基于温度-应力试验的超高掺量粉煤灰常态大坝混凝土早龄期热裂性能研究

The cracking resistance behavior of the eco-energy saving and high-performance concrete UHVFACDC at early age is studied by bridging the dam concrete material with it's real performance appear in the structure. It provides new idea for temperature control and cracking prevention of dam from the view point of raw material constituents. It is expected to bring remarkable energy-saving and environmental protection benefits as well as durable dam. (1) The ultra-high volume fly ash conventional dam concrete (UHVFACDC) can be obtained by changing test and evaluation method of workability as well as optimizing mix design which takes the raw material constituents, w/b ratio and temperature into consideration. (2)The temperature-stress tests (TSTM) are performed led by the measured temperature history curves in the internal part of the dam. The physical and mechanical behaviors, mechanism and prediction models at early age are investigated from the viewpoint of wholism which takes temperature, restraint, deformation and stress into account. Thus, the cracking resistance evaluation method and indexes of UHVFACDC at early age are proposed based on the test results of TSTM. (3)The temperature stress FEM simulation program of dam are improved by employing the reliable thermal and mechanical models based on the TSTM tests. Thus, the temperature field and stress field of dam which come near the truth are achieved. The cracking resistance evaluation method and indexes at early age are also proposed based on the temperature stress FEM simulation calculation. The calculated cracking resistance index is verified with the tested result of (2) each other. (4)Finally, the cracking resistance behavior at early age is compared with that adopted different temperature control measures. The cracking resistance mechanism of UHVFACDC is clarified.

从大坝混凝土材料与其在结构中的性能相联系的整体论出发，研究生态节能高性能"超高掺量粉煤灰常态大坝混凝土（"超高掺砼"）"的早龄期抗裂性。从原材料组份角度为温控防裂提供新思路，以获得显著的节能环保效益和耐久的大坝。（1）改变工作度检测和评价方法，综合考虑原材料组份、水胶比和温度等因素，优化配合比，获得粉煤灰掺量高达70%以上的"超高掺砼"。（2）以现有大坝内部实测温度历程曲线为引导做温度-应力试验（TSTM），综合考虑温度、约束、变形和应力等因素的耦合作用，研究其早龄期物理力学性能、机理及模型。基于TSTM提出"超高掺砼"的早龄期抗裂性评价方法和指标。（3）基于TSTM建立可靠的热学和力学模型对大坝温度场和应力场进行仿真计算。提出温度应力仿真早龄期抗裂性评价方法和指标。并与（2）的结果相互验证。（4）对比采取不同温控措施的两种大坝混凝土早龄期抗裂性能，阐明"超高掺砼"的抗裂机理。

采用先进的温度-应力试验(TST)，研究超高掺量粉煤灰常态大坝混凝土（F80）的早龄期物理力学性能和抗裂性。从原材料组份角度为温控防裂提供新思路，为改进大坝温度应力仿真有限元程序提供依据。主要研究内容和成果如下：（1）以大岗山210m高双曲拱坝35%掺量粉煤灰C18040混凝土为基准混凝土(F35)，在保证和易性和强度与F35基本一致的条件下，用等浆体体积法采用Ⅰ级、Ⅱ级、Ⅲ级粉煤灰和统灰分别等质量取代35%、60%、70%、80%、85%、90%水泥，并大幅度降低用水量和水胶比，研发出F80。测定二者的坍落度、含气量、维勃稠度VB，并测试其不同龄期的各项物理力学性能。结果表明采用F80可降低成本。（2）采用温度匹配模式（TMC）和绝热模式(AC)两种温度养护历程，综合考虑温度、约束、收缩等因素，进行TST，测得2种大坝混凝土的早龄期物理力学性能和发展规律。建立其早龄期热膨胀系数模型、自生收缩模型和徐变模型等，作为输入材料模型改进大坝温度应力仿真有限元程序。测得2种大坝混凝土各14项早龄期抗裂指标，结合其中的开裂温度、开裂应力、应力储备、最大压应力和第二零应力时间等特征值，基于层次分析法提出新的早龄期抗裂性综合评价方法。结果表明，无论AC还是TMC养护模式下，F80的开裂敏感性更低。（3）用改进的温度应力仿真程序，计算大岗山大坝的热应力，提出温度应力仿真早龄期抗裂性评价方法。由大坝仿真计算发现，热膨胀系数时变性对混凝土温度应力仿真影响较大，对早龄期温度应力仿真影响尤为显著，这有助于更好地探究大坝混凝土早期的开裂难题。（4）采用三种温控措施：F35大坝原温控措施；不通冷却水；简化的温控措施，计算F80大坝，所得大坝混凝土的抗裂性不低于F35大坝。因此采用F80代替F35，可从原材料组份角度简化温控措施。F80更经济、环保，是性能优且具有发展前景的可持续发展的大坝混凝土。