A Geochemical Analysis: Application of a Chelating Agent on Potential ASR Reactive Aggregates

• Main Author: Garcia, Jennifer N
• Format: Others
• Published: Digital Archive @ GSU 2011
• Subjects: INDEX WORDS: Aggregate; ASR; Tiron; NaOH; Chelation; Geochemical; ASTM; Geography; Geology
• Online Access: http://digitalarchive.gsu.edu/geosciences_theses/39; http://digitalarchive.gsu.edu/cgi/viewcontent.cgi?article=1038&context=geosciences_theses

Alkali Silica Reaction (ASR) is a deleterious, expansive reaction in concrete. Several ASTM methods test potential aggregates for ASR risk. One method uses NaOH digestion, followed by spectroscopic methods, to estimate the amount of reactive silica present in an aggregate. NaOH, however, can digest both crystalline (i.e. quartz) and non-crystalline (e.g. opal), or poorly crystalline silica, potentially yielding falsely high estimates of reactive silica. Studies in soil and plant sciences have used Tiron, an alkaline chelating agent (C6H4S2O8Na2), as a method of digesting opaline silica for spectroscopic analysis. Here we test this approach by analyzing reactive silica in road aggregate. Tiron extraction of reactive silica is more selective, in some cases extracting only ~ 30% of the silica compared to the harsher NaOH extraction: variation is due to differences in aggregate mineralogy, specifically SiO2. In conducting chelation analyses, UV/VIS seems to be a better approach than AA.