The main aim of this project is to determine experimentally the decisive damage mechanisms relied to the phase transition of the pore solution in concrete.
The damage is separated into the cause, the ice formation within the pore system and the consequence that leads to a change of the pore system.
The change of the pore system which leads to permanent residual damage is characterized by expansion measurement, microscopical analysis (SEM, confocal microscope etc.), mercury intrusion (MIP) and acoustic emission technique.
The investigations will show the possible damage mechanisms caused by the frost-thaw resistance of concrete.
From a knowledge of the relevant damage mechanisms will be derived, which test criteria result from a desired freeze-thaw resistance.
The topic is studied by means of calorimetric methods, ultrasonic pulse transit time measurement, temperature distribution and expansion measurement.
The extensive studies with very different methods were performed. The results were consistent and allowed to derive a qualitative model for the processes involved in freezing and thawing of concrete.
The freezing and thawing processes can be divided into five phases which can be assigned to a certain temperature range and are characterised by a dominant damage mechanism. The model is based on the assumption that no isolated ice formation within the concrete occurs, but that an ice front penetrates from the surface and that the concrete is homogenously saturated.
The model was used to qualify the damage mechanism in the analogue laboratory tests.
Based on the site experiments, it was found that for damage formation on-site just phases 2 and 5 are important.
The only conclusion that can be derived from any performance test is, that there is a low probability to get substantial damage on-site, if damage in a laboratory test is small.