# Effects of Freeze-Thaw and Wet-Dry Cycles on Tension Stiffening Behavior of Reinforced RAC Elements
## 5 Conclusions  
The present study reports on an analysis of the structural performance of reinforced concrete elements after degradation processes. Specifically, it summarizes the results of an experimental investigation aimed at analyzing the tension stiffening behavior of steel-concrete composites, of normal strength concretes containing RCAs with different attached mortar contents, after being separately undergone to freeze-thaw and wet-dry cycles. According to the obtained results, the following considerations can be highlighted for both aging processes:  
* The degraded elements' curves presented lower values of strength for both the multiple cracking phase and post cracking phase than the curves of the non-degraded elements. However, after degradation, all composites still present the standard behavior of the tension stiffening test, with the four well-defined phases;
* In the elastic phase, the results show that the presence of RCAs did not significantly influence the elastic modulus of non-degraded samples;
* Both elastic modulus and first crack strength were more impacted by the degradation processes in the concrete with the highest amount of attached mortar in its aggregate. This impact is caused by the greater flow of water and aggressive agents inside the concrete, provided by its greater porosity;
* All mixtures showed a reduction in the stress-strain performance of insulated concrete after degradation. Specifically, the attached mortar content also directly impacted the maximum strength of the concrete matrix;
* The presence of RCAs does not interfere with the cracking pattern of concrete submitted to the aging processes of this study. The spacing behavior was similar for reference and degraded samples. In general, the largest crack openings throughout the test were verified for samples subjected to higher levels of degradation;* A degradation law relating the aging effect to the open porosity of concrete was developed for both degradation processes--freeze-thaw and wet-dry cycles. Regardless of the aggregate origin, for higher degradation degrees, the total mortar volume in the concrete is the main property for understanding the cycles effects on structural performance. The higher total mortar volume in the concrete composition (and, consequently, the higher concrete water absorption), the higher the impact that degradation will have on the following structural properties: pre-cracking elastic modulus, first crack composite strength, first crack matrix strength, final post-cracking matrix strength and, finally, steel-concrete bond strength;
* The feasibility of using recycled aggregates in structural elements exposed to aggressive external agents can be guaranteed as long as the open porosity is properly considered in the concrete mix-design: this is, certainly, possible if a fundamental characterization of the raw materials is performed (e.g., evaluation of the Attached Mortar content in RCA) and, moreover, a specific mixture proportioning method is used for the RAC (e.g., using the Compressible Packing Method proposed herein). Conceptualization, M.P., E.M. and R.D.T.F. ; methodology, C.S.R. and M.A. ; validation, C.S.R., M.P., M.A. and L.C.M. ; formal analysis, C.S.R. and M.P. ; investigation, C.S.R. and M.A. ; resources, R.D.T.F. ; data curation, C.S.R., M.P. and L.C.M. ; writing--original draft preparation, C.S.R. ; writing--review and editing, M.P., M.A., L.C.M., E.M. and R.D.T.F. ; visualization, C.S.R. and M.P. ; supervision, M.P., E.M. and R.D.T.F. ; project administration, R.D.T.F. ; funding acquisition, R.D.T.F. All authors have read and agreed to the published version of the manuscript. This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior--Brasil (CAPES)--Finance Code 001. This work was carried out with support from CNPq, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico--Brasil. The present research is also part of the activities carried out by the second Author (M.P.)