Problem statement
Shortly after the completion of the shopping center in Storlien, extensive cracking and settlements were discovered in the steel fiber reinforced concrete floor on the ground in premises for Coop, Eurocash and Sportringen. The aim of the project was to map the extent and causes of the damage, including the presence of voids under the floor, and to analyze the composition and design conditions of the concrete.
Results
The investigation showed extensive voids under the steel fiber reinforced concrete floor in storage areas, especially at Coop and Eurocash. At Coop, the slab had settled by about 50 mm with corresponding voids under the floor. At Eurocash, settlements of about 20 mm and voids of 15-20 mm were noted, while Sportringen showed less extensive voids and cracks. Thin-slip analyses showed that the concrete did not meet frost resistance requirements and contained over 15% potentially reactive aggregate particles, which increases the risk of alkali-silica reactions. The steel fiber content of the concrete showed large variations and was on average below the prescribed value. In conclusion, the risk of continued settlement and cracking was assessed as high, with potential consequences for both safety and operation.
Solution
The project was implemented in several stages:
- Visual inspection of storage and retail areas.
- Non-destructive testing with Impulse Response (IR) to identify delaminations and voids.
- Ultrasound tomography (MIRA) to measure thickness and detect anomalies.
- Endoscopy via drilled holes for verification of cavities.
- Thin section analysis of concrete samples for the determination of vct, aggregate and frost resistance.
- Calculations of the required steel fiber quantity for shrinkage sizing.
The methodology provided an overall picture of both causes of damage (lack of subsoil support, variable fiber quantity, shrinkage cracks) and consequences, which formed the basis for recommendations for action.
Equipment
- Impulse Response (IR)
- Ultrasound tomography (MIRA)
- Endoscope (videoscope)
- Core drilling equipment
- Laboratory equipment for barrel grinding
- Standard equipment for visual inspection and documentation
Standards
- EN 1990: Eurocode – Basic rules
- EN 1991-1-1: Eurocode 1 – Loads on structures
- EN 1992-1-1: Eurocode 2 – Concrete structures
- SS 137003:2015 – Alkali reactive ballast
- ISO 16311-1/2 – Condition assessment of concrete structures
