Chloride and Carbonation Synergy on Concrete-Spacer Interfaces: Insights into Durability Performance

This study investigates the influence of cement-based spacers, including site-produced (SSPO) and industrially manufactured (SSIM), on reinforcement corrosion in concrete exposed to chloride ions and accelerated carbonation. Prismatic specimens with a nominal 2.5 cm cover were tested. SSPO spacers exceeded the specified thickness but showed high dimensional variability, while SSIM spacers were more consistent but thinner than required. Under chloride exposure, SSIM reached the most electronegative corrosion potential (− 718.27 mV), with a 0.75% mass loss, followed by SSPO (− 631.40 mV, 0.64%) and SREF (− 572.77 mV, 0.54%). Under accelerated carbonation, corrosion potentials reached − 477.7 mV for SSIM, − 429.2 mV for SSPO, and − 334.9 mV for SREF. Carbonation depths were 23.8 mm for SSIM, 23.6 mm for SSPO, and 22.1 mm for SREF. Despite having the lowest total water absorption (3.77%) and capillary absorption (0.35 g/cm ² ), SSIM spacers underperformed due to insufficient cover and interface discontinuities. A strong correlation (R ²  = 0.8523) was found between mass loss and corrosion rate. These findings emphasize the pivotal influence of spacer geometry, porosity, and interface integrity on the long-term durability of reinforced concrete structures under aggressive environmental conditions.