基于微结构的高性能混凝土火灾劣化机理及损伤评估理论研究

The deterioration mechanism and damage assessment of high-performance concrete after exposure to fire are the bottlenecks and difficulties for modern structural engineering to improve the fire resistance and post-disaster damage identification, and the key to solve the problem is the deterioration evolution discipline and its mechanism in the internal micro-structure at high temperature. The project intends to observe the fire damage of high-performance concrete from the three-dimensional dynamic point under the microscopy by use of the X-ray CT (Computerized Tomography) technology; analyze the deterioration evolution in its internal micro-structure of high-performance concrete with and without polypropylene fibers at room temperature, high temperature, and under the action of both temperature and load; discuss the fractal law, fractal parameters and fractal characteristics of crack distribution of micro-structural changes in concrete in line with the fractal theory; quantitatively observe and analyze the number, length, width and shape of the internal cracks; .reveal the variation and mechanism of the internal micro-structural eigenvalue changing with temperature and load respectively. According to the heat transfer theory, the thermal parameters of high-performance concrete will be evaluated, the concrete temperature field will be simulated by using the numerical method; the situation of concrete surface and reinforced exposed to fire will be speculated .using infrared thermal imaging and electrochemical nondestructive testing and so on; and the fire damage assessment theories and methods of high-performance concrete will be established based on the micro-structural changes.

高性能混凝土火灾劣化机理及其损伤评估，是解决现代工程结构提高抗火性能及灾后损伤鉴定的瓶颈与难点，而揭示其内部微结构高温劣化演化规律及机理则是解决该难题的关键。本项目拟采用X射线CT（Computerized Tomography计算机层析扫描）技术进行高性能混凝土火灾损伤的三维动态显微观测，分析掺聚丙烯纤维前后的高性能混凝土在常温、高温以及高温和荷载同时作用下内部微结构劣化演化规律；引入分形理论，研究混凝土微结构变化分形规律、分形参数及裂隙分布的分形特征；定量观测与分析内部裂隙的数量、长度、宽度及形态；揭示内部微结构变化特征值随温度及温度与荷载变化的劣化演化规律及机理。测定高性能混凝土热工参数，根据传热学原理，采用数值方法模拟混凝土内部温度场；采用红外热像与电化学等无损检测新技术，推定混凝土表面受火温度和钢筋受火情况；建立基于微结构变化的高性能混凝土火灾损伤评估理论与方法。

针对高性能混凝土（HPC）火灾劣化机理及其损伤评估理论与方法，项目研究完成了以下工作：①HPC力学性能随温度的劣化演化规律，测定了20℃-800℃不同温度等级高温作用后C40、C60、C80 HPC及掺与不掺PP纤维情况下的抗压强度、劈拉强度、轴压强度、弹性模量、断裂性能，总体各性能指标均随温度的升高呈下降趋势，劈拉强度、弹性模量300℃劣化渐趋严重，其他性能指标400℃劣化渐趋严重。②HPC微结构火灾劣化机理，③采用X射线CT技术进行了HPC火灾损伤的三维动态显微观测，分析了掺PP纤维前后的HPC在常温、高温作用下内部微结构劣化演化规律，建立了细观孔隙率、平均孔径、最可几孔径随温度变化的关系式；进行了不同温度作用后混凝土试块的压汞测试，引入分形理论，研究了混凝土孔结构变化的分形规律、分形参数及裂隙分布的分形特征，建立了总孔隙率、孔体积分形维数、温度与抗压强度的关系式；观测与分析了内部裂隙的数量、长度、宽度及形态；采用扫描电镜观测了高温后HPC微结构的变化；采用XRD分析了高温后HPC组成成分的变化。总体HPC总孔隙率随温度升高而增加，300℃前最可几孔径为约50nm的毛细孔，400℃后大于50nm的大孔显著增加，800℃后各级孔径孔隙均增加明显，内部裂隙的数量、长度、宽度随温度升高而增长；高温后孔隙具多重分形特征，转折孔径约为50nm，孔体积分形维数随温度升高渐趋减小；HPC组成成分随温度升高脱水分解或破坏；掺加PP纤维可提高HPC的抗火性能。③HPC热物理性能演化，测定了HPC导热系数、比热及热膨胀率等热工参数，根据传热学原理，采用数值方法模拟了混凝土内部温度场；④采用红外热像仪，测试了不同温度作用后混凝土的红外温升值，建立了其与受火温度的关系式；采用钢筋锈蚀仪，测试了高温后混凝土中钢筋的电势、电流密度，建立了钢筋损伤的判据。⑤建立了高性能混凝土火灾损伤评估模型与方法。