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Executive summary
Infrastructure Victoria investigated the economic costs and benefits of investing in climate adaptation for the road network. Certain adaptation measures, such as foamed bitumen stabilisation (FBS), increased construction cost but produced a positive return on investment. Renolith-enhanced cementitious stabilisation is an alternative adaptation measure. Renolith and FBS both immunise roads to water induced degradation. However, Renolith actually reduces the cost of road construction. With Renolith, the normal trade-off of construction cost vs lifecycle cost does not apply. Compared to business as usual (BAU) unbound granular construction, the potential return on investment is infinite (ie. Lower construction cost and lower lifecycle cost).
Context
Engineers Australia February 2023 submission to the House of Representatives Standing Committee on Regional Development, Infrastructure and Transport: Engineering a resilient and sustainable rural, regional and remote road network | Engineers Australia recommended:
…include more climate resilient and recycled materials.
…greater uptake of materials which have waterproofing benefits.
…embed sustainability, resilience and circular economy principles at all stages of the asset lifecycle.
More recently, research by Infrastructure Victoria (Weathering the storm, 2024) found:
Due to the effects of climate change, flooding events in metropolitan Melbourne and regional Victoria are becoming more frequent and existing roads across the state are not sufficiently resilient to withstand their impacts.
Flooding presents significant issues for road infrastructure, causing damage to various components of the road, including road surfacing and pavement, embankments and retaining walls, culverts, and transverse and longitudinal drainage systems.
Infrastructure Victoria investigated the economic costs and benefits of investing in climate adaptation for the road network. Eight adaptation measures were assessed. One adaptation considered in the supporting technical report Adapting Victoria’s infrastructure to climate change – Phase 3: Economic analysis of adaptation for roads was the use of Foamed bitumen stabilisation (FBS).
Foamed bitumen stabilisation
Foamed bitumen stabilisation (FBS) is a pavement treatment methodology involving insitu or plant mix stabilisation of pavement materials with bitumen and lime/cement. It is used to improve the strength of granular materials while retaining a flexible pavement. The process involves generating foamed bitumen by injecting small quantities of water and air into regular road-grade bitumen under high pressure, causing the bitumen to expand up to 20 times its initial volume (Austroads, 2017). In the foamed state, bitumen is highly effective at coating finer particles of pavement material and binding the mixture and making it more resilient to shrink / swell effects.FBS materials and pavements have been the focus of multiple national research projects, spanning more than 10 years, to validate their performance characteristics and improve design approaches. With support from Austroads, Road Agencies and contractors, this research has included full scale construction trials on major arterial roads. The FBS construction process is 25% faster than the traditional pavement construction methodology and the subgrade is exposed for less time which reduces construction risk.
FBS may not be suitable for strengthening all types of existing pavement materials. Suitability is mainly determined by measuring the engineering properties of insitu pavement materials. As an example, in southwest Victoria, the pavements are typically in scoria and may not be suitable for FBS.
The study found that FBS increased road construction cost but produced a positive return on investment.
Stabilisation
FBS is one stabilisation technique. There are many. Each has its advantages in certain scenarios. Austroads AGPT04D-19 states:
The use of stabilisation technology for stabilising and recycling materials for pavement construction and maintenance is widely accepted as a cost-effective method of improving long-term performance and reducing whole-of-life costs of modern, heavily-trafficked pavements.
Cement stabilised vs Renolith vs FBS
Cementitious stabilisation is a very fast and cost-effective construction method, but is susceptible to shrinkage cracking which can be a vector for water ingress. Renolith is a nanopolymer enhancement to cementitious stabilisation which addresses this limitation and improves material performance. It reduces permeability and is highly resilient to shrink/swell effects. Like FBS, Renolith greatly reduces the potential for water-induced damage.
The premise of the Infrastructure Victoria report is that additional investment is required to improve road resilience. However, by pivoting to Renolith-nanotechnology enhanced cementitious stabilisation, both improved resilience and reduced construction costs can be achieved simultaneously. With Renolith, the normal trade-off of construction cost vs lifecycle cost does not apply. Compared to business as usual (BAU) unbound granular construction, the potential return on investment is infinite (ie. Lower construction cost and lower lifecycle cost).
The chart below illustrates the concept.
Renolith-enhanced cementitious stabilisation is highly sustainable. It has been used to form high performing pavement base layers from a wide range of materials including sands, clays, silts, gravels and crushed rock. It has been proven in over 70 million square metres of pavement, including freeways, highways and many sealed and unsealed roads. Many of these pavements were constructed in wet and adverse environments, such as the arctic circle, the swamps of Siberia and monsoonal Southeast Asia.
A summary of the key features of each technique is shown below.
Conclusion
The climate is changing, which increases risks to the road network. Roads are particularly susceptible to extreme wet weather events. Certain adaptation measures, such as foamed bitumen stabilisation (FBS), can reduce the risks. Renolith-enhanced cementitious stabilisation is an alternative adaptation measure. Renolith and FBS both immunise roads to water induced degradation. However, FBS increases costs, whilst Renolith actually reduces the cost of road construction. With Renolith, the normal trade-off of construction cost vs lifecycle cost does not apply. Compared to business as usual (BAU) unbound granular construction, the potential return on investment is infinite (ie. Lower construction cost and lower lifecycle cost).