## 5 Conclusions  
In this work, the use of mechanical connectors is proposed for bringing post-cracking strength to interfaces of Portland cement concrete overlays for pavement applications. To this end, the mechanisms that may produce interfacial debonding and common practices to reduce the risk of debonding were presented. Two types of connectors (screws and bended rebars) were tested on two real-scale pavements to analyze the structural performance of overlays with the sewed interface. From this, the following conclusions are derived:  
* The mechanical behavior of mechanicals connectors is analogous to that of steel rebars reinforcement and fibers in concrete. They begin to resist stresses just after the interface cracking and increase the resisted load when the crack opens. Thanks to this, the layers still work together after debonding thereby preventing excessive stress increments in the materials.
* Screw anchors are a fast-track suitable solution to provide residual post-cracking strength to the interface of concrete overlays on existing pavements. They can be installed with light tools by non-skilled operators, without significantly affecting the construction process and timing. Pull-off tests in bonded whitetoppings showed both an increment in average maximum tensile strength and a homogenization (reduction of dispersion) of the resistant behavior. The averages and coefficient of variations of maximum strength were 0.53 MPa and 6.53% in interfaces with screws and 0.35 MPa and 51.80% in interfaces without screws.
* After three years of very heavy traffic, the 229.4 m \(\times\) 3.10 m \(\times\) 0.10 m overlay with screw anchors in the interfaces performed correctly without developing structural cracks. In this case, damages only  
Figure 16: Roundabouts after two years: area with full-depth reconstruction (**a**), general view of cracks in the WT solution (**b**), detail of corner crack (**c**), and transition between WT and OL solutions (**d**).  
appeared in the first hours due to excessive evaporation, insufficient curing and/or an excessive distance between joints.
* The use of bent rebars may be an excellent low-cost alternative for sewing the interface of bi-layer concrete pavements. The overlay of the four roundabouts presented higher structural performance in the areas with two layers of concrete and bended rebars than those with an asphalt bottom layer. After two years of traffic, about 10% the total of roundabouts slabs were cracked, none of them in regions with mechanical connectors in the interface.
* Portland cement overlays with mechanical connectors placed in their interface performed satisfactorily in structural terms after being subjected to a high flow of heavy vehicles. This constructive solution might be an opportunity to extend the use of overlays in situations where a high risk of interfacial debonding exists.  
Conceptualization, R.-D.L.-C., A.A and P.P.; methodology, R.-D.L.-C. and P.P.; validation, and formal analysis, R.-D.L.-C. and S.C.; investigation, R.-D.L.-C.; writing--original draft preparation, R.-D.L.-C.; writing--review and editing, P.P.; visualization, S.C. and A.A.; supervision, S.C., A.A and P.P.; project administration, P.P.; funding acquisition, A.A. All authors have read and agree to the published version of the manuscript.  
This research was funded by Spanish Ministry of Economy and Competitiveness, grant number IPT-2012-0313-370000.  
The authors would like to thank the Spanish Ministry of Economy and Competitiveness for the financial support provided by the project \"Desarrollo de Mejores Rehabilitaciones Locales en Infraestructuras (MERLIN)\" (Subprograms INNPACTO) IPT-2012-0313-37000. Ministerio de Economia y Competitividad (Spain). The first author also wishes to thank the Agencia de Gestio d'Ajuts Universitaria i de Recerca of the Generalitat de Catalunya and the European Social Fund of the European Union for their financial support provided by the Fl-DGR grant.  
The authors declare no conflict of interest.