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Rock-pocket and honeycomb defects impair overall stiffness, accelerate aging, reduce service life, and cause structural problems in hardened concrete members. Traditional methods for detecting such deficient volumes involve visual observations or localized nondestructive methods, which are labor-intensive, timeconsuming, highly sensitive to test conditions, and require knowledge of and accessibility to defect locations. The authors propose a vibration response-based nondestructive technique that combines experimental and numerical methodologies for use in identifying the location and severity of internal defects of concrete members. The experimental component entails collecting mode shape curvatures from laboratory beam specimens with size-controlled rock pocket and honeycomb defects, and the numerical component entails simulating beam vibration response through a finite element (FE) model parameterized with three defect-identifying variables indicating location (x, coordinate along the beam length) and severity of damage (α, stiffness reduction and b, mass reduction). Defects are detected by comparing the FE model predictions to experimental measurements and inferring the low number of defect-identifying variables. This method is particularly well-suited for rapid and cost-effective quality assurance for precast concrete members and for inspecting concrete members with simple geometric forms.
Keywords: concrete defect detection; experimental modal analysis; nondestructive testing and evaluation; statistical inference; uncertainty quantification.
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INTRODUCTION
Rock pockets and honeycombs are local, internal defects that may form in concrete members due to mortar paste failing to fill the space around the coarse aggregates. Rock pockets (clusters of loose aggregates not bound by mortar paste) and honeycomb defects (voids within the concrete) are typically the result of poor concrete mixing, leakage of wet concrete from the form, or insufficient consolidation. Consequently, the presence of such internal defects can degrade the performance of a concrete member with the severity of this degradation being proportional to the size of the defect. Depending on their size and location, the degrading effects of these internal defects may be evident immediately or may manifest years after the structural member has been in service. Such internal defects, if extensive or if located near the anchorage, can bring about compression failure (that is, crushing) in prestressed precast beams during tendon stressing (Eiji et al. 2006). Moreover, the presence of internal defects accelerates the degrading effects of aging caused by operational and environmental determinants, such as...