Spatially resolved analysis of the progression of freeze‐thaw damage in concrete

To assess the durability of concrete structures, it is necessary to understand not only how deterioration evolves over time but also how the damage progresses through the structure. To determine the evolution of the freeze‐thaw damage, different damage criteria were examined in a spatially resolved manner during the CIF test. By measuring the ultrasound pulse velocity (UPV) in different axes, depth‐dependent changes of the relative dynamic modulus of elasticity (RDME) were investigated. The RDME started to decrease in regions close to the surface, whereas the RDME in regions farther from the test surface decreased with higher speed. Changes in the water content during the CIF test were examined by nuclear magnetic resonance (NMR). The freeze‐thaw exposed specimens showed an increase in their water content that is assumed due to the micro‐ice‐lens pump as well as microstructural changes. These changes progressed from the surface into deeper layers of the specimens, following an increase of saturation also progressing into the concrete. To consider the frost damage evolution in service life design, the authors propose the use of depth‐dependent threshold values for freeze‐thaw exposed concrete structures.