【作者】 李清海；

【导师】 姚燕；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2007， 博士

【摘要】 虽然水泥基材料作为一种大宗建筑材料在工程建设中已经得到非常广泛的应用和研究,但当其在高温或在局部高温环境中应用时,其性能往往遭到严重的破坏。深入研究水泥基材料在高温下的热膨胀机理,掌握其在高温时的变化规律,对于理解高温或局部高温环境中水泥基材料的行为有所帮助,并对混凝土构件和结构的耐高温设计提供理论依据,且在指导水泥基材料的高温安全性、耐久性方面有重要意义。本文针对目前水泥基材料热变形性能研究方法不足,结论不系统的现状,采用差示热膨胀测试方法,结合高温下力学性能测试及TG-DTA、DSC-TG、XRD和SEM等分析方法,首次系统研究了硬化水泥基材料高温热膨胀性能及其影响因素。重点研究了水泥石和集料的热膨胀率变化规律及其机理,建立了水泥石和集料高温热膨胀系数的数学模型;对不同集料品种和掺量下水泥基材料热膨胀率和抗压强度的作用机理进行了研究;同时研究了掺合料的种类和掺量对水泥基材料热膨胀率的影响及机理;结合压汞法（MIP法）,系统研究了气相对水泥基材料热膨胀率的影响及机理;通过掺入C₃A和C（S|—）H₂的方法,研究水化硫铝酸钙对硅酸盐水泥热膨胀率变化规律的影响;还对比研究了由常用的三大系列水泥（硅酸盐水泥、高铝水泥和硫铝酸盐水泥）制成的水泥基材料热膨胀性能之间的差异。本文首先对水泥石和集料在高温下的热膨胀率进行深入的研究,首次提出了用差示热膨胀法测试水泥基材料热膨胀性能,并设计了专用试件成型方法。实验结果发现:水泥石在三种升温条件下（I:直接从室温至600℃;II:先经过室温至180℃的热循环,然后再升温至600℃;III:先经过从室温至400℃的热循环,然后再升温至600℃）的热膨胀率随温度的升高均呈现为先升高后降低的趋势;升温条件II和III同I相比较,水泥石在受热时出现热收缩的温度分别提高了约70℃和260℃,首次得出热循环提高了水泥石热收缩温度的结论。另一方面,集料的热膨胀率也随温度的升高而增大,并在570℃⁶00℃区间内膨胀率曲线出现明显的峰值。同时借助于DSC/TG和XRD测试手段,探索了水泥石和集料热膨胀性能变化机理。实验发现,水泥石和集料之间的热应力差是导致热循环中混凝土强度下降的主要原因。首次应用“函数求导法”和“直接微分法”对水泥石和集料在高温条件下各自热膨胀率与温度之间的关系进行了分析,建立了对材料设计及应用具有很强指导意义的热膨胀系数与温度之间的数学模型。本文首次对不同集料、不同灰砂比（m（c）/m（s））的混凝土从室温至600℃范围内的热膨胀率进行测定与分析,对比了石英砂、石灰石和花岗岩三种集料对硬化水泥基材料热膨胀性能的影响。结果发现,集料掺量增大,混凝土热膨胀率增幅越大;集料品种不同时,混凝土热膨胀率增幅会有所差异。借助TG-DTA、XRD等测试手段,探索高温下混凝土强度变化与水泥石强度、水泥石与集料界面区热膨胀应力差二者之间的影响关系。本文首次研究了掺合料对硬化水泥基材料热膨胀性能的影响。结果发现:在实验掺量范围内（10%²0%）,掺合料（硅灰、粉煤灰或磨细矿渣）的掺入使水泥石在高温时产生比对比水泥石更大的热收缩,热收缩量从大到小依次是硅灰>磨细矿渣>粉煤灰。硅灰掺量的变化对水泥石热收缩影响较小;磨细矿渣掺量增多,水泥石热收缩增大;粉煤灰掺量增加,水泥石热收缩量由大变小。并通过TG-DTA、XRD和SEM图谱对上述变化规律进行了机理分析。本文首次研究了掺入引气剂后,气相对硬化水泥基材料热膨胀性能的影响,并利用MIP和XRD等方法对其机理进行了探索。研究发现:引入气相的水泥石与对比水泥石试样的热膨胀率曲线变化趋势大致相同。引入气相后,在室温至150℃之间,气相缓解了水泥石的膨胀;在150℃之后,引入的气相为水化产物提供了脱水通道,使水泥石体积产生更加明显的收缩,收缩量随着引气剂掺量的增加而增大。本文首次通过在普通硅酸盐水泥中掺入C3A和CS—H2,使水泥石中水化生成更多的水化硫铝酸钙,以研究水化硫铝酸钙对硬化硅酸盐水泥石热膨胀率的影响。结果发现:掺加C₃A和C（S|—）H₂后,水泥石热膨胀率的变化趋势与对比水泥石的基本一致,但水化硫铝酸钙增加了水泥石的高温（>150℃）收缩量,对水泥石热稳定性不利。并运用DTA-TG、XRD和SEM对其机理进行了探索与分析。对三大系列水泥（硅酸盐水泥、高铝水泥和硫铝酸盐水泥）制成的水泥基材料热膨胀率变化规律的对比研究发现:三种水泥石的热膨胀率曲线均随着温度的升高先上升,而后显著降低,达到一定温度后,曲线变得平缓,此时的热收缩量从大到小依次是:普通硅酸盐水泥>硫铝酸盐水泥>高铝水泥。由于组成成分的不同,三种水泥石热稳定性、热收缩量及收缩速率有着显著差异。论文还运用TG-DTA、XRD和SEM等方法,探索分析了三种水泥石高温热膨胀率变化与各自水化产物之间的关系,对三种水泥的高温使用有指导意义。更多还原

