Early-age mechanical properties and microstructures of Portland cement mortars containing different admixtures exposed to seawater

This study investigated the effects of seawater exposure on the mechanical, durability, and microstructural properties of cement mortars, which contained silica fume, metakaolin, or glass powder at two different replacement ratios. Test variables included the exposure conditions, exposure periods, supplementary cementitious material types, and replacement ratios. Compressive, flexural, and pull-off strengths were measured periodically. Mass change, water absorption, and rapid chloride permeability tests were conducted to evaluate the durability performance of Portland cement mortars (PCMs). Microcomputed tomography was utilized to obtain the pore information from representative PCMs. Test results revealed that seawater exposure yielded positive effects, including flexural strength and durability improvements during short-term exposure periods while those effects might not be last for long period. Metakaolin was the most effective supplementary cementitious material to minimize the reduction in compressive strength, while silica fume contributed to durability improvements. On the other hand, PCM containing GP did not show significant changes in strength and durability. Strong correlations between the flexural strength and durability were observed, and it was explained by additional hydration (i.e., matrix densification) of PCMs (except for the GP) due to the seawater curing which filled specific size of pores ranging 50–200 µm.