Next Article in Journal
A Study on the Impact of Cultural Inheritance and Innovative Practices on Tourist Behavior in Industrial Heritage-Themed Districts: A Case Study of Xi’an
Previous Article in Journal
Experimental Investigation of the Long-Term Deflection Behavior of Prestressed Concrete Double Tees
Previous Article in Special Issue
Experimental and Statistical Evaluations of Recycled Waste Materials and Polyester Fibers in Enhancing Asphalt Concrete Performance
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Buildings
Volume 15
Issue 16
10.3390/buildings15162845
buildings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effect of the Integration of Alfa Natural Fibers and Demolition Waste on the Mechanical and Thermal Properties of Warm Mix Asphalt

by
Haifa Chehata
1,2,
Abir Jendoubi
1,
Abderrahim Boudenne
2,* and
Jamel Neji
1
1
Materials, Optimization and Energy for Sustainability Laboratory, National Engineering School of Tunis, Tunis EL Manar University, Tunis 1002, Tunisia
2
CERTES, Universite Paris Est Creteil, 61 Av. du Général de Gaulle, 94010 Créteil, France
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(16), 2845; https://doi.org/10.3390/buildings15162845
Submission received: 7 July 2025 / Revised: 8 August 2025 / Accepted: 9 August 2025 / Published: 12 August 2025
(This article belongs to the Special Issue Advanced Studies in Asphalt Mixtures)
Browse Figures
Versions Notes

Abstract

This study investigates the impact of incorporating construction and demolition waste (CDW) aggregates and Alfa natural fibers on the performance characteristics of asphalt mixtures, with a focus on mixing temperature. Several formulations were developed and evaluated through multiphysics property measurements, including density, ultrasonic pulse velocity, rutting resistance, thermal conductivity, and spectral reflectance. The results indicate that Alfa fibers enhance thermal resistance and spectral reflectance. Notably, incorporating 1% Alfa fiber and 20% CDW while reducing the mixing temperature to 150 °C significantly improves rutting resistance. These combined effects result in an optimized formulation that is more resistant to thermal stress during service, thereby enhancing its performance at elevated temperatures. These findings highlight the potential of integrating CDW and natural fibers into asphalt mixtures to develop environmentally friendly and thermally resilient materials, particularly for warming climate regions.

1. Introduction

The quest for more efficient and environmentally conscious construction practices has led to significant innovations in asphalt technology, notably the development of Warm Mix Asphalt (WMA) as a viable alternative to traditional Hot Mix Asphalt (HMA) [1]. The production of HMA requires high temperatures, which in turn demand substantial energy [2]. Consequently, there is a growing interest in developing methods to lower temperature levels, thereby reducing greenhouse gas emissions and decreasing energy consumption while maintaining the same road performance and sufficient workability as HMA [3]. The mixing temperature of WMA is typically 10–38 °C lower than that of HMA [4].
Another major challenge in roads remains the excessive consumption of natural aggregates, which significantly contributes to environmental degradation, resource depletion, and increased carbon emissions [5]. This has spurred research into discovering materials that are both environmentally friendly and economically viable for construction. By incorporating suitable waste materials into road construction, the industry can address pollution and disposal challenges, while promoting more responsible and efficient practices [6].
In this context, various studies have explored the incorporation of alternative eco-friendly materials into asphalt mixtures, including reclaimed asphalt pavement (RAP) [7], recycled polyethylene [8], plastic waste [9], steel slag [10], fly ash [11], and iron ore residues [12], demonstrating their potential to enhance overall pavement performance.
Beyond these alternatives, construction and demolition waste (CDW) is emerging as a promising replacement for natural aggregates in asphalt mixtures. Several recent studies have demonstrated that CDW can significantly improve rutting resistance and contribute to overall pavement durability and performance [13,14,15]. For example, Radević et al. [16] reported that incorporating recycled concrete aggregate (RCA) in asphalt mixtures significantly enhances rutting resistance, with 30% RCA content yielding better performance against permanent deformation. Similarly, Albayati et al. [17] confirmed that RCA incorporation enhances rutting performance. El-Tahan et al. [18] also demonstrated that treated CDW enhances resistance to water damage and fatigue durability in asphalt mixtures.
Similarly, the integration of natural fibers into asphalt mixtures has gained widespread attention in pavement technology. The review proposed by Guo et al. [19] shows that natural fibers improve resistance to cracking, rutting, and moisture damage, thereby extending the lifespan of asphalt pavement. In this context, Ramalingam et al. [20] investigated the use of sisal fibers in asphalt and found that these fibers improve both fatigue and moisture resistance of bituminous concrete. Additionally, Xie et al. [21] studied the combined use of bamboo and basalt fibers in asphalt mastic and demonstrated that these fibers significantly improve rutting resistance. Table 1 provides a summary of previous research on the use of recycled aggregates and natural fibers in asphalt mixtures.
Given the advantages highlighted in previous studies regarding the incorporation of natural fibers into asphalt mixtures and their potential to enhance the mechanical performance, our research specifically investigates the use of Alfa fibers (AF) as a natural fiber additive in asphalt mixtures. Stipa tenacissima, commonly known as “Alfa”, grows naturally in arid and semi-arid environments, covering millions of hectares across North African countries such as Tunisia, Algeria, Libya, and Morocco, as well as parts of Southern Europe [25]. In recent years, Alfa fibers (AF) have attracted significant attention from the scientific community in North Africa due to their favorable mechanical properties, low thermal conductivity, local abundance, and renewability, making them an attractive option for use in building materials [26]. Alfa fiber is a natural lignocellulosic material composed predominantly of 43.9% cellulose, 27.67% hemicellulose, and 17.96% lignin [27]. It exhibits a tensile strength of approximately 94 ± 3 MPa and a modulus of elasticity of about 5.3 ± 0.5 GPa and is distinguished by its low density and moderate thermal stability [28]. Ajouguim et al. [29] studied the effect of Alfa fiber morphology on the hydration and mechanical properties of cement mortars. They reported that Alfa fiber exhibits a rough and irregular surface morphology, characterized by structural defects and the presence of impurities such as waxes and fats.
While growing attention has been given to environmentally responsible asphalt technologies, most existing studies have focused on either the use of recycled materials in asphalt mixtures or the addition of natural fibers separately. Moreover, limited attention has been paid to evaluating the combined effects of these components on both the mechanical and thermophysical behavior of asphalt. Thus, this study aims to investigate the feasibility and benefits of using CDW and AF in the fabrication of asphalt mixtures. To achieve this, an extensive experimental study was conducted to evaluate the performance of WMA incorporating varying contents of both CDW (15%, 20%, and 25%) and Alfa fibers (0.5%, 1%, and 2%). The aim was to identify an optimal formulation that enhances the mechanical and thermal properties of the asphalt, particularly under moderate climatic conditions representative of those in Tunisia.

2. Materials and Methods

2.1. Materials

2.1.1. Aggregates

The aggregates used in this study were sourced from a quarry located in the northern region of Tunisia. To verify their suitability for use in formulating asphalt concrete mixes, these aggregates underwent a series of tests to evaluate their physical properties. As detailed in Table 2, the tests assessed various characteristics, including particle size distribution, density, abrasion resistance, and water absorption. The results obtained from these natural aggregates were meticulously compared with the European standard specifications NF EN 13043 [30] to ensure compliance and performance reliability. This comparative analysis was crucial in determining the potential of these aggregates in contributing to the durability and efficiency of asphalt mixes.

2.1.2. Construction and Demolition Waste

The construction and demolition waste (CDW) used in this study was sourced from the demolition of buildings. These aggregates consisted primarily of concrete, mortar, mineral aggregates, and bricks, as illustrated in Figure 1a,b. The approach for recycling and repurposing CDW into bituminous mixtures involves several critical steps. Initially, CDW is processed using a jaw crusher, a mechanical device designed to reduce large chunks of material into smaller, manageable pieces. This initial crushing stage is crucial for transforming bulky debris into usable aggregates. Afterward, the crushed material undergoes sieving to separate particles based on size, ensuring uniformity and suitability for use in construction applications. The fraction of CDW used in this study was 8/14 mm. The properties of the construction and demolition waste (CDW) aggregates are detailed in Table 3. A key observation is the notably higher water absorption of CDW aggregates in comparison to natural aggregates. This finding is consistent with the results reported by Fatemi et al. [35], who attributed the increased water absorption to the inherently porous and heterogeneous structure of CDW aggregates. Their study also indicated that the abrasion resistance of CDW aggregates slightly exceeds the standard limits. However, when combined with natural aggregates, these deficiencies are effectively compensated.

