Structural characterization of alkali-silica reaction gel: An x-ray absorption fine structure study

This paper sets out to acquire information on the atomic structure of the alkali-silica reaction gel by using the x-ray absorption fine structure (XAFS) technique to improve the understanding of the mechanism of expansion. The gel generates mechanical stress in the concrete, which cracks it. XAFS enables the study of the local atomic structure around each of the atomic species in the material, even in disordered structures. Analyses were made at the potassium (3608 eV) and silicon (1839 eV) absorption K-edges. Information was obtained about the local order (first and second neighbors) around the absorbing atoms and the nanoscale arrangement in the gel. The results show that most accepted structural models that are used to describe the gel are inaccurate and that a chemically inhomogeneous nanostructured material can be the better choice to explain the ASR gel structure and its chemical behavior.