Advanced Recycling of Modified EDPM Rubber in Bituminous Asphalt Paving

Abstract

One of the environmental problems worldwide is the enormous number of surgical masks used during the COVID-19 pandemic due to the measures imposed by the World Health Organization on the mandatory use of masks in public spaces. The current study is a potential circular economy approach to recycling the surgical masks discarded into the environment during the COVID-19 pandemic for use in bituminous asphalt pavement. FTIR analysis showed that the surgical masks used were made from ethylene propylene diene monomer (EPDM) rubber modified with polypropylene. The effects of the addition of surgical masks in bituminous asphalt on the performance of the base course were demonstrated in this study. The morphology and elemental composition of the bituminous asphalt pavement samples with two ratios of surgical mask composition were investigated by SEM-EDX and the performance of the modified bituminous asphalt pavement was determined by Marshall stability, flow rate, solid–liquid ratio, apparent density, and water absorption. The study refers to the technological innovation of using surgical masks in the formulation of AB 31.5 bituminous asphalt base course, which brings tremendous benefits to the environment by reducing the damage caused by the COVID-19 pandemic.

1. Introduction

The COVID-19 pandemic has resulted in significant health, financial, and environmental challenges worldwide [1]. The global public health initiative necessitated the use of surgical face masks as a crucial measure in combatting the spread of the coronavirus, leading to an increased demand for facemasks worldwide [2]. An estimated compound annual growth rate of 20% is projected for the supply of surgical and facial masks from 2020 to 2025, with this upward trend expected to persist [3]. The World Health Organization estimated at the beginning of the COVID-19-pandemic that approximately 89 million masks would be required each month to stem the spread of the pandemic [4]. Global production capacity of surgical masks is anticipated to rise alongside the surge in COVID-19 infection cases [5]. The effects of wearing facemasks on the cardiopulmonary system have been shown by several authors [6,7,8,9,10]. Disposable face masks, composed of polymeric materials, are entering the environment primarily through disposal in landfills, dumpsites, and littering in public spaces, subsequently finding their way into freshwater sources and oceans as a new source of microplastic fibers [11]. Currently, the primary recycling methods for disposable medical mask waste encompass high-temperature incineration, landfill decomposition, and chemical and mechanical recycling [12,13]. Surgical masks are obtained using different polymers and inorganic additives, and usually, there is no available detailed information on their composition [14], but the chemical composition of most disposable face masks is polypropylene, polyethylene, and polyurethane [15]. The high-temperature incineration method causes a variety of toxic byproducts that cause serious environmental pollution. The landfill degradation process involves breaking down polymers using soil microorganisms, but it is slow and can lead to secondary soil pollution. Mechanical recycling involves melting and combining pulverized disposable surgical masks with other materials to create lower-grade products. Chemical recycling converts high molecular weight polymers into smaller compounds through processes like pyrolysis or gasification, allowing them to be reformed into new materials. However, the current methods of recycling and treating waste surgical masks do not fully maximize waste utilization or generate significant energy and economic benefits for value-added utilization [12,13]. In order to efficiently minimize the impact of medical waste on humans and the environment, implementing a circular economy approach is crucial for success. Certain solid waste materials that have shown positive modification effects are being extensively utilized as modifiers in asphalt production [16]. To sustain the circular economy, we proposed in a previous study the use of recycled polypropylene and waste grit in a hot asphalt mixture used as the wear layer in road construction [17,18,19]. The authors of [20] conducted exploratory research on concrete incorporating face masks, demonstrating that the mechanical properties of concrete can be enhanced by integrating fibers made from surgical masks into the concrete mixture. Other researchers investigated the viability of incorporating disposable medical masks in asphalt binder, assessing its impact on the overall performance of asphalt. They observed positive effects on the high-temperature anti-rutting and low-temperature anti-cracking performance of both the asphalt binder and asphalt mixtures [21]. Researchers investigated the potential of repurposing face masks as an additive for hot mix asphalt to enhance the mechanical properties of asphalt pavement, creating a pathway to mitigate the rising pollution from personal protective equipment [22]. Other researchers stated that waste polypropylene fiber can significantly enhance the impact resistance and ductility of concrete, attributing this to its crack-bridging and reinforcing properties [23]. Several research studies in the literature have examined the fundamental mechanical properties of conventional aggregate concrete containing only face mask fibers [24]. The authors of one study devised a novel fiber-hybridization method to repurpose disposable medical face masks as fiber materials for creating environmentally friendly recycled concrete [25]. The used medical masks were repurposed as an agent to reduce viscosity and depress pour point in order to analyze its effectiveness in improving the flow characteristics of crude oil samples by authors [25]. The authors of further research presented a solution to use waste masks in fibered or crushed form in concrete. The results showed that both forms of mask waste can be used in concrete and the optimum value that increased the mechanical and durability properties was 0.5% crushed mask fiber [26]. Other researchers developed an expansion joint using styrene–butadiene–styrene as the filling material for rubber-modified asphalt which significantly improved the elasticity and adhesion of the asphalt mixture [27]. The authors of a later study designed a novel mask by modifying a surgical face mask with the adoption of a sealing frame and support and enhanced the filtration efficiency, concentration of CO₂, O₂, and N₂, dead space, and water vapor compared with the face masks from the market [28].

