Nyrstar Smelter – Protecting New Acid Storage Tanks

Adding Life to Concrete – How MARKHAM protected the concrete of new tanks used for acid storage.

OBJECTIVE

In 2002, the Nyrstar smelter in Hobart replaced six ‘pure solution’ acid storage tanks with four larger-capacity tanks. The tanks store an aggressive acid solution, full details of which are provided in the appendix below.

The requirements for the new concrete in the project included:

• No curing compounds to be used on the inside face.
• Tank lining to bridge any hairline cracks which develop during normal use.
• Lined areas must be resistant to periodic high-pressure cleaning.
• Resistant to impact from tools and equipment that may drop from upper platforms.
• Resistance to sludge build-up.
• Floor to be slip-resistant and resistant to abrasion.

SOLUTION

Hydrogel waterproofing admixture was selected for inclusion in the concrete mix. This provides integral protection against the ingress of the acid solution into the porosity of the concrete, thereby protecting the reinforcing steel as well as the concrete itself.

The resulting concrete has enhanced self-healing properties, meeting the requirement for hairline cracks to be bridged.

Additionally, placement at time of construction was made easier by the admixture providing improved rheology.

RESULTS

At time of construction the pour sequence proceeded well, with a slump of 80mm and excellent pumping placement.

Subsequently the tank performance proved to be in full accordance with the contract requirements.

Further inspection was carried out in 2012 i.e. after 10 years of use in production. At that time the smelter asset engineer stated “It has provided what was needed for this demanding project and no maintenance work has been necessary”. By way of comparison, a neighbouring spill bund of the same age in the same complex, which was untreated, showed notable spalling deterioration.

Comparison with silane-treated elements: at the time of the above inspection, it was noted that silanes had been used for the treatment of a number of concrete elements in other parts of the immediate complex. These had been exposed to fumes only, not ‘pure solution’, yet their average age was 5-7 years and ongoing maintenance was required. This underscores the importance of treating the concrete from within, as a coating alone does not prevent the internal movement and action of chemicals in solution.

Download this case study in PDF format.

This and more case studies are also available for download in our library.