Civil Engineering May 2021 | Vol 29 No 4

46 May 2021 Civil Engineering The magic of zinc in corrosion control Zinc is a truly magic metal that few people and engineers appreciate for its multitude of applications and versatility. For those in the corrosion world, where we seek to extend the life of atmospherically-exposed steel, zinc is best-known in terms of corrosion control, writes Simon Norton from the International Zinc Association, Africa Desk. Zinc is an abundant and essential element that is non-toxic and safe to use. It quietly performs magic all around us, protecting railways, bridges, concrete, power pylons and mining structures from catastrophic failure due to corrosion. Zinc is used extensively to coat steel to prevent corrosion. Zinc oxide is a unique and very useful material in modern civilisation. It is widely used in the manufacture of paints, rubber products, cosmetics, pharmaceuticals, floor coverings, plastics, printing inks, soap, storage batteries, textiles, electrical equipment, and other products. Zinc sulphide is used in making luminous dials, X-ray and television screens, and fluorescent lights. Zinc has an extraordinary capacity to protect uncoated steel structures against premature corrosion. If zinc is alloyed with aluminium to form Zincalume, and this is coated onto thin steel sheets (continuous galvanising) and receives a resilient organic coating, then that becomes long-lasting roof sheeting or cladding for buildings. Where zinc really comes into its own is in hot dip galvanising of steel items, wire, poles, steel structures, and reinforcing steel for concrete systems. Once the hot dip gal- vanised item is exposed to the atmosphere and a corrosive environment, the zinc that is metallurgically bonded to the steel starts to perform its magic. Hot dip galvanising of steel takes place in a galvanising kettle. Once the steel is removed from the molten zinc in the kettle, it is ready either to be painted with an organic coating system to give even more corrosion protection to the steel, or it can be left unpainted and used as is and exposed to the atmosphere. When the steel is immersed in the molten zinc in the kettle and removed for cooling, the result is a metallurgically magic system that protects the underlying steel, although in fact with time the zinc is being sacrificed to protect the steel.  A new innovation is patching up South African roads Potholes are a widespread problem in South Africa. Every week, an average of 1 000 potholes are reported to authorities in Johannesburg alone. Shisalanga Construction is tackling the nationwide pothole problem with a new innovation – a prototype pothole patching trailer unit able to patch between five and eight tonnes of asphalt a day. “It’s like transporting a mini asphalt plant conveniently hitched to your vehicle. The trailer is a packaged unit that has everything one might need to patch up potholes successfully,” says Lisa Mills, Financial Manager at Shisalanga Construction. The portable unit significantly streamlines the patching process. The compact trailer can function with as little as three to five workers at a time, thereby reducing the need for large teams of manpower and reducing unnecessary costs. The mobility of the trailer also prevents the back-and-forward nature of transporting hot mix, which can result in excessive costs. Shisalanga’s portable trailer provides a convenient solution: hot storage within the unit can keep as much as eight tonnes of mix suf- ficiently warm without compromising the quality of compaction. To curb the issue of asphalt debris, the pothole patching trailer includes a rejuvenation pack to re-use in situ material taken out of potholes. This technology recycles and extends the life of old asphalt by mixing it on site to be used for repaving. As eco-friendly alternatives to regular hot mix asphalt, Shisalanga’s Eco Asphalt and Warm Mix Asphalt (WMA) both guarantee high performance while simultaneously lowering the carbon footprint associated with paving. Eco Asphalt utilises locally sourced recycled plastic in the binder which enhances the binder properties of the mix. WMA reduces carbon emissions as it can be paved at lower temperatures while still achieving the best compaction to ensure longevity of the patch. “In time our trailer will become a game-changer for SMMEs and municipalities who either don’t have easy access to a plant or don’t have a massive budget for pothole patching,” adds Deane Koekemoer, Managing Director at Shisalanga Construction.  Galvanised zinc protects coastal electrical infrastructure for up to 30 years Shisalanga’s new pothole patching trailer