Bridge design ticks all the boxes for sustainability
The long-running debate around climate change and carbon pricing mechanisms has become synonymous with sustainability for many people. However, in order to deliver true sustainable outcomes for transport infrastructure, it is necessary to consider a broad range of economic, social and environmental aspects, explains David Coe, Director, pitt&sherry.
“An excellent definition of sustainability for the transport sector is the one devised by VicRoads, which is used to focus their commitment to sustainability,” said Coe. “It states, ‘the ability to meet the needs of society to move freely, gain access, communicate, trade and establish relationships without sacrificing other essential human or ecological values today or in the future’. We can see from this definition that there is no reference to climate change or reducing carbon emissions, it is about providing a balanced approach to transport for our society.”
In developing the definition, VicRoads has developed key indicators under INVEST (Integrated VicRoads Environmental Sustainability Tool, developed in 2011) which include air quality, biodiversity, cultural heritage, stakeholder engagement, noise management, design and resource management. The tool is one of several developed by road authorities worldwide to indicate the sustainability of transport projects.
“The INVEST tool is ideal for benchmarking projects to ensure that sustainability issues are addressed,” said Coe. “Bridges form an integral part of most transport infrastructure projects and bridge engineers are strongly placed to influence the sustainability outcomes of such projects. Indeed, it can be argued that bridge engineers have always been involved in delivering sustainable solutions through the design, construction and maintenance of bridges and associated structures.”
To highlight the point, Coe cites a number of examples:
- As part of the City of Melbourne’s rehabilitation of Princes Bridge, the heritage-listed structure was strengthened to accommodate increased traffic loads while the facade was refurbished to maintain the heritage features of the structure. During the removal of the lead-based paint, it was important to provide maximum dust containment, mitigation and disposal to minimise the effects of the paint dust on air quality.
- As part of the replacement of the Sorell Causeway bridge in Tasmania, there was extensive stakeholder engagement on the location and key design aspects for the new structure. As part of the environmental considerations for the new bridge, which crosses the Ramsar listed Pitt Water Nature Reserve, it was necessary to relocate an endangered species of sea star to other areas within the reserve before construction could commence.
- During the final stages of planning for the Brighton Bypass, artefacts dating back at least 20,000 years were discovered on the levees to the Jordan River. The stakeholder engagement process was complex, and at times controversial, and included several proposals to protect the important Aboriginal heritage site. In the end, the compromise solution was to construct a 70 m span bridge over the levees. The design and construction required the bridge to be launched over the site to minimise impact of the structure and associated construction activities.
“We can see from these examples, and there are plenty of others, that bridge engineers have integrated a broad range of tools and considerations into their design and construction processes that embed, and often deliver, innovative, sustainability solutions. It is a natural part of their psyche, to design new bridges and rehabilitate existing structures to meet the future needs of society while minimising the impact on the environment. It is about optimising the use of materials to deliver efficiently designed durable new bridges and it’s about strengthening and widening existing bridges to deliver rehabilitation solutions to extend their useful life,” says Coe.
In order to deliver the required strength to carry current and likely future loads along with the required minimum 100-year design life, the majority of bridges will continue to extensively use steel and cement as primary construction materials. Both materials have high levels of embedded energy and produce large quantities of greenhouse gases in the production phase. “While there are some very interesting developments around geopolymer cement that would substantially reduce the carbon footprint of concrete, it is likely traditional cement-based concrete will be used for the majority of bridge construction in the foreseeable future,” says David Coe.
“The key driver to reducing the level of steel and cement has been to lower the overall cost of a project. To do that, bridge engineers and construction companies have utilised alternative materials that maintain, and often enhance, the integrity of the bridge at a more competitive rate. The use of fly ash and blast furnace slag in concrete mixes has been common practice for many years. In recent times it has been labelled as ‘green cement’, which it is, but is certainly not a new concept to our industry.”
The producers of steel and cement are liable entities required to pay the ‘carbon tax’ under the Clean Energy Act. As these companies have been deemed to be internationally trade exposed, under the Act they have a 94.5% carbon price shield. “The end result to the construction of bridges is a 0.1 to 0.2% price increase, which is relatively negligible,” says Coe.
“We are starting to see a greater usage of alternative materials such as fibre reinforced polymer (FRP), hybrid composite beams (HCB) and geopolymers. Quite rightly, the general use of these alternative materials is driven by the requirement to deliver sustainable economic solutions. As the cost of producing these materials reduces and understanding their long-term properties increases, their use, most likely for specific solutions, will become more widespread.
In essence, bridge designers and engineers are enablers of sustainability. The guiding principles for INVEST for transport - accessibility, reliability, safety, travel time and consideration of environmental and social impacts - go well beyond carbon emissions and the carbon tax. The solutions developed by bridge engineers to extend and strengthen an existing structure or to design a new bridge consider material usage, environmental and social impacts to deliver cost-effective solutions with a minimum design life of 100 years.
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