Proposed changes to the criteria for concrete durability promise to put Australia at the international forefront when it comes to the development of more sustainable, longer-lasting construction materials.
According to Farhad Nabavi, an expert on the sustainability of concrete structures with Xypex Australia, existing international standards governing concrete building materials fail to address one of the primary factors in its premature deterioration.
“Chloride-induced corrosion of steel reinforcement in concrete is one of the most important factors when it comes to concrete service life. It’s very widespread in Australia, accounting for anywhere between 80 to 90 per of steel corrosion in concrete around the country,” said Nabavi to Sourceable.
“Unfortunately we don’t have anything in the standards – not just Australian standards but even US standards, concerning the chloride-diffusion coefficient for concrete as a durability criteria.”
Nabavi notes that scientific studies have also established that chloride-induced corrosion is the primary cause of diminished service life for concrete structures.
“We have chloride induced corrosion and carbonation induced corrosion, but studies have found that the dominant process in the premature deterioration of concrete structures is chloride-induced corrosion of steel reinforcement,” said Nabavi.
This problem is particularly acute in maritime events where buildings are subject to heightened exposure to salt water.
“While most built assets exposed to a marine environment are supposed to have a design service life of around 50 years – meaning that we shouldn’t have to perform any repairs on them during that period of time, in reality we can see that structures in marine environments or exposed ice and salt generally need repair work after just ten or fifteen years.
For Australia the problem of chloride-induced corrosion of the built environment particularly acute, given the coastal concentration of the country’s urban population.
“The liveable cities in Australia are all along the coastline – with many built assets oftentimes within just one or two kilometres of saltwater environments.,” Nabavi said. “Here in Melbourne we have to conduct frequent and extensive repairs because of that chloride diffusion into concrete structures.”
Despite the fact that chloride-induced corrosion has been identified as the primary factor behind concrete decay, Nabavi notes that international standards do not contain specific parameters for ameliorating the problem.
“The chloride diffusion coefficient is one of the most important durability criteria for concrete, but we don’t yet have these factors in our standards – they generally only make reference to the maximum water-cement ratio, minimum compressive strength or maximum crack width,” he said. “If the later were useful or applicable for these structures, we shouldn’t see so many of them suffering from the corrosion of steel reinforcement.
“This shows that the standards need to be reviewed and they need to modified. The current standards are also prescriptive rules, when should move towards performance-based specifications for prolonging the service life of our infrastructure.”
Nabavi pointed out that the concrete industry in Australia is keenly aware of this omission, however, with efforts already afoot for the inclusion of more applicable criteria in materials standards.
“The Concrete Institute of Australia has already taken action to move towards this kind of criteria last year,” he said “They have done a very good job as the revised criteria cover most parameters that influence the durability of concrete and the service life of the structure.”
While the introduction of such criteria could dramatically improve the durability and quality of Australia’s built environments, Nabavi notes that their successful implementation will require the cooperation from industry and improvements to building practices.
“We will need two parallel operations – one is the establishment of standards, the second is increasing the quality of construction practices,” he said. “While the standards are good, it will take some time for them to become established within the industry – there should be some training for companies and engineers in the new durability criteria for concrete structures.”