高强混凝土经不同高温历程后性能劣化研究

摘要

An experimental study was conducted on the performance deterioration of high strength concrete (HSC,C60)subjected to different heating temperature and time.Comprehensive means of scanning electron microscopy,mercury pressure measurement,ultrasonic detect and micro hardness tester were used to investigate the microstructure changes of HSC.The changes specimen color,compressive strength,elastic modulus,mass loss,burst mechanism,and the microstructure of HSC were analyzed.The results show that the color of HSC is shallow after different high temperature history,and it will be rusty red from one hour of 300 ℃ to two hours of 300 ℃,the appearance can be grayish white at 700 ℃ to 900 ℃.Moreover,HSC will burst at 500 ℃,and the cracking temperature is much lower than ordinary concrete.The root causes of the deterioration of macro-mechanical properties are gel molecules,cement hydrates and other thermal decomposition.The surface and internal cracks and micro-cracks,high-strength concrete microstructure gradually deteriorate.With the rise of heating temperature and time,the compressive strength,elastic modulus and mass loss of HSC decrease gradually.On this basis,the change of heating temperature is related to the performance degradation of HSC and has a greater impact.%对经历不同加热温度和不同恒温时间的C60高强混凝土性能劣化进行了试验研究,并利用超声、显微硬度检测、扫描电子显微镜及汞压力测孔等综合手段观察其高温后细微观结构的变化.重点分析了高强混凝土外观、抗压强度、弹性模量、质量损失、高温爆裂机理、细微观结构的变化规律.研究结果表明,经不同高温历程后,高强混凝土的色泽变浅,从300℃恒温1h时开始混凝土试块呈铁锈红色,直到400℃恒温2h时铁锈红色消失,700～ 900℃试块外表呈灰白色;高强混凝土会在500℃时发生爆裂,较普通混凝土的爆裂温度低很多;凝胶分子、水泥水化物等受热分解,使其表面和内部产生孔隙和微裂纹,高强混凝土细微观结构逐渐变差,这是造成宏观力学性能劣化的根本原因.随着加热温度的升高与恒温时间的增长,高强混凝土的抗压强度、弹性模量和质量总体呈下降趋势,且相对恒温时间的不同,加热温度的变化对高强混凝土力学性能劣化的影响更大.