ASCET is an international research project initiated by WGIAGE1 OECD2 / NEA3. WGIAGE Concrete subgroup is a working group within the OECD / NEA whose task is to address issues concerning
- the maintenance of the integrity of concrete structures,
- proposals for general principles to optimally handle the challenges of integrity, especially with regard to ageing of concrete structures.
The aim of the ASCET project is to create a basis for general recommendations regarding management of ageing related concrete degradation in nuclear facilities. The goal is to produce comprehensive recommendations for numerical simulations of concrete degradation mechanisms. In ASCET phase 3 the participants were able to perform numerical simulations with access to test results from previous experiments with degraded concrete structures.
A bond-slip model was used for numerical simulations with a finite element program. The bond-slip model used bond-slip laws to connect the reinforcement to the concrete.
The numerical simulations showed that the
- model can have a significant impact on crack-pattern, failure mode and ductility,
- failure load capacity is relatively independent of the bond interaction between the concrete and the reinforcement,
- model was very sensitive with regard to the stiffness of the bondslip. Cliff-edge effects in the load-displacement curve were found for small changes of the stiffness. These effects were, in each case, accompanied by a changed failure mode and crack-pattern.
- Alkali Silica Reaction (ASR) effects on the bond itself were not studied. But, it was shown that a more successful simulation of a ASR-affected shear wall was obtained if a lower-than-average bond stiffness was used.
Degradation of concrete structures important to safety have been identified by SSM as a potential problem area since the Swedish nuclear facilities are getting older. The results from this research project are therefore valuable when it comes to ageing management and radiation safety assessments of degraded concrete structures in nuclear facilities.
1 Working Group on Integrity and Ageing of Components and Structures
2 Organization for Economic Co-operation and Development
3 Nuclear Energy Agency