By Jack McLean, National Manager – Remedial Engineering Services, Freyssinet

Ultra-high-performance concrete and the shift to long-life infrastructure.

Across Aotearoa New Zealand and the wider Australasian region, infrastructure owners are confronted with the growing challenge of aging assets. Many concrete and steel structures – including culverts, bridges, marine assets and retaining systems – were originally designed for service lives of 30–50 years. Today, a significant proportion of this infrastructure is operating beyond that horizon, and the signs of deterioration are becoming harder to ignore. Cracking, spalling, corrosion and water ingress are now common across asset portfolios.

The implications are not just technical. For asset owners, repeated repair cycles are driving up maintenance costs, increasing disruption, and placing pressure on already-constrained capital and operational budgets. In this context, the industry is beginning to shift from short-term intervention strategies towards materials and methods that deliver genuine long-term performance.

Breaking the repair cycle

Traditional repair systems remain essential, but their limitations are well-established. Cementitious mortars and patch repairs can restore functionality in the short term, but they are often vulnerable to the same deterioration mechanisms that caused the original damage.

Permeability, shrinkage, and cracking allow the ingress of chlorides and carbon dioxide, which initiate reinforcement corrosion. In aggressive environments, particularly coastal or high-moisture exposure zones, these repair systems can have relatively short service lives, often requiring replacement within 5–15 years.

This creates a cycle of intervention that is difficult to sustain, particularly for critical infrastructure networks where access, downtime and safety are major considerations.

For New Zealand, where infrastructure is frequently exposed to marine conditions, high rainfall and complex loading demands, there is increasing interest in solutions that address not just the symptoms of deterioration, but also the underlying causes.

A different class of material

Ultra-high-performance concrete (UHPC) represents a significant departure from conventional concrete technology. Developed over the past three decades, it is characterised by a dense, highly engineered microstructure achieved through a low water-to-binder ratio, fine particle packing, and the inclusion of fibres.

The resulting material delivers a combination of properties that are difficult to achieve using traditional systems:

• compressive strengths exceeding 150 megapascals
• very low permeability
• high-tensile capacity and crack resistance
• excellent durability in aggressive environments.

Importantly, these characteristics allow UHPC to function as more than just a structural material; it becomes a durable barrier that resists the ingress of moisture, chlorides and carbon dioxide that drive long-term degradation.

Durability by design

The performance of UHPC is best understood through its ability to limit the key mechanisms responsible for infrastructure deterioration:

• Chloride ingress: This primary cause of reinforcement corrosion is significantly reduced. UHPC has been shown to exhibit diffusion coefficients up to three orders of magnitude lower than conventional concrete. This effectively slows chloride penetration to a fraction of the rate seen in traditional materials.
• Electrical resistivity: This important indicator of corrosion risk is also substantially higher. Laboratory studies have recorded values up to 20 times greater than standard concrete, restricting the electrochemical processes required for corrosion to develop.
• Porosity and moisture movement: These are similarly minimised. With total porosity typically below eight per cent and limited connectivity between pores, UHPC restricts the movement of water and contaminants into the material matrix.
• Carbonation resistance: This is also significantly improved. By limiting carbon dioxide ingress, UHPC maintains the alkaline environment that protects embedded steel, delaying or preventing corrosion initiation.

Taken together, these characteristics position UHPC as a material designed not just for strength, but for durability.

From concept to application

One of the most significant developments in recent years has been the emergence of spray-applied UHPC as a practical repair solution.

Traditionally, UHPC has been associated with precast or cast-in-place construction. Advances in pumping and spray technology now allow it to be applied as a thin overlay, typically between 10–30 millimetres, onto existing structures.

For asset owners and contractors, this opens up new possibilities:

• application without formwork, reducing time and cost
• suitability for vertical and overhead surfaces
• effective use in confined or difficult access environments
• strong bonding to both concrete and steel substrates.

Bond strengths exceeding 2.5 megapascals have been recorded, demonstrating the material’s ability to integrate with existing structures and provide a durable composite system.

This combination of performance and constructability is particularly relevant for infrastructure – such as culverts, tunnels and marine assets – where traditional repair approaches can be complex and disruptive.

Evidence from the field

International experience, particularly in Europe, is helping to validate UHPC’s performance outside the laboratory.

In marine environments, UHPC overlays have been applied to deteriorating quay walls exposed to tidal conditions and high chloride concentrations. Thin sprayed layers have demonstrated strong adhesion, excellent consolidation, and no visible cracking or debonding after several years of exposure.

In transport infrastructure, UHPC has been used to rehabilitate tunnel linings that are subject to moisture ingress and chloride contamination. These applications have delivered improved abrasion resistance, reduced permeability and stable performance under dynamic loading conditions.

These projects reinforce a key point. UHPC is not just a high-performance material in theory; it is a viable, scalable solution in real-world environments.

Whole-of-life thinking

While the up-front cost of UHPC is higher than conventional repair materials, its value becomes clearer when assessed over the full life cycle of an asset.

Traditional repairs may require repeated intervention over relatively short timeframes. By contrast, UHPC-based solutions have the potential to extend service life by 50 years or more with minimal maintenance.

For infrastructure owners, this shift delivers tangible benefits:

• reduced maintenance frequency
• lower life cycle costs
• decreased operational disruption
• improved safety and reliability.

In an environment where infrastructure resilience and funding efficiency are under increasing scrutiny, these outcomes are highly relevant.

Barriers and opportunities

Like any emerging technology, UHPC presents challenges. Material costs remain high and successful application requires specialised equipment, experienced personnel, and rigorous quality control.

Surface preparation, curing practices, and mix design are all critical to achieving the desired performance outcomes. Without appropriate attention to these factors, the benefits of UHPC may not be fully realised.

These barriers are not static, however. With a competent and experienced repair partner to manage the design and application of this technique, these barriers will be suitably overcome. As supply chains mature and industry experience grows, costs are expected to moderate and confidence in application will continue to increase.

A material aligned with the future

The direction of travel for infrastructure is clear: longer service lives, greater resilience and improved whole-of-life performance.

For Aotearoa New Zealand, this includes infrastructure that can withstand coastal exposure, high rainfall and evolving environmental demands while remaining cost-effective to maintain over decades.

UHPC aligns closely with these objectives. Its combination of strength, durability, and adaptability offers a pathway to move beyond short-term repairs and towards infrastructure that is genuinely future ready.

As adoption continues to grow internationally, and local capability develops, UHPC is set to play an increasingly important role in how infrastructure is designed, repaired, and managed across the region.

Images courtesy of Freyssinet.