Pore structure of CO₂-cured seawater sea-sand concrete with sufficient carbonation and its mechanical behaviors under uniaxial compression

Seawater sea-sand concrete (SSC) structures reinforced with fiber reinforced polymer (FRP) bars were proposed to capture CO₂ by means of carbonation curing in this study. FRP-SSC structures allowed sufficient carbonation to occur since the steel corrosion in traditional reinforced concrete structures would not exist. Herein, the pore structure of CO₂-cured SSC with sufficient carbonation was examined, and the mechanical behaviors under uniaxial compression were also investigated. MIP testing was employed, and surface fractal dimension in various pore-size regions was calculated. The results indicate that CO₂ curing leads to a more significant variation in smaller mesopores of SSC than CC. Regarding middle capillary pores, the surface fractal dimension in almost all CO₂-cured specimens ranges from 2.6617 to 2.8124, which means that these pores show distinct fractal characteristics, but this phenomenon does not be observed in water-cured specimens. This indicates that CO₂ curing can greatly reduce ink-bottle pores in concrete. Furthermore, the compressive strength gain of CO₂-cured SSC with sufficient carbonation is above 30% at the 180-days age. The compressive strength gain can be attributed to the improvement in the surface fractal dimension. Moreover, CO₂-cured specimens exhibit higher peak stress, smaller peak strain, and greater elastic module, resulting in lower plasticity. Consequently, CO₂ curing renders SSC and CC more brittle.