# Impact of Fiber Type on Chloride Ingers in Concrete: A MacroXRF Imaging Analysis
## 5 Conclusions  
The aim of this study was to compare glass and polypropylene fibers applied to concrete to see if the types and contents would have an influence on mechanical strength and durability in the presence of chlorides. Through the experimental research carried out, the results for the concretes studied were as follows:  
* The use of fibers to improve the compressive strength was not effective, as increasing the fiber content in both concrete batches led to strength reductions of up to 56% in the concretes with 0.5% glass fiber;
* The colorimetric test set out in NT Build 492 showed results with little significant difference and was therefore not used to further discuss chloride penetration;
* The XRF results provided greater clarity to the analyses through two-dimensional maps, revealing that fiber-reinforced concretes exhibited lower chloride penetration compared to the reference concretes. MacroXRF analyses allowed for a more precise identification of chloride ion penetration depths, minimizing potential reading errors that could occur in visual analyses based on the reaction of AgNO\({}_{3}\) with chloride;
* Both fiber types studied in this work (polpropylene and glass) at a 0.25% content demonstrated positive effects on chloride penetration resistance, likely due to reduced permeability in fiber-reinforced samples compared to plain concrete. Notably, polypropylene fiber, being less rigid, exhibited superior performance in resisting chloride penetration, making it a more suitable choice for this purpose. These results highlight that the addition of fibers, especially in high percentages, can compromise the mechanical integrity and durability of concrete due to increased porosity and difficulty in compaction. Careful optimization of the fiber content is essential to balance the benefits and disadvantages in practical applications. Implementing the concepts of particle packing during the dosage of fiber-reinforced concrete can contribute to a better distribution of particles in the mix. This process can make the microstructure more compact and minimize the negative effects on compressive strength. These findings underscore the importance and advantages of the MacroXRF test in quantifying specific elements such as chlorine. The XRF results contribute to expanding discussions observed in previous studies, where chloride identification and porosity analysis were primarily conducted through visual inspection and water absorption tests. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15158495/s1](https://www.mdpi.com/article/10.3390/app15158495/s1)]([https://www.mdpi.com/article/10.3390/app15158495/s1](https://www.mdpi.com/article/10.3390/app15158495/s1)), Figure S1: Specimens after demolding; Figure S2: Hydraulic press with a cylindrical specimen after the compression test; Figure S3: Presspanel after the compression test of (a) the 2 nd GF25 sample and (b) the 3 rd GF25 sample; Figure S4: Sample about to fail in the compression strength test; Figure S5: PF50 sample after diametral compression and silver nitrate spraying. The whitish area indicates the presence of chlorides, while the brown area indicates the absence of chlorides; Table S1: Compressive strength data obtained during the tests. Conceptualization, all the authors; methodology, all the authors; software, S.F.M.d.S., J.T.d.A. and M.J.d.A. ; validation, all the authors; formal analysis, S.F.M.d.S., W.S.d.J., J.T.d.A. and M.J.d.A. ; investigation, S.F.M.d.S., W.S.d.J., R.Q.d.O.N. and T.M.S.d.A. ; resources, S.F.M.d.S., W.S.d.J., J.R.d.C.P. and J.T.d.A. ; data curation, S.F.M.d.S., W.S.d.J., J.R.d.C.P. ; J.T.d.A. and M.J.d.A. ; writing--original draft preparation, S.F.M.d.S., W.S.d.J., J.R.d.C.P. and L.A.S. ; writing--review and editing, S.F.M.d.S., W.S.d.J., J.R.d.C.P. and L.A.S. ; visualization, all the authors; supervision, J.R.d.C.P. and J.T.d.A. ; project administration, J.R.d.C.P. ; funding acquisition, J.R.d.C.P. All authors have read and agreed to the published version of the manuscript.