# Impact of Fiber Type on Chloride Ingers in Concrete: A MacroXRF Imaging Analysis
## 2 Materials and Methods
### Test Methods
#### 2.4.2 Chloride Ion Migration Test  
The assessment of ionic chloride migration in a non-steady-state regime was guided by the Nordtest NT Build 492 test method [35]. During sample preparation, the 10 \(\times\) 20 cm cylindrical specimens were cut into four slices of 5 cm height each, discarding the top and bottom slices and retaining the two central slices, as recommended by the IBRACON Recommended Practice Guide: Procedures for Chloride Diffusion and Migration Testing Aiming at Estimating Service Life in Concretes [36]. Both central slices were subjected to the migration test, although one was reserved for subsequent X-ray macrofluorescence analysis. A stepwise immersion procedure was carried out in a Ca(OH)\({}_{2}\) solution until the slices were fully saturated, as confirmed by a constant mass. This procedure was also employed by [37].  
An apparatus was then assembled for the test. The specimen slices were placed inside a plastic tube sealed with a silicone-based adhesive to guarantee watertightness. The anodic solution consisted of sodium hydroxide and distilled water (0.3 M NaOH), while a 10% sodium chloride (NaCl) solution was used as the cathodic solution. Stainless steel rods functioned as both the anode and cathode. The power supply's initial voltage was set to 30 V. After measuring the initial current, the voltage was adjusted and kept stable to match the duration corresponding to the initial current. Figure 2 illustrates the test setup, and Figure 3 shows the test in progress.  
Figure 2: Test apparatus setup.  
Once the testing period concluded, the passing currents were re-measured. The samples were then removed from the apparatus, surface-dried, and subjected to diametral compression, solely to break the specimens and expose an internal surface. After that, a 0.1 M silver nitrate (AgNO\({}_{3}\)) solution was sprayed onto the surface of the sample. The depth of silver chloride (AgCl) precipitation, indicating the accelerated penetration of chloride ions (X\({}_{\text{di}}\)), was measured around 15 min after spraying. Measurements were conducted at 10 mm intervals, with five to seven readings recorded. Figure 4 illustrates a reference for the penetration measurements.  
Once the X\({}_{\text{di}}\) penetration values were available, the average value for each sample was calculated, followed by the non-steady-state migration coefficient D\({}_{\text{ns}}\) given by Equation (1), based on [PERSON]'s second law [38]:  
\[\text{D}_{\text{ns}}=\frac{0.0239\times(273+\text{T})}{(\text{U}-2)\times\text {t}}\times\left(\text{X}_{\text{d}}-0.0238\sqrt{\frac{(273+\text{T})\times\text {L}\times\text{X}_{\text{d}}}{\text{U}-2}}\right) \tag{1}\]  
where:  
D\({}_{\text{ns}}\): non-steady-state migration coefficient (\(\times 10^{-12}\) m\({}^{2}\)/s);  
T: average value of the initial and final temperatures in the anolyte solution, (\({}^{\circ}\)C);  
U: absolute value of the applied voltage (V);  
Figure 4: Measurement of chloride penetration depths (X\({}_{\text{di}}\)). Sample represented: RC.  
Figure 3: Apparatus for chloride migration testing.  
t: test duration (hour);  
X\({}_{d}\): average value of the penetration depths (mm);  
L: thickness of the specimen (mm).