Multiscale modeling of damage and fracture in freeze-thawed shotcrete

Abstract

Degradation of fracture resistance, which is a phenomenon encountered in shotcrete as exposed to the cold environment, can lead to structural failure. Microstructural damage induced by freeze-thaw (F-T) cycles serves as the presage to macroscopic failure processes. To reveal the fundamental mechanisms of degradation, it is crucial to characterize and model the F-T damage in multiscales for the heterogeneous nature of shotcrete. In this paper, X-ray micro-computed tomography (micro-CT) is employed to describe the F-T damage in microscale and mesoscale shotcrete. Changes of the modulus of elasticity in cement paste and interfacial transition zone are analyzed using the cloud map obtained from the nanoindentation test. Micro-CT images capture the microstructural geometry, such as microcracks, aggregates, pores, and cement paste. Subsequently, microstructure-based finite-element modeling is developed to simulate the overall mechanical properties and fracture behavior of freeze-thawed shotcrete. The effect of F-T-induced damage is investigated on the three-phase fracture processes in terms of load versus deflection curves and cracking paths of shotcrete beams. The modeling results for damage and fracture are validated against the experimental data using the three-point bending tests of shotcrete beams.