Feasibility of Using Ferronickel Slag as a Sustainable Alternative Aggregate in Hot Mix Asphalt

Abstract

Ferronickel slag (FNS) is a byproduct produced during ferronickel alloy manufacturing, primarily used in the manufacturing of stainless steel and iron alloys. This material is produced by cooling molten slag with water or air, posing significant disposal challenges, as improper storage in industrial yards can lead to environmental contamination. This study investigates the chemical and mineralogical characteristics of reduction ferronickel slag (RFNS) and its potential use as an alternative aggregate in hot mix asphalt (HMA). The research is based on the practical application of HMA containing RFNS in an experimental area, specifically the parking lot used by buses transporting employees of Anglo American, located at the Codemin Industrial Unit in Niquelândia, Goiás, Central Brazil. Chemical analysis revealed that RFNS primarily consists of MgO, Fe₂O₃, and SiO₂, which are elements with minimal environmental impact. The lack of significant calcium content minimizes concerns about expansion issues commonly associated with calcium-rich slags. The X-ray diffractogram indicates a predominantly crystalline structure with minerals like Laihunite and Magnetite, which enhances wear and abrasion resistance. HMA containing 40% RFNS was tested using the Marshall methodology, and a small experimental area was subsequently constructed. The HMA containing RFNS met regulatory specifications and technological controls, achieving an average resilient modulus value of 6323 MPa. Visual inspections conducted four years later confirmed that the pavement remained in excellent condition, validating RFNS as a durable and effective alternative aggregate for asphalt mixtures. The successful application of RFNS not only demonstrates its potential for local road paving near industrial areas but also underscores the importance of sustainable waste management solutions. This research highlights the value of academia–industry collaboration in advancing environmentally responsible practices and reinforces the contribution of RFNS to enhancing local infrastructure and promoting a more sustainable future.

1. Introduction

In recent years, growing attention to environmental preservation has underscored the importance of recycling industrial byproducts. Industries such as steel and metallurgy face the challenge of managing the waste generated during the production of iron, steel, and other metal alloys [1,2,3]. Leading companies in the ferronickel sector, such as Anglo American and Votorantim Metais, play a key role in managing these waste products. In Brazil, Anglo American has consolidated its nickel and iron ore production operations into a unified structure with notable facilities in Barro Alto and Codemin, located in Barro Alto and Niquelândia (GO), respectively. The Codemin facility in Niquelândia, operational since 1982, is the oldest of Anglo American’s operations in the country, while production at Barro Alto began in 2011. Together, these facilities produce approximately 40,000 tons of ferronickel annually [4,5].

Ferronickel production involves several key stages, including ore preparation (crushing, homogenization, and drying), calcination, reduction, and refining. During the reduction phase, ferronickel is obtained, which is then sent to refining to remove impurities like sulfur and phosphorus. After this, the alloy is ready for commercial use, primarily in the stainless steel industry. Both the reduction and refining processes generate slag as a byproduct.

Ferronickel slag (FNS) aggregate, a co-product of this process, is produced by cooling molten slag with water or air. However, the large amounts of waste generated pose significant disposal challenges. Industries often store these materials in industrial yards, which can lead to severe environmental contamination over time [6,7,8,9]. It is important to highlight that the properties of ferronickel slag do not follow a general rule. Therefore, for each new deposit, its properties must be determined, as they may vary depending on the origin and the beneficiation method of the ore [10]. The chemical composition of FNS, which includes oxides like Fe₂O₃, SiO₂, and CaO, is similar to that of common Portland cement components and thus has been the subject of several studies investigating its use in concrete [6,11,12,13,14,15,16,17,18,19,20].