In order to overcome the issue of environmental pollution, this study proposed the use of surgical masks in bituminous asphalt pavement type AB 31.5. The investigation of bituminous asphalt pavement samples with two weight ratios of surgical masks examines the morphological characterization and the Marshall characteristics. The novelty of incorporating surgical masks into bituminous asphalt paving, particularly as a base layer in road construction, lies in the potential to address environmental concerns effectively. Despite existing studies on this topic, the focus on minimizing environmental impact by repurposing surgical masks in road construction can lead to significant sustainability benefits. This innovative approach aims to offer a practical solution for reusing medical waste while also enhancing the performance and durability of road infrastructure.

2. Materials and Methods

2.1. Life Cycle Assessment

The goal of this study is to recycle surgical masks in bituminous asphalt pavement with the aim of extending their life cycle and implementing circular economy principles for responsible waste management. In Figure 1, the life cycle assessment of surgical masks with a sustainable approach to extending their life cycle is presented.

Implementing the circular economy by extending the life cycle of protective equipment such as surgical masks for use in technical-grade road construction is an innovative and sustainable approach. Extending the life cycle of surgical masks by recycling and using them in the construction of road base layers can bring several benefits.

The use of recycled materials contributes to reducing the consumption of natural resources and minimizing the waste generated, thereby having a positive impact on the environment. Surgical masks can find a new useful life without being thrown into the environment and polluting the soil or water. Such practices support the circular economy, promoting the reuse and recycling of materials, reducing carbon emissions, and contributing to efficient resource management. The use of surgical masks in road construction can bring practical benefits, such as improving insulation properties, water resistance, and the ability to stabilize the soil in the road base layer. This practice can lead to reduced construction and maintenance costs of road infrastructure by using more durable and sustainable materials. Thus, the implementation of the circular economy in extending the life cycle of surgical masks for their use in road infrastructure can bring advantages both from an environmental and economic point of view, contributing to more efficient management of resources and protecting the environment for future generations.

