Alkali-silica reaction (ASR) is a chemical reaction between alkalis present in portland cement and amorphous or otherwise disordered siliceous minerals in particular aggregates. Through this reaction, reactive silica binds with hydroxyl and alkali ions and forms a gel, known as ASR gel. Recently, microwave materials characterization techniques have shown great potential for detecting ASR in mortar. However, the comprehensive understanding of variables that affect the extent of ASR in mortar and their interaction with microwave signals, in particular the effect of environmental exposure conditions requires more investigations. Therefore, parameters related to these conditions must be considered when using microwave techniques for ASR detection and evaluation. In this paper, the effect of exposure conditions on ASR gel formation and microwave dielectric properties of mortar samples is investigated. To this end, extended measurements of the complex dielectric constants of three different sets of mortar samples are presented at S-band (2.6-3.95 GHz). The samples were cast with potentially reactive ASR-aggregates and subjected to different environmental conditions. The results show slightly different permittivities for the differently stored samples, potentially indicating different amount of ASR gel. This observation was corroborated through UV fluorescence microscopy, where different amounts of ASR gel were observed in the samples. Moreover, the results indicate that ASR gel evolution may be better tracked through loss factor measurements, while pre-existing-gel may be better detected through permittivity measurements.
A. Hashemi et al., "Effect of Exposure Conditions on the Long-Term Dielectric Properties of Mortar Samples Containing ASR Gel," Proceedings of the 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation (2016, Atlanta, GA), vol. 1806, American Institute of Physics (AIP), Jul 2016.
The definitive version is available at http://dx.doi.org/10.1063/1.4974709
43rd Annual Review of Progress in Quantitative Nondestructive Evaluation (2016: Jul. 17-22, Atlanta, GA)
Electrical and Computer Engineering
National Science Foundation (U.S.)
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Article - Conference proceedings
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