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.
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.
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 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.
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.
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 AS12126.96.36.1991 “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.
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