【Abstract】 While the cement-based materials have been widely used in construction and building, their properties can be greatly altered when the structure have exposed to high temperature for overlong periods. The knowledge on the thermal expansion performance of a cement-based material and the underlying mechanism are thus critical in the prediction of its behavior after burning, and also of great help in the design of structures encountered high temperature or in the repair of damaged structures. However, research on thermal expansion performance of cement-based material have long been hindered by insufficient data and shortage of convincing evidences due to inaccessibility to appropriate testing instruments.In the dissertation project, an integrative methodology was applied to study the performance and mechanism of the thermal expansion of harden cement-based materials for the first time with the help of equipments NETZSCH D/L 402EP and TG-DTA, XRD and SEM. The objectives and consequently the experiment comprises six parts: 1) to determine thermal expansion rate for hardened cement paste and aggregate, and to establish mathematical models for computing thermal expansion coefficient; 2) to compare thermal expansion rate and compressive strength for cement-based materials that are mixed with different aggregates; 3) to determine the effect of mineral additives on thermal expansion performance of cement-based materials; 4) to determine the influence of occluded air on thermal expansion performance of cement-based materials; 5) to determine the effects of calcium sulfoaluminate hydrates on thermal expansion of Portland cement-based material; and 6) to compare hardened cement paste made with Portland cement, calcium aluminate cement and sulphoaluminate cement with respect to their thermal expansion performance.In the first experiment, studies focused on the thermal expansion properties of hardened cement paste and aggregates. A special molding method was first applied in the test of thermal expansion coefficients for cement-based materials in three heating treatments - (I) directly heated from 20°C to 600°C, (II) 3 thermal cycles ranging from 20°C to 180°C, then heated from 20°C to 600°C and (III) 3 thermal cycles ranging from 20°C to 400°C, then heated from 20°C to 600°C. In all treatments, the rate of thermal expansion increased with an increasing temperature during the initial stage and then decreased as the temperature continued to rise. A conclusion that the temperature at which the shrinkage started was postponed due to the treatment of preliminary heat cycles in treatment II and III was arrived for the first time. The temperature of maximum thermal expansion in treatment I was 70°C lower than that in treatment II, and 260°C lower than that in treatment III. On the other hand, the thermal expansion rate of aggregates increased with a rising temperature, with an obvious peak occurring range from 570°C to 600°C. The DSC/TG and XRD images revealed that the difference in thermal stress between hardened cement paste and aggregate was a major factor contributing to the decrease in concrete strength. A function derivative method and a direct differential method were first used to develop mathematical models for the relationships between temperature and thermal expansion rates for hardened cement paste and for aggregates respectively.In the second experiment, the influences of quartz sand, limestone and granite at different cement/sand ratios was studied. The thermal expansion rate of concrete increased much quickly as the dosage of aggregate increased, and the increase rate varied with the nature of aggregate in use. The effects of hardened cement paste strength and stress difference in interface zone on concrete strength, was studied by TG/DTA and XRD.In the third experiment, the influence of mineral addtives on the thermal expansions was first studied by adding variable dosage of silica fume, fly ash and blast-furnace slag. At high temperature range the shrinkage rates of cement-based material amended by mineral addtive were greater than those of the reference cement. The order of thermal shrinkage was silica fume > blast-furnace slag > fly ash. While the thermal shrinkage rate was insignificantly affected by the dosage of silica fume, it increased with an increasing content of blast-furnace slag, but decreased with an increasing content of fly ash. The mechanism has been studied through TG-DTA、XRD and SEM.In the fourth experiment, the effect of air on thermal expansion of cement-based materials was first studied through adding air entraining agent, its mechanism was studied by means of MIP and XRD. The curve of thermal expansion rate for hardened cement paste that had been amended with air entraining agent was similar to that for the reference. The occurrence of air phase in hardened cement paste can reduce the expansion rate when heated from room temperature to 150℃. Above 150℃, air phase provides a way for water escape, so the shrinkage become more evident in harden cement paste. Thermal shrinkage rate increased with an increasing dosage of air entraining agent.In the fifth part of the experiment, more calcium sulfoaluminate hydrates were observed in cement-based material amended with C3A and dehydrate gypsum. While the thermal expansion curves were alike, the shrinkage rate of mixing samples was greater than that of the reference. It indicates that the addition of calcium sulfoaluminate hydrates can increase the shrinkage rate of cement-based materials at high temperature (>150°C) and thus pose an adverse effect on their heat stability.In the last part of the experiment, the thermal expansions of hardened cement paste of three types of cement (Portland cement, calcium aluminate cement and sulphoaluminate cement) were compared. The thermal expansion rates for all three cements increased at first, then decreased as temperature continued to rise, and finally became stable at certain temperature. In decreasing order, the thermal shrinkage rate was Portland cement > sulphoaluminate cement > calcium acuminate cement. The heat stability, thermal shrinkage and shrinkage rate at high temperature varied with cement composition. Relationships between thermal expansions of the three hardened cement paste and their hydration substance have been discovered using TG/DTA, XRD and SEM. The results provde guidance that can be used in the application of three types of cement pastes at high temperature.更多还原