2.1.3. Bitumen

The binder used in this research was 35/50 penetration-grade bitumen, and its characteristics, as determined experimentally, are presented in Table 4. The results confirmed that the bitumen’s properties fully comply with the European standard specifications EN 12591 [36], as detailed in Table 4. Throughout the investigation, temperature was carefully neutralized, as all tests were carried out under nearly identical conditions. This approach is supported by Prosperi et al. [37], who reported that variations in mixing temperature between 140 °C and 170 °C have minimal impact on the rheological behavior of asphalt mixtures.

2.1.4. Alfa Fiber

In this study, Alfa fiber was sourced from a Tunisian factory located in Kasserine and incorporated into the asphalt mixture at rates of 0.5%, 1%, and 2% by weight of the total mixture. The AFs were rinsed with water to remove dust and impurities and then air dried at room temperature for 72 h. After drying, they were cut to a length of 30 mm. Figure 2 provides an illustration of the Alfa fiber used in this study.

2.2. Sample Preparation

In this research, specimens were fabricated in accordance with the European standard EN 13108-1 [42]. Asphalt samples were prepared using a combination of various aggregates, including crushed sand (0/4), coarse aggregate (4/8), coarse aggregate (8/14), and construction and demolition waste (CDW), along with 35/50 penetration-grade bitumen. Figure 3 presents the aggregate gradation curve used in asphalt mixtures in this study, ensuring compliance with the specifications outlined in NF EN 13108-20 [43]. The Marshall method was used to determine the optimum bitumen content for the conventional asphalt mixture, fixed at 5.2%, and this value was maintained consistently across all formulations. The air void of the asphalt mixtures was measured at 5.4%, 5.6%, 5.9%, and 6.2% for mixtures containing 0%, 0.5%, 1%, and 2% of AF, respectively. Based on these values, the target air void content of 5.8% ± 0.4% was adopted for all formulations, complying with the limit specifications of the XP P98-151 standard [44]. Following the relevant standards, we ensured that all specimens met the recommended compaction levels, thereby minimizing the influence of air void content on the test results.
Table 5 presents a detailed overview of the nomenclature for the various asphalt mixes, accompanied by a comprehensive breakdown of the constituents and proportions used in each formulation.
Figure 4 illustrates the procedure for manufacturing samples that contain AF and CDW. Initially, the mixed aggregates and the bitumen were heated to a temperature of 140 °C, 150 °C, or 160 °C. In the second phase, the mixer was preheated to a temperature of 10 °C higher than the mixing temperature for 10 min to ensure optimal mixing conditions. Once the mixer reached the desired temperature, all aggregates were added and mixed. The aggregates were incorporated into the asphalt mixture based on their weight proportions, as shown in Table 5. Alfa fibers were blended with the aggregates before the bitumen was introduced, ensuring uniform distribution and preventing fiber agglomeration. Following this, the bitumen was carefully incorporated into the mixture. The bitumen and all constituents were then blended in the mechanical mixer for an additional 60 s to achieve a homogeneous mix.
Following mixing, the asphalt mixture was poured into preheated parallelepiped molds measuring 500 × 180 × 100 mm3 and compacted using a roller compactor to form the specimens. The specimens were then allowed to cool at room temperature (22 °C) for 72 h before demolding. Finally, the specimens designated for thermophysical tests were cut to dimensions of 100 × 100 × 100 mm3, as shown in Figure 5a,b.

2.3. Experimental Methods

2.3.1. Density

The density of the various specimens is calculated by determining their dry weight and volume. The volume was obtained by measuring the length of one side of each sample using a ruler. The density is calculated using Equation (1).
ρ = M/V
where ρ (g/cm3) is the density, M (g) is the dry weight of the sample, and V (cm3) is the volume.

2.3.2. Determination of the Ultrasonic Pulse Velocity

The ultrasonic pulse velocity test on asphalt mixtures involves measuring the speed at which an ultrasonic pulse travels through the material. This test is used to assess the homogeneity of the asphalt mixture. Cubic samples measuring 100 × 100 × 100 mm3 were used, with their surfaces smoothed and aligned to guarantee precise measurements. In this research, ultrasonic pulse velocity (UPV) was measured using the GrindoSonic MK-7 device (GrindoSonic BVBA, Leuven, Belgium), in accordance with the principles of the EN 12504-4 standard [45], utilizing a setup with two transducers: one acting as a transmitter and the other as a receiver. The transmitter sends an ultrasonic pulse through the specimen, and the receiver detects the pulse on the opposite side. The time taken for the pulse to travel through the specimen is recorded. By knowing the distance between the transducers and the time of travel, the ultrasonic velocity is calculated using Equation (2).
Velocity = D/T
where Velocity (m/s) is the ultrasonic velocity, D (m) is the distance between the transmitter and the receiver, and T (s) is the time taken for the pulse to travel through the specimen.
The GrindoSonic MK-7 offers high precision, providing measurement accuracy better than 0.005%. For each sample, ultrasonic velocity was measured three times to ensure reliability.

2.3.3. Microscopic Investigation of Asphalt Mixtures

Optical microscopy observations were conducted using the VHX-7000 digital microscope (Keyence Corporation, Osaka, Japan), a high-resolution imaging system equipped with a zoom lens offering magnification from 20× to 6000×. This system provides precise measurements with 4000 resolution, allowing for detailed examination of the external surface morphology of Alfa fibers and their interactions with aggregates and the asphalt matrix, particularly in terms of adhesion. The microscope setup used in this study is presented in Figure 6.

2.3.4. Rutting Resistance

The wheel tracking test is a laboratory procedure used to evaluate the rutting resistance of asphalt mixtures under simulated traffic loading. The process begins with the preparation of two parallelepiped samples measuring 500 × 180 × 100 mm3 in size, as shown in Figure 5c, according to the European standard EN 12697-22 [46]. These samples are then subjected to repeated rolling wheel loads to mimic the stress and strains experienced by pavements in real-world conditions. The test is conducted using a wheel tracking device, as shown in Figure 7, which applies a loaded wheel that moves back and forth across the surface of the asphalt specimen at a controlled temperature of 60 °C within a temperature-controlled chamber to ensure uniform thermal distribution. The test is carried out over a specified period, and the depth of the rut formed in the asphalt surface is measured periodically to assess the material’s resistance to deformation. Linear variable displacement transducer (LVDT) sensors are used to continuously monitor and record rut depth as the wheel repeatedly passes over the specimen. Based on the manufacturer’s specifications, these sensors provide high measurement accuracy of approximately 1 µm and excellent repeatability down to 0.1 µm. They are connected to a monitoring system to ensure accurate data acquisition. Rut depth measurements are taken at ten predefined locations on each specimen during each cycle to account for heterogeneity.
Prior to each test, the sensors and equipment are calibrated using reference materials to ensure the accuracy of the measurements. The results provide valuable data on the mixture’s resistance to permanent deformation.

2.3.5. Thermophysical Characterization

At the micro-scale level, asphalt concrete is characterized by a heterogeneous composition with a random distribution of aggregates and bitumen. However, at the macro-scale level, these constituents exhibit homogeneous distribution, forming an isotropic structure. Mirzanamadi et al. [47] considered asphalt concrete as a homogenous and isotropic material in their analysis. Following this approach, the present study operates under the assumption that asphalt concrete is a homogeneous and isotropic material, simplifying the analysis for a comprehensive understanding of its thermal properties.
Samples for all formulations, each measuring 100 × 100 × 100 mm3, were prepared for the measurement of thermophysical properties, as shown in Figure 5a. These properties were evaluated using the Isomet 2114 device (Applied Precision s.r.o, Bratislava, Slovakia) in accordance with ISO 22007-2 [48], which specifies the transient plane source (TPS) method. According to the manufacturer’s specifications, the measurement accuracy for thermal conductivity is ±5% of the reading, and for volumetric heat capacity, it is ±10%. The reproductively of the measurements for both properties is approximately 3% of the reading. Prior to testing, the device was calibrated with a standard reference sample to ensure accuracy.
During testing, the sensor, which served as both a heat source and a temperature detector, was placed in direct thermal contact with one face of the specimen (Figure 8). A short heat pulse was applied through the sensor, and the resulting temperature response over time was recorded. Based on these data, the device accurately calculated thermal conductivity, thermal diffusivity, and volumetric heat capacity. All measurements were conducted in a climate chamber at a controlled temperature of 20 °C to minimize the effects of ambient variations, and readings were taken only after thermal equilibrium was achieved. To further ensure the reliability of the results and reduce statistical uncertainty, each specimen was tested on all six faces, with three repeated measurements per face. Finally, the mean values of thermophysical properties as well as their statistical uncertainties were calculated.

