Foamed bitumen pavements thwart ex-Tropical Cyclone Debbie

Photo of Camp Cable Road on Mt Lindesay Rd intersection underwater during flood

Transport and Main Roads’ investment in research and innovation is paying big dividends in the wake of ex-Tropical Cyclone Debbie, with millions of dollars saved 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, displaying impressive strength in the face of catastrophic weather.

Foamed bitumen stabilised base with a combination of triple blend (a combination of lime, cement and fly ash) stabilised subbase and subgrade has not only provided the required structural strength for the traffic loading, but has stood up to some of the worst Debbie had to offer.

When 3-metre floodwaters inundated Camp Cable Road on the Mt Lindesay Highway, district staff understandably feared the worst. When waters receded, however, the foamed bitumen pavement was found completely intact.

Photo of Camp Cable Road on Mt Lindesay Rd intersection in use

While some conventional thin asphalt/granular pavements suffered catastrophic damage from flooding, foamed bitumen pavements in similar circumstances have shown 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. Additionally, Yeppen floodway in Rockhampton has emerged from the deluge with a clean bill of health.

These are just the latest examples of how foamed bitumen is contributing to a more resilient state road network for Queensland, with the technology already used widely in coastal regions of the state, and districts reporting a success rate of more than 80%.

For Transport and Main Roads, it shows how investing in research, industry consultation and technology transfer is paying off in hard savings.

By utilising foamed bitumen, the department is not only saving on the cost of construction—foamed bitumen costs less per cubic metre than asphalt—but also on the cost of maintaining and rehabilitating roads after natural disasters like ex-Tropical Cyclone Debbie.

Adding to its better long-term performance, foamed bitumen stabilised pavement also exhibits comparable (and in some cases superior) fatigue properties to asphalt, and significantly reduces or eliminates shrinkage cracking compared to cement treated pavements.

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 wetting and coating the finer particles of the pavement material, forming a mortar, and binding the mixture together.

Foamed bitumen stabilisation results in finer particles being coated in bitumen. Millions of fine particles coated with bitumen act like “welding spots” to hold the mineral aggregates together providing a water-tight structure. In addition, coated fines act like “rubber”, providing the flexibility when a load acts on them. These combined effects delivers a pavement has improved fatigue properties, and is more resilient to flooding.

In addition to this, when the structural design includes subbase/subgrade stabilisation using triple-blend additives massively increases the foamed bitumen pavement’s resilience to flooding, and so should be considered anywhere that is subject to this kind of extreme weather.

Through project-linked training, and the development of new testing, design and construction procedures, TMR is delivering this more durable, cost-effective pavement in suitable areas throughout Queensland.

For more information about foamed bitumen technology, see Transport and Main Roads’ MRTS07C (Insitu Stabilised Pavements using Foamed Bitumen).