2.2. Bituminous Asphalt Paving Sample Preparation

The hot asphalt mix used in this study consisted of base courses with the designation bituminous asphalt pavement AB 31.5, whereby the value 31.5 indicates the maximum grain size of the granulate [29]. The samples of bituminous asphalt pavement type AB 31.5 were prepared in accordance with the indicative normative AND 546-2013, Norm on the hot execution of bituminous coatings for the bridge path, (2013) and AND 605-2016: Normative regarding hot asphalt mixes [29,30], tested in the Laboratory for Analysis and Testing in Construction—Class II of SC. Antrepriza de Constructii Drumuri si Autostrazi SRL Road Company. The weight percentages of the components of the standard base course of bituminous asphalt type AB 31.5 consist of 40.8% natural screened aggregate with a size greater than 4.0 mm, 50% crushed sand with a grain size between 0.1 and 4.0 mm, 5% limestone filler, and 4.2% road bitumen type 50/70 [29,31]. The bitumen properties of penetration at 25 °C type 50/70 are as follows: softening point 46/54 °C; resistance to hardening at 163 °C: change in mass 0.5%, retained penetration 50 min, softening point after hardening 58 °C, flashpoint 230 min; solubility at specification 99 min; kinematic Viscosity 135 °C specification 295 min [32]. Two formulations were prepared for the Marshall test with the addition of a percent by weight of surgical masks. Surgical masks used (worn surgical masks cannot be used in the laboratory due to public safety measures for the prevention of SARS-CoV-2 contamination). When placed in the casting mixture (160 °C), there is no risk of soil contamination/population and, due to the fact that the sterilization process takes place at a temperature of 130 °C, the masks become inert. Thus, the weight proportions of the asphalt mix sample constituents consist of 40.8% natural screened aggregate with a size above 4.0 mm, 50% crushed sand with a particle size between 0.0 and 4.0 mm, 5% graded limestone filler with a particle size of 0.063 and 0.100 mm, 4.1% paving bitumen type 50/70 with 0.1% surgical masks for sample 1, and 3.9% paving bitumen type 50/70 with 0.3% surgical masks for sample 2, as shown in

Table 1. Recipes for bituminous asphalt pavement samples type AB 31.5.

Component	Standard	Sample 1	Sample 2
Crushed siliceous stone [%]	40.8	40.8	40.8
Crushed sand [%]	50	50	50
Sort limestone filler [%]	5	5	5
Road bitumen 50/70 [%]	4.2	4.1	3.9
Surgical masks [%]	-	0.1	0.3

. The bituminous asphalt paving samples were modified with the masks by bitumen replacement, i.e., a percent of 0.1% surgical masks added for Sample 1 and a percent of 0.3% surgical masks added for Sample 2, with a bitumen percent of 4.1% for Sample 1 and 3.9% for Sample 2.

The formulation of hot bituminous asphalt type AB 31.5 containing 0.3% surgical masks as used in Sample 2 was the subject of the patent filed in 2021 [33]. The samples used for Marshall tests have a cylindrical shape with a diameter of 10 cm and a height of 6.3 cm.

Figure 2 shows the gradation determined for the bituminous asphalt paving, and the size distribution of the aggregate particles used in the asphalt composition for the standard sample and for the sample with a surgical mask content of 0.3% can be seen. The grading results show a well-balanced granulometry that ensures a homogeneous mixture, offering resistance and long-term durability.

2.3. Characterization Methods

The quantitative determination was conducted using the FTIR-attenuated total reflection (FTIR-ATR) method, which records spectra through attenuated total reflection. The Fourier transform infrared (FTIR) spectra of the surgical mask were captured using an IR-Spirit-T FTIR Spectrometer from Shimadzu, equipped with a built-in ATR accessory type QATR-S, DLATGS detector, and KBr beam splitter. The scan range was set between 400–4600 cm⁻¹ with a resolution of 2 cm⁻¹, and each scan was repeated 45 times. The FTIR spectrometer was operated within a temperature-controlled (20 °C) air-conditioned chamber.

The morphology and elemental composition of the bituminous asphalt paving samples were examined by scanning electron microscopy (SEM) in high vacuum conditions with a 4th generation TESCAN VEGA electron source and tungsten filament which combines SEM imaging and elemental composition analysis directly in a single Essence™ from TESCAN software (1.2.1.0 build 5762, March 2023) window. This integration greatly streamlines the collection of morphological and elemental information from the sample, positioning VEGA SEM as a highly effective analytical tool for routine material evaluation in quality control, failure analysis, and research settings. Prior to analysis, the samples underwent a coating process with a 6 nm thick conductive layer of Au utilizing the SPI-Module™ sputter coater system.

