早龄期行为变化对堆石坝面板混凝土开裂敏感性的影响研究

By bridging face-slab concrete (FSC) of a rockfill dam with it’s real performance appear in the face-slab structure, the stress and cracking sensitivity of FSC at early age is predicted. It provides new idea for cracking prevention research of FSC from the view point of behavior changes of concrete at early age. It also provides experimental and research basis for the development from qualitation to quantitation of cracking resistance design and construction of FSC in the national norm. 1) By employing the raw materials of FSC of a large rockfill dam which is building in China, referring to the construction mix proportion, three different kinds of FSC are made including reference FSC (JC), JC with Nano material and JC with MgO, respectively. 2) The temperature history curves which correspond to the different embients (TMC) are obtained by temperature data tested in the face-slab of the rockfill dam as well as by combining the FEM simulation. 3) The temperature-stress tests (TST) are conducted led by the temperature history curve which is the TMC being employed before temperature peak and the designed simulating cracking temperature history part being employed after temperature peak, the law of behavior changes of FSC at early age , physical and mechanical behaviors and the corresponding prediction models are studied. 4) The stress calculation program of FSC is improved by the obtained physical and mechanical behaviors based on the TST. The cracking resistance evaluation method of FSC at early age based on the temperature stress simulation is proposed. 5）Based on the TST results, the regulation mechanism and effect of additive on the cracking resistance of FSC at early age is investigated. It provides reference to cracking resistance measures for FSC.

将堆石坝的面板混凝土(FSC)与其在面板结构中的表现相联系，用现代技术预测其早龄期应力及开裂敏感性。从混凝土早龄期行为变化的角度为面板防裂研究提供新思路，为国家规范中FSC的抗裂设计和施工由定性向定量发展提供试验和研究依据。1）采用国内在建的某大型堆石坝面板混凝土为基准混凝土（JC）,并在JC内分别掺纳米抗裂剂、氧化镁膨胀剂配制三种不同的FSC。2）采用堆石坝面板实测的温度数据，结合有限元仿真计算，获得FSC在不同环境下的温度历程曲线(TMC)。3）温峰前用TMC曲线，温峰后用模拟开裂的自行设计的温度历程曲线引导做温度-应力试验（TST），研究FSC的早龄期行为变化规律、物理力学性能及其相应的模型。4）由TST获得早龄期物理力学性能，改进FSC的应力计算程序，提出其早龄期温度应力仿真抗裂性评价方法。5）基于TST结果，研究外加剂对FSC早龄期抗裂性的调控机理和作用，为抗裂措施提供参考。

从混凝土早龄期行为变化的角度出发，采用先进的温度-应力试验（TST），研究堆石坝面板混凝土(FSC)的开裂敏感性。这为FSC的抗裂设计和施工提供新思路和研究依据。1）采用国内在建的某大型堆石坝FSC的施工配合比为基准面板混凝土（JC）,在JC内分别掺入商用纳米抗裂剂、碳纳米材料（CNTs）和氧化镁膨胀剂（MEA）配制4种不同的FSC（JC、WC、NC和PC）。测试和分析影响抗裂性的FSC的如下基本物理力学性能：初、终凝时间；不同龄期抗压强度、抗拉强度、极限拉伸值、抗拉弹模；胶凝材料水化热；干缩；自生体积变形；线膨胀系数；不同湿度梯度毛细管负压；孔结构MIP。结果表明：按照性能优劣排序，NC面板混凝土性能最优、PC第二。2）结合胶凝材料水化热试验结果和施工现场的环境温度确定FSC的用于TST的温度匹配养护TMC曲线。3）采用TMC、半绝热和恒温三种养护模式做TST，测试4种FSC的温度、变形和约束应力的发展，获得其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、自收缩模型和徐变模型。测试获得4种FSC的各14项早龄期开裂参数，提出优化的层次分析法（AHP），定量评价FSC抗裂性能的优劣，得到PC的抗裂性能最优，其次是NC。4）基于TST获得的FSC的早龄期热膨胀系数模型、自收缩模型和徐变模型，改进混凝土面板的温度应力仿真程序。模拟结果表明可提高仿真精度。5）基于4种FSC的基本物理力学性能、TST和微结构MIP试验结果，研究抗裂外加剂对FSC早龄期抗裂性的调控机理和作用。结果表明：掺入CNTs可改善FSC的微结构，由此可有效提升FSC的抗裂性。