Problem
The culvert under the boiler plant in Valdemarsvik showed extensive damage in the form of cracking, corrosion and severe degradation. Damage was concentrated in areas under the boilers themselves, there were two boilers, – ie where the largest load was. The purpose of this project was to carry out a condition assessment, analyze the load-bearing capacity and develop proposals for measures to restore the function and safety of the structure.
Investigation of the culvert.
Results
The inspections showed that the reinforcement of the floor and diagonal beams was heavily corroded and in several cases no longer effective. The depth of carbonation was measured at 20-40 mm, which in combination with small cover layers is one reason for ongoing reinforcement corrosion, another is the lack of maintenance since the facility was built more than 50 years ago. Chloride levels were low (<0.4%). Numerical modeling showed that the structure under one of the boilers was basically carrying the load through the arch action, as the reinforcement capacity was exhausted. Crack widths exceeded allowable levels according to the Eurocode. The conclusion was that the structure did not meet requirements in either service or ultimate limit states and that urgent strengthening measures were necessary.
Solution
The survey was conducted using a combination of:
- Visual inspection of boiler room and culvert
- LIDAR scanning for 3D documentation of the construction.
- Georadar (GPR) and ultrasound tomography (UPE) to map reinforcement and delamination.
- Sampling for carbonation depth and chloride content.
- Numerical analysis in AxisVM to analyze the bearing capacity.
Proposals for action included:
- Casting of new foundations
- Scrapping of box girder and repair measures of cross girder with new reinforcement and concrete/shotcrete.
- Repair and reconstruction of floor slabs with new reinforcement
- Redirection of vapor emissions to prevent future vapor blasting.
The methodology ensured an overall view of the structure and provided a basis for long-term sustainable reinforcements.
Equipment
- LIDAR scanner
- Georadar ((GPR)
- Ultrasound tomography (UPE)
- Coating thickness gauges
- Equipment for carbonation and chloride sampling
- Numerical analysis software (AxisVM)
Standards
- EN 1990: Eurocode – Basic rules
- EN 1991-1-1: Eurocode 1 – Loads on structures
- EN 1992-1-1: Eurocode 2 – Concrete structures
- EN 1504 – Repair and protection of concrete structures
- ISO 16311-1/2 – Condition assessment of concrete structures
- SS-ISO 13822 – Assessment of existing structures
