Micro-Mechanical Properties of Individual Phases in Cement Pastes under Brine Solution Using Nanoindentation and Scanning Electron Microscopy

Abstract

Understanding the micro-mechanical properties and the microstructure of cement-based materials under the saline lake environment in western China can provide a scientific basis for the durability design. In this study, cement pastes ((w/c=0.35) and (w/c=0.53)) were prepared and soaked in brine solution to carry out the dry-wet cycle test, the chemical composition of which is similar to saline lake solution. The micrographs of corroded regions and corrosion products were observed and analyzed under scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Micro-mechanical properties of different phases were tested by nanoindentation, and multi-peaks fitting was carried out for the experimental frequency distributions of the indentation modulus and indentation hardness by Gaussian function. In the meantime,the statistical distribution of micro-mechanical properties was summarized for the hydrates in corroded cement paste, which has included the low density calcium–silicate–hydrates (LD C-S-H gel), high density calcium–silicate–hydrates (HD C-S-H gel) and calcium hydroxide (CH). The results show that micro mechanical properties of each phase in cement paste after brine corrosion decreased significantly. In addition, the water-cement ratio has little effect on the micro mechanical properties, but much effect on volume fraction of each phase.