Characterization of microstructural damage evolution of freeze-thawed shotcrete by an integrative micro-CT and nanoindentation statistical approach

It is crucial to investigate the evolution of microstructure to understand the deterioration mechanisms of shotcrete under cyclic freezing and thawing (F-T). In this study, nanoindentation and X-ray micro-CT techniques are integrated to characterize microstructural damage of shotcrete and its evolution due to F-T actions. An integrated statistical method of nanoindentation and micro-CT (NI-MCT) is developed with the Gaussian mixture deconvolution method to demonstrate the increase and correlation of the heterogeneous phase in cement paste and interfacial transition zones in the process of F-T cycles. The micromechanical property allows to segment the micro-CT images of cement paste into pores/cracks, porous phase, calcium silicate hydrate, and calcium hydroxide/unhydrated clinker. The integrated NI-MCT method can provide new knowledge on the evolution law of F-T-induced damage in cement paste and serve as an effective tool in characterizing and quantifying the damage and its evolution process for cement-based heterogeneous materials.