## 4 Experimental Validation
### Mechanical Behavior of Concrete Overlays with Bended Rebars  
Pull-off and real-scale tests subjected to traffic loads showed that the use of screw anchors might be a proper constructive technique to reduce the risk of premature failure due to interfacial debonding. Having this in mind, a similar solution using \(\prod\)-shaped bended rebars was studied in the pavement restoration of four roundabouts placed on the N-II National Road at La Jonquera (Spain). The original pavements of the roundabouts consisted of 31 cm thick asphalt concrete on 25 cm thick graded aggregate and were subjected to very heavy traffic (>4.000 trucks/day). The damage caused by the combination of traffic loads and continuous fuel spills made it necessary to replace the asphalt layer several times at different depths. The pavements of the four roundabouts were reconstructed to provide a permanent solution. Two different structural solutions were proposed. The first one (WT) was a whitetopping in which 12 cm of the bituminous mix was replaced by Portland cement concrete, where the mix composition is shown in Table 7. The second solution (OL) was a full-depth reconstruction which consisted of two layers of Portland cement concrete with bent rebars in the interface. The bottom layer was lean concrete placed up to level -12 cm (same level as the asphalt of WT solution) while the top layer was the prolongation of the concrete of the WT. The WT was the general solution for the pavements while the OL was constructed in the most damaged areas of the four roundabouts. Figure 12 shows the visual aspect of the pavement before restoration. The asphalt presented widespread and several damages due to fuel spills combined with traffic fatigue (bitumen loss, cracking, wheel path rutting, potholes, etc.). Visual inspection and load plate tests were performed on all four roundabouts to determine the most severely affected regions. Four areas were detected with an exceptionally low ballast coefficient (K\({}_{60}\)), while for the rest of the pavement a Winkler coefficient of 391 MPa was assumed as a representative value. The first construction activity was the cold-milling of the top 12 cm of asphalt concrete, leaving 30 to 50 cm wide unmilled strips on the outer and interior edges of the roundabouts. The asphalt of the \begin{table}
\begin{tabular}{c c} \hline \hline
**Material** & **Content** \\ \hline CEM I 52.5 R (kg/m\({}^{3}\)) & 430 \\ Aggregate 10/20 mm (kg/m\({}^{3}\)) & 750 \\ Aggregate 4/12 mm (kg/m\({}^{3}\)) & 200 \\ Aggregate 0/4 mm (kg/m\({}^{3}\)) & 900 \\ Polyolefin fibers (kg/m\({}^{3}\)) & 4.0 \\ Water (L/m\({}^{3}\)) & 155 \\ Superplasticizer (L/m\({}^{3}\)) & 3.0 \\ Water reducer (L/m\({}^{3}\)) & 5.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Concrete mix of the overlay. Figure 11: Shrinkage cracks: transversal (**a**), longitudinal (**b**) and detail (**c**). four areas with more damage was full-depth milled until the graded aggregate was visible, followed by replacement with C15 lean concrete (fc = 15 MPa at 28 days) up to a height of -12 cm concerning the initial surface level. As presented in Figure 13a, the \(\prod\)-shaped bended rebars were placed in the top surface of the C15 concrete protruding 50 mm above it. The protrusion height was defined to ensure more than twice the maximum aggregate size of the mix (20 mm) to avoid hollows after concrete vibration. An accuracy of \(\pm\)10.0 mm was assumed for the rebars placement process. The rebars were arranged to form a grid of 25 cm \(\times\) 25 cm so that the interface would become homogenously sewn in both the traffic and its perpendicular directions (see Figure 13b). After that, the concrete of the 12 cm thick overlay was placed over the continuous surface formed by the milled asphalt and the C15 repairs. The concrete was a CF-5.0 type (see Table 7) with 4.0 kg/m\({}^{3}\) of short structural polyolefin fibers (12 mm in length), nominal flexural strength at 28 days of fct,fl  
Figure 12: Previous pavement condition of the roundabouts.