Chloride induced mechanical degradation of ultra-high performance fiber-reinforced concrete: Insights from corrosion evolution paths

Chloride-induced corrosion of ultra-high-performance fiber-reinforced concrete (UHPFRC) inevitably affects structural durability. However, the process of multi-fiber corrosion and mechanical deterioration still lacks sufficient understanding. This work aims to reveal the fiber corrosion degradation mechanism from a microscopic to macroscopic view, applying multiple analytical analyses of atomic absorption spectrometry, SEM-EDS, nano-indentation, polarization, and macroscopic mechanical testing. Results show that the flexural strength of specimens decreases significantly with the increase of corrosion degree, and a clear reduction of up to 47% is found at a high corrosion degree. Elastic modulus and nano-hardness of corroded samples vary in a wide range of 30–189 GPa and 0.16–6.41 GPa. With the increase in fiber content, two distinctive corrosion mechanisms are proposed. The corrosion path deteriorates from fiber edge to inner by the invasion of erosive solution through the matrix at low contents (<2 vol%). Considering impurities, greater interfacial defects and macro-cell potential differences at high contents (≥2 vol%), another corrosion path originates from the fiber inner outward to the matrix. Fiber corrosion damages the fiber’s structural integrity and induces matrix deterioration, the micromechanics of the matrix along the fiber edge 20 μm decreases at least 10% more than the concrete matrix. This work firstly sheds light on the mechanical deterioration of UHPFRC from the perspective of fiber corrosion paths considering different initiation scenarios.