2.3.6. Spectral Reflectance Test

To evaluate the thermal radiative property of asphalt mixtures, spectral reflectance measurements were performed on several samples using a high-performance Lambda spectrometer (Figure 9). The measurements were achieved across distinct regions of the electromagnetic spectrum: ultraviolet (UV), visible (VIS), and near-infrared (NIR) light, spanning wavelengths from 280 to 2500 nm. The instrument was carefully adjusted to capture data in the UV (280–400 nm), VIS (400–760 nm), and NIR (760–2500 nm) ranges under controlled lighting conditions to minimize environmental variables. According to the instrument specifications, the wavelength accuracy was better than 0.05 nm for the ultraviolet (UV) and visible (VIS) and better than 0.2 nm for the near infrared (NIR), ensuring reliable and high-resolution spectral reflectance data. Three measurements were taken for each sample to ensure accurate and reproducible results.

3. Results and Discussion

3.1. Density

As can be seen from Figure 10, the densities of the asphalt mixtures are mainly distributed in the range of 1.80 to 2.40 g/cm3. The results indicate that the density of samples containing Alfa fibers is lower than that of samples without fibers. The addition of 0.5%, 1%, and 2% Alfa fiber reduced the density by 12.5%, 17.5%, and 25%, respectively, compared to conventional asphalt (BB0/14). The incorporation of Alfa fiber into asphalt mixtures has been observed to reduce the overall density of the composite material. This reduction in density is primarily due to the lower specific gravity of Alfa fiber, which is approximately 1.40 g/cm3 [49]. Indeed, as the Alfa fiber content increases, the formation of voids becomes more prevalent, resulting in a further reduction in the material’s overall density. The findings are consistent with the existing literature; Ahmed et al. [50] explored the incorporation of bamboo and sugarcane bagasse as natural fiber in HMA. These authors demonstrated that the addition of these fibers led to an increase in air voids within the mixture, which subsequently decreased the density of the asphalt.
Furthermore, the incorporation of construction and demolition waste (CDW) into asphalt mixtures has been shown to decrease the density of asphalt. For example, asphalt containing 20% CDW (A0-160 and A0-150) exhibits a density of approximately 2.30 g/cm3, which is about 4% lower than the density of conventional asphalt, measured at 2.40 g/cm3. This decrease in density can be attributed to the fact that CDW aggregates typically possess a lower density compared to natural aggregates. For instance, a similar study has indicated that certain recycled aggregates, particularly those sourced from CDW, often exhibit slightly lower densities compared to natural aggregates [51].

3.2. Ultrasonic Pulse Velocity

Ultrasonic pulse velocity (UPV) is a valuable technique for evaluating the quality and integrity of asphalt mixtures, including those modified with construction and demolition waste and Alfa fibers. UPV measures the speed at which ultrasonic waves travel through the asphalt material, providing insights into its density, uniformity, and internal structure. Figure 11 presents the UPV measurements for different asphalt samples. The results indicate that the conventional asphalt sample (BB0/14) exhibits the highest measured value (4730 m/s) compared to all other formulations. These findings confirm the high density and structural cohesion of conventional asphalt mixtures evaluated, as reflected by the elevated UPV values. Additionally, the UPV values for asphalt samples containing 20% CDW (A0-160 and A0-150) are slightly lower than those of the conventional asphalt, with values of 4691 m/s and 4651 m/s, respectively.
However, the values for the asphalt mixtures containing both CDW and Alfa fibers are noticeably lower, ranging from 3591 m/s to 4104 m/s. For instance, A2-150, which contains 20% CDW and 2% AF, shows the lowest UPV of 3591 m/s. The reduction in UPV can be attributed to the presence of AF, which introduces more voids and disrupts the compactness of the mixture. This interpretation is supported by previous studies [52,53], which have shown that UPV is sensitive to the presence of voids, cracks, and other structural discontinuities within the material. Tang et al. [54] further reported that the destruction or degradation within asphalt mixtures facilitates air infiltration, which attenuates the propagation of ultrasonic waves and reduces pulse velocity. In line with these findings, the lower UPV values observed in this study can be explained by the porosity caused by the incorporation of Alfa fibers and CDW, which creates more air pathways and disrupts the continuous medium necessary for efficient ultrasonic wave propagation.
Since ultrasonic wave propagation in asphalt is closely linked to key physical properties such as density, UPV testing proves to be a valuable, non-destructive tool for assessing the internal structure and compaction state of asphalt mixtures.
Figure 12 illustrates the variation in ultrasonic pulse velocities (UPVs) as a function of density for all asphalt formulations. A strong positive correlation can be clearly observed between these two parameters, as confirmed by a high coefficient (R2) value of 0.9206. This relationship indicates that denser asphalt mixtures tend to exhibit higher UPV values, likely due to reduced void content and improved continuity within the internal structure, which collectively enhance the propagation of ultrasonic waves through the material.

3.3. Microscopic Investigation of Asphalt Mixtures

To examine the adhesion mechanism between Alfa fibers and the asphalt binder, digital video microscopy was employed. Initially, observations were conducted on the Alfa fibers to characterize their surface morphology. As shown in Figure 13, the fibers exhibit a rough and irregular surface texture, which is expected to enhance mechanical interlocking with the bituminous matrix. Similar surface features were previously reported by Garrouri et al. [28] using scanning electronic microscopy (SEM), where the longitudinal morphology of Alfa fibers revealed a rough outer layer with a noticeable surface irregularity, including deposits of waxes and impurities.
Subsequently, microscopic images were captured of the A1-150 mixture, containing 1% Alfa fibers, to evaluate the internal microstructure of the asphalt mixture modified with both Alfa fibers and construction and demolition waste. Figure 14 presents magnified optical micrographs highlighting the distribution and interaction between the CDW particles, Alfa fibers, and the asphalt binder. The Alfa fibers appear well dispersed within the bituminous matrix, often oriented in various directions. As shown in Figure 14b, the A1-150 micrograph at 200× magnification reveals the fiber–matrix interaction, indicating that the fibers are embedded within the binder, thereby contributing to the reinforcement of the internal structure of the mixture. These observations are consistent with ones reported by Cui et al. [55], who demonstrated that the rough surface of bamboo fiber enhances asphalt absorption and improves the interfacial adhesion with the asphalt matrix.

