Ph.d.-forsvar - Abdul Faheem

Abdul Faheem forsvarer sin ph.d.-afhandling ”Influence of thermal boundary conditions and temperature distribution in concrete on frost scaling 
– experimental and numerical study”

Resumé (kun på engelsk):

Frost resistance of concrete is a durability concern in cold climates such as Denmark. Though it was discovered decades ago that frost action causes damage in concrete, the fundamental mechanism of frost damage is still not completely understood. The aim of this PhD thesis is to improve the understanding of how frost deterioration evolves in concrete. It was attempted to achieve this aim by combining experimental work and numerical modeling.

Thermal boundary conditions are rarely studied in relation to frost scaling (removal of small flakes from the concrete surface). In standardized testing, a liquid layer of a certain thickness is involved when concrete is exposed to freeze/thaw cycles. It is noted that the primary thermal boundary conditions that influence the temperature distribution in concrete are related to this layer and the temperature of the surroundings. Thus, the salt concentration in the external liquid, the thickness of the external liquid layer, and the surrounding temperature of the specimen being tested were considered thermal boundary conditions that influence the temperature distribution. This thesis focused on the influence of these thermal boundary conditions and resulting temperature distributions on frost scaling.

The statistical analysis of experimental results showed that the salt concentration significantly affects frost scaling. The interesting aspect is that the salt concentration is also interacting with other thermal boundary conditions such as the surrounding temperature. It was concluded that both the unfrozen external liquid (above concrete) and unfrozen pore liquid (below the concrete surface) can be transported to the freezing area in the vicinity of the concrete surface. Thermal boundary conditions and resulting temperature distributions influenced this transport and thus the extent of frost scaling. It was possible to replicate the experimental results using the developed numerical model. The results of the present thesis support that the fundamental mechanism of frost damage is cryogenic suction that explains the transport of unfrozen liquid to ice. The common European standard to test frost resistance of concrete consists of three methods, and It states that “There is no correlation between the results obtained by the three methods”. It is noted that different thermal boundary conditions in the three test methods may be the reason, and it may be possible to establish a correlation by combining experimental work and numerical modelling where the focus is thermal boundary conditions in the three methods.

Principal supervisor: 
Associate Professor Marianne Tange Hasholt
Co-supervisor: Professor Ole Mejlhede Jensen

Examiners:
Associate Professor Wolfgang Kunther, DTU
Professor Erik Schlangen, TU Delft, Netherlands
Professor Stefan Jacobsen, NTNU, Norway

Chairman at defence:
Associate Profeesor Alexander Michel

Tidspunkt

man 24 jan 22
13:00 - 16:00

Hvor

https://dtudk.zoom.us/j/67199927857
The defense will be recorded