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A one-day Nordic Concrete Research workshop on “Accelerated freeze-thaw testing of concrete” attracted approx. 30 participants. The workshop included presentations on various aspects, such as observed frost damage in the field and the importance of the temperature curve during testing as well as other interactions with the surroundings of the concrete. The workshop also included examples of recent research, which can improve our knowledge about the frost damage mechanism and therefore provide input to improving the standardised test methods. The present paper is a summary of the nine presentations and the discussion arising from the presentations.

In Germany hydraulic structures like weirs or locks under the responsibility of the Federal Min-istry of Transport and Digital Infrastructure have an average age of about 80 years. They often show static characteristics, such as construction methods or very large cross sections that are no longer common practice today. When retrofittings are planned new calculations to verify its conformity with stability requirements become necessary. As no adapted regulations have been released for re-assessing the statics of existing solid hydraulic structures a Code of practice has been developed. Compressive and tensile strength derived from concrete cores are decisive input parameters for the calculations. During the last decades concrete cores of more than hundred existing hydraulic structures have been examined by the Federal Waterways Engineering and Research Institute (BAW). These investigations were analysed comprehensively concerning the variation of strength properties and the correlation between compressive and tensile strength in massive hydraulic structures. Furthermore given correlations and factors in technical guidelines which were usually derived by investigations on lab specimen at an age of 28 days were verified concerning their applicability on in situ concrete of old, massive structures. The findings are presented in the paper.

A better knowledge on the exposure conditions of structures can help to evaluate the transferability of lab tests results to practical application or to generate a basis for modeling of different durability aspects. About 20 years and 10 years ago, a monitoring system was installed in two locks to get information on the temperature exposure and the degree of saturation of the concrete cover zone by means of continuous resistivity measurements with the Multi‐Ring‐Electrodes (MRE) and Multitemperature Probes (MTP) at different distances to the concrete surface. Due to the fact that resistivity is influenced by many more parameters than just the degree of saturation it is very complex to determine the degree of saturation. Uncertainties remain as concrete properties develop over the years and the cover zone which is of mayor interest for durability is additionally affected by casting and curing and later on by the exposure conditions. A deficiency of the Arrhenius equation to compensate for temperature effects on resistivity under certain conditions finally helps to overcome that difficulty. A data evaluation concerning freeze‐thaw attack gives examples and indicates possible further applications like carbonation. [ABSTRACT FROM AUTHOR]