混凝土持续加载下细观力学过程与宏观构件徐变性能综合研究

Researches on concrete creep never fade charms. The origin of concrete creep is quite complicated, which requires varieties of advanced and innovative theories and techniques. Up to date, concrete creep remains one of the cutting-edge and important topics in the field of modern structural concrete. Due to the coupling between creep and damage, and the multi-phase and multi-scale nature of concrete materials, the progress moves slowly on the concrete creep researches and the existing knowledge of concrete creep is far from being well established. This project intends to investigate the creep behavior and the damage development of concrete under sustained loading both at the meso- and macro- scales, and to illustrate the interaction between the creep behavior and the damage property through experimental study, theoretical analysis, and numerical modeling. Finally, the link between the macro creep and the meso creep of concrete is built. The main researches in this project include: The meso-damage development of concrete under sustained loading and the interaction between the macro concrete creep and the meso-damage development are investigated through a combined techniques. Then a meso-creep model incorporating the effect of the interfacial transition zone and the damage development will be developed based on mesomechanics and damage mechanics. The meso-creep model will be verified and improved based on the experimental results and the finite element modeling. Finally, an improved concrete creep model at the macro scale is to be established from the meso-creep model according to the multi-scale theory. The expected results in this project are of scientific and social benefits, which will contribute to the improvement of the modern concrete creep model and the security of the service safety of concrete structures.

混凝土徐变研究历久弥新，研究对象复杂，表征手段多层次，创新空间大，是现代结构物混凝土领域一个前沿和重要课题。但混凝土具有多物相、多尺度、徐变和损伤相互耦合等特征，导致目前徐变研究进展缓慢、成果仍未成熟。本项目拟通过试验研究、理论分析、和模型建立的方法，在细观和宏观尺度上研究混凝土的徐变行为和损伤发展规律、阐明二者的相互作用机理，建立徐变在细观和宏观尺度上的联系。研究内容主要包括综合采用微、细观力学测试方法、CT扫描技术、细观试样长时加载等实验手段探究持续荷载下材料细观损伤演化规律与宏观构件徐变行为双向影响作用机理；结合细观力学和损伤力学等理论建立考虑界面过渡区及损伤影响的细观徐变力学模型，并基于试验结果和有限元方法验证和完善细观徐变力学模型；最后构建跨尺度徐变理论与计算体系。预期成果对完善现代混凝土的徐变理论体系、保障的结构物安全服役具有重要科学价值和社会价值。

本项目从微细观尺度出发，重点研究细观尺度和宏观尺度上混凝土徐变细观力学过程及其两尺度上的联系。采用先进的设备技术来观察荷载作用下材料的力学性质演化规律，结合显微技术和压痕、划痕方法在纳米和微米尺度上研究混凝土的微观徐变行为，建立微观徐变模型，构建基于微观力学原理的混凝土徐变多尺度模型。为现代混凝土徐变理论体系的进一步完善提供微观层面的理论补充。主要的研究成果包括：（1）采用纳米划痕技术测试水泥基材料在微观层面的断裂性能。从微观角度研究水泥基材料不同物相的断裂性能，对于理解水泥基材料的劣化机理，以及纳米材料对水泥净浆断裂韧性增强机理具有重要意义。（2）考虑界面性质影响的水泥基材料徐变多尺度预测模型。建立细观徐变力学模型并植入计算软件，选择恰当的界面单元来考虑界面过渡区的影响，在细观尺度上数值分析混凝土的徐变行为。（3）硬化水泥浆体的在微观尺度上的徐变（及徐变恢复）性质测试与模拟。本研究提出一种“加载-保载-卸载-再保载”的微米压痕试验制度，实现了水泥净浆微观可恢复徐变及不可恢复徐变的评估。（4）考虑徐变及环境因素影响的混凝土结构物变形与受力计算。建立徐变在细观、宏观各尺度上的理论与具有本质物理意义的计算模型，构建跨尺度混凝土徐变计算体系，应用于一些结构物的力学计算。