Ultra-high performance concrete (UHPC) is widely used for its excellent compactness and durability. However, steel fibers in UHPC may form conductive paths, affecting electrochemical testing of internal rebars. To assess the applicability of current testing standards in UHPC, specimens of UHPC, high-performance concrete (HPC), and normal concrete (NC) with different cover thicknesses are designed. Open circuit potential (OCP), linear polarization resistance (LPR), and Tafel polarization curves are adopted to compare the corrosion behavior during 180 days of chloride immersion. Results show that UHPC has the most negative OCP, followed by NC and HPC. According to ASTM C876, this would indicate the highest corrosion risk for UHPC, contradicting its well-known superior chloride resistance. Hence, ASTM C876 is not applicable to UHPC. Corrosion current density (Icorr) is smallest in UHPC, followed by HPC and NC, consistent with chloride resistance ranking, indicating good applicability of the linear polarization method to UHPC. The anodic Tafel slope is larger than the cathodic one for all specimens, showing anodic control, unaffected by steel fibers. Larger cover thickness leads to higher OCP, higher polarization resistance, and lower Icorr. At 30 mm cover, internal rebars in UHPC are essentially non-corroded.
Kong et al. (Mon,) studied this question.