Insights into alkali-silica reaction and delayed ettringite formation through advanced characterization techniques
Niki Rashidi, Mohammad Mehdi
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Alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are expansive chemical reactions, which can damage concrete structures. However, for both ASR and DEF, the relationships between constituent materials, microscale damage propagation, and bulk expansion are not well understood. To address these knowledge gaps, this study quantifies ASR and DEF-induced damage at the microscale by nonlinear impact resonance acoustic spectroscopy (NIRAS), and when augmented with data from other standard and advanced materials characterization approaches, provides a basis for the new understanding of the factors influencing the extent and rate of damage by these reactions. This dissertation makes three main contributions. First, the influence of ASR gel composition on its structure and the potential for expansion is explored through the characterization of lab-produced samples by small-angle neutron scattering, 1H nuclear magnetic resonance relaxometry, and rheological measurements. Relying upon that improved understanding of the effects of gel composition along with an understand physics of nonlinear acoustic measurements, in the second part, a hypothesis is presented for interpreting the relationship between measured expansion and temporal material nonlinearity. In the third part, a similar approach is used to explore the relationship between compositional and environmental factors, and microscale damage and expansion derived from DEF.