Basic study on reaction products in ASR with Raman spectroscopy

Alkali-silica reaction (ASR) can be considered to be a serious durability concern for concrete structures. At this point, to avoid ASR, the use of non-reactive aggregate is advised, or the use of low alkali cement or blended cement, or cement of limited alkali content is recommended. However, complete avoidance of ASR over long time periods is difficult and the precise mechanism of ASR remains unclear. So far, our research group have studied the properties of reactive aggregate and ASR products with Raman spectroscopy. As a result, formation of a large amount of CaCO3, in addition to Na2O-SiO2 was observed around aggregates in accelerated test specimens. Initial results in this study showed a difference in the reaction products formed between accelerated tests and real-life samples, when examined using Raman spectroscopy. Subsequently, in order to consider the reasons for this difference, a series of samples were prepared by reacting calcium ions with sodium silicate solutions of varying Na2O/SiO2 ratios. The results clearly showed that the difference in behaviour between artificial and real samples was due to changes in the sodium contents of the products.