关系；从室温到565℃，混凝土高温下的比热较高温后的比热高，且波动大，，DSC曲线上，高温下混凝土存在两个明显的吸热峰（143℃左右和483℃左右），高温后无此峰值效应；200℃前，混凝土及其各组分的热膨胀率相差较小，随着温度的升高，膨胀率发生较大变化，其中，硬化浆体膨胀率逐渐减小，砂浆与骨料的体积膨胀率之和与混凝土体积膨胀率不相等；混凝土、骨料及四种硬化浆体的热膨胀率均随温度的降低而减小，冷却速度不同，膨胀率不同，减水剂减缓了硬化浆体的膨胀率；热重-差热曲线表明，混凝土质量在100℃、440℃和710℃左右下降最为明显。 四、高性能混凝土微结构的高温演化研究。利用压汞测孔仪、X射线CT扫描仪，对混凝土高温前后的内部微结构进行了定性、定量的分析。混凝土的总孔隙率随温度升高而增加；不同温度作用后，混凝土内部孔径分布发生变化，300℃前，最可几孔径主要为毛细孔（孔径＜50nm），300℃后，更多集中于大孔（孔径＞50nm）；高温前后的混凝土孔隙特征具有多重分形特征，转折孔径在50nm左右，孔径范围一定时，孔体积分维数随孔隙率增加而减小，大孔对混凝土抗压强度影响显著；建立了混凝土立方体抗压强度与温度、孔隙率，以及抗压强度与大孔孔体积分维数随温度变化的关系及模型；混凝土CT图像两个平面（x-y平面、x-z平面）不同代表层所反映的内部结构基本相同，高温作用后，混凝土内孔隙数量增多，孔径增大，骨料与浆体界面形成微裂缝并进一步扩展至浆体中，与浆体中孔隙连通；二值化图像中，混凝土各层孔隙率随温度升高总体呈增加趋势，与压汞法中对应孔径的孔隙率变化规律基本一致。 本文旨在为高性能混凝土高温性能的研究奠定较为系统的理论和试验研究基础，从宏观和微观角度，对后续有关高性能混凝土高温性能的研究提供一定的借鉴和参考。
[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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