What is an expansion joint

Concrete expands in summer and contracts in winter. Traffic loads introduce continuous cyclic stresses. Humidity changes dimensions. Bearings rotate. Bridges move constantly, and an expansion joint exists to manage this movement.

Without it, thermal expansion would generate internal stresses large enough to crack concrete decks, damage bearings, distort supports, or force loads into areas never designed to carry them. The joint creates a controlled discontinuity in the deck, allowing longitudinal movement, and sometimes transverse movement and rotation, while still transferring loads safely across the gap.

You see the same principle in buildings: floor slabs, façade systems, long walls, even ceramic floors use expansion joints. The physics is the same, but the scale and loading are not.

Some short- and medium-span bridges are now built jointless, using integral abutments and transition slabs buried in the embankment to absorb movement. But once spans increase or movement ranges exceed soil accommodation capacity, expansion joints become unavoidable.

But what material are bridge expansion joints made of, and when would you design them with aluminium?

Materials traditionally used in bridge expansion joints

Steel dominates the market, especially in modular and finger-type joints used on medium- to long-span bridges. Steel offers high stiffness and strength, and it’s well understood in design standards.

Rubber (elastomeric) elements are often integrated for sealing. Concrete forms the deck interface. In some systems, composite materials are introduced for corrosion resistance. Steel works, but it comes with weight, corrosion management, and fabrication complexity. In rehabilitation projects especially, added dead load is a serious constraint.

Without it, thermal expansion would generate internal stresses large enough to crack concrete decks, damage bearings, distort supports, or force loads into areas never designed to carry them. The joint creates a controlled discontinuity in the deck, allowing longitudinal movement, and sometimes transverse movement and rotation, while still transferring loads safely across the gap.

This is when aluminium starts to make sense.

Why aluminium is used in bridge expansion joints

Aluminium is not used everywhere in bridge joints, but when it is, it’s usually very strategic.

The first strategic driver is density. Aluminium weighs roughly one third of steel, which matters when it comes to bridge rehabilitation. Lightweight aluminium deck and joint structures can increase load-carrying capacity without replacing foundations or primary structural members. Reducing dead load can extend the service life of the entire structure.

Installation becomes easier as well. We’ve manufactured bespoke profiles in bridge expansion joints for a client who needed it to be in aluminium for this very reason. The prefabricated aluminium joint sections could be lifted into place faster without requiring a crane, unlike when using steel, which reduced how long traffic is closed for and how long the labour needed to be on site for.

There is also the corrosion resistance benefit. Aluminium forms a natural oxide layer that protects the surface. In many environments, this reduces the need for repainting cycles and long-term corrosion management strategies typically associated with steel systems.

And from a fabrication standpoint, steel cannot match aluminium extrusion.

With bespoke aluminium profiles, you can place material exactly where it is structurally required. You can integrate drainage channels, fixing interfaces, stiffening ribs, tolerances for movement, and geometric transitions into a single custom-made aluminium profile. With steel, achieving equivalent geometries often requires welding multiple components together, increasing fabrication time and introducing additional fatigue-sensitive weld details.

From a sustainability perspective, aluminium is fully recyclable without degradation of properties. When end-of-life recycling is included in lifecycle assessments, aluminium systems can achieve a lower overall carbon footprint, particularly in applications where weight reduction improves overall structural efficiency.

In buildings and construction more broadly, aluminium has already proven itself in façades, curtain wall systems, roofing structures, pedestrian bridges, and lightweight decks. The same advantages apply: weight reduction, corrosion resistance, design flexibility, and fabrication precision.

But aluminium is not without challenges.

The aluminium fatigue limit concern

In practice, most welded steel bridge details are also designed for finite fatigue life. Modern design codes such as Eurocode 9 for aluminium and Eurocode 3 for steel define fatigue categories based on stress ranges and detail geometry. In real bridge applications under cyclic traffic loading, both materials require fatigue verification. And aluminium structures are more sensitive to fatigue when exposed to cyclic loading. They are also more sensitive to thermal variation due to a higher coefficient of thermal expansion.

These are not flaws. They are design parameters.

Proper aluminium design avoids sharp stress transitions, abrupt section changes, and stress concentrations. Smooth load paths, appropriate alloy selection, and high-quality weld detailing are critical.

Advanced joining methods such as friction stir welding can improve performance. This solid-state welding process produces low distortion, excellent mechanical properties, and reduced residual stresses compared to conventional fusion welding. For large structural aluminium assemblies, this directly supports fatigue performance and dimensional stability.

And, interestingly, residual stresses produced by constraining thermal deformation are lower in aluminium than in steel (approximately 30% lower). This can be advantageous in certain restrained configurations.

When correctly engineered, aluminium profiles created for expansion joint systems can meet all relevant structural criteria: global stability, local stability, fatigue performance, ultimate limit states, and serviceability deflection requirements.

The material is predictable, but the performance depends on design quality.

Expansion joint considerations regardless of material

Expansion joints are wear components. They sit in one of the most aggressive environments on the bridge: direct traffic impact, continuous cyclic loading, water ingress, de-icing salts, debris accumulation, and snowplough contact. Whether the system is steel, aluminium, or hybrid, it operates under severe mechanical and environmental stress.

They will need to be replaced.

Typical service life ranges from 10 to 20 years depending on traffic volume, climate, detailing, and maintenance strategy. A 10-year replacement cycle in heavily trafficked infrastructure is not unusual. The bridge expansion joint aluminium profile we produced are replaced every 10 years.

The critical distinction is whether replacement occurs because the joint reached its predicted fatigue life under known loading, which is controlled engineering, or because of premature failure due to poor detailing, corrosion, or stress concentration.

No expansion joint should be expected to last the full design life of the bridge. They are designed with a defined service life and integrated into maintenance planning.

Aluminium does not eliminate replacement cycles. Neither does steel. But the question isn’t whether replacement happens, but whether the system delivers predictable performance, structural reliability, and lifecycle efficiency until that replacement point.

Designing bridge expansion joints with aluminium

Consider using aluminium when reducing dead load directly improves the bridge’s performance. In rehabilitation projects, a lighter expansion joint can avoid costly foundation upgrades and extend the life of the existing structure.

It also makes sense in aggressive environments where corrosion and maintenance are major concerns. Aluminium’s natural oxide layer reduces long-term protection requirements compared to steel.

When the geometry is complex, bespoke aluminium extrusion is a major advantage. Custom profiles allow you to integrate drainage, stiffening, fixing interfaces, and movement tolerances into a single engineered section, which reduces part count, limits fatigue-sensitive welds, and improves structural efficiency.

Overall, aluminium for bridge expansion joints is particularly attractive when installation speed, prefabrication, weight reduction, extrusion-led design optimisation, and lifecycle sustainability are project drivers.

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Contact us if you're looking to build your expansion joints with aluminium and need a one-stop-shop to manufacture your bespoke aluminium profile.