Coating test targets concrete cancer

Concrete cancer often ruins the budgets of coastal renovations but a new test to grade concrete coatings should provide homeowners with more protection.

University of Queensland civil engineering student Farshid Homayouni has devised the test which measures the longevity of concrete coatings by measuring its resistance against carbon dioxide.

Concrete is often coated to shield it from concrete cancer, which occurs when carbon dioxide or wind-borne salts penetrate into its pores.

This eats away at the protective layer and corrodes the steel reinforcement inside which causes cracking and spalling of the concrete known as concrete cancer.

It’s a problem that costs more than $200 million a year to fix, according to a 1997 report on concrete infrastructure along the Australian coast.

To prove his test, Mr Homayouni used more than 300 concrete samples, most of which he cast but some he drilled out of Brisbane buildings and bridges such as the Story Bridge.

The samples were exposed to a year of weathering before they were tested in a gas diffusion test rig which showed the degradation of the coating.

Mr Homayouni said his test was more reliable than manufacturers because it used concrete from the field compared to fresh coatings on ceramic tiles or paper in a lab.

There are many different types of concrete coatings, such as water based, polymers and acrylics, but no industry standards.

“Standard testing methods do not provide any dependable guidelines as to the expected life of coatings in different environments and as such maintenance routines cannot be optimised,” Mr Homayouni said.

“Claims of superiority is almost a universal sales pitch . That is unsubstantiated however as there is no proper industry-wide standard that provides a reliable and consistent testing method.”

Mr Homayouni, who is finishing his PhD under supervision of Dr Hamid Ronagh, said he wanted to test all concrete coatings to find the best one. He also wants to pitch the test rig for commercial use by councils, engineers, contractors, homeowners and developers.

In the five years to 2001, the Gold Coast alone spent $80 million patching up concrete cancer, according to a survey of big concrete repairers.

Media: contact Mr Homayouni (phone: 0422 103 591, 07 3365 4157, email: f.homayouni@uq.edu.au) or Miguel Holland at UQ Communications (phone: 3365 2619, email: m.holland@uq.edu.au)