Discussion of the paper “Effect of the chemical composition of synthetic alkali-silica gels on their structure, swelling behavior and water uptake” by Miriam E. Krüger, Harald Hilbig, Ludwig Stelzner and Alisa Machner, Cem. Conc. Res. 184 (2024): 107596

In the discussed study, synthesized ASR products of unknown internal relative humidity (RH) were brought into contact with water using the osmotic cell test. They were not conditioned to an identical RH corresponding to the one of ASR affected concrete before the test. Moreover, swelling and osmotic pressure depend on the difference in the ionic concentration between two solutions. ASR products formed in reactive concrete aggregates are only exposed to the pore solution of the concrete and not to water. Using water in an osmotic cell test leads to results that are not representative for ASR in concrete.