【作者】 徐洪国；

【导师】 水中和；

【作者基本信息】 武汉理工大学 ， 材料学， 2011， 博士

【摘要】 水泥混凝土材料是一种非均质的多相复合材料,其中各组成物相的热膨胀性能均不相同。当环境温度发生剧烈变化时,混凝土内各组分间会产生不均匀的热膨胀,并由此产生热应力,以致界面出现微裂纹,严重时会引起混凝土结构的开裂。本论文针对大温差地区的气候特征,系统模拟研究了水泥混凝土材料在大温差环境(室温～85℃)服役下各组成相间热膨胀性能的差异。通过观察水泥混凝土材料在热疲劳循环作用下的性能变化,深入研究了硬化水泥石和水泥混凝土的热膨胀性能及物相间热相互作用机理。在此基础上,对比了不同掺量下粉煤灰、硅灰和苯丙乳液对水泥混凝土材料热膨胀性能的影响,探讨了适应于大温差地区下的热变形协调性混凝土制备技术。此外,本论文还采用了红外热像仪研究了混凝土结构的温度分布与热损伤趋势分析,并结合实体工程对我国北方大温差地区的空心薄壁墩结构进行了时变温度效应规律和热应力研究。试验结果表明,在室温～85℃的温度范围内,硬化水泥石和粗集料的热膨胀性能存在明显的差异。水泥混凝土经多次热疲劳循环后,界面过渡区产生微裂纹,并沿着集料边缘方向扩展,且微裂纹的宽度随热疲劳循环次数的增加而增大。随着热疲劳循环次数的增加,水泥混凝土的抗压强度逐渐降低。粉煤灰、硅灰和苯丙乳液的掺入,均能不同程度的降低硬化水泥石的热膨胀率和热膨胀系数,其降低程度随外掺物掺量的增加而增大。粉煤灰能降低升温早期的热膨胀率及热膨胀系数,硅灰对升温后期的热膨胀率及热膨胀系数影响较大,苯丙乳液能同时大幅降低水泥石最大热膨胀参数和最小热膨胀参数。粉煤灰、硅灰和苯丙乳液的掺入均能对混凝土的热膨胀系数有不同程度的降低效果,苯丙乳液影响效果最大,粉煤灰影响效果其次,硅灰影响效果最小。利用粉煤灰、硅灰和苯丙乳液制备的热变形协调性混凝土均能不同程度的改善混凝土热疲劳循环后的宏观和微观性能,宏观性能体现在热疲劳循环后,掺外掺物的混凝土抗压强度损失均能得到不同程度的减小,混凝土内部的微裂缝也得到一定程度的控制。粉煤灰、硅灰的掺入可降低水泥混凝土材料中Ca(OH)2的含量并改善其孔结构,从而能有效限制水泥混凝土材料的热膨胀性能。苯丙乳液的掺入能在水泥混凝土材料中的C-S-H凝胶和未水化水泥颗粒表面形成了一层密实的聚合物薄膜,因此增强了材料的韧性,形成了一个膨胀“缓冲区”,从而降低了水泥混凝土材料自身的热膨胀系数。在上述研究的基础上,通过采用矿物掺和料、有机聚合物等对水泥浆体热膨胀性能的调节,提高了水泥浆体、砂浆和粗集料之间的热变形协调性,从而发展了具有较高抗热膨胀变形能力的热变形协调性混凝土设计和制备技术。利用红外热像仪和温度传感器对大温差条件混凝土结构的温度分布进行了观察和分析,重点探讨了结构表面温度分布与其内部结构特征之间的关系。在此基础上,发展了基于温度分布的混凝土结构损伤发展趋势的无损评估方法。利用此方法,不但可以直接发现结构表面附近的宏观缺陷(空鼓、蜂窝等),还可以判断在大温差作用下,混凝土的温度场分布、结构热应力和热损伤发展趋势,为防止结构热损伤的发生提供技术支撑。论文还结合我国内蒙古阿尔山地区一座空心薄壁墩结构桥梁工程建设,开展了低热膨胀系数混凝土配合比设计和制备技术研究,且在服役期间利用红外热像仪对薄壁墩结构的实时温度监测,研究了薄壁墩结构的时变温度场与结构热应力。更多还原

【Abstract】 The cement concrete is a heterogeneous material that is composed of multiple ingredients with different thermal expansion properties. A drastic temperature variation causes different thermal volumetric changes of the components and hence thermal stress in the interface is generated. If the stress is greater than the bond strength between paste matrix and the aggregate, thermal cracking takes place and thus degradation of the concrete is observed. The thermal behavior and migration of thermal cracking of concrete in an extremely cold and dry climate with large temperature variations is investigated in this thesis via thermal compatibility study of components in concrete. The thermal expansion/shrinkage of cement paste and concrete in the cyclic thermal treatment is tested, based on which the evolution of thermal interface cracking is revealed. The effects of fly ash, silica fume and styrene-acrylic latex on the thermal expansion of hardened concrete are tested and analyzed, based on which practical solution for preventing thermal microstructural cracking of concrete in cold climate with large temperature variations is proposed. Thermal methods for detecting defects in concrete structure are established, which is also tested with a highway bridge in the North China.The research results have shown that, distinct thermal mismatch between the hardened cement paste and a coarse aggregate in concrete exists in the range of room temperature to 85℃. After number of thermal cyclic shocks, cracks in the interfacial transition zone of concrete are observed, propagating along the edge of the aggregates. The thermal cyclic shocks lower the compressive strength of concrete. The water to cement ratio of cement paste is an important factor on the thermal expansion coefficient of the hardened paste.The addition of fly ash, silica fume and styrene-acrylic latex lowers the thermal expansion rate and coefficient of hardened paste. The increase of addition level is accompanied by the decrease of the thermal expansion coefficient. The styrene-acrylic latex is the most effective in lowering the thermal expansion coefficient.The effects of fly ash, silica fume and styrene-acrylic latex on the thermal properties of hardened concrete are similar to those on cement paste. By adding fly ash, silica fume or styrene-acrylic into concrete, the thermal sensitivity is greatly reduced and hence the thermal stability is optimized by changing the microstructure of concrete.The introduction of fly ash and silica fume could reduce the amount of Ca(OH)2 in concrete and improve its pore structure, while the thermal expansion rate of the materials was thus limited. Besides, the addition of styrene-acrylic latex in concrete formed a impermeable membrane on the surface between C-S-H gel and unhydrated cement particles. As a deformation adsorption layer, the membrane thus enhanced the ductility of the material and lowered its thermal expansion coefficient.Based on the studies below, the thermal expension properties of cement paste were midified by the use of mineral admixture, arganic polymers and so on. The thermal deformation capability among cement, mortar and coarse aggregate was improved, which leaded to the development of the design and preparation of concrete with higher thermal expansion resistance and thermal deformation coordination.By using infrared imaging and temperature sensors, the temperature distribution of concrete structure under large temperature difference was observed and analyzed, focusing on the relationship between its surface temperature distribution and internal structure characteristic. Based on this, the non-destructive damage assessment was developed on trends of temperature distribution of the concrete structure. With this method, not only macro-structural defects could be found directly near the surface (hollowing, cellular, etc.), you could also determine the temperature distribution, structure, thermal stress and thermal injury trends under large temperature difference, in order to provide technical support for preventing thermal injury of structures. This paper introduced a hollow thin-walled structure of the bridge in Aershan region of Inner Mongolia in China, and carried out the study of design and preparation for low thermal expansion concrete. What’s more, time-varying temperature field and thermal stress of thin-walled pier were investigated by monitoring the real-time temperature using infrared imaging.更多还原