No abstract

This article investigates the application of vibro-acoustic modulation testing for diagnosing damage in concrete structures. The vibro-acoustic modulation technique employs two excitation frequencies on a structure. The interaction of these excitations in the measured response indicates damage through the presence of sidebands in the frequency spectra. Past studies using this technique have mostly focused on metals and composites (thin plates or laminates). Our research focuses on concrete, which is a highly heterogeneous material susceptible to a variety of chemical, physical, and mechanical damage processes. In particular, this article investigates diagnosing cracking in concrete from an expansive gel produced by an alkali–silica reaction in the presence of moisture. Past studies have been limited to damage detection using vibro-acoustic modulation testing, whereas this article extends the technique to damage localization. A cement slab with pockets of reactive aggregate is used to investigate the diagnosis technique. The effects of different testing parameters, such as locations, magnitudes, and frequencies of the two excitations, are analyzed and incorporated in the damage localization methodology. A Bayesian probabilistic methodology is developed to fuse the information from multiple test configurations in order to construct damage probability maps for the test specimen. The results of vibro-acoustic modulation–based damage localization are validated by petrographic study of cores taken from the slab.

No abstract

No abstract

A large-scale testing program on alkali silica reaction (ASR)-affected concrete structural members without shear reinforcement representative of structural members found in nuclear power plants is presented. Three concrete specimens, designed to experience a free expansion rate of approximately 0.15% per year were fabricated and placed within a controlled environmental chamber (38 ± 1 o C (100 ± 2 o F) and 95 ± 5% relative humidity (RH)). Sixty-four (64) embedded transducers and twelve (12) long-gauge fiber-optic sensors provide evidence of strong anisotropic expansion and oriented ASR-induced cracking resulting from the confinement effect caused by the reinforcement layout and additional structural boundary conditions. Surface cracking is not indicative of internal ASR-induced damage/expansion. 2. Large-scale testing program 2.1 Test specimens The structural specimen detail was designed to closely