Amid the devastation caused by Cyclone Debbie in March, Queensland’s foamed bitumen stabilised pavements have emerged unscathed.
Investing in research and innovation has paid big dividends for Queensland’s Department of Transport and Main Roads, with millions of dollars saved in the wake of Cyclone Debbie through more resilient pavements.
The department’s foamed bitumen pavements, which when constructed in the right environment with appropriate stabilisation are more resilient to flooding, have survived unscathed in some of the worst-hit parts of the state.
When 3-metre floodwaters inundated Camp Cable Road on the Mt Lindsay Highway, district staff understandably feared the worst. When waters receded, however, the foamed bitumen pavement was found completely intact.
While some conventional thin asphalt/granular pavements, such as Rosewood-Karrabin Road in Ipswich, suffered catastrophic damage from flooding, foamed bitumen pavements in similar circumstances showed amazing resilience.
The Bruce Highway (Sandy Gully) near Bowen showed no evidence of damage despite heavy rainfall. Similarly, pavement construction in Warrill View (south of Ipswich) was able to continue without delay, after the unsealed foamed bitumen pavement was inundated. Yeppen floodway in Rockhampton also emerged from the deluge with a clean bill of health.
Transport and Main Roads Chief Engineer Julie Mitchell said these are just the latest encouraging examples of foamed bitumen’s resilience.
“We are already using this technology widely in coastal regions of Queensland, and seeing excellent results,” said Ms. Mitchell.
“By using foamed bitumen the department is not only saving on the cost of construction, but also on the cost of maintaining and rehabilitating roads after natural disasters like Debbie.”
But what is foamed bitumen, and how does it work?
Foamed bitumen is formed by injecting a small quantity of cold water into hot bitumen to produce an instantaneous expansion. In this foamed state, bitumen is highly efficient at coating the finer particles of the pavement material.
These coated fines act in two ways: first as ‘welding spots’, binding together mineral aggregates in a water-tight structure, and second as ‘rubber’, providing greater flexibility under loading. These combined effects deliver a pavement with improved fatigue properties and greater resilience to flooding.
This resilience to flooding is massively increased when the foamed bitumen stabilised base is combined with a subbase and subgrade stabilised with triple blend (a mix of lime, cement and fly ash).
Through project-linked training, and the development of new testing, design and construction procedures, Transport and Main Roads is delivering this more durable, cost-effective pavement in suitable areas throughout Queensland.