While steel and blast furnace slags have been extensively evaluated as recycled mineral additions, such as railway ballast [21,22,23,24], in pavement bases or sub-bases [25,26,27,28,29,30,31], or in surface layers of hot mix asphalt (HMA) [32,33,34,35,36,37,38,39,40], FNS remains underexplored in pavement engineering. In one study, Liu et al. [41] confirmed greater adhesion of bitumen to the surface of slags compared to limestone aggregates due to their porous structures, which provided a larger infiltration interface for the asphalt mortar. Further, it was found that amine and amide N–H stretching vibrations and SiO–H stretching vibrations led to chemical reactions between the asphalt and steel slag aggregate, which could improve the adhesion performance between the asphalt and steel slag aggregate. Hasita et al. [42] compared the mechanical performance of the mixture with different aggregate sizes from limestone, granite, and steel slag. The results showed that the Marshall stability of slag asphalt was 46.5% and 50% higher than limestone and granite asphalt, respectively, which was due to the lower Los Angeles abrasion and aggregate crushing value of the steel slag in comparison to limestone and could improve the deformation resistance of the asphalt concrete. The resilient modulus improved due to the higher void mineral aggregate content of the slag asphalt mixture. High voids in mineral aggregate content can cause mixtures to have higher deformation resistance and higher strength, enabling higher stress absorption before failure. Further, a higher rutting resistance (43.2%) was observed due to the rougher and stronger aggregates of the steel slag [42]. Masoudi et al. [35] investigated the effect of slag aggregate on the mechanical performance of warm mix asphalt and found that warm mix asphalt containing slag aggregates was less susceptible to aging in comparison to HMA with limestone aggregates.

Recent studies have shown increasing interest in using FNS as an alternative material in pavement construction, particularly in bases and sub-bases, due to its low susceptibility to expansion and its predominant composition of MgO, Fe₂O₃, and SiO₂, which are elements that do not pose significant environmental risks when exposed to the environment [43,44,45,46,47]. Despite this, the application of FNS in asphalt mixtures remains limited [48,49,50].

In this context, evaluating the feasibility of using FNS as an alternative aggregate in HMA offers new possibilities for industrial waste management while highlighting the critical role of academia–industry collaboration in developing environmentally sustainable solutions. Furthermore, employing FNS near production sites can provide economic and environmental advantages, such as lower transportation costs and the paving of unpaved roads, reducing the need for natural aggregate extraction and promoting a more sustainable approach.

This study aims to analyze the chemical and mineralogical properties of reduction ferronickel slag (RFNS) from the reduction process at the Codemin Industrial Unit of Anglo American. Additionally, this study will evaluate the feasibility of RFNS as an alternative aggregate in HMA, based on a practical application in an experimental area located in the bus parking area of the Codemin facility. The objective is to demonstrate the effectiveness of RFNS in paving local roads near industrial areas, presenting it as a viable solution to the challenges associated with managing waste generated from iron production processes.

2. Materials and Methods

The waste sample was evaluated through a series of tests to assess its physical, chemical, and mineralogical properties, as well as to verify the feasibility of its application in paving. Figure 1 presents a flowchart outlining the sequence of tests and characterizations performed. In addition to detailing the tests conducted on the waste materials, the flowchart provides a step-by-step guide to the entire process, from the production of the HMA to its application in the experimental area, followed by subsequent inspection. Each stage will be explained in the following subsections, offering a comprehensive understanding of the procedures involved.

2.1. Raw Materials

In this research, RFNS samples were collected from the Barro Alto unit, operated by Anglo American, Santa Genoveva, Goiânia, in the State of Goiás, Brazil. Figure 2 shows the visual aspect of the RFNS studied in this work.

The stone aggregates used in this study are crushed limestone subdivided into the following fractions: gravel 1, gravel 0, and dust, as shown in Figure 3. The asphalt binder used is a petroleum asphalt cement (PAC) 50/70 type binder.

2.2. Physical Characterization

Granulometric analysis of the stone aggregates and RFNS was carried out according to Brazilian standards [51], using the sieving method. In addition, density [52], absorption [53], adhesiveness [54], triton impact [55] and Los Angeles abrasion [56] tests were performed on the stone aggregates.

The PAC 50/70 was characterized using conventional penetration tests [57], softening point [58], brookfield viscosity [59], flash point [60], and ductility [61], conducted before and after the RTFOT test [62].

2.3. Mineralogical, Chemical, and Environmental Characterization of the RFNS

2.3.1. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX)

The samples were morphologically analyzed by SEM using the QUANTA FEG 250 microscope, manufactured by FEI (Czech Republic). The samples were coated with gold utilizing a Leica ACE600 high-vacuum coating chamber. Both belonging to the electron microscopy laboratory (LME) of the military institute of engineering—(IME), Rio de Janeiro, Brazil. SEM analysis was performed using the following parameters: electron beam power of 20 kV, working distance ranging between 10.5 and 13 mm, a spot size of 5, and image magnification at 40 and 150×, utilizing the secondary electron detector. For EDX analysis, a detector from the manufacturer Bruker was employed, coupled to the microscope column.

