In this study, cover meter measurements were conducted to measure the concrete cover. In addition, ultrasonic echo measurements were conducted to determine the location of the rebars in more detail. An automated scanning system was used for data collection to make this study as objective as possible. Furthermore, this system made it possible to produce measurement grids of sufficient density and to provide good spatial resolution, characteristics beneficial especially for the application of imaging techniques. TEST BLOCK For an objective study, it is necessary to create defined conditions under which the methods can be validated. Figure 1 shows the design of the specimen used in this study. It has a 25-cm (10-in.) thickness and reinforcing steel on both sides (upper and lower layers). Its lateral dimensions are 2.00 × 1.50 m (6.6 × 5 ft). For identification of the different layers of reinforcement to be made easier, the four layers are shown separately in the four parts of Figure 1. In fact, all four layers are included in just one specimen (Figure 2). The reinforcement running in the y-direction (short side) on the front of the specimen was divided into two sections. In one section, the rebar diameters varied from No. 3 (9.525 mm) to No. 9 (28.65 mm), the concrete cover was approximately 59 mm (2.32 in.). The rebar diameter was gradually increased to study the influence of the steel diameter on the measurements. The second section served to inves- tigate the influence of the rebar spacing on the accuracy of the mea- surements. The spacing varied from 25 cm (10 in.) to 3.75 cm (1.5 in.). All rebars in this section had the same-diameter No. 3 (9.525 mm) and concrete cover of approximately 59 mm (2.4 in.). The reinforcement in the x-direction on the front of the block covered only half of its y-length (height), so that a possible influence of that layer on the detection of the first layer could be studied as well. This second layer consisted of an area with wider spacing [10 cm (4 in.)] between the rebars and an area with spacing as small as 3.5 cm (1.38 in.). Among other purposes, it served to investigate how far the localization of the second layer was affected by the spacing of the reinforcement in the first layer. In the first section of the reinforcement in the y-direction at the back of the block, the depth of the rebars (all No. 3 rebars, 9.525-mm diameter) was gradually increased. This served to investigate the depth at which a rebar of that diameter could be detected and to determine the relation of accuracy to depth. The second section served to investigate the maximum depth at which the rebars of three reinforcement layers could be detected. Some of the rebars were congruent; others lay in a shifted position Rebar Detection with Cover Meter and Ultrasonic Pulse Echo Combined with Automated Scanning System Daniel Algernon, Dennis R. Hiltunen, Christopher C. Ferraro, and Charles Ishee 123 A sufficient concrete cover is essential to ensure the durability of reinforced concrete structures. Nondestructive testing methods that can measure the concrete cover are therefore promising tools. As a part of a research project funded by the Florida Department of Transportation, the capabilities and limitations of cover meter measurements in relation to this testing problem were investigated. Researchers designed a reinforced concrete test block on which properties such as rebar depth, size, and spacing and number of reinforcement layers were varied; the effects these variations had on the measurements were studied. The use of an automated testing frame consisting of two scanners that examined the test block from both sides ensured high positioning accuracy and constant quality in data acquisition and made possible the collection of the data along an extremely dense grid. In addition to the cover meter measurements, which referred only to the cover of the layer closest to the surface, ultrasonic pulse echo measurements were conducted, and a synthetic aperture focusing technique was applied to the data to make the rebars become apparent in refined B-scan images. A significant problem affecting durability of reinforced concrete bridges in coastal areas, as can be found, for example, around Miami or Tampa, Florida, is the corrosion of reinforcing steel due to infil- tration of the concrete by salt water. To protect the reinforcing steel from corrosion, a sufficient concrete cover is essential. In cases in which the concrete cover is too small, the durability of the reinforcing steel and therefore the structural component can be significantly reduced. Nondestructive testing methods that can determine the actual concrete cover can help to protect the steel from corrosion and thereby help to increase the lifetime of a structure. For the assurance of efficient application in the field, the capabilities of different test methods in determining actual concrete cover, as well as other relevant testing problems, were the subjects of a research project funded by the Florida Department of Transportation (DOT), in which a first-stage facility for the calibration and validation of nondestructive testing methods was established. D. Algernon and C. C. Ferraro, 365 Weil Hall, and D. R. Hiltunen, 265F Weil Hall, Civil and Coastal Engineering Department, University of Florida, Gainesville, FL 32611-6580. C. Ishee, Florida Department of Transportation, State Materials Office, 5007 Northeast 39th Avenue, Gainesville, FL 32609. Corresponding author: D. Algernon, daniel.algernon@gmx.de. Transportation Research Record: Journal of the Transportation Research Board, No. 2251, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 123–131. DOI: 10.3141/2251-13