## 4 Conclusions  
This paper presents the results of an experimental study on the recycling of PPFRC and on the feasibility of using the RA and RF obtained from the process. For this purpose, two parent concretes (PCs) with different fiber contents (3 and 9 kg/m\({}^{3}\)) were made, and their mechanical properties were characterized. The tested specimens were crushed to obtain the RA and RF for making new concrete. From the results obtained from the study, the following conclusions can be drawn:  
* In terms of PPFRC recycling, the fiber content in the concrete being crushed does not affect the particle size distribution of the RA and the shape of the RF, only the fiber recovery rate. The percentage of recovered fiber increases with the fiber content of the original concrete.
* Concretes with 100% coarse RA can achieve the same compressive strength as the parent concrete, but with a lower modulus of elasticity by increasing the cement content and lowering the water-cement ratio. When the mixture design is the same, concrete with 100% recycled fiber has little effect on the compressive strength and modulus of elasticity when the fiber content is low compared to concrete with virgin fiber, while both properties are slightly reduced when the fiber content is high.
* The residual flexural tensile strength of concrete is decreased by approximately 50% when 100% of virgin fibers are replaced by RF. This is explained by the smaller average length of RF. However, concrete with 100% coarse RA has improved the residual flexural tensile strength compared to natural aggregate due to the recycled aggregate embedded fiber. The residual (flexural and compression) strength of concrete can increase when RA obtained from PPFRC recycling is used, due to the contribution of the fibers that remain embedded in the RA. This means that the RA obtained from PPFRC recycling can bring a higher added value to new concrete and should, therefore, be treated and stockpiled differently in CDW plants. Both RA and RF as recycled materials can be used in structural applications, such as buildings, by adjusting the mixture design. However, there are still knowledge gaps, such as the porosity of the RA and the influence of the distribution of the RF on the interfacial transition zone (ITZ) of the concrete, which are still worth investigating.  
The results of this study are valid for the range of parameters and variables tested herein. Future studies should include tests with different fiber types and properties (e.g., length), as well as hybrid mixes of virgin and recovered fibers. It is hoped that the results of this study can provide an impetus for the consideration of PPFRC and its potential benefits within the context of a circular economy.  
Conceptualization, G.L. and N.T.; methodology, N.T.; investigation, G.L.; writing--original draft preparation, G.L.; writing--review and editing, N.T. and A.d.l.F.; supervision, A.d.l.F.; funding acquisition, A.d.l.F. All authors have read and agreed to the published version of the manuscript.  
This study has received funding from the China Scholarship Council (CSC) grant number 202106930007 and MBCC Group. The APC was waived by the journal.  
The data presented in this study are available on request from the corresponding author.  
The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.