Alkali-silica reaction – a multidisciplinary approach

In the last four years, a multidisciplinary study involving several research groups in Switzerland tackled a number of unsolved, fundamental issues about the alkali-silica reaction (ASR) in concrete. The covered topics include SiO2 dissolution, the characterization of various ASR products formed at different stages of the reaction in both concrete and synthesis, crack formation and propagation. The encompassed scale ranges from nanometers to meters. Apart from conventional techniques, novel methods for the field of ASR have been used, e.g. combination of scanning electron microscopy with dissolution experiments, combination of focused ion beam with transmission electron microscopy, several synchrotron-based methods, synthesis of ASR products for in-depth characterization, time-lapse X-ray micro-tomography combined with contrast-enhancing measures and numerical models of ASR damage based on realistic crack patterns. Key achievements and findings are the quantification of the effect of aluminum on dissolution of different silicates, the variance in morphology and composition of initial ASR products, the differences and similarities between amorphous ASR products and calcium-silicate-hydrate, the link between temperature and the structure of the crystalline ASR products, the behavior of the crystalline ASR products at varying relative humidity, ASR propagation in 4D and numerical modelling based on realistic crack patterns.