Nondestructive Evaluation of Alkali-Silica Reaction (ASR) in Concrete
Strow, Meredith L
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Alkali-silica reaction (ASR) is a concrete deterioration mechanism which can result in expansion cracking. Evaluation of ASR deterioration is commonly conducted by petrographic examination testing on samples extracted from an affected structure. The purpose of this study is to aid in the pursuit of nondestructive testing which can detect and relatively quantify the amount of ASR gel present within concrete. Eight concrete prisms were produced using reactive and nonreactive concrete mixes. The reactive mix design included reactive fine aggregate, nonreactive coarse aggregate and high alkali portland cement whereas the nonreactive mix contained the same constituents plus fly ash. All specimens were conditioned per ASTM C1293 to accelerate ASR and each set was tested to 28, 90, 180 and 365 days. Electrical impedance spectroscopy (EIS) and microwave testing were performed on the specimens to measure impedance, bulk resistance, dielectric constant and water volume fraction. Petrographic examination and Damage Rating Index (DRI) testing was performed to confirm the presence and extent of ASR. Acoustic microscope image analysis was performed as another method of evaluating the extent of ASR deterioration. Nonreactive specimens showed only 6.11% length expansion and 34.69% positive mass change compared to reactive specimens at 365 days. EIS and microwave testing techniques were successful in distinguishing between reactive and nonreactive specimens. In comparison to nonreactive specimens, reactive specimens revealed smaller real impedance, larger imaginary impedance and smaller bulk resistance from EIS testing. From microwave testing, reactive specimens exhibit smaller dielectric constant in ambient air and saturated conditions and larger dielectric constant in dry condition compared to nonreactive specimens. Microwave testing also revealed reactive specimens measured much lower water volume fractions. EIS and microwave testing revealed general differences between reactive and nonreactive specimens as well as property changes within each sample set over time. Petrographic examination and DRI testing provided further information to correlate EIS and microwave results to confirmed characteristics of the concrete. Acoustic microscope images did not show discernable cracking; additional image processing is required to provide more valuable information.
electrical impedance spectroscopy
damage rating index