2.3.2. X-ray Diffraction (XRD)

To perform the XRD analysis, the samples were inserted into a monocrystalline silicon substrate. The analysis was performed using the X’Pert Pro MRD System from PANalytical with Cobalt K$\alpha$ radiation (1.789 Å), at a scan speed of 4°/min, power of 40 mA × 40 kV, and scanning range from 20° to 55°. The tests were conducted in line focus configuration, using the X’Pert Data Collector software, version 2.2j (2010), to input the equipment’s operating parameters. The diffraction data was processed using the X’Pert HighScore Plus software, version 2.0a (2004).

2.3.3. Optical Microscopy (OM)

Olympus optical microscope, model BX53M, with Olympus digital camera, model, and Olympus LCMicro image acquisition and analysis software, installed in the Metallography Laboratory of the IME, Rio de Janeiro, Brazil. A 40× magnification in dark field mode was employed to observe the physical characteristics of the RFNS sample.

2.3.4. Environmental Analysis

For the environmental characterization, leaching and solubility tests were conducted according to the guidelines of NBR 10004 [63], using samples provided by Anglo American company, located in the city of Niquelândia, Goiás, Brazil.

2.4. Dosage

In order to investigate the incorporation of RFNS into HMA, the Marshall methodology guidelines were used, as prescribed by DNER standard 043 [64], to determine the appropriate mix of HMA containing RFNS. The dosage aimed to meet the specifications of technical standard DNIT 031 [65], with gradation falling within range C, to constitute a bearing layer in flexible pavement.

2.5. Experimental Area

Following the laboratory dosage and verification of the volumetric and mechanical properties, based on Marshall dosage criteria, a small experimental area was constructed in 2013. This experimental area involved paving the parking lot used by the buses transporting employees of Anglo American, situated at the Codemim Industrial Unit in Niquelândia, Goiás, Central Brazil. Figure 4 presents the location map of the site, while Figure 5 illustrates the condition of the parking lot prior to the commencement of the work.

During the experimental monitoring phase, resilience modulus (RM) tests were performed on specimens extracted from the paved section. This evaluation was conducted in accordance with the procedures outlined in the Brazilian standard DNIT 135 [66].

3. Results and Discussion

3.1. Physical Evaluation (Ferronickel Slag and Virgin Aggregates)

The granulometry of gravel 1, gravel 0, stone dust, cement, and ferronickel slag was analyzed in the physical assessment, as shown in

Table 1. Particle size distribution of coarse gravel 1, coarse gravel 0, stone dust, cement, and RFNS measured by various sieve sizes.

Sieve #	Coarse Gravel 1	Coarse Gravel 0	Stone Dust	Cement	RFNS
1 and ½”	100.0	100.0	100.0	100.0	100.0
1”	100.0	100.0	100.0	100.0	100.0
¾”	100.0	100.0	100.0	100.0	100.0
½”	42.5	98.9	100.0	100.0	100.0
3/8”	4.8	82.8	100.0	100.0	100.0
No. 4	0.2	13.1	95.5	100.0	97.7
No. 10	0.2	4.5	61.9	100.0	63.8
No. 40	0.2	2.7	33.3	100.0	4.0
No. 80	0.2	2.4	27.7	100.0	0.8
No. 200	0.2	1.5	15.3	92.0	0.4

.

Table 2. The physical properties of the materials used, including coarse aggregates, dust, cement, and slag.

Material	True Density (g/cm³)	Apparent Density (g/cm³)	Absorption (%)	Adhesiveness	Treton Impact (%)	Los Angeles Abrasion (%)
Coarse Aggregate 1	2.82	2.79	1.7	Satisfactory	30.61	25.6
Coarse Aggregate 0	2.88	2.75	-	Satisfactory
Dust	2.85	-	-	-	-
Cement	3.10	-	-	-
Slag	3.3	2.99	0.1	Satisfactory *

* With the addition of DOPE.

shows the physical parameters used to characterize the materials analyzed. The parameters considered were real density, apparent density, absorption, adhesiveness, Treton impact, and Los Angeles abrasion.

