Alkali—silica reaction (ASR) is a chemical distress mechanism that adversely affects the service life of concrete pavements. Key aspects of the reaction, such as the roles of calcium and aluminum on the structure of the gel and their correlation with swelling properties, have not yet been fully understood owing to the complex reaction mechanism. These problems emphasize the importance of developing analytical techniques, such as Raman spectroscopy, to effectively study ASR products. The research presented in this report explores the possibility of using Raman spectroscopy to provide valuable insight into the structure of ASR gels, both in synthetic systems as well as concrete and mortar samples. This information will aid in better understanding of the mechanism of the reaction and improve repair strategies for damaged structures. The research team used published literature to verify the structural information derived using Raman spectroscopic analysis, thus establishing the validity of the methodology. Increasing alkali content in synthetic ASR gels resulted in depolymerization of the silicate structure, and a strong correlation was observed between the peak position of the most intense band in the low frequency region and alkali/silica ratio for gels with a composition similar to field ASR gels. Further, an attempt was made to use Raman spectroscopy to characterize ASR gels within concrete and mortar samples, and limitations of applying this technique to probe products within a cementitious matrix were identified. Finally, the study touched on the possibility of using surface-enhanced Raman spectroscopy to improve sensitivity of the technique when applied to concrete samples.
This FHWA report is available online at https://www.fhwa.dot.gov/publications/research/infrastructure/20042/20042.pdf