超高性能混凝土(UHPC)是一种具有超高强、高韧性和优异耐久性的新型复合材料。然而，UHPC的拉伸应变率通常不超过1%，一旦开裂将沿着主裂缝不断扩展，急剧降低强度和耐久性。本项目将基于颗粒最紧密堆积理论并借鉴工程水泥基复合材料(ECC)的微观力学和断裂力学设计理论，研究基体、骨料和纤维特性对纤维-基体界面粘结性和界面微观组成及结构的影响，揭示纤维-基体界面过渡区粘结形成和破坏机制。基于纤维-基体界面的应力传递机制，研究并模拟UHPC在静态和动态荷载下的抗拉和抗折性能，建立基于纤维-基体界面特性的UHPC多尺度失效模型。综合利用微观力学、断裂力学理论、统计学理论对纤维拔出荷载-位移关系及相关模型进行分析，确定纤维桥接应力-裂缝开口宽度的关系。根据强度和能量破坏准则，提出基于纤维-基体界面特性的UHPC关键力学性能参数的调控理论和方法，为UHPC满足不同的结构设计要求和应用提供原材料选择依据和理论基础。

Ultra-high performance concrete (UHPC) is a new type of composite material with ultra-high strength and toughness, and excellent durability. Despite those superior characteristics, its tensile strain usually does not exceed 1%. Once it ruptures, it will propogate to form major crack, which can dramatically reduce strength and durability. This proposed project intends to investigate the influences of matrix, aggregate, fiber characteristics on fiber-matrix bond properties and microstructure at the fiber-matrix interfacial transition zones (ITZs) based on the principle of close packing of granular particles and micromechanics and fracture mechanics design theories of Engineered Cementitious Composites (ECC). The interface bond formation and failure mechanisms associated with the ITZs will be elucidated. Based on the stress transfer mechanism at the fiber-matrix interface, the tensile and flexural properties of UHPC under static and dynamic loading will be evaluated and simulated. The multi-scale failure model of UHPC in the basis of characteristics of fiber-matrix interface will be established. The relationship between fiber bridging stress and crack opening will be determined through analyzing the fiber pullout load-displacement relationship and relevant models by means of micromechanics, fracture mechanics, and statistics. Based on the strength and energy criteria, theories and methods for regulating key parameters of mechanical properties of UHPC will be proposed. The research will provide scientific basis for raw material selection and theory for UHPC with different structural design requirements and application.