The physical and mechanical properties were determined through tests conducted on Marshall cylinders. The test principle involves identifying the compressive strength of a cylindrical sample when subjected to a force applied by a generator. This test is performed on a sample contained within the mold at a temperature of 60 °C. The Marshall method is a common approach used to determine the optimal mix design for asphalt paving. The Marshall method provides a systematic approach to designing high-quality asphalt mixes that meet the specific requirements of a paving standard. The general steps involved for the Marshall method are as follows: selection of aggregate based on factors such as size, shape, and gradation to ensure good compaction and durability of the asphalt mix; selection of asphalt binder; mixing of design through blending of components in the right proportions; compaction testing of the bituminous asphalt paving in a mold to a specific density using a hammer; and density and stability testing. The compacted samples are then subjected to testing to determine parameters such as density, stability, flow, and solid–liquid ratio.

The physical–mechanical characterizations were performed according to Romanian Standard SR EN 12697-6 [34] and SR EN 12697-34 [35] as follows:

Stability (S) represents the load at which the cylindrical specimen fractures at 60 °C, measured in kN.

The flow index (I), measured in mm, indicates the deformation of the vertical diameter of the specimen at the point of fracture.

The apparent density (g/cm³) is the mass of a unit volume of compacted bituminous asphalt pavement, accounting for the air-filled voids. It is calculated using the formula that relates sample mass to volume (1):

$${\rho }_a=\frac{m_u}{V} \left(\frac{\mathrm{g}}{{\mathrm{c}\mathrm{m}}^3}\right)$$

(1)

For the standard sample, the following holds:

-

${\rho }_a$ represents the apparent density of the bituminous asphalt pavement (g/cm³);

-

m_u is the mass of the sample measured on the analytical balance in a dry state;

-

V denotes the volume of the cylindrical sample with a diameter of 10 cm and a height of 6.3 cm.

Water absorption [%] refers to the amount of water absorbed by the externally accessible voids in a bituminous asphalt paving sample. This was determined through evaporation after immersing the sample in water using the static thermal method. Following removal from the water, the sample was wiped with a damp cloth to eliminate excess surface and gravity water. Subsequently, the wet sample underwent drying in an oven at 60 °C and relative humidity below 2.5%. The water absorption or wetting capacity is expressed as a percentage of the initial sample mass and the mass after wetting. The volume percentage of water absorption is calculated using the following relationship:

$$A=100\frac{m_i}{m_f}$$

(2)

where the following holds:

-

m_i represents the initial mass of the sample.

-

m_f is the final mass of the sample after wetting.

Each test result in this research study is the average of three replicate tests.

3. Results and Discussion

3.1. Structural Characterization of Bituminous Asphalt Paving Samples

The resulting FTIR spectra of components of the surgical mask used in this study are shown in Figure 3. The surgical mask is made of an elastic ear loop (blue color), heat-welded seam (brown color), and non-woven fabric (red color). Analyzing the FTIR database revealed that the tested surgical mask exhibited similarities with the spectrum of ethylene propylene diene (EPDM) rubber modified with polypropylene (PP). The FTIR spectrum showed intense bands in the wavenumber 2914, 2354, 1643, 1454, 1372, 1161, 827, 670 and 448 cm⁻¹.

