PSI - Issue 78

Irene Matteini et al. / Procedia Structural Integrity 78 (2026) 992–999

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The wave velocity was set at 0.15 m/ns and 0.10 m/ns for asphalt and concrete respectively, as indicated by hyperbola fitting on the reflectors. The resulting profiles (B-scan) were then interpolated to compile a 3D volume that was horizontally sliced to provide 2D maps of the key features (C-scan) at different depths. Given the limited documentation available of this structure, the goal of the survey was on one hand to provide information on how it was built - configuration of the deck, thickness, steel reinforcement layout, cover maps- and on the other to understand its condition to proper guide the next phase, which includes in-depth testing to follow. 2.3. MMGPR Survey Results The key insights are illustrated in the following section, aimed at providing an overview of the findings from the surface of the asphalt down to the bottom of the slab. Figure 3 (C-scan) provides a map of the shallow anomalies (1 to 3 cm) displaying a peculiar crack pattern in the asphalt layer, with three main cracks orthogonal to the bridge axis, close to the abutments and approximately at mid span.

Fig. 3. C-scan view displaying asphalt crack patterns. Image generated with GPR Insights.

Multiple layers of asphalt were detected from the scans. The recurring stratigraphy, illustrated in Figure 4 (B-scan), presents two different layers of asphalt with an indicative thickness of 10 and 15 cm detected above the concrete deck. The concrete deck is estimated to have a net thickness of 35 cm with two outer rebar layers. Figure 5 (C-scan) displays the upper layer of the steel reinforcement of the deck, consisting in a 20 x 20 cm square mesh, followed by a deeper layer of rebars orthogonal to the bridge axis with a 60 cm spacing laying in between the two mesh layers.