The gold standard

The City of Gold Coast’s road rehabilitation program for 2016 involved some innovative approaches to recycling road pavement, ones that present an insightful case study for industry.With the 2018 Commonwealth Games fast approaching, the City of Gold Coast – the City – has a lot on its plate.

Preparation for the international multi-sporting event is complex and has many factors to take into consideration, one major element being transportation.

As one of the largest local authorities on Australia’s east coast, the City has a network of some 3200 kilometres of sealed roads it needs to maintain.

While it may seem like an imposing task to prepare the city’s road network for the large influx of visitors, the City is already ahead of the game.

Its forward planning and innovative thinking has repeatedly been recognised by industry and its peers.

The City won the Innovation or Excellence in Recycling Stabilised Pavements in Local Government award at the 2016 AustStab Awards of Excellence for its most recent road rehabilitation program.

“The award demonstrates that the City’s pavement and management team is on the right track for innovation and excellence within the industry,” says Bart Bartley, the City’s Coordinator Transport Assets.

“This year, the City road rehabilitation program has pushed the boundaries in terms of innovation, economic and environmental sustainability and community benefits,” he says.

The City has been a long-term advocate and regular user of in-situ stabilisation in its road rehabilitation works. The City’s 2015-16 program of works demonstrated innovative approaches to in-situ stabilisation, which provides some best practice for other local government bodies around Australia.

As part of its 2015-16 program of works and its sustainable pavement management plan, the City has proposed and implemented a pavement recycling program.

The 2015-16 program consisted of a number of urban and rural streets that required rehabilitation. The City accomplished this year’s program work successfully and effectively with its full service stabilisation contractor, Stabilised Pavements of Australia (SPA).

The main works included profiling existing asphalt surfacing (where needed), to maintain surface levels. It also encompassed in-situ cement and foamed bitumen stabilisation in accordance with Queensland Department of Transport and Main Roads specifications, compaction and proof rolling, and reinstatement of localised areas of weak pavements.

As the majority of works were undertaken in residential and high-traffic areas, the City recognised that transient dust emissions from traditional ground spreading on site was a risk for the environment and the community.

The tender for the works was released to market with the condition that all cement spreading needed to be completed using enclosed spreading methods. SPA met these requirements by using a Wirtgen 2500K enclosed spreading stabiliser with an integrated additive tank and water trailer. Not only could the contractor spread material at calibrated rates, but the machine also generated minimal dust in the process.

As a result, there were no dust issues, concerns or complaints raised by residents or the general public over the course of the program.

In addition to employing innovative dust management techniques, the City was keen to use foamed bitumen with general blend (GB) cement as the secondary agent on two busy streets – Old Coach road in Upper Coomera and Hardy’s Road in Mudgeeraba.

“The main incentive for trialling foamed bitumen with GB cement was to meet the challenge of minimising the disruption to local traffic and time delays,” says Mr. Bartley.

The City also wanted to improve the early strength of the pavements for traffic, the gravel performance quality and extend the pavements lifespan.

The mix design used was 3.5 per cent C170 bitumen and 1.5 per cent GB cement. This specification required a working time of four hours, so SPA and City elected to use two stabilisers consecutively.

One machine was used to incorporate the secondary agent (the cement), and the other for the foamed bitumen. This allowed SPA to quickly follow mixing of the foamed bitumen as the bitumen tanker was connected and ready to go as soon as the cement pass was done.

“The addition of cement significantly reduces the moisture susceptibility, increases the strength stability, tensile strength and helps develop a high elastic modulus in the stabilised material,” adds Mr. Bartley.

The City anticipates that the new pavements will last approximately 20 years with thin asphalt surfacing. It is undertaking ongoing pavement testing and monitoring to evaluate the pavement and material performance.

The City’s 2016 pavement rehabilitation program involved the stabilisation and recycling of existing, previously stabilised pavements.

The suite of works included a number of streets being re-stabilised 20 years after its first recycling service. One key example is Yarrimbah Drive in the suburb of Nerang.

The City and SPA used the street as a trial for the combined used of GB cement and a propriety liquid polymer. The mix design incorporated 3.5 per cent GB cement and 1 per cent Global Road Technology’s (GRT) polymer cement modifier (PCM), which was trialled against an adjacent section on the same street using just the 3.5 per cent GB cement.

During the works, the road was exposed to 200 millimetres of rainfall and, while the conventional cement stabilisation section was sealed, due to construction logistics, the section that contained GRT’s PCM was not. Both sections were opened to traffic during this period.

The City found that the section containing GRT’s PCM performed exceptionally well and the product proved its worth under extreme environmental conditions.

Like its combination in-situ foam and cement stabilisation, the City continues to monitor these pavement treatments to see how each section performs.

As part of the 2016 program, the City successfully completed eight pavement rehabilitation and recycling projects covering a total 30,000 square metres.

“The City’s in-situ pavement recycling techniques offer an innovative and sustainable pavement rehabilitation option, when compared against total reconstruction using standard replacement options,” says Mr. Bartley.

He asserts that the program is achieving some significant milestones for the CIty, particularly in meeting its environmental sustainability targets.

The program overall, for instance, involved the recycling of 81,100 cubic metres of existing granular base material.

“The pavement recycling has saved the city many cubic metres of virgin quarry materials being imported to site, and saved the existing pavement material from being hauled and wasted in a landfill,” says Mr. Bartley.

Likewise, the successful program has resulted in numerous economic savings.

The cement in-situ stabilisation projects provided savings of $550,000, or 67 per cent of the base layer reconstruction or granular replacement cost.

The combination of cement and foamed bitumen in-situ stabilisation projects resulted in savings of $270,000, or 46 per cent on the cost of base and surface layer reconstruction.

“Pavement rehabilitation and preservation is a long-term, rewarding process when managed and implemented efficiently. These can cost between 25 per cent and 50 per cent less when carried out at the right time,” says Mr. Bartley. “By applying cost-effective surfacing treatments to structurally sound pavements at the right time – every 20 years, for instance – the pavement can be restored almost to its original condition and could last up to 80 years.”

Following the success of its 2016 program with SPA, the City is looking at continuing future stabilisation programs using the same full-service format, and is likely to also include the surfacing component to be managed by the successful contractor as well.

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