3.4. Rutting Resistance

Figure 15 illustrates the evolution of rutting depth as a function of the number of cycles for five different asphalt mixtures: conventional asphalt BB0/14, A0-150, A0.5-150, A1-150, and A2-150. Initially, all five samples exhibit a rapid increase in rutting depth within the first 1000 cycles, a common behavior as the asphalt mixtures begin to deform under repeated loading.
By the 10,000-cycle mark, the A0-150 mixture, containing 20% of CDW and produced at a fabrication temperature of 150 °C, shows improved rutting resistance compared to the conventional BB0/14 asphalt. At 30,000 cycles, the rut depth of A0-150 is reduced by 15% relative to the conventional mix, indicating that the inclusion of CDW enhances the mixture’s structural integrity and its ability to withstand deformation. These results emphasize the beneficial role of CDW in improving the rutting resistance of asphalt, which has been supported by similar studies on recycled materials. For example, previous research has shown that incorporating recycled concrete aggregates (RCAs) or CDW into asphalt mixtures can lead to significant improvements in resistance to permanent deformation [35].
The incorporation of 0.5% and 1% Alfa fibers into the asphalt mixture reduces rut depth by 18% and 20%, respectively, after 30,000 cycles compared to conventional asphalt. This enhancement can be attributed to the ability of fibers to partially absorb the asphalt binder, which limits binder migration and consequently reduces rutting. Furthermore, the fibrous structure of Alfa fibers reinforces the asphalt matrix, enhancing its cohesion and mechanical stability under repeated loading. These findings are consistent with those reported by Jia et al. [56], who observed that the addition of bamboo fibers in asphalt mixtures similarly decreased rutting by absorbing binder and enhancing matrix reinforcement, thereby confirming the effectiveness of natural fibers in improving rutting resistance.
However, when the Alfa fiber content increases to 2% in the A2-150 formulation, the rut depth rises by 27% at 30,000 cycles relative to the conventional asphalt mix (BB0/14). This suggests that a 2% fiber concentration does not enhance rutting resistance and may, in fact, compromise the overall performance of the mixture.
Figure 16 illustrates the relationship between rut depth and Alfa natural fiber content in asphalt, highlighting its impact on deformation resistance over 30,000 load cycles. As the fiber content increases from 0% to 1%, rut depth decreases, indicating improved resistance to deformation. The range of 0.5% to 1% appears to create a plateau effect, suggesting an optimal dosage for maximizing performance. While the existing literature typically limits natural fiber content in asphalt to 0.5% by weight [19], this study’s preliminary findings indicate that 1% Alfa fiber significantly enhances rutting resistance. Conversely, increasing the fiber content to 2% proves ineffective, as rut depth rises by approximately 60% compared to the 1% formulation, disrupting the asphalt’s structural balance and reducing its resistance to permanent deformation. These results suggest that 1% Alfa fibers provide the best improvement in asphalt durability and load-bearing capacity, enhancing resistance to deformation under traffic loads. These results underscore the potential of combining 20% CDW and 1% Alfa fibers to create more durable, rut-resistant asphalt mixtures.

3.5. Thermophysical Properties

Thermal conductivity (TC) is a key property influencing heat transfer through asphalt pavements, impacting their durability and behavior under thermal stresses. To gain a deeper understanding of the thermophysical properties of asphalt pavements, it is important to investigate how various compositions and fabrication temperatures impact these characteristics. Figure 17a illustrates the thermal conductivity measured values for different asphalt samples, showcasing the influence of different compositions and mixing temperatures. A comparative analysis between asphalt mixtures reveals that conventional asphalt (BB0/14) exhibits the highest thermal conductivity at 1.64 ± 0.03 W/(m·K), closely followed by the A0-160 and A0-150 samples, which include 20% of CDW and demonstrate values of 1.58 ± 0.04 W/(m·K) and 1.59 ± 0.03 W/(m·K), respectively. This slight reduction in thermal conductivity observed with incorporation of CDW in asphalt mixtures can be explained by findings in the literature [57], which indicate that CDW generally exhibits lower thermal conductivity than natural aggregates.
Conversely, when Alfa fibers are introduced, the thermal conductivity significantly decreases. For instance, the A0.5-150 sample, which contains 20% CDW and 0.5% AF, exhibits a thermal conductivity of only 1.34 ± 0.02 W/(m·K). This reduction is also evident in samples containing higher proportions of AF, such as A2-150, which shows the lowest TC at 0.92 ± 0.01 W/(m·K), representing a 44% reduction compared to the conventional asphalt concrete BB0/14. This decrease can be primarily attributed to the low thermal conductivity of AF, measured at 0.042 W/(m·K) [58], which minimizes heat transfer within the asphalt matrix. Additionally, the addition of AF leads to an increase in the porosity of asphalt mixtures. This enhanced porosity introduces more air voids within the asphalt, which are poor conductors of heat, further diminishing TC [59]. As a result, asphalt containing AF demonstrates increased resistance to heat transfer, potentially improving its thermal insulation properties. A similar study conducted by Ajouguim et al. [60] demonstrated that the addition of 1% wt. of AF in compacted earth bricks decreases TC.
Thermal diffusivity describes how quickly heat spreads through a material. As depicted in Figure 17b, a similar behavior to thermal conductivity is observed, where the thermal diffusivity of the samples varied within the range of 1.00 ± 0.03 mm2/s to 0.64 ± 0.01 mm2/s. The results indicate a decrease in thermal diffusivity as the AF content increases. The thermal diffusivity of A1-160 is 34% less than that of A0-160. For the A2-150 composition, there was a reduction of 36% in thermal diffusivity compared to BB0/14. The reduced thermal conductivity contributed to the lower thermal diffusivity, meaning that heat spreads more slowly through the asphalt.
Volumetric heat capacity refers to the amount of heat energy absorbed by a unit volume of pavement at a given temperature [61]. In asphalt mixtures, a higher volumetric heat capacity indicates a greater ability of the pavement to absorb and store thermal energy, thereby minimizing temperature fluctuations [62]. Figure 17c shows the volumetric heat capacity of various formulations. The trend in volumetric heat capacity closely follows the trend observed in TC. Samples containing Alfa fibers exhibit lower thermal conductivity, which consequently results in lower volumetric heat capacity. For the A1-150 and A2-150 compositions, there was a reduction of 11% to 12.8%, respectively, in volumetric heat capacity compared to BB0/14. The decrease in volumetric heat capacity may affect the thermal behavior of the pavement by reducing its ability to absorb and store thermal energy.
The density of asphalt mixtures is closely correlated with their thermal conductivity, as both properties are influenced by the composition and structure of the material. Generally, denser asphalt mixtures tend to exhibit higher thermal conductivity because they have fewer air voids, allowing for more efficient heat transfer through the solid matrix of aggregates and binder. The increased contact area between particles in denser mixtures facilitates the conduction of heat, resulting in improved thermal conductivity. This observation is consistent with the findings of Hassn et al. [63], who investigated the effect of air void content on thermal properties of asphalt mixtures and demonstrated that lower air void levels significantly enhance thermal conductivity. Conversely, asphalt mixtures with lower density, such as those containing Alfa fibers, have a higher proportion of air voids, which act as insulating spaces that hinder the flow of heat and reduce thermal conductivity. The correlation between density and thermal conductivity is well illustrated in Figure 18, which shows a linear relationship (R2 = 0.8897). The observed strong correlation implies that as density decreases, thermal conductivity also decreases. This characteristic makes the material particularly suitable for insulation purposes, as lower densities typically indicate lower thermal conductivity. This result is also in agreement with the findings of Elhamdouni et al. [64], who reported that incorporating Alfa fibers into clay-based materials reduces thermal conductivity by increasing air void content.
As shown in Figure 19, there is a positive correlation between UPV and thermal conductivity. This is because a denser asphalt matrix, which allows for higher UPV, typically has better aggregate interlock and reduced air void content, leading to improved heat transfer capabilities. Essentially, fewer air gaps and a more continuous phase within the material enhance its ability to conduct heat. These findings are aligned with those reported by Akçaözoğlu et al. [65], who investigated the thermal conductivity and ultrasonic wave velocity of cementitious composites incorporating waste PET lightweight aggregate. They found that, as thermal conductivity decreased, ultrasonic wave velocities also declined, which they attributed to the porous structure of the composites, limiting both heat conduction and wave propagation within the material.
The relationship between rutting resistance and thermal conductivity in asphalt mixtures is essential for optimizing pavement performance, particularly in hot climates. Indeed, the most optimized formulations in terms of rutting resistance, BB0/14, A0-150, A0.5-150, and A-150, were selected and presented in Figure 20 to enable analysis between these two key properties.
Figure 20 clearly demonstrates the benefits of incorporating Alfa fiber (AF) into the asphalt mixtures. As thermal conductivity decreases from approximately 1.64 W/(m·K) in the conventional mixture to around 0.99 W/(m·K) in the mixture containing both construction and demolition waste (CDW) and Alfa fiber (A1-150), a corresponding reduction in rut depth is observed. Our findings suggest that lower thermal conductivity helps prevent excessive deformation under traffic loads, leading to improved rutting resistance. This inverse relationship, where higher thermal conductivity correlates with lower rutting resistance, highlights the importance of thermal properties in maintaining pavement integrity.
This observation aligns with the findings of Shanbara et al. [66], who reported that pavements reinforced with jute and coir fibers, when maintained at lower temperatures, exhibit reduced permanent deformation. This result highlights the significant impact of temperature on the performance of asphalt mixtures, particularly under the stress of traffic loads.
In this context, incorporating low-conductivity materials such as Alfa fibers can help regulate internal pavement temperatures, thereby enhancing resistance to deformation. This improvement is primarily due to the low thermal conductivity of Alfa fibers (0.042 W/(m·K)) [58], which is significantly lower than that of the conventional asphalt mixture BB0/14 (1.64 W/(m·K)). By reducing the overall thermal conductivity of the asphalt mixture, Alfa fibers increase its thermal resistance, thereby slowing down heat propagation. As a result, the pavement can better withstand deformation caused by high temperatures and heavy traffic.

