| With its discovery in 1940, alkali-silica reaction (ASR) has been recognized as a debilitating plague to concrete structures. Due to the production of ASR gels that swell by imbibing water from their surroundings, an expansive pressure is exerted within a cementitious composite, resulting in damages such as map cracking, spalling, deformations, and reductions in mechanical strength. Unfortunately, structural health monitoring (SHM) of civil infrastructure for major issues like ASR require an immense amount of manpower far greater than the current supply of civil engineering professionals in today's society. A potential solution for this issue lies in the developments for nondestructive evaluation (NDE) of civil infrastructures which has proven to be an effective approach for collecting information on the condition of a material, a component, or a system. Changes in the material properties of a structure afflicted with ASR can be quickly and harmlessly determined by using noninvasive measurement technologies and in-depth analytic techniques.;In this study, a continuous wave imaging radar system along with synthetic aperture radar (SAR) imaging algorithms, an ultrasonic testing instrument, and an open-ended coaxial probe for dielectric measurement were utilized in order to non-destructively detect and quantify damages from ASR gels on 25 x 25 x 285 mm mortar bars stored in a 1N NaOH solution at 80°C for 7, 14, 21, and 28 days. Nondestructive detection of the damage from ASR gels was carried out by observing the differences between mortar bars made from reactive aggregates susceptible to ASR and a control group made from a nonreactive aggregate. Amplitudes from the SAR images of mortar bars made from reactive aggregates were found to be greater than those from SAR images of mortar bars made from a nonreactive aggregate. In addition, lower ultrasonic pulse velocities for the mortar bars made from reactive aggregates indicated periods of peak damage due to the evolution of cracks caused by the swelling of the ASR gels. Quantification of damage from ASR gels was achieved by using a linear function to model the ratio between total SAR amplitude and length expansion percentage with respect to time stored in the NaOH solution. In addition, the evolution of ASR gels with time and their effects on the measurements using the NDE methods were observed from a multiphysical perspective in their increasing and decreasing trends for ultrasonic pulse velocity, total SAR amplitude, and dielectric constant. Several mechanisms including the evolution of crack damage, moisture influence from ASR gels, and cement hydration were considered in order to characterize the damages from ASR gels on the mortar bars for each time period of storage in the 1N NaOH solution at 80°C. |
