Journal of Infrastructure Systems

Moisture ingress is one of the major deteriorating factors for building materials. Today, the only approved way to assess such damage is the gravimetric Darr method, which is essentially destructive. Substantial progress has been made using the geophysical complex-resistivity method, which can be applied non-destructively and provides spatial information along two-dimensional sections, rather than punctual along one borehole. Considerable advantages of complex resistivity are its sensitivity to textural properties, as well as the pore-fluid chemistry of wet, porous media. In a comprehensive laboratory study, and later in field scale experiments, it could be shown that complex resistivity may even be able to distinguish between salt content and saturation degree in a single measurement. A comparison with complementary nondestructive testing techniques points to the benefit and further research to be explored in multimethodical approaches.

Ultrasonic seismic methods can be used in the condition assessment of bridge decks by evaluating changes in material characteristics and detecting the development of defects and zones of deterioration. The impact-echo method is of special benefit in the evaluation of corrosion-induced deck delamination because of its nondestructive nature and ability to detect delaminated zones at various stages of deterioration: from initial to progressed and developed. The traditional approach in the condition assessment of bridge decks by impact-echo is based on a review of individual test-point records. A new approach based on three-dimensional data visualization is proposed. The developed three-dimensional visualization platform allows for both the advanced presentation and an automated interpretation of impact-echo data. The data presentation is provided in terms of three-dimensional translucent visualizations of reflectors in a bridge deck section and horizontal and vertical cross sections through all distinctive zones, including a zone of delamination. The associated interpretation platform enables the overall assessment of the condition of the deck, through cumulative distributions of reflection intensity of different reflective layers, and the identification of deteriorated zones of the deck to be repaired or rehabilitated in an efficient and intuitive way.

The assessment of concrete cover deterioration generally involves the analysis of cores taken from the structure. Nonetheless, monitoring the drilling operation is itself a way to scan the material condition at increasing depth, which comes at no extra cost once the acquisition of samples has been planned. As an example, the feed rate of the cutting tool proved to be a sensitive indicator of the local damage undergone by the structure. On the other hand, hammer drilling small holes is definitely a faster and less invasive alternative for determining the variability of the mechanical properties within the concrete cover. Although this method does not provide an undisturbed material sample, the visual inspection of the remaining hole (voids, delamination cracks, and color changes) and the analysis of the ground-concrete powder (chemo-physical analyses) proved to be a viable alternative to the traditional examination of cores.

In the framework of the DISWall research project, funded by the European Commission, the authors have been working on the development of quality-assessment procedures for modern reinforced masonry buildings based on nondestructive testing methods. Two specific types of reinforced masonry systems were considered, both based on concentrated vertical reinforcements and on the use of perforated clay units. This contribution focuses on results obtained by radar and sonic techniques. They were applied in the laboratory on two masonry specimens, which were built with known defects. Tests were also carried out on-site, on real walls of a selected case study. On the basis of the results of these experiments, a fully nondestructive quality-control procedure appears feasible and promising. The data can be collected and analyzed in real time with an automatic classification algorithm. The procedure requires the use of a high-frequency GPR (ground-penetrating radar) system. Depending on the type of masonry system, sonic test equipment might also be required to investigate some specific problems that cannot be diagnosed by the GPR. Feedback from the building sector is now essential to understand the interest in and the potential market for this nondestructive testing application. As a result, new investments could be planned to perform the further testing activities that are needed to standardize the procedure.

The new Río Cuarto Bridge, currently under construction in the Province of Córdoba, Argentina, consists of a 110-m long, cable-stayed main span with a prestressed concrete deck, steel pylons, and two 50-m–long side spans founded on groups of drilled shafts. The construction method, structural configuration of the superstructure, and post-tensioning sequence of the cables required a detailed characterization of the axial load behavior of the drilled shafts, both for the temporary support shafts and the foundation piers. Small-strain and working load level predictions were made during design, on the basis of conventional site investigation information and in situ geophysical testing. A series of nondestructive evaluations, coupled with nonlinear extrapolations calibrated to represent the measured small-strain range, were carried out in lieu of conventional verification of design predictions by means of more cumbersome large-strain testing. The testing program consisted on monitoring accelerations generated at the top of the shaft as a result of a small amplitude dynamic load measured by means of a dynamic force transducer. A nonlinear numerical model was then calibrated so as to reproduce the initial stiffness measured during the small-strain testing program to extrapolate the load-deflection curve into the service load range and thus define load-deflection curves of the shafts at each pier location up to service load levels. To obtain an experimental validation of the approach at the site, a conventional static load test, carried up to the service load level, was performed on a main pier shaft. Results showed a reasonable agreement between the nondestructive evaluation with nonlinear extrapolation, large-strain measurements, and design predictions for the main pier shafts, whereas some differences were observed between the design predictions and small-strain measurements at other locations, primarily as a result of as-built conditions unforeseen in the original design. Thus, the nondestructive testing program was instrumental in the verification of the as-built behavior of the shafts and allowed the development of load-deflection curves for the drilled shafts that accurately represented the behavior up to the service load level.