Concrete NZ: The case for concrete roads

New Zealand’s approach to road construction has long been dominated by asphalt, but as infrastructure demands evolve, the question of long-term cost-effectiveness and sustainability has become increasingly pressing.

Recognising the need for a thorough analysis of concrete pavement as an alternative, Concrete NZ commissioned Infometrics Ltd to reassess the case for concrete roads. This report builds on earlier studies conducted in 2013, 2018, and 2020, which suggested that while concrete roads may require higher initial investment, their whole-of-life costs, price stability, and environmental performance offer significant advantages over asphalt roads.

The latest findings reaffirm that concrete pavements provide superior cost efficiency over a 40-year life cycle, significantly reducing both maintenance expenses and financial risks associated with price volatility.

Additionally, the study highlights the environmental benefits of concrete, particularly in terms of CO₂ emissions, positioning it as a more sustainable choice for the country’s future road infrastructure.

To test this, 20,000 simulations of roading construction and maintenance costs were run, applying results from overseas and New Zealand data. The results were compelling: concrete roads were found to be between 11.8 per cent and 22.9 per cent cheaper than asphalt roads over their full life cycle, with a weighted average cost advantage of 17.5 per cent. This aligns closely with past findings but is now backed by newer cost data and a refined methodology.

While the report primarily focuses on New Zealand-specific cost data, its findings are echoed in international studies. Across multiple countries, concrete roads have proven to be a more financially sound investment over time, largely due to lower maintenance requirements and more predictable pricing.

A 2017 Australian study by Arcadis, which analysed 72 road construction scenarios, found that concrete roads cost 11-18 per cent less to build than asphalt roads and required 43-55 per cent less maintenance expenditure over 40 years, leading to an overall 25 per cent cost advantage. Similar trends emerged from Canada, the United States, Korea, and India, where whole-of-life analyses consistently favored concrete.

These findings are particularly relevant for New Zealand, given the country’s increasing focus on cost-efficient infrastructure investment. A report conducted in 2013 by consultancy firm Opus to understand the Ruakura Development’s pavement options for each of its various zones remains one of the few local examples comparing concrete and asphalt roads. It suggested that concrete pavements were, on average, 20 per cent cheaper than asphalt pavements over their full life span, reinforcing the conclusions drawn from the global research.

To further validate these comparisons, the report examined price volatility – a crucial factor in long-term financial planning. Unlike bitumen, which is derived from petroleum and subject to volatile global oil prices, cement prices remain relatively stable. Over the past three decades, asphalt prices have fluctuated five times more than concrete prices, introducing an unavoidable financial risk for government agencies and private road contractors.

Additionally, New Zealand’s dependence on imported bitumen heightens this risk. With the closure of the Marsden Point oil refinery, the country now relies entirely on imported asphalt materials, exposing it to supply chain disruptions and cost surges. In contrast, cement is both produced domestically and imported, providing greater pricing stability and supply security.

Beyond financial considerations, the environmental implications of road materials are becoming an increasingly important factor in infrastructure decision-making. Traditional assessments of CO₂ emissions have often pointed to asphalt as the greener option, due to lower emissions during the manufacturing stage. However, these assessments have failed to consider whole-of-life carbon impacts – a crucial oversight that significantly shifts the equation in favor of concrete.

While it is true that asphalt production initially emits less CO₂ per kilometre of road, this advantage is short-lived. The higher frequency of maintenance and resurfacing required for asphalt roads means that, over time, its total carbon footprint catches up to and often surpasses that of concrete roads. When factoring in long-term maintenance emissions, the report finds little to no difference in total CO₂ output between the two materials.

However, one factor decisively tilts the balance toward concrete: CO₂ absorption, or “carbon uptake.” Unlike asphalt, concrete has the ability to absorb CO₂ from the atmosphere throughout its lifespan. According to the Intergovernmental Panel on Climate Change, this natural process can reabsorb 15-30 per cent of the CO₂ emitted during cement production, making concrete a far more sustainable option when viewed over a 50-year life cycle.

In practical terms, this means that a properly designed and maintained concrete road could reduce its total net CO₂ emissions by 35-53 per cent compared to an equivalent asphalt road. Recognising this advantage, the Infrastructure Sustainability Council is now incorporating CO₂ absorption metrics into its sustainability rating tools, which could influence future government procurement decisions.

Overall, the report presents a compelling case for rethinking New Zealand’s reliance on asphalt roads. The evidence is clear: when considering long-term costs, price stability, and environmental impact, concrete roads are the superior choice.

The study confirms that while asphalt roads may appear cheaper in the short term, their higher maintenance requirements and price volatility make them more expensive over time. By contrast, concrete roads, though initially more costly to construct, provide significant savings over their full life cycle, making them a financially responsible investment for New Zealand’s infrastructure future.

Equally important are the environmental benefits. With concrete’s natural CO₂ absorption capabilities, its net carbon footprint is demonstrably lower than asphalt over its lifetime. As sustainability becomes a growing priority in infrastructure planning and policy, the advantages of concrete roads will become even more pronounced.

New Zealand has an opportunity to rethink its approach, prioritising long-term value over short-term cost savings. If policymakers and industry leaders take these findings into account, concrete roads could play a far greater role in shaping the country’s transport infrastructure for decades to come.