Evaluating mechanical properties and failure mechanisms of hardened binder paste in ultra-high performance concrete through a microscale structure driven multiscale modeling framework

Accurately evaluating mechanical properties and failure mechanisms of hardened binder paste (HBP) is of critical importance to the design and service of ultra-high performance concrete (UHPC). In practice, it remains challenging due to the highly complex microscale structure of HBP in UHPC. To that end, this study proposes a microscale structure driven multiscale modeling framework, in which the intrinsic heterogeneity of HBP is fully accounted for. The microscale modeling consists of a high-resolution X-ray computed tomography test (XCT) for acquiring the realistic microscale structures, a greyscale-to-property mapping derived for addressing the micromechanical heterogeneity among individual voxels, and a phase-field method for performing the tensile fracture simulation. The macroscale modeling manifests itself as an upgrading of micromechanical properties by means of a non-coupled parameter amplification method and the phase-field method. Mechanical properties, i.e., elastic modulus and tensile strength are compared between modeling and experiment for the sake of validation. Along with that, distinct failure mechanisms at the micro- and macro-scales are revealed in details of crack nucleation, propagation and coalescence. Special attention is paid to a fundamental interpretation of the model parameters. Overall, the proposed multiscale modeling framework offers a novel numerical tool for evaluating mechanical properties and failure mechanisms of cementitious materials with multiple binders, particularly advancing the understanding of structure-property relationships in UHPC.