The transmittance band distribution on the FTIR spectra of the surgical mask sample showed broad ranges from 1161 to 1454 cm⁻¹ and 2914 cm⁻¹ attributed to CH₂ asymmetric stretching, which are characteristic for the FTIR spectrum of polypropylene (PP) [36]. The FTIR spectrum also showed bands at 1643, 827, 670, and 448 cm⁻¹; the band at 1643 cm⁻¹ was attributed to C=C stretching, which is characteristic for EPDM, the weak transmittance band at 827 cm⁻¹ could be attributed to the possible degradation (cross-linking) processes between EPDM rubber and PP, and the band at 670 cm⁻¹ corresponds to the Si-O-Mg bond in talc filler [37], while the band from 448 cm⁻¹ is associated with the S-S of cross-linked EPDM-PP [38]. The FTIR spectra of the surgical masks used in this study showed that the chemical composition is mainly ethylene propylene diene (EPDM) rubber modified with polypropylene (PP). In Figure 4 are presented the FTIR spectrum of spectra of standard bituminous asphalt pavement (black), Sample 1 (0.1% EDPM-PP) (green), and Sample 2 (0.3% EDPM-PP) (orange). The FTIR spectra of all three components of the surgical mask display almost identical peaks, albeit with varying intensities, distinctly indicating the presence of EPDM-PP.

Figure 5 depicts SEM images of the standard bituminous asphalt pavement type AB 31.5, Sample 1, and Sample 2. The standard sample appears smooth and uniform. Observably, a compact arrangement between the components is evident with the addition of EPDM-PP in Sample 1 and Sample 2. Due to the different surface microstructures of the bituminous asphalt pavement, the structure of the interface of the standard sample was different from that of the samples with EPDM-PP (Sample 1 and Sample 2). The morphology of Sample 1 shows a higher porosity than the sample with higher EPDM-PP content.

In the SEM image of Sample 2 (containing 0.3% EPDM-PP), it is evident that the crushed silica crisps, crushed sand, and limestone filler are effectively embedded in a polymer matrix. This embedding matrix and the interconnections between the components exhibit minimal pores and reduced roughness.

After the asphalt was embedded in the polymer matrix, its loading area increased due to the content of surgical masks, which significantly improved its resistance to external forces. In Sample 2, the fibers originating from the surgical masks that connect the components of the asphalt mix can be seen at higher magnification.

The elemental composition of Sample 2 (with 0.3% surgical masks), consisting of the most important chemical elements C, O, Ca, and Si, is shown in Figure 6. The high concentration of carbon, oxygen, and silicon indicates the presence of surgical masks. It can be noted that the fibrous structures have a high percentage of carbon, most likely originating from polypropylene staple fibers. The presence of calcium (Ca) is also favorable due to its good interaction with bitumen.

3.2. Physical–Mechanical Properties of Bituminous Asphalt Paving Samples

The Marshall test is a crucial laboratory procedure used to evaluate the properties of bituminous asphalt pavement, including those improved with EDPM-PP (ethylene propylene diene monomer–polypropylene) additives. This test provides valuable insights into the performance characteristics of asphalt mixes, helping to ensure that they meet specified requirements for use in road construction and paving projects. Here are some key aspects of the Marshall test as it pertains to bituminous asphalt pavement improved with EDPM-PP:

The primary objective of the Marshall test for bituminous asphalt pavement improved with EDPM-PP is to assess its mechanical properties, durability, and resistance to deformation under simulated traffic and environmental conditions. By subjecting the asphalt specimens to controlled loading and temperature conditions, the test aims to determine their stability, flow, density, and other key performance indicators.

During the sample preparation phase, the bituminous asphalt pavement improved with EDPM-PP is compacted in the Marshall molds to achieve the desired density and air void content. The compaction process involves applying a specific number of blows with a compaction hammer to ensure proper aggregate particle orientation and interlocking, as well as consistent distribution of the bitumen and EDPM-PP additives within the mixture. Once the specimens are prepared and conditioned, they are subjected to stability and flow tests under controlled loading and temperature conditions. The stability test measures the resistance of the bituminous asphalt pavement to deformation and rutting, providing insights into its ability to withstand traffic-related stresses. The flow test, on the other hand, assesses the deformation or consolidation of the specimen under compressive loading, indicating its flow characteristics under applied pressure.

