混凝土微-细观断裂机理及模型研究

混凝土开裂是导致结构服役寿命降低的主要原因。由于缺乏微观断裂实验技术，目前实验与理论研究以混凝土宏、细观开裂行为为主，对微观层面的开裂机理认识不足。基于此，本项目将开展以下四个方面的研究：1）基于微观样品的XCT扫描结果，提出混凝土微观结构三维空间分布精确表征方法，建立微观结构的数字化模型；2）开发微观样品力学性能测试方法，研究水灰比、矿物掺合料、龄期等因素对微观力学响应的影响规律，建立微观强度、弹性模量的概率分布方程；3）基于微观结构数字化模型和实测微观力学特征，建立微观断裂模型，揭示混凝土微观断裂机理，建立混凝土微观应力-应变本构关系；4）提出微观与细观断裂模型的有效关联机制，建立微-细观跨尺度模型，将微观应力-应变本构关系传递到细观模型，研究裂缝由微观到细观的发展机理，揭示混凝土微观结构对于细观力学性能的影响机制。研究成果将为混凝土材料的抗裂与增韧设计提供重要的理论依据。

Concrete cracking is the primary cause that decreases the service life of structures. Due to the lack of experimental techniques on fracture testing of the micro-scale sized specimens, most of the current studies, both experimental and numerical, focus on the fracture behavior of concrete at macro- and meso-scales, which neglect the fracture mechanism at the micro-scale. To this end, the current study focuses on the following four aspects: 1) To characterize the 3D microstructure in a high-resolution and build a digital microstructure of concrete on the basis of the XCT techniques; 2) To develop multiple mechanical testing approaches on micro-scale sized specimens and study the influence of water-to-cement ratio, mineral admixtures, hydration time on the micromechanical properties of concrete. Afterwards, probability distribution functions of strengths and elastic moduli at the micro-scale would be proposed; 3) Based on the experimentally measured mechanical responses and digital microstructure, a micro-scale fracture model would be built up to reveal the fracture mechanism and stress-strain constitutive relations of concrete at the micro-scale; 4) A up-scaling approach that connecting models at micro- and meso-scales would be proposed to establish a multi-scale fracture model in which the stress-strain constitutive relations obtained from the micro-scale model would be passed to the meso-scale. The multi-scale would be used for the crack propagation process from the micro-scale to meso-scale and reveal the mechanism on how the microstructure influences the meso-scale mechanical behavior of concrete. The outcome of the current study would offer theoretical basis for developing new cementitious materials with high resistance to cracks.