In Table 2, gravel 1 and gravel 0 showed close actual densities, with values of 2.82 ${\mathrm{g}/\mathrm{cm}}^3$ and 2.88 ${\mathrm{g}/\mathrm{cm}}^3$, respectively, and both showed satisfactory adhesion. RFNS required the addition of DOPE to achieve satisfactory adhesiveness, as well as a higher actual density of 3.3 ${\mathrm{g}/\mathrm{cm}}^3$. The high density of slag is a result of the abundance of iron in its chemical composition, as pointed out by Balbo and Silva [67,68]. The low absorption of the slag (0.1%) is due to the absence of pores in the nickel–iron slag, as was observed through its glassy appearance in the Optical Microscopy test. This was a preponderant factor, as it favored low binder absorption.

3.2. Asphalt Binder

The properties of the 50/70 binder used in the mix are described in

Table 3. The characteristics of the 50/70 binder used in this paper.

Test–CAP 50/70	Units	Limits	Results
Penetration (100 g, 5 s, 25 °C, 0.1 mm)	0.1 mm	50 to 70	50
Softening Point, min.	°C	52	58.6
Brookfield Viscosity at 135 °C, SP 21, 20 rpm, min.	-	274	375
Brookfield Viscosity at 150 °C, SP 21, min.	cP	112	183
Brookfield Viscosity at 177 °C, SP 21	-	57 to 285	68
Flash Point, min.	°C	235	348
Ductility at 25 °C, min.	cm	60	>100
Effect of Heat and Air (RTFOT) at 163 °C, 85 min
Increase in Softening Point, max.	°C	8	65.5
Retained Penetration, min.	%	55	55
Ductility at 25 °C, min.	cm	20	>100
Relative Density	-	-	1.04

and comply with the limits established by the Brazilian standard DNIT 095 [69].

3.3. Mineralogical, Chemical, and Environmental Analysis of Ferronickel Slag

3.3.1. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX)

Figure 6 illustrates the SEM image of the sample fraction, with a magnification degree of 40 and 150×, respectively. It is possible to identify that the surface of the grains is smooth with an absence of pores, that there are some fissures, and that their shape can be interpreted as irregular.

The EDX analysis of the ferronickel slag indicated the presence of the following elements and their respective percentages: O (38.35%), Si (20.16%), Mg (17.14%), Fe (15.79%), C (5.54%), Al (1.96%), and Cr (1.05%), as illustrated in Figure 7. The chemical composition of the ferronickel slag aggregate was then verified, revealing that it primarily consists of MgO, Fe₂O₃, and SiO₂, which are elements that do not pose significant environmental risks. It is well established that the hydration reaction between calcium oxides and magnesium oxides can contribute to the expansion of metallurgical slags, potentially limiting their use in asphalt pavements. However, the chemical characterization of FNS showed negligible levels of calcium, with no detectable calcium oxide (CaO), suggesting that expansion issues typically associated with calcium-containing slags are unlikely to affect the application of FNS in asphalt.

In steel slags, expansion is mainly caused by the transformation of calcium oxide into hydroxide in the presence of water or air. In contrast, the absence of calcium in FNS may account for the minimal expansion observed in this material, underscoring its promising potential as an aggregate for use in paving applications.

3.3.2. X-ray Diffraction (XRD)

The X-ray diffractogram (Figure 8) obtained for the RFNS sample reveals a high incidence of peaks, suggesting that the slag structure is predominantly crystalline. The diffractogram also indicates the presence of the mineral Laihunite [Fe²⁺Fe³⁺₂(SiO₄)₂].

Branco [70] defines Laihunite as an iron silicate, Fe₃(SiO₄)₂ (number from ICDD:70-1861), which occurs in monoclinic, tubular, or prismatic crystals ranging from 0.3 mm to 0.6 mm. According to Kitamura et al. [71], Laihunite is a type of distorted olivine mineral. The authors studied Laihunite using X-ray diffraction, electron probe microanalysis, and analytical electron microscopy, concluding that Laihunite is a mixture of Laihunite and Magnetite, formed through the oxidation of Fayalite.

Fayalite, a mineral of the olivine group, was named by Gmelin in 1840 after its type locality on Faial Island (Ilha do Faial), Azores District (Açores), Portugal. While it is very rare in nature, Fayalite is commonly found in the metallurgy industry, particularly in iron slags [72]. According to Wenk and Bulakh [73] and Deer, Howie and Zussman [74], the hardness of Laihunite is comparable to that of quartz, a mineral often found in the sand fraction.

