The South African engineering and construction industry should seek to increase the uptake of refined zinc and zinc coatings to refurbish decaying infrastructure and ensure that newly constructed infrastructure is resistant to corrosion, says zinc-focused professional body International Zinc Association (IZA) director Simon Norton.

The use of refined zinc has various benefits for the built environment, as it can ensure that steel structures do not succumb to the adverse impacts of corrosion, which could cause irreparable damage, potentially resulting in loss of human life or near-fatal injuries should extreme structural damage occur.

Norton says zinc coatings can be used in the rehabilitation of existing buildings or applied during the construction. Developers or engineers could advocate for the removal of existing, ageing structures for hot dip galvanising with zinc; use zinc metal spray on exposed steel if it cannot be galvanised after surface preparation, overcoating it with organic coating or paint; or apply zinc-rich paint after surface preparation, thereafter, coating it with organic top coatings.

“Zinc can be used in its anti-corrosion role in a variety of ways in reviving and reinforcing old or deteriorating steel infrastructure. The deterioration of steel structures could have occurred in painted, atmospherically-exposed steel that was never galvanised and has since rusted. Additionally, in ageing concrete, corrosion of the reinforcing steel will lead to cracking and spalling,” says Norton.

He adds that engineering consultants can offer property owners a turnkey solution by inspecting the building site to identify what type of zinc solution will be required for the steel repair or new steel application.

In the case of a new construction, it is likely that the steel, concrete and/or roofing components will be hot dip galvanised, and any additional zinc thermal sprays or zinc-rich paints will be applied thereafter, alongside a resilient organic topcoat.

“The appropriate zinc anti-corrosion coating must be chosen. If degraded steel can be removed, then it should be hot dip galvanised. If it cannot be removed, then use zinc thermal spray or zinc-rich paints,” he notes.

It is, however, noted that in some cases hot dip galvanising alone will not provide effective corrosion resistance and the steel should be duplex coated, and engineering consultants would be required to advise the client on the best solutions during such processes.

Norton adds that it is important to consider the nature of building components, such as anchors, and whether they will be inserted into soil or concrete. This would require engineering consultants to determine the corrosivity of the soil.

However, the steel will require hot dip galvanising if it is being inserted into concrete platforms or slabs. If a galvanised steel anchor is inserted into soil, it must be overcoated with a resilient organic coating.

Additionally, he says that rehabilitation of steel structures within 10 km of the coast require thorough inspection and should either be hot dip galvanised or coated with zinc-rich paint and then an organic topcoat. 

Norton also highlights the need for continuous education about the use of zinc coatings for anti-corrosion applications and, therefore, prolonging infrastructure lifespan, with the IZA playing an important role by educating consulting engineers about zinc’s benefits when hosting seminars on corrosion protection.

“The South African government must pressurize the minerals process industry to build a modern, zinc refinery in South Africa, so that refined zinc is available for new infrastructure corrosion protection and for export to Africa,” he says.

The step would allow the zinc industry to return to its peak production output, such as it was before 2011 when the country’s yearly consumption of refined zinc was about 129 000 t. Consumption has declined to about 60 000 t a year over the last five years.

“If mining, rail and water treatment plant rehabilitation were booming and local authorities were well managed then the construction industry would have its hands full . . . if government plays its cards right over the next three years, it could unleash a substantial boom, and the resultant use of refined zinc would skyrocket, and infrastructure would be protected for years to come,” he concludes.