Corrosion Performance of Galvanised Steel Roofing in the Highveld Industrial Airshed: A Three-Year Mass Loss Investigation

{ "background": "Galvanised steel roofing is a critical structural component across the continent, yet its long-term durability in highly polluted industrial atmospheres remains inadequately quantified. The Witbank-Middelburg priority area represents a severe case of industrial air pollution, posing a significant threat to infrastructure service life.", "purpose and objectives": "This study aimed to quantify the atmospheric corrosion rate of commercially available galvanised steel roofing sheets through direct mass loss measurement over an extended exposure period within this highveld industrial airshed. The objective was to establish a robust corrosion rate function to inform material selection and maintenance scheduling.", "methodology": "Triplicate samples of hot-dip galvanised steel sheet were exposed at four sites with varying pollution gradients. Mass loss was measured quarterly over 36 months. Corrosion progression was modelled using a power function, $C = A t^B$, where $C$ is corrosion loss, $t$ is time, and $A$ and $B$ are fitted parameters. A generalised linear model assessed the influence of sulphur dioxide and particulate matter concentrations.", "findings": "The mean annual corrosion rate at the most polluted site was 42.7 µm/year (95% CI: 39.1 to 46.3), exceeding rates typical of rural atmospheres by a factor of eight. The time exponent $B$ was 0.86, indicating a near-linear corrosion progression. The statistical model showed sulphur dioxide concentration was the dominant predictor of mass loss (p < 0.001).", "conclusion": "Galvanised steel roofing in this industrial airshed corrodes at an exceptionally high rate, leading to a significantly reduced service life compared to benign environments. The near-linear mass loss trend suggests minimal protective patina formation.", "recommendations": "Specifiers should consider using thicker zinc coatings or alternative protective systems for roofing in comparable industrial regions. Revised maintenance intervals, informed by the derived corrosion function, are urgently required for asset management.", "key words": "Atmospheric