Manhole Corrosion Protection Technology

Gold Coast City Council - QLD, Australia

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PROTECTA-Mag extends lifespan and reduces cost of manhole maintenance at Gold Coast City Council (GCCC), Queensland, Australia.

case study summary


When the Gold Coast City Council (GCCC) needed to extend the working lives of its manholes, it contacted Calix to conduct a trial of its PROTECTA-Mag technology. The successful trial demonstrated how the technology can dramatically extend the lifespan of manholes, saving the Council money on maintenance and replacement.

  • Demonstrate sewer protection without stopping flow.
  • Achieve a high pH surface area.
  • Penetrate concrete surface and neutralise acid.
  • Inhibit growth of H2S oxidising bacteria.

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PROTECTA-Mag extends lifespan and reduces cost of manhole maintenance at GOLD COAST CITY COUNCIL.

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Benefits of PROTECTA-Mag

No confined space entry – no network shutdown.

Provides an enduring high pH surface with anti-bacterial properties.

Life-long corrosion protection to the asset.

Provides an enduring high pH surface coating.

Penetrates the surface of the concrete to neutralise residual acid near the surface.

The high wall pH inhibits the growth of specific acid forming bacteria (e.g. thiobacillus concretus).

The high pH also inhibits any root ingress.

Spraying is carried out without stopping flow of the sewer and without man entry.

Non hazardous and safe to handle.

The overspray of PROTECTA-Mag entering the sewer flows is complementary and beneficial for any downstream Sewage Treatment Plant (STP) and odour control.


Calix presented their spray PROTECTA-Mag technology for rehabilitation of manholes to Gold Coast City Council (GCCC).

The technology was found to be cost effective, safe and thus decision was taken to have the technology tested. GCCC earmarked a manhole in Ormeau for the trial coating.

The Technology

PROTECTA-Mag is a special magnesium hydroxide slurry with proprietary additives, to allow spray application and fast gelling characteristics on concrete surfaces. PROTECTA-Mag, when sprayed on the surface of corroding concrete firstly neutralises the sulphuric acid present on the concrete. The coating raises the pH of the concrete surface which eliminate the bacteria colonies responsible for producing the sulphuric acid.

When sprayed on the crown of sewer main lines, high pH and corrosion protection are maintained for 3+ yrs.

Calix has designed and built a mobile purpose rigs for “Vertical Spray Applications”, used for corrosion protection of manholes that have not deteriorated to point of structural repair of have water ingreas.

Depending upon the depth of the manholes, the operation can be carried out manually or by auto spray heads lowered on a winch. The corroded manhole is spray cleaned with pressurised water jets and then coated with a PROTECTA-Mag spray using an airless pump. Multiple coats are carried out to achieve a coating thickness of 1 to 1.5mm. The operators carry out a detailed site risk assessment before starting the work and a site clean and sign off before leaving the site. For manholes up to a depth of 3 metres, the entire process lasts around 60-90 mins. For deeper manholes, the process time would be 2-3 hrs. All required MSDS, safety equipment, harnesses, gas meters etc are available on the mobile rig.

The Process

The process is very simple and effective and carried out without stopping the sewer flow and without man entry. Along with manhole walls and benching, accessible areas of the flow canal are also coated. PROTECTA-Mag coatings every few years provides a lifetime protection to the asset. New PROTECTA-Mag coating can be easily applied on the existing surface, unlike other technologies like epoxy where the peeled coating needs to be manually chiselled out.

The coating does not have structural properties, thus structurally compromised manholes cannot be rehabilitated using the PROTECTA-Mag technology.

After arriving at the site, Calix team carried out a detailed site risk assessment including H2S levels around the manhole and other nearby manholes in the Ormeau pump station. Around the manhole on the southern edge of the pump station the H2S was found to be above acceptable levels. This area was assigned as an exclusion zone in the risk assessment.

Tripod was set around the manhole, manhole cover removed and replaced with safety cover.

The manhole and its conditions were surveyed and cleaning and coating process was planned accordingly. There was a metal grill, an overflow in the manhole. The manhole walls showed extensive corrosion, especially the top area.

The high-pressure water cleaning head was lowered into the manhole.

The high pressure water pump was switched ON. The cleaning head with its rotating nozzles were moved along the depth of the manhole cleaning loose concrete and any other dirt on the concrete walls. The cleaning pressure and speed is adjustable as per the degree of cleaning that needs to be achieved. The top around 500mm of the manhole and the underside of the manhole collar were cleaned using a hand held lance, without man entry into the manhole.

The PROTECTA-Mag spray head was now lowered into the manhole (fig 7). PROTECTA-Mag was pumped using the airless pump and coating applied in multiple passes. The underside of the manhole collar and the rear of the manhole cover were sprayed with PROTECTA-Mag using a hand held lance.

The coated manhole was put back on the manhole. All equipment was stored back on the rig and any waste removed from the site.

A sign-off was carried out before the Calix team left the site. One more manhole coated and protected with Calix PROTECTA-Mag spray technology.


The corrosion process

The pH on the surface of any concrete sewer asset is the measure of the corrosion rate, lower the pH higher the corrosion rate (fig 10). Low pH allows colonies of Sulphur Oxidising Bacteria (SOB) to thrive. These SOBs are responsible for oxidising the H2S gas to sulphuric acid leading to acid corrosion. As pH reduces, more bacterial colonies are formed, thus more sulphuric acid generated leading to more corrosion (fig 11). The PROTECTA-Mag has a high pH. On spraying onto the cleaned manhole concrete, it neutralises any residual acid and quickly gels to form a strong bond with the concrete and also a protective layer. The high pH inhibits the formation of bacterial colonies. The high surface area of Calix MgO imparts anti- bacterial properties thus the PROTECTA-Mag coating can resist bacteria much longer.



Calix test method

The direct relationship between concrete pH and corrosion being an established fact, Calix checks the corrosion protection efficacy of its coating technology by testing the surface pH. For conducting this test Sydney Water and thus Calix follow the Australian Standard AS1289.1.1.2001 “Methods of testing soils for engineering purposes”.

For conducting the pH test, Calix scraped the coated layer which also included some concrete behind the coat. These samples were tested for pH as per the test method specified in the standard mentioned above.

To see the detailed results of each test conducted by Calix, click here.


36 months test conclusion

At the 3rd year after initial coating condition of manhole still looks good with some increased staining but overall
coating integrity still good. The PROTECTA-Mag layer continues to strongly adhere to the walls.

pH test results

Higher pH results of scrape tests may be due to lack of base concrete dislodged during scrape. High levels of H2S observed during testing but surface pH remains high. Hence, we can conclude that the asset is protected and free from corrosion.

PROTECTA-Mag – treat the cause, not the symptom

With an emphasis on creating a sustainable future for existing infrastructure, Calix has developed a cost-effective, reliable and innovative solution to corrosion in ageing sewer

Download the Solution Spec Sheet

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