3.6. Spectral Reflectance

Spectral reflectance is an important thermal radiation property that quantifies the amount of light reflected from asphalt surfaces, significantly influencing the material’s heat absorption and thermal performance. High spectral reflectance indicates effective heat management and can help mitigate urban heat island effects, as materials with greater reflectance absorb less solar radiation and remain cooler [67]. This characteristic not only contributes to lower pavement temperatures but also positively impacts the overall durability and longevity of the pavement [68]. Figure 21 presents the reflectance of various asphalt samples across different wavelengths (nm) in the ultraviolet (UV), visible (VIS), and near-infrared (NIR) spectral regions. The asphalt samples examined include conventional asphalt (BB0/14) and four modified asphalt mixtures: A0-150, A0.5-150, A1-150, and A2-150.
The results show that all samples exhibit an increasing trend in reflectance with increasing wavelength, transitioning from the UV to the VIS and finally to the NIR regions. In the UV region, differences between the samples are minimal, indicating that the addition of CDW and AF does not significantly impact reflectance in the UV spectrum.
However, in the visible spectrum, there is a noticeable separation in reflectance among the samples. The A2-150 formulation, which contains 20% CDW and 2% AF, shows the highest reflectance across this region, followed by the A1-150, A0.5-150, and A0-150 samples. The conventional asphalt (BB0/14) exhibits the lowest reflectance.
In the NIR region, reflectance continues to increase, where the differences between the samples become more pronounced. The A2-150 sample maintains the highest reflectance, which could be beneficial for thermal management in asphalt pavements, as it reduces heat absorption. The A0-150, A0.5-150, and A1-150 samples show intermediate reflectance levels, while the conventional asphalt (BB0/14) remains at the lower end. This suggests that the incorporation of CDW and AF to asphalt influences its thermal properties by enhancing its reflectance, particularly in the NIR region, potentially reducing heat absorption. Among all tested mixtures, the A2-150 sample consistently exhibits the highest reflectance across all regions, which may imply better heat dissipation properties due to reduced thermal absorption. In contrast, the conventional asphalt (BB0/14) shows the lowest reflectance, indicating greater light and heat absorption. The reflectance patterns observed in the A0-150, A0.5-150, and A1-150 mixtures highlight the role of CDW and AF content in modulating the reflective behavior of asphalt.
The incorporation of construction and demolition waste (CDW) into asphalt mixtures has been shown to significantly increase reflectance. This enhancement can be attributed to the presence of CDW, which reflects greater UV radiation compared to conventional aggregates. This increased reflectance can lead to a reduction in surface temperature, thereby contributing to the development of cooler pavements with improved resistance to heat-induced aging. These findings are consistent with previous studies, which have confirmed that construction waste materials exhibit higher reflectance than traditional asphalt mixtures, supporting their potential as environmentally beneficial and thermally advantageous additives in pavement engineering [57]. Furthermore, the addition of Alfa fibers into asphalt mixtures enhances their spectral reflectance, which contributes to greater resistance against UV-induced degradation. This finding is aligned with recent research conducted by Yang et al. [69], who demonstrated that the use of biomass-based fibers (sugarcane bagasse) significantly improves asphalt’s resistance to aging caused by UV exposure.

4. Conclusions

This study has demonstrated the potential of incorporating construction and demolition waste (CDW) aggregates and Alfa fibers into asphalt mixtures to enhance both mechanical and thermophysical properties. Microstructural analysis via optical microscopy revealed strong adhesion among Alfa fibers, aggregates, and the asphalt binder, indicating a well-integrated and cohesive structure. In terms of mechanical performance, the inclusion of 20% CDW significantly improved rutting resistance, while the addition of 1% Alfa fiber provided optimal reinforcement. No further enhancements were observed at higher fiber contents.
Regarding thermal behavior, the integration of CDW and Alfa fibers led to a reduction in thermal conductivity, indicating improved insulating capacity. Spectral reflectance analysis further showed that their presence increased solar reflectance, which could contribute to lower surface temperatures. A strong correlation was identified among thermal conductivity, ultrasonic pulse velocity (UPV), and density, suggesting that these parameters collectively influence the overall performance of asphalt mixtures.
Despite these promising results, several limitations must be acknowledged. The CDW content was restricted to 20%, and the effects of higher substitution rates on mechanical performance remain unexplored. Moreover, a comprehensive life-cycle assessment (LCA) and energy consumption analysis were not performed, both of which are critical to fully evaluate the environmental and economic implications of this approach. Addressing these aspects in future studies will further validate and optimize the use of CDW and Alfa fibers in asphalt applications.
Finally, the combined use of CDW and Alfa fibers in asphalt mixtures offers a promising pathway toward enhancing pavement durability and thermal performance, effectively fulfilling the objectives established at the outset of this research.

Author Contributions

Conceptualization, A.B.; methodology, A.B. and J.N.; validation, A.B., J.N. and A.J.; formal analysis, H.C.; investigation, H.C.; resources, J.N.; data curation, H.C.; writing—original draft preparation, H.C.; writing—review and editing, A.B. and J.N.; visualization, A.B.; supervision, A.B. and J.N.; project administration, J.N.; funding acquisition, J.N. All authors have read and agreed to the published version of the manuscript.

Funding

Funding was provided by an internship program at the University of Tunis EL Manar: Research Grants for PhD students.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest. 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.

