## 5 Conclusions  
The present work experimentally studied the bond behaviour of an NSM CFRP joint under sustained loading and different service temperature conditions. Four experimental campaigns consisting of eight NSM CFRP-concrete pull-out single shear tests (SL tests) were performed under sustained loading for 1000 h inside a climatic chamber at different temperature conditions, combining steady and cyclic objective temperatures. After that, post-sustained loading tests (PSL tests), where the specimens were tested under monotonic loading until failure, were carried out.  
From the SL tests the following conclusions can be drawn:  
* Overall, the slip values obtained in specimens under 15% and 30% \(P_{u}\) were proportional to the applied load;
* Similar slips were obtained in specimens with short and long bonded lengths under a sustained loading level of 15% \(P_{u}\);
* Higher slips were obtained in the 10 mm grooved specimens in comparison with the 7.5 mm grooved specimens under high steady temperatures;
* Significant slip oscillations, caused by the thermal expansion of the materials, were observed in series with temperature cycles;
* As the mean temperature of the thermal cycle increased, so too did the slip at the loaded end;
* Specimens under temperature cycles (S3-A, S3-B and S4) experienced increases of slip that ranged between S1 and S2 slips, since the temperatures in the NSM groove fell between 20 and 40 \({}^{\circ}\)C;
* The decisive effect of the preconditioning cycles was observed during the initial loading days as the specimens that had been submitted to preconditioning temperature cycles experienced lower increases in slip during the first temperature cycles.  
Figure 10: Comparison between the instantaneous behaviour and the post-SL behaviour of the specimen PSL-225-10-30 in series (**a**) S1, (**b**) S2, (**c**) S3-B and (**d**) S4.  
From the PSL tests the following conclusions can be drawn:
* The ratio of the PSL ultimate load with respect to the initial instantaneous ultimate load was globally close to unity. However, some differences were observed in series S2 with its global increment of 6.3% and in series S3-B with a global reduction of 8%;
* Overall, no change in the failure modes were observed in the instantaneous post-sustained loading tests;
* A global reduction in the initial stiffness in the load-slip curve was observed, followed by its recovery at higher loads as the load of the PSL test surpassed the value of the sustained loading.  
During their service life, civil structures are submitted to a combination of sustained loading and cyclic environmental conditions. This study has helped to appreciate and understand the effect thermal cycles have in constantly loaded CFRP-concrete joints. The bonded joints have been shown to be affected by creep and have their mechanical properties reduced. Therefore, it can be concluded that environmental conditions must be taken into account when designing of CFRP strengthened civil structures.  
While this study limited the sustained loading tests to 1000 h, further studies would need to extend this further, especially for higher average temperatures where the high increases of slip were observed in this work.  
Conceptualization, J.G. and C.B.; methodology, J.G.; validation, J.G., C.B. and L.T.; formal analysis, C.B., L.T., M.B. and R.P.; investigation, J.G.; data curation, J.G.; writing--original draft preparation, J.G.; writing--review and editing, C.B., L.T., M.B and R.P.; supervision, C.B. and L.T.; project administration, C.B., M.B. and R.P.; funding acquisition, C.B., M.B. and R.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Spanish Ministry of Science, Innovation and Universities, (projects BIA2007-84975-S2-2-P and BIA2007-84975-S2-1-P) and the University of Girona (grant number IFUdG2018/18).  
Not applicable.  
The authors acknowledge the support of SIKA in supplying the CFRP strips and epoxy adhesive used in this study.  
The authors declare no conflict of interest.