Corrosion is the primary cause of structural degradation in steel bridges. Surface preparation determines the lifespan of the entire protective coating system. Without the correct cleanliness grade, primers fail to bond. Coatings break down ahead of schedule.
This article covers applicable technical standards, sandblasting techniques for bridge structures, and four real case studies from FES Global Group.
Technical standards for bridge surface preparation
The primary reference is EN ISO 8501-1. It defines steel surface cleanliness grades before coating application. Each grade specifies the required level of rust, mill scale, and contamination removal.
| Grade | Description | Typical application |
|---|---|---|
| Sa 2 | Thorough blast cleaning | Low-exposure structures, routine maintenance |
| Sa 2½ | Very thorough blast cleaning | Standard for steel bridges in C4–C5 environments |
| Sa 3 | Blast cleaning to visually clean steel | Structures in C5-M or CX: fluvial, coastal, marine |
EN ISO 12944 defines corrosivity categories for the surrounding environment. It determines the required protective coating system.
- C4 — industrial zone or moderate coastal environment
- C5 — aggressive industrial or marine environment
- C5-M — marine or high-salinity fluvial environment
- CX — offshore or extreme conditions
Project specifications define the required treatment cycle per structure. The supervising engineer or inspector verifies compliance with the contract specification and EN ISO 8504 (preparation methods).
Sandblasting techniques for bridge structures
Technique selection depends on structure type, surrounding environment, and operational constraints. The project engineer defines the method in the contract specification.
| Technique | Achievable grade | When to use |
|---|---|---|
| Dry abrasive blasting | Sa 2½ / Sa 3 | Exposed steel, zones clear of live traffic below |
| Wet / slurry blasting | Sa 2 / Sa 2½ | Over watercourses, live traffic below, dust-sensitive zones |
| Vacuum blasting | Sa 2½ | Urban environments, enclosed spaces, zero-dust requirement |
| Laser cleaning | Selective | Heritage bridges, listed structures, stone elements |
Working on live infrastructure
Road and railway bridges cannot be closed for extended periods. Site planning must ensure traffic continuity throughout the works. Operational programming is a core part of the contract deliverable.
Operational solutions used by FES Global Group:
- Night shifts and weekend working windows
- Certified aerial work platforms: Zoomlion and Genie to 30+ m
- Fixed side scaffolding for continuous soffit access
- Dust and abrasive containment systems
- Direct coordination with the infrastructure operator (highway authority or railway manager)
On railway structures, all works take place within agreed night-time possessions. Operators are trained and certified for working in proximity to live track.
Case Study 1 — Po River Railway Bridge, Pavia (2025)
Structure: double-track steel truss bridge. Total length: 764 metres.
Line: Milan–Genoa. Client: GEMA S.p.A.
Funding: Italian National Recovery and Resilience Plan (PNRR).
Location: Bressana-Bottarone, Pavia, Italy.
FES carried out specialised surface treatments and steel structure protection. The fluvial environment required a C5-M corrosion protection system. Scaffolding was installed along both sides of the bridge deck. Access was maintained across the full 764-metre length. The project formed part of the national railway renewal programme under the PNRR.
Case Study 2 — A22 Motorway Viaduct, Trento (2025)
Structure: motorway viaduct on reinforced concrete and steel. Section: Trento Sud.
Client: A22 Autostrada del Brennero S.p.A.
Contract duration: April–July 2025.
The A22 Brennero motorway is the primary trans-Alpine corridor between Italy, Austria, and Germany. FES carried out a combined intervention on concrete and steel surfaces. The site operated on night shifts throughout the contract period. No disruption to motorway traffic. Scope included dry blasting, mechanical cleaning, powder coating, and specialist anti-corrosion treatment.
Case Study 3 — Corda Molle Bridge, Brescia (2025)
Structure: dual-arch motorway bridge. Junction A4–A21, Poncarale, Brescia.
Client: Itinera S.p.A. on behalf of Autoviapadane.
Team: 23 specialist operators. Platforms: 6 (Zoomlion + Genie).
Treatment cycle applied:
- High-pressure washing + salt tests + dust tests
- Dry sandblasting to Sa 2.5 on heavily degraded areas
- Surface-tolerant epoxy primer: 300 µm DFT in two coats
- Stripe coat on edges, corners, and bolt heads
- High-performance fluorinated enamel as topcoat
Finishing colours: RAL 7047 for the arches, RAL 5010 for the deck and connecting pipes. Optimal protection in an aggressive urban corrosivity environment.
Case Study 4 — Ticino Bridge, Vigevano–Abbiategrasso (2023)
Structure: four-arch steel road bridge. Provinces of Pavia and Milan, Italy.
Team: 6 specialist operators.
Light sandblasting followed by a full anti-corrosion cycle on all four arches. Fast-curing topcoat to minimise site programme. High UV resistance and long-term weathering performance.
Post-intervention technical documentation
At project completion, the certified applicator provides a full technical documentation package. This is required by the client, the supervising engineer, and the infrastructure authority.
- Technical data sheets (TDS) for all products applied
- DFT measurements per coat and per zone (dry film thickness)
- Salt test and dust test acceptance results
- FROSIO or NACE inspection report
- ISO 8501-1 surface grading records prior to each application
Documentation forms part of the contract deliverable. It is required for warranty validation and regulatory sign-off by the concession authority.
Why choose FES Global Group for bridge works
FES Global Group has been executing surface treatment works on bridges and infrastructure since 2000. Every bridge contract is carried out by certified operators. Supervision is provided by FROSIO or NACE-certified inspectors.
FES manages all phases in-house: surface preparation, protective coating application, quality control, and final documentation. No subcontracting chain. One technical contact for the entire contract.
FES operates in Italy, Germany, Austria, and Switzerland. Certifications and technical references are available on request.