Imperfect Interface Effect on Creep Property of Hardened-Cement Pastes: Investigations from Nano to Micro Scales

Abstract

Prediction of the mechanical properties of cement-based materials across scales according to micromechanics-based homogenization is affected by many factors, which include the homogenization scheme, the mechanical property, volume fraction, and geometry of each phase, and the interface property between different phases, and so on. In this study, the micro creep properties of cement pastes with w/c ratios of 0.3, 0.4, and 0.5 were homogenized from the calcium silicate hydrate scale. The influences of the homogenization scheme, phase geometry, and interface property were assessed. The homogenized creep results were then compared to the measured ones by the microindentation technique. It was found that the creep property is underestimated significantly under the perfect interface condition, and the poor assessment cannot be improved effectively by using different homogenization schemes or considering different phase geometries. However, the measured creep of cement pastes by microindentation test can be reproduced by considering the proper imperfect interface between different phases. The imperfect interface is modeled as spring layers of vanishing thickness in the tangential directions for simplicity, which is characterized by only one interface parameter. The larger the interface parameter, the more imperfect the interface, and the interface parameter increases with increasing w/c ratio. The findings in this study suggest that the imperfect interface might be a key factor during the creep upscaling of cement pastes from nanoindentation to microindentation scales.