Bridges (cable trays) are metallic or non-metallic structures used to support and protect cables and wires, which are widely used in the fields of construction, electric power, communication and data centres. Its main materials include steel (galvanised, stainless steel), aluminium alloy, fibreglass reinforced plastic (FRP), etc. The environmental impact and recycling methods of bridge racks differ from one material to another.

1. Environmental impacts of bridge frames 

(1) Environmental impacts at the production stage 

Steel bridge frames: 

The production of galvanised steel bridge frames involves zinc mining and electroplating process, which may generate heavy metal pollution (e.g. zinc, cadmium).

Carbon emissions are high (about 1.8 tonnes of CO₂ per tonne of steel production).

Aluminium bridges: 

The smelting of aluminium (electrolysis) is extremely energy intensive (approx. 15,000 kWh/tonne of aluminium) and has high carbon emissions when relying on thermal power.

However, aluminium is highly corrosion resistant and has a long service life, which reduces the frequency of replacement.

Fibreglass Reinforced Plastic (FRP) Bridges: 

Made from resin and fibreglass, the production process releases volatile organic compounds (VOCs) that can affect air quality.

It is not biodegradable and produces toxic gases (e.g. dioxins) if incinerated after disposal.

(2) Environmental impact at the use stage 

Galvanised steel bridge may corrode the zinc layer in a humid environment, releasing zinc ions to contaminate soil and water bodies.

Stainless steel bridge is corrosion-resistant and has less environmental impact, but at a higher cost.

Glass fibre reinforced plastic (FRP) bridges are acid and alkali resistant and are suitable for the chemical industry, but may produce micro-plastic pollution after aging.

(3) Environmental Impacts at the Abandonment Stage 

If the bridge is discarded haphazardly, the metal parts (e.g. galvanised steel) may leach heavy metals into the soil.

Fibreglass reinforced plastic (FRP) bridges are difficult to degrade, landfill occupies land resources, and incineration pollutes the air.

2. Recycling and Sustainable Management of Bridges 

(1) Recycling of Metal Bridges (Steel, Aluminium) 

Recycling Rate: 

The recycling rate of steel can be more than 90% (about 40% of global steel comes from recycling).

The recycling rate of aluminium is about 75% (the energy consumption of recycled aluminium is only 5% of virgin aluminium).

Recycling process: 

Dismantling and sorting: manual or mechanical separation of different metal bridges.

Crushing and sorting: Magnetic separation of ferrous bridges, eddy current sorting of aluminium bridges.

Smelting and regeneration: smelt into new steel or aluminium.

(2) Recycling Challenges of FRP (Fiberglass Reinforced Plastic) Bridges 

Technical Difficulties: 

The composite structure of glass fibre and resin is difficult to separate, and the current main treatment methods are landfill or incineration (not environmentally friendly).

Emerging technologies (e.g. pyrolysis) can decompose FRP, but they are costly and not yet applied on a large scale.

Sustainable alternatives: 

Development of recyclable composites (e.g. thermoplastic FRP).

Policies promote Extended Producer Responsibility (EPR), which requires manufacturers to be responsible for recycling.

(3) Measures to Increase Bridge Recycling Rate 

Standardised Design: Adoption of easy-to-disassemble structures and reduced use of mixed materials.

Green certification: e.g. Cradle to Cradle (C2C) certification to encourage recyclable materials.

Policy support: EU Waste Framework Directive requires that the recycling rate of construction waste (including bridges) be ≥70%.

3. Environmentally friendly alternatives for bridges 

Material type Advantages Disadvantages Applicable scenarios 

Galvanised steel Low cost, high strength Zinc pollution, easy to corrode Ordinary buildings, power engineering 

Stainless steel Corrosion-resistant, long life High cost Chemical industry, marine environment 

Aluminium alloy Lightweight, corrosion-resistant Higher price Data centre, telecommunication base station 

Fiberglass reinforced plastics (FRP) Acid- and alkali-resistant, insulating Difficulty of recycling, risk of microplastics Chemical industry, waste water treatment plants 

Future trends: 

Bio-based composites (e.g. plant fibre reinforced Future trends: bio-based composites (e.g. plant fibre-reinforced resins) to replace traditional FRP. 

Intelligent bridges (with sensors to monitor corrosion status) for longer service life.

4. Conclusions and Recommendations 

Give preference to recyclable materials (e.g. steel, aluminium bridges) and avoid FRP (unless special needs).

Promote a closed-loop recycling system and establish a network for sorting and recycling construction waste.

Combine policy and technological innovation to improve the recycling feasibility of FRP bridges.