Due to its crystalline structure and the presence of minerals such as Laihunite and Magnetite, FNS offers several advantages when used in asphalt mixtures. The high hardness of the minerals present in the slag can enhance the wear and abrasion resistance of the mixtures, thereby improving their durability and extending their service life.

3.3.3. Optical Microscopy

In the Optical Microscopy (OM) analysis, shown in Figure 9, the surface of the FRNS aggregate was examined at 40× magnification. The analysis revealed that the aggregate has a smooth surface with no visible pores or cracks. The shape of the grains ranges from spherical to irregular, and the absence of pores may impact the adhesion of the binder to the aggregate. Additionally, the aggregate exhibited a color and vitreous sheen similar to that observed in the mineral Fayalite.

3.3.4. Environmental Analysis

Table 4. Characterization of ferronickel reduction slag.

Raw Sample		Leaching	Solubilization
Parameters	Contents (% and ppm)	Levels (mg/L)	Levels (mg/L)
Silicon	43.60%	2.80	8.10
Magnesium	0.36%	4.60	4.58
Aluminum	3.90%	<0.05	<0.05
Iron	14.90%	0.95	0.19
Total Hardness as CaCO3	1.49%	26.41	26.41
Mg Hardness	1.49%	18.92	18.86
Chromium	1.30%	<0.05	<0.05
Nickel	0.14%	<0.02	<0.02
Titanium	0.15%	<0.01	<0.01
Manganese	0.34%	<0.11	<0.05
Niobium	<5.00 ppm	<0.10	<0.10
Copper	106.00 ppm	<0.02	<0.02
Vanadium	184.00 ppm	<0.01	<0.01
Zirconium	27.00 ppm	<0.01	<0.01
Cobalt	66.00 ppm	<0.10	<0.10

Test report provided by Anglo American.

presents the chemical characterization data of the RFNS sample, including the contents found in leaching and solubilization tests. Additionally,

Table 5. Spectrogram analysis for ferronickel reduction slag.

RFNS	Major Constituents Concentration: >5%	Silicon, Magnesium, Iron
	Minor Constituents Concentration: <5% and >0.1%	Aluminum, Chromium, Calcium
	Traces: Concentration: <0.1%	Nickel, Titanium, Manganese, Niobium, Copper, Vanadium, Zirconium, Cobalt

Test report provided by Anglo American.

provides a qualitative characterization of the raw RFNS, highlighting the highest and lowest concentrations of the chemical constituents identified in the analyzed sample, as well as traces of the minimum chemical composition detected.

The RFNS exhibited notable levels of potentially hazardous metals, including nickel, chromium, copper, and vanadium, as shown in Table 4. Despite these elevated concentrations, the material was classified as type II B inert, as detailed in Table 5, because none of these metals exceeded the concentration limits established by the Brazilian standard NBR 10004 [63]. This classification confirms that the metals are in a stable form that is not prone to leaching or solubilization, thereby posing no environmental contamination risks in its intended application.

3.4. Dosage Design

Based on the physical characterization of the aggregates present in the asphalt mixture, detailed in Table 1 and Table 2, and the granulometric trace falling within range C of the standard DNIT 031 [65], as illustrated in Figure 10, the mixture is composed of 22% gravel 1, 15% gravel 0, 20% dust, 3% cement, and 40% RFNS.

Following the Marshall methodology protocol, the volumetric, stability, and tensile strength of the mix dosed in the laboratory are presented in

Table 6. Marshall mix design parameters.

Item	Values	Limits
Binder Content	4.3%	-
Bulk Density	2.52	-
Air Voids (%)	3.5	3–5
Voids in Mineral Aggregate—VMA (%)	15.5	-
Void-Filled with Bitumen—VFB (%)	77.0	75–82
Maximum Theoretical Density	2.51	-
Minimum Stability (kgf) 75 blows	850	500
Indirect Tensile Strength (MPa)	0.75	0.65

, where it can be observed that the obtained values were satisfactory, within the limits of the DNIT 031 standard [65], for the ideal binder content of 4.3%. It is noteworthy that the void volume reached almost the lower limit, demonstrating that the asphalt mass became quite dense after compaction, with few voids.

3.5. Experimental Area Analysis

Figure 11 presents an image of the parking lot for passenger boarding and disembarking after completing the laboratory phase and standard asphalt mixture application procedures [65].

