Multi-scale collaborative performance research of ultra high performance concrete: from materials to structures

Abstract

Ultra-high performance concrete (UHPC) is an advanced composite material with multi-scale characteristics and complex microstructure, which has shown great potential for application in fields such as civil engineering, water conservancy engineering, and construction engineering. With the development of structural design and construction technology towards refinement, multi-scale modeling of concrete materials and structures, and integrated material structure analysis have become hot research areas. The multi-scale analysis method developed based on homogenization theory establishes the relationship from microscopic materials to macroscopic components by introducing representative volume elements (RVEs) containing microstructural information. This method can not only accurately predict the equivalent thermodynamic properties of materials, but also reveal their performance evolution laws, providing theoretical guidance for material design and proportioning optimization. This study focuses on the multi-scale mechanical properties of UHPC materials and structures, and systematically conducts computational analysis and research in the following four aspects: (1) multi-scale analysis of UHPC material properties; (2) Multi scale study on fiber orientation and toughening mechanism; (3) Multi scale characterization of interfacial bonding performance between ordinary concrete and UHPC; (4) Multi scale evaluation of bending performance of reinforced concrete UHPC composite beams. The specific research content and main conclusions are as follows: (1) A micro-scale numerical finite model including the coarse aggregates, cement paste, interface zone and steel fibers was constructed using the random modeling method. The concrete damage plasticity (CDP) model and cohesion model were integrated to reveal the damage evolution characteristics of each phase component during the compression process. The numerical simulation results show that the damage initiation in the interface transition zone (ITZ) is earlier than that in the mortar and coarse aggregate phases, and its damage development pattern has significant differences; The stress state of fibers exhibits a compressive tensile transition characteristic, and their toughening efficiency is strongly correlated with the spatial distribution angle. (2) Based on the Mori Tanaka homogenization theory, the influence of fiber volume fraction and coarse aggregate content on the elastic mechanical properties of UHPC was systematically studied through the experiments and multi-scale numerical simulations. Further combined with the continuous progressive damage model, the damage evolution parameters of UHPC under uniaxial tensile, compressive, and four point bending loads were calibrated, and a quantitative correlation model between microscopic component parameters and macroscopic mechanical response was established. (3) The orientation distribution characteristics of fibers near the fracture surface were quantitatively characterized based on image processing technology. The orientation distribution function (ODF) was reconstructed using the mixed closure approximation method, and the reliability of the method was verified through experimental data. A multi-scale strength prediction model considering fiber orientation tensor was established by combining the two-step mean field homogenization method and Puck failure criterion, the collaborative effect mechanism of fiber content and spatial distribution on the tensile properties of UHPC was revealed. (4) A multi-scale interface analysis method based on the equal roughness transformation is proposed. By constructing RVE models with different roughness characteristics, the equivalent traction-separation constitutive relationship of the multi-scale interface is obtained. This research reveals the failure mechanism of interfaces under tensile and shear loads, quantitatively evaluated the sensitivity of roughness parameters to interface strength, and provided theoretical support for the design of heterogeneous concrete interfaces. (5) A multi-scale interface modeling technique has been developed, which maps microscopic geometric features to equivalent mechanical parameters of macroscopic interfaces through the homogenization method. The three-point bending test indicates that the calculation model can accurately predict the structure failure mode, load-deflection curve, and interface slip behavior of composite beams with different interface roughness. The research results show that increasing interface roughness can significantly enhance the overall collaborative performance of composite beams and effectively suppress the development of interface cracking.