In addition to stability and flow testing, the Marshall test involves evaluating the compacted density and air void content of the asphalt specimens improved with EDPM-PP. These analyses provide critical information about the degree of compaction achieved during specimen molding, as well as the amount of air voids present in the bituminous asphalt pavement, which can impact its long-term performance, permeability, and resistance to moisture damage.

The results of the Marshall test for bituminous asphalt paving improved with EDPM-PP play a critical role in predicting the performance of the bituminous asphalt pavement under actual field conditions. Additionally, the test data can be used to optimize the mix design by adjusting the composition, proportion of additives, and binder content to achieve the desired performance targets, such as enhanced resistance to cracking, fatigue, and deformation.

In the context of regulatory compliance and quality assurance, the Marshall test serves as a tool for verifying that the EDPM-PP-modified bituminous asphalt pavement meets the specified performance requirements and industry standards. Compliance with test-based performance criteria is essential for ensuring the durability, safety, and longevity of asphalt pavements, particularly when enhanced with additives such as EDPM-PP.

Marshall stability measures the maximum load that bituminous asphalt can withstand at a temperature of 60 °C and correlates well with measurements of rutting in bituminous asphalt pavement during operation.

In line with STAS recommendations [34,35], AB 31.5 bituminous asphalt pavement should ideally exhibit a Marshall stability of at least 6.3 kN. All test results of the bituminous asphalt samples meet the performance standards in Romania, as depicted in Figure 4. Notably, the rut resistance improves with the rising EDPM-PP content. With an increase in EDPM-PP content to 0.3% (as seen in Sample 2), the mixture’s strength enhances due to the presence of polymer matrix fibers, impacting gradation and mechanical properties. Figure 4 illustrates that stability increases with higher surgical mask content, attributed to its lower specific gravity compared to standard asphalt. This allows it to penetrate between particles, enhancing aggregate interlocking and overall stability. Consequently, the bituminous asphalt featuring 0.3% EDPM-PP (Sample 2) exhibits optimal stability, leading to improved deformation resistance in the mixture. The flow rate, as per STAS 12697-34 [35], can range between 1.5 to 4.5 mm. In Figure 7, the flow rates of both standard and modified hot asphalt mix samples are illustrated. It is evident from the figure that the flow rate rises with the inclusion of EDPM-PP but decreases notably at a higher content of 0.3% EDPM-PP. This shift can be correlated with the enhanced interlocking of fibers from the surgical masks with the asphalt binder and aggregates. The flow values escalate with the surgical mask content, suggesting increased deformations under the same pressure. This observation underscores that as the EDPM-PP content elevates, the resistance to deformation improves, particularly when the surgical mask content reaches 0.3%. Also, the flow rate values of bituminous asphalt pavement samples meet the performance standards needed in Romania for this type of bituminous asphalt pavement.

The solid–liquid ratio must meet a minimum threshold of 1.6 kN/mm. As illustrated in Figure 8, both standard and bituminous asphalt pavement samples containing EDPM-PP adhere to Romania’s performance standards. Notably, the solid–liquid ratio sees an increase with a higher EDPM-PP content, indicative of the strengthening effect as the surgical masks interacts with bitumen. Additionally, Figure 8 displays the water absorption levels for both the standard and modified bituminous asphalt pavement samples featuring EDPM-PP. Per Romanian Standard STAS 12697-34/2020, water absorption values should fall within the range of 1.5–6.0%. In samples with a minimal percentage of surgical masks, water absorption aligns with the standard sample, decreasing as the EDPM-PP content rises.

Furthermore, Figure 9 depicts the apparent density of bituminous asphalt pavement samples. For AB 31.5 bituminous asphalt pavement, the apparent density should not be less than 2.330 g/cm³ in accordance with SR 12697-6/2020.