During the technological control of the experimental area, the binder extraction test was performed using electric rotarex equipment, as described in the Brazilian standard DNER053 [75]. This process revealed a slight increase in the optimal binder content (0.66%) in the final mixed batch, attributed to the calibration of the asphalt plant. This calibration ensures accurate measurement and blending of the binder, aligning the plant’s performance with specified standards and correcting any discrepancies during production. Such adjustments are routine and maintain the quality and consistency of the asphalt mixture, and the observed variation is considered acceptable. Additionally, the granulometry of the mixed batch was verified and remained within the limits of range C of the DNIT [65], with some variations but still within the working range and tolerances allowed for each sieve.

Furthermore, small disaggregation points of the coating were observed in some areas, as shown in Figure 12.

However, this disaggregation stabilized after a few months of operation, and the pavement condition after four years of operation can be considered satisfactory and in good condition, as verified in Figure 13.

Table 7. The RM of the samples collected from the experimental area.

	Force (Unit)	Displacement (Unit)	$\mathit{MR}=\frac{\mathit{F}}{\mathbf{\Delta }\mathit{t}}({0.9976}_{\mathit{\mu }}+0.2692)$
Sample 1	313.25	0.003808	7099
	313.83	0.003678	7364
	312.55	0.003758	7178
		Average	7214
Sample 2	218.45	0.00292	6457
	219.52	0.003075	6160
	220.5	0.003194	5959
		Average	6192
Sample 3	250.91	0.003813	5679
	251.5	0.003889	5581
	250.06	0.003972	5433
		Average	5564

presents the average results obtained from the RM test, according to the Brazilian standard DNIT 135 [66], on three test specimens extracted from the section. The overall average result was 6323 MPa, a significant and satisfactory value based on typical values between 2000 and 8000 MPa for asphalt concretes at 25 °C [76]. Furthermore, the behavior is explained by the presence of Fayalite and Magnetite in the RFNS, which are hard, dense, and hydrophobic components that produce greater elastic deformation of the binder before rupture. In this sense, the cracking of the asphalt coating, caused by the resilient deformation of the underlying layers, can be attenuated due to the value found.

4. Conclusions

This work included the experimental study of the addition of ferronickel slag to the asphalt coating layer of a passenger boarding and disembarking parking lot at the Codemin Industrial Unit in Niquelândia, Goiás. According to the analyses conducted, the conclusions reached are as follows:

• Reduction ferronickel slag (RFNS) is considered inert, as it has low concentrations of harmful elements to the environment, allowing its use in pavements without soil or water contamination;
• The chemical analysis of RFNS revealed that it is primarily composed of MgO, Fe₂O₃, and SiO₂, which pose minimal environmental risk. The absence of significant calcium content reduces concerns about expansion issues typical of calcium-rich slags. The X-ray diffractogram indicated a predominantly crystalline structure with minerals like Laihunite and Magnetite, suggesting that FNS has high hardness. This crystalline structure and mineral content enhance the wear and abrasion resistance of asphalt mixtures, potentially improving their durability and extending their service life;
• The hot mix asphalt (HMA) containing RFNS meets the regulatory specifications and technological control during the execution of the experimental area and obtained an average resilient modulus value of 6323 MPa, indicating the coating’s efficiency regarding pavement mechanics parameters;
• Visual inspections conducted four years after the construction of the experimental area showed that the pavement is still in excellent condition. These findings confirm that RFNS slag is a promising alternative aggregate for asphalt mixtures, providing both durability and long-term performance for local road infrastructure projects. The successful application of RFNS highlights both its viability for local road paving near industrial sites and its potential for promoting sustainable waste management solutions. The results underscore the importance of academia–industry collaboration in advancing environmentally responsible practices, reinforcing the contribution of RFNS to enhancing local infrastructure and promoting a more sustainable future.

Future research should include a comprehensive evaluation of production costs and environmental impacts across the life cycle of these asphalt mixtures, from material extraction to disposal. This analysis will facilitate a more accurate assessment of how the technical application of these sustainable mixtures aligns with economic and environmental goals, providing robust data for strategic decision-making in the pavement sector. Additionally, it is essential to conduct in-depth laboratory tests to further investigate the behavior of asphalt mixtures containing RFNS. Key tests should include evaluating resilience modulus, permanent deformation, and fatigue performance. These assessments will help determine the suitability of RFNS mixtures for higher-traffic volume roads, enabling the broader application of this industrial byproduct in diverse pavement scenarios.