References

  1. Darshan, N.; Kataware, A.V. Exploring different approaches to understand effect of WMA modification on mixing and compaction temperatures of asphalt binders: A laboratory study. Constr. Build. Mater. 2025, 458, 139562. [Google Scholar] [CrossRef]
  2. Androjić, I.; Alduk, Z.D.; Dimter, S.; Rukavina, T. Analysis of impact of aggregate moisture content on energy demand during the production of hot mix asphalt (HMA). J. Clean. Prod. 2020, 244, 118868. [Google Scholar] [CrossRef]
  3. Almeida-Costa, A.; Benta, A. Economic and environmental impact study of warm mix asphalt compared to hot mix asphalt. J. Clean. Prod. 2016, 112, 2308–2317. [Google Scholar] [CrossRef]
  4. Zhao, S.; Huang, B.; Shu, X.; Woods, M. Comparative evaluation of warm mix asphalt containing high percentages of reclaimed asphalt pavement. Constr. Build. Mater. 2013, 44, 92–100. [Google Scholar] [CrossRef]
  5. Wang, J.; Zhang, R.; Zhou, H.; Huang, W.; Feng, D.; Li, X. Optimizing of asphalt mix design considering mixture performance, environmental impact, and life cycle cost. J. Clean. Prod. 2025, 512, 145618. [Google Scholar] [CrossRef]
  6. Hasheminezhad, A.; Ceylan, H.; Kim, S. Sustainability promotion through asphalt pavements: A review of existing tools and innovations. Sustain. Mater. Technol. 2024, 42, e01162. [Google Scholar] [CrossRef]
  7. Daryaee, D.; Habibpour, M.; Norouzi, Y. Chemical properties and mechanical performance of bitumen and asphalt Mixtures with Reclaimed Asphalt Pavement (RAP) under varying temperature conditions. Constr. Build. Mater. 2025, 489, 145343. [Google Scholar] [CrossRef]
  8. Boarie, A.; Abdelsalam, M.; Gamal, A.; Rabah, M. Laboratory and Environmental Assessment of Asphalt Mixture Modified with a Compound of Reclaimed Asphalt Pavement and Waste Polyethylene. Buildings 2024, 14, 1186. [Google Scholar] [CrossRef]
  9. Gkyrtis, K.; Pomoni, M. An Overview of the Recyclability of Alternative Materials for Building Surface Courses at Pavement Structures. Buildings 2024, 14, 1571. [Google Scholar] [CrossRef]
  10. Coelho, L.M.; dos Santos, W.W.; Guimarães, A.C.R.; Monteiro, S.N. Influence of the Baily Gradation Method on the Mechanical Behavior of Asphalt Mixture Containing Steel Slag as an Alternative Aggregate. Buildings 2024, 14, 3942. [Google Scholar] [CrossRef]
  11. Woszuk, A.; Bandura, L.; Franus, W. Fly ash as low cost and environmentally friendly filler and its effect on the properties of mix asphalt. J. Clean. Prod. 2019, 235, 493–502. [Google Scholar] [CrossRef]
  12. Silveira, V.L.; Guimarães, A.C.R.; Coelho, L.M.; dos Santos, W.W.; da Silveira, P.H.P.M.; Monteiro, S.N. Recycling Iron Ore Waste through Low-Cost Paving Techniques. Sustainability 2024, 16, 5570. [Google Scholar] [CrossRef]
  13. Abedin Khan, Z.; Balunaini, U.; Costa, S. Environmental feasibility and implications in using recycled construction and demolition waste aggregates in road construction based on leaching and life cycle assessment—A state-of-the-art review. Clean. Mater. 2024, 12, 100239. [Google Scholar] [CrossRef]
  14. Zhu, J.; Wu, S.; Zhong, J.; Wang, D. Investigation of asphalt mixture containing demolition waste obtained from earthquake-damaged buildings. Constr. Build. Mater. 2012, 29, 466–475. [Google Scholar] [CrossRef]
  15. Pesandín, A.; Pérez, I. Laboratory evaluation of hot-mix asphalt containing construction and demolition waste. Constr. Build. Mater. 2013, 43, 497–505. [Google Scholar] [CrossRef]
  16. Radević, A.; Đureković, A.; Zakić, D.; Mladenović, G. Effects of recycled concrete aggregate on stiffness and rutting resistance of asphalt concrete. Constr. Build. Mater. 2017, 136, 386–393. [Google Scholar] [CrossRef]
  17. Albayati, A.; Wang, Y.; Wang, Y.; Haynes, J. A sustainable pavement concrete using warm mix asphalt and hydrated lime treated recycled concrete aggregates. Sustain. Mater. Technol. 2018, 18, e0008. [Google Scholar] [CrossRef]
  18. El-Tahan, D.; Gabr, A.; Dessouky, S.; El-Badawy, S. Study of the Performance of Warm-Mix Asphalt Containing Recycled Concrete as Coarse Aggregate in Egypt and the Middle East. J. Mater. Civ. Eng. 2024, 36, 1–14. [Google Scholar] [CrossRef]
  19. Guo, Y.; Tataranni, P.; Sangiorgi, C. The use of fibres in asphalt mixtures: A state of the art review. Constr. Build. Mater. 2023, 390, 131754. [Google Scholar] [CrossRef]
  20. Ramalingam, S.; Murugasan, R.; Nagabhushana, M.N. Laboratory performance evaluation of environmentally sustainable sisal fibre reinforced bituminous mixes. Constr. Build. Mater. 2017, 148, 22–29. [Google Scholar] [CrossRef]
  21. Xie, T.; Ren, W.; Chen, Y.; Sheng, J.; Wang, L. Enhancing the performance of Asphalt Mastic with Natural Fiber Reinforcement Basalt and Bamboo Fibers. Appl. Sci. 2023, 13, 7946. [Google Scholar] [CrossRef]
  22. Hussein, F.K.; Isamel, M.Q.; Huseien, G.F. Rock Wool Fiber-Reinforced and Recycled Concrete Aggregate-Imbued Hot Asphalt Mixtures: Design and Susceptibility Evaluation. J. Compos. Sci. 2023, 7, 428. [Google Scholar] [CrossRef]
  23. Jia, H.; Chen, H.; Sheng, Y.; Meng, J.; Cui, S.; Richard Kim, Y.; Huang, S.; Qin, H. Effect of laboratory aging on the stiffness and fatigue cracking of asphalt mixture containing bamboo fiber. J. Clean. Prod. 2022, 333, 130120. [Google Scholar] [CrossRef]
  24. Liu, K.; Li, T.; Wu, C.; Jiang, K.; Shi, X. Bamboo fiber has engineering properties and performance suitable as reinforcement for asphalt mixture. Constr. Build. Mater. 2021, 290, 123240. [Google Scholar] [CrossRef]
  25. Helaili, S.; Chafra, M.; Chevalier, Y. Natural fiber alfa/epoxy randomly reinforced composite mechanical properties identification. Structures 2021, 34, 542–549. [Google Scholar] [CrossRef]
  26. Elfaleh, I.; Abbasi, F.; Habibi, M.; Ahmad, F.; Guedri, M.; Mondher, N.; Garnier, C. A comprehensive review of natural fibers and their composites: An eco-friendly alternative to conventional materials. Results Eng. 2023, 19, 101271. [Google Scholar] [CrossRef]
  27. Hanana, S.; Elloumi, A.; Placet, V.; Tounsi, H.; Belghith, H.; Bradai, C. An efficient enzymatic-based process for the extraction of high mechanical properties of alfa fibers. Ind. Crops Prod. 2015, 70, 190–200. [Google Scholar] [CrossRef]
  28. Garrouri, S.; Lakhal, W.; Benazzouk, A.; Sediki, E. Potential use of Alfa fibers in construction material: Physico-mechanical and thermal characterisation of reinforced specimen. Constr. Build. Mater. 2022, 342, 127787. [Google Scholar] [CrossRef]
  29. Ajouguim, S.; Page, J.; Djelal, C.; Waqif, M.; Saâdi, L. Impact of Alfa fibers morphology on hydration and mechanical properties of cement mortars. Constr. Build. Mater. 2021, 293, 123514. [Google Scholar] [CrossRef]
  30. EN 13043; Aggregates for bituminous mixtures and surface treatments for roads, airfields and other trafficked areas. European Committee for Standardization: Brussels, Belgium, 2003.
  31. EN 1097-6; Tests for mechanical and physical properties of aggregates- Part 6: Determination of particle density and water absorption. European Committee for Standardization: Brussels, Belgium, 2022.
  32. EN 933-8; Tests for geometrical properties of aggregates- Part 8: Assessment of fines—Sand equivalent test. European Committee for Standardization: Brussels, Belgium, 2015.
  33. EN 1097-2; Tests for mechanical and physical properties of aggregates—Part 2: Methods for the determination of resistance to fragmentation. European Committee for Standardization: Brussels, Belgium, 2020.
  34. EN 1097-1; Tests for mechanical and physical properties of aggregates—Part 1: Determination of the resistance to wear (micro-Deval). European Committee for Standardization: Brussels, Belgium, 2023.