All bituminous asphalt pavement samples comply with Romania’s performance standards. The solid–liquid ratio values decline with higher EDPM-PP content. The base layer’s performance is closely linked to the density of the bituminous asphalt pavement. It is evident that the apparent density increases with the addition of surgical masks. Achieving a higher apparent density is crucial to prevent potential rutting issues caused by insufficient air voids due to base layer densification from traffic loads. In summary, the sample containing 0.3% surgical masks recorded the highest apparent density among the samples tested.

Incorporating EDPM-PP derived from surgical masks into bituminous asphalt pavement used as a base layer in road construction can have significant environmental benefits. Despite the existing research findings, there are several reasons to consider this approach from an environmental standpoint: utilizing EDPM-PP from surgical masks in asphalt pavement provides a sustainable solution for recycling these materials, reducing waste in landfills, and promoting a circular economy approach; by repurposing EDPM-PP in road construction, we reduce the dependency on virgin materials, conserving natural resources and lowering the environmental impact associated with traditional construction materials; incorporating recycled materials like EDPM-PP can lead to energy savings during production processes, as recycling typically requires less energy compared to manufacturing new materials from raw sources; recycling EDPM-PP from surgical masks in asphalt pavement helps mitigate greenhouse gas emissions associated with conventional production methods, contributing to overall carbon footprint reduction; reusing EDPM-PP in road construction helps alleviate environmental pollution by preventing these materials from ending up in landfills or being improperly disposed of, thus reducing the burden on ecosystems and waste management systems; and embracing the use of recycled materials like EDPM-PP demonstrates a commitment to sustainable practices in construction, aligning with broader environmental objectives and fostering a culture of responsible resource management.

Incorporating EDPM-PP from surgical masks in bituminous asphalt pavement not only offers environmental benefits but also supports the transition towards more eco-friendly infrastructure development, contributing to a greener and more sustainable future.

4. Conclusions

One solution to address pressing environmental concerns stemming from the increased use of surgical masks during the COVID-19 pandemic, in line with World Health Organization directives mandating their use in public spaces, is recycling to mitigate environmental impact. This study presents an innovative approach to combat pandemic-generated waste by repurposing used face masks in bituminous asphalt pavement. Analyses utilizing FTIR spectroscopy revealed that the composition of the surgical masks studied closely resembles ethylene propylene diene (EPDM) rubber modified with polypropylene (PP). Incorporating EDPM-PP into the base layer mix of bituminous asphalt pavement type AB 31.5 resulted in enhanced performance of the mixture, as confirmed by test results.

SEM analysis indicated that when 0.3% EDPM-PP was added to the bituminous asphalt pavement, the crushed siliceous stone chipping, crushed sand, and limestone filler were effectively integrated into a polymer-matrix-like structure, exhibiting increased resistance to external forces. The study observed improvements in the Marshall properties of the bituminous asphalt pavement with the inclusion of ethylene propylene diene rubber modified with polypropylene, wherein higher stability, solid–liquid ratio, and apparent density were noted, attributed to the fibrous reinforcement from the surgical masks enhancing aggregate interlock. Following analysis of Marshall results, 0.3 percent EDPM-PP was identified as the optimal content for the mixture.

In summary, the utilization of surgical masks as a cohesive material proved effective in stabilizing bituminous asphalt pavement components, thereby mitigating the significant environmental impacts resulting from the COVID-19 pandemic on a global scale. The findings of this research present valuable insights for industry stakeholders and government bodies seeking to explore sustainable practices within the pavement sector. Overall, the implementation of circular economy strategies in extending the lifespan of surgical masks through their incorporation into road infrastructure showcases a win-win scenario. It not only contributes to a more sustainable and environmentally friendly approach, but also reaps economic benefits by optimizing resource utilization and paving the way for a greener future for generations to come. Future studies aim to further experiment with innovative approaches to advance sustainable solutions in road construction.

5. Patents

The recipe of Sample 2 of bituminous asphalt pavement type AB 31.5 with a content of 0.3% of surgical masks was the subject of the patent entitled RECYCLING OF SURGICAL MASKS IN HOT ASPHALT MIXTURES, RO135384A0, 2021.