Hydration and microstructure of cement paste mixed with seawater – An advanced investigation by SEM-EDS method

This study aimed to investigate the microstructural hydration features of Portland cement incorporating with natural seawater (SW). Special attention was paid to characterizing the pore structure, hydrated and anhydrous phases using microscopy techniques, such as secondary electron (SE), backscattered electron (BSE) imaging and energy dispersive spectrometry (EDS) mapping. Through the utilization of algorithms, information extracted from these methods underwent self-corrected, denoising, and imaging calibration, which significantly contributed to the calculation of pore volume, identification and segmentation of various phases, and quantitative characterization. By leveraging the chemical and spatial information from EDS mapping, highly detailed distribution maps of the different cement phases could be obtained, surpassing the conventional BSE grayscale segmentation method in phase identification. Statistical analysis revealed that the deviation of the phase quantification was reduced when using a magnification of 250 times. Higher content of hydrate phases with lower porosity can be observed in SW samples exhibited a higher content of hydrate phases with lower porosity, indicating a stimulated hydration effect. However, accurately determining hydrate phases with small crystal sizes, such as ettringite, necessitated an increase in mapping resolution. Therefore, the use EDS mapping for quantification of various cement phases in submicroscopic and microscopic characterization is both feasible and promising.