  35. Fatemi, S.; Imaninasab, R. Performance evaluation of recycled asphalt mixtures by construction and demolition waste materials. Constr. Build. Mater. 2016, 120, 450–456. [Google Scholar] [CrossRef]
  36. EN 12591; Bitumen and bituminous binders—Specifications for paving grade bitumens. European Committee for Standardization: Brussels, Belgium, 2009.
  37. Prosperi, E.; Bocci, E.; Bocci, M. Effect of Bitumen Production Process and Mix Heating Temperature on the Rheological Properties of Hot Recycled Mix Asphalt. Sustainability 2022, 14, 9677. [Google Scholar] [CrossRef]
  38. EN 1426; Bitumen and bituminous binders—Determination of needle penetration. European Committee for Standardization: Brussels, Belgium, 2024.
  39. EN 1427; Bitumen and bituminous binders—Determination of the softening point—Ring and Ball method. European Committee for Standardization: Brussels, Belgium, 2015.
  40. EN 12607-1; Bitumen and bituminous binders—Determination of the resistance to hardening under the influence of heat and air—Part 1: RTFOT method. European Committee for Standardization: Brussels, Belgium, 2024.
  41. EN ISO 2592; Determination of flash and fire points—Cleveland open cup method. European Committee for Standardization: Brussels, Belgium, 2017.
  42. EN 13108-1; Bituminous mixtures—Material specifications-part 1: Asphalt concrete. European Committee for Standardization: Brussels, Belgium, 2016.
  43. EN 13108-20; Bituminous mixtures—Material specifications—Part 20: Type Testing. European Committee for Standardization: Brussels, Belgium, 2016.
  44. XP P98-151; Bituminous mixtures—Specifications and test methods for manufacturing, laying and compacting of bituminous mixes for roads and airfields. French Standardization Association: Paris, France, 1996.
  45. EN 12504-4; Testing concrete in structures—Part 4: Determination of ultrasonic pulse velocity. European Committee for Standardization: Brussels, Belgium, 2004.
  46. EN 12697-22; Bituminous mixtures—Test methods for hot mix asphalt—Part 22: Wheel tracking. European Committee for Standardization: Brussels, Belgium, 2020.
  47. Mirzanamadi, R.; Johansson, P.; Grammatikos, S.A. Thermal properties of asphalt concrete: A numerical and experimental study. Constr. Build. Mater. 2018, 158, 774–785. [Google Scholar] [CrossRef]
  48. ISO 22007-2; Plastics—Determination of thermal conductivity and thermal diffusivity—Part 2: Transient plane heat source (hot disc) method. International Organization for Standardization: Geneva, Switzerland, 2015.
  49. Ajouguim, S.; Page, J.; Djelal, C.; Saâdi, L. Effect of treated Alfa fibers on hydration kinetics, mechanical, and adhesion properties of fiber cement composit. J. Build. Eng. 2023, 71, 106558. [Google Scholar] [CrossRef]
  50. Ahmed, K.U.; Geremew, A.; Jemal, A. The comparative study on the performance of bamboo fiber and sugarcane bagasse fiber as modifiers in asphalt concrete production. Heliyon 2022, 8, e09842. [Google Scholar] [CrossRef] [PubMed]
  51. Kareem, A.I.; Sahib Banyhussan, Q.; Al-Taweel, H.M. Measurement of aggregates breakage of asphalt mixtures with construction and demolition waste. Mater. Today Proc. 2022, 61, 420–427. [Google Scholar] [CrossRef]
  52. Al-Mufti, R.; Fried, A. Improving the strength properties of recycled asphalt aggregate concrete. Constr. Build. Mater. 2017, 149, 45–52. [Google Scholar] [CrossRef]
  53. Borinaga-Traviño, R.; Orbe, A.; Canales, J.; Norambuena-Contreras, J. Thermal and mechanical properties of mortars reinforced with recycled brass fibres. Constr. Build. Mater. 2021, 284, 122832. [Google Scholar] [CrossRef]
  54. Tang, N.; Guo, S.; Yang, Y.; Sun, W. Ultrasonic waves generated by smart aggregates for concealed crack detection in asphalt mixture. Constr. Build. Mater. 2024, 438, 137183. [Google Scholar] [CrossRef]
  55. Cui, S.; Sheng, Y.; Wang, Z.; Jia, H.; Qiu, W.; Temitope, A.A.; Xu, Z. Effect of the fiber surface treatment on the mechanical performance of bamboo fiber modified asphalt binder. Constr. Build. Mater. 2022, 347, 128453. [Google Scholar] [CrossRef]
  56. Jia, H.; Sheng, Y.; Lv, H.; Kim, Y.R.; Zhao, X.; Meng, J.; Xiong, R. Effects of bamboo fiber on the mechanical properties of asphalt mixtures. Constr. Build. Mater. 2021, 289, 123196. [Google Scholar] [CrossRef]
  57. Shamsaei, M.; Carter, A.; Vaillancourt, M. Using construction and demolition waste materials to alleviate the negative effect of pavements on the urban heat island: A laboratory, field, and numerical study. Case Stud. Constr. Mater. 2024, 20, e03346. [Google Scholar] [CrossRef]
  58. Charai, M.; Mezrhab, A.; Moga, L.; Karkri, M. Hygrothermal, mechanical and durability assessment of vegetable concrete mixes made with Alfa fibers for structural and thermal insulating. Constr. Build. Mater. 2022, 335, 127518. [Google Scholar] [CrossRef]
  59. Qiu, H.; Wu, Y.; Chen, H.; Wang, R.; Yu, J.; Lin, Y. Influence of SiC on the thermal energy transfer and storage characteristics of microwave-absorbing concrete containing magnetite and/or carbonyl iron powder. Constr. Build. Mater. 2023, 366, 130191. [Google Scholar] [CrossRef]
  60. Ajouguim, S.; Talibi, S.; Djelal-Dantec, C.; Hajjou, H.; Waqif, M.; Stefanidou, M.; Saadi, L. Effect of Alfa fibers on the mechanical and thermal properties of compacted earth bricks. Mater. Today Proc. 2021, 37, 4049–4057. [Google Scholar] [CrossRef]
  61. Mohajerani, A.; Bakaric, J.; Jeffrey-Bailey, T. The urban heat island effect, its causes, and mitigation, with reference to the thermal properties of asphalt concrete. J. Environ. Manag. 2017, 197, 522–538. [Google Scholar] [CrossRef] [PubMed]
  62. Sabri, K.F.; Wang, Y.D.; Liu, J. Improving rheological and thermal performance of Gilsonite-Modified binder with phase change materials. Constr. Build. Mater. 2023, 399, 132557. [Google Scholar] [CrossRef]
  63. Hassn, A.; Aboufoul, M.; Wu, Y.; Dawson, A.; Garcia, A. Effect of air voids content on thermal properties of asphalt mixtures. Constr. Build. Mater. 2016, 115, 327–335. [Google Scholar] [CrossRef]
  64. Elhamdouni, Y.; Khabbazi, A.; Benayad, C.; Dadi, A.; Ahmid, O.I. Effect of fiber on thermophysical characteristics of a material based on clay. Energy Procedia 2015, 74, 718–727. [Google Scholar] [CrossRef]
  65. Akçaözoğlu, S.; Akçaözoğlu, K.; Atis, C.D. Thermal conductivity, compressive strength and ultrasonic wave velocity of cementitious composite containing waste PET lightweight aggregate (WPLA). Compos. Part. B 2013, 45, 721–726. [Google Scholar] [CrossRef]
  66. Shanbara, H.K.; Ruddock, F.; Atherton, W. Predicting the rutting behaviour of natural fibre-reinforced cold mix asphalt using the finite element method. Constr. Build. Mater. 2018, 167, 907–917. [Google Scholar] [CrossRef]
  67. Zhang, X.; Li, H.; Jia, N.; Xie, N.; Kousis, I.; Santamouris, M. Laboratorial investigation on optical, thermal and pavement performance of biomimetic dark reflective coatings with composite structure for pavement cooling. Build. Environ. 2024, 266, 112057. [Google Scholar] [CrossRef]
  68. Chen, Z.; Zhang, H.; Yang, X.; Leng, Z.; Tang, Y. Cooling efficiency of thermochromic asphalt pavement material and its contribution to field performance enhancement of asphalt mixture. Constr. Build. Mater. 2024, 411, 134562. [Google Scholar] [CrossRef]
  69. Yang, L.; Luo, W.; Muhammad, Y.; Meng, F.; Li, J.; Zhao, Z.; Li, J. Surface modification of bagasse fibers based on polyphenol-induced self-supplied lignin for the creation of composite SBS-modified asphalt. Ind. Crops Prod. 2024, 208, 117835. [Google Scholar] [CrossRef]
Buildings 15 02845 g001
Figure 1. (a) Construction and demolition waste sample; (b) composition of CDW.
Figure 1. (a) Construction and demolition waste sample; (b) composition of CDW.
Buildings 15 02845 g001
Buildings 15 02845 g002
Figure 2. Alfa fibers: (a) Alfa fiber mats; (b) straightened Alfa fibers; (c) Alfa fibers cut into 30 mm lengths.
Figure 2. Alfa fibers: (a) Alfa fiber mats; (b) straightened Alfa fibers; (c) Alfa fibers cut into 30 mm lengths.
Buildings 15 02845 g002
Buildings 15 02845 g003
Figure 3. Aggregate gradation curve used for asphalt mixtures.
Figure 3. Aggregate gradation curve used for asphalt mixtures.
Buildings 15 02845 g003
Buildings 15 02845 g004
Figure 4. Manufacturing procedure of asphalt mixture test specimens with and without construction waste and Alfa fibers.
Figure 4. Manufacturing procedure of asphalt mixture test specimens with and without construction waste and Alfa fibers.
Buildings 15 02845 g004
Buildings 15 02845 g005
Figure 5. Samples for experimental testing: (a) samples for thermophysical measurements; (b) single sample for thermophysical tests; (c) sample for rutting measurements.
Figure 5. Samples for experimental testing: (a) samples for thermophysical measurements; (b) single sample for thermophysical tests; (c) sample for rutting measurements.
Buildings 15 02845 g005
Buildings 15 02845 g006
Figure 6. Digital optical microscopy device.
Figure 6. Digital optical microscopy device.
Buildings 15 02845 g006
Buildings 15 02845 g007
Figure 7. Rutting test equipment.
Figure 7. Rutting test equipment.
Buildings 15 02845 g007
Buildings 15 02845 g008
Figure 8. Thermophysical testing equipment.
Figure 8. Thermophysical testing equipment.
Buildings 15 02845 g008
Buildings 15 02845 g009
Figure 9. High-performance Lambda spectrometer.
Figure 9. High-performance Lambda spectrometer.
Buildings 15 02845 g009
Buildings 15 02845 g010
Figure 10. The density of all samples.
Figure 10. The density of all samples.
Buildings 15 02845 g010
Buildings 15 02845 g011
Figure 11. Ultrasonic pulse velocity test of all formulations.
Figure 11. Ultrasonic pulse velocity test of all formulations.
Buildings 15 02845 g011
Buildings 15 02845 g012
Figure 12. Correlation between ultrasonic pulse velocity and density.
Figure 12. Correlation between ultrasonic pulse velocity and density.
Buildings 15 02845 g012
Buildings 15 02845 g013
Figure 13. Optical microscopy images of Alfa fiber. (a) Alfa fiber (100×); (b) Alfa fiber (500×).
Figure 13. Optical microscopy images of Alfa fiber. (a) Alfa fiber (100×); (b) Alfa fiber (500×).
Buildings 15 02845 g013
Buildings 15 02845 g014
Figure 14. Optical microscopy images of asphalt: (a) A1-150 (100×); (b) A1-150 (200×).
Figure 14. Optical microscopy images of asphalt: (a) A1-150 (100×); (b) A1-150 (200×).
Buildings 15 02845 g014
Buildings 15 02845 g015
Figure 15. Rutting depth of asphalt mixtures.
Figure 15. Rutting depth of asphalt mixtures.
Buildings 15 02845 g015
Buildings 15 02845 g016
Figure 16. Rutting depth for 30,000 passes as a function of Alfa fiber content.
Figure 16. Rutting depth for 30,000 passes as a function of Alfa fiber content.
Buildings 15 02845 g016
Buildings 15 02845 g017
Figure 17. Thermophysical properties of all compositions: (a) thermal conductivity, (b) thermal diffusivity, and (c) volumetric heat capacity.
Figure 17. Thermophysical properties of all compositions: (a) thermal conductivity, (b) thermal diffusivity, and (c) volumetric heat capacity.
Buildings 15 02845 g017
Buildings 15 02845 g018
Figure 18. The relationship between thermal conductivity and density.
Figure 18. The relationship between thermal conductivity and density.
Buildings 15 02845 g018
Buildings 15 02845 g019
Figure 19. Ultrasonic pulse velocity correlates with thermal conductivity.
Figure 19. Ultrasonic pulse velocity correlates with thermal conductivity.
Buildings 15 02845 g019
Buildings 15 02845 g020
Figure 20. Relation between rut depth for 30,000 passes and thermal conductivity.
Figure 20. Relation between rut depth for 30,000 passes and thermal conductivity.
Buildings 15 02845 g020
Buildings 15 02845 g021
Figure 21. Spectrum reflectance of asphalt specimens in the UV-VIS-NIR band.
Figure 21. Spectrum reflectance of asphalt specimens in the UV-VIS-NIR band.
Buildings 15 02845 g021
Table 1. Summary of key studies from the literature.
Table 1. Summary of key studies from the literature.
StudyMaterial UsedKey Findings
Zhu et al. [14]CDWImproved permanent deformation resistance
Pesandín et al. [15]CDW (5-30%)Up to 20% of CDW yielded fatigue life similar to conventional mix
Radević et al. [16]RCA (30%)Enhanced rutting resistance
El-Tahan et al. [18]Treated CDWEnhanced resistance to water damage and improved fatigue durability
Xie et al. [21]Bamboo + Basalt FibersEnhanced rutting resistance
Hussein et al. [22]RCA + Rock Wool fibersImproved cracking resistance and mixture stability
Jia et al. [23]Bamboo FiberIncreased cracking resistance and mixture stiffness
Liu et al. [24]Bamboo FiberImproved the overall performance of the asphalt, in terms of thermal stability and resistance to cracking
Table 2. Physical properties of the aggregates.
Table 2. Physical properties of the aggregates.
CompositionPropertyUnitValueSpecificationsTest Method
Fine aggregate 0–4 mmDensityg/cm32.69-EN 1097-6 [31]
Sand equivalent test%68≥50EN 933-8 [32]
Coarse aggregate 4–8 mmDensityg/cm32.6-EN 1097-6 [31]
Water absorption%0.66≤2EN 1097-6 [31]
Coarse aggregate 8–14 mmDensityg/cm32.58-EN 1097-6 [31]
Los Angelos Abrasion test%21≤25EN 1097-2 [33]
Micro-Deval wearing test%18≤25EN 1097-1 [34]
Water absorption%0.58≤2EN 1097-6 [31]
Table 3. Physical properties of construction and demolition waste aggregates.
Table 3. Physical properties of construction and demolition waste aggregates.
PropertyUnitValueTest Method
Densityg/cm32.1EN 1097-6 [31]
Water absorption%5.8EN 1097-6 [31]
Los Angeles Abrasion test%33EN 1097-2 [33]
Micro-Deval wearing test %31EN 1097-1 [34]
Table 4. Conventional properties of bitumen.
Table 4. Conventional properties of bitumen.
PropertyUnitValueSpecificationsTest Method
Penetration (25 °C)0.1 mm3835 to 50EN 1426 [38]
Softening point°C5250 to 58EN 1427 [39]
Retained penetration%67.31≥53EN 12607-1 [40]
Softening point variation°C2≤11EN 12607-1 [40]
Flash point °C240≥240 °CEN ISO 2592 [41]
Table 5. Nomenclature and description of mixtures.
Table 5. Nomenclature and description of mixtures.
Mixture
Nomenclature		NA Content
(%)		CDW
(%)		Alfa Fibers
Content (%)		Asphalt Binder (%)Mixing T
(°C)
BB0/14100005.2160
A0-160802005.2160
A0-150802005.2150
A0.5-15080200.55.2150
A1-160802015.2160
A1-150802015.2150
A1-140802015.2140
A2-150802025.2150
B1-150752515.2150
C1-150851515.2150
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Chehata, H.; Jendoubi, A.; Boudenne, A.; Neji, J. Effect of the Integration of Alfa Natural Fibers and Demolition Waste on the Mechanical and Thermal Properties of Warm Mix Asphalt. Buildings 2025, 15, 2845. https://doi.org/10.3390/buildings15162845

AMA Style

Chehata H, Jendoubi A, Boudenne A, Neji J. Effect of the Integration of Alfa Natural Fibers and Demolition Waste on the Mechanical and Thermal Properties of Warm Mix Asphalt. Buildings. 2025; 15(16):2845. https://doi.org/10.3390/buildings15162845

Chicago/Turabian Style

Chehata, Haifa, Abir Jendoubi, Abderrahim Boudenne, and Jamel Neji. 2025. "Effect of the Integration of Alfa Natural Fibers and Demolition Waste on the Mechanical and Thermal Properties of Warm Mix Asphalt" Buildings 15, no. 16: 2845. https://doi.org/10.3390/buildings15162845

APA Style

Chehata, H., Jendoubi, A., Boudenne, A., & Neji, J. (2025). Effect of the Integration of Alfa Natural Fibers and Demolition Waste on the Mechanical and Thermal Properties of Warm Mix Asphalt. Buildings, 15(16), 2845. https://doi.org/10.3390/buildings15162845

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Article metric data becomes available approximately 24 hours after publication online.
Back to TopTop