A Review of Sustainable Pavement Aggregates

Abstract

Prior research has demonstrated that incorporating solid waste from various sources, such as plastics, civil engineering waste, and industrial and mining waste, into pavement and civil works mixes has notable environmental benefits. This includes reducing the over-exploitation of aggregate banks and preventing waste materials from being deposited in open-pit landfills for extended periods. This review focuses on sustainable aggregates produced from solid waste with rheological or mechanical properties suitable for replacing conventional aggregates in asphalt or hydraulic concrete mixtures. The aim is to determine the optimal replacement percentage in the mixture to directly impact pavement performance. This review also delves into the impact on fatigue resistance and permanent deformation based on the type of waste material used in construction. Additionally, using sustainable aggregates presents added benefits for pavement binders, such as inhibiting reflection cracks, reducing traffic noise, and prolonging the service life of the pavement. However, it is crucial to study the percentage of replacement of sustainable aggregates in conjunction with other materials using mathematical models and simulations to ensure a substantial contribution to the sustainability of the construction industry.

1. Introduction

The construction of flexible pavements consumes large amounts of asphalt, water, and stone aggregate. Consequently, their design establishes an interaction between the economic, environmental, and social aspects. This interaction is inherent in pavement materials and requires the search for sustainable alternatives [1]. Pavements cover 16.3 million kilometers of the planet, which represents increasing challenges in terms of the availability of construction materials. Thus, the expectation for 2050 is to reach the figure of 25 million kilometers in the construction of new roads [2]. In this respect, the sustainability of pavement performance improves with the reasonable allocation of traffic flow on a road network [3]. Road engineering tends to use recycled materials as a way to address environmental issues around the world [4]. However, waste must be reduced from the design phase of civil works [5]. A sustainable pavement meets human needs, conserving natural resources, as well as the planet’s ecosystems through alternative inputs, obtained from reclaimed asphalt pavement (RAP), recycled concrete (RCA), waste foundry sand (WFS), rubber, polymers, and waste glass (WG) [6]. These solid residues are incorporated as aggregates, coarse and fine, as they occupy approximately 90% of the weight of the asphalt mixtures [7]. RAP is the most commonly used recycled material as an aggregate in pavement layers with or without binder and is frequently used in combination with other recycled materials [8]. Reclaimed asphalt pavement (RAP) for making new hot mix asphalt (HMA) is a recognized technique with economic and environmental benefits that can be maximized by increasing the content of this recycle in the aggregate volume [9]. RAP can be effectively reused, contributing to the reduction of pavement deterioration and the consumption of natural resources, while obtaining results comparable to the conventional aggregate of sand [10]. Another waste material used in construction, recycled concrete aggregate (RCA) is a sustainable alternative to newly mined aggregate in concrete manufacturing that provides the ability to replace up to 25% of the construction, without significantly affecting concrete strength [11]. The use of RCA reduces costs and carbon dioxide footprint, in addition to conserving raw materials [12]. It is important to properly process the RCA and use post-processing measures to strengthen it [13]. In addition, the use of recycled concrete aggregates (RCA) in the construction of road pavements can be applied in all pavement layers, showing the physical and mechanical properties of natural aggregates [14]. In parallel, the residue of waste foundry sand (WFS) has pozzolanic properties that contribute to the improvement of the strength of the concrete [15]. The use of recycled tire rubber in asphalt pavements has proven beneficial in improving overall pavement performance; this material reduces permanent deformation, improves resistance to rutting, reduces construction and maintenance costs, and increases resistance to fatigue damage [16]. However, it is necessary to further investigate micromechanical models in order to better understand the multiphysics interactions between the constituents in the rubber-modified binder material and, thus, be able to more accurately predict its mechanical properties [17]. The use of plastic waste in road construction can reduce the emission of greenhouse gases and decrease the amount of plastic that is dumped into the environment [18]. The incorporation of recycled PET in the tread layer of pavements offers benefits in terms of both physical-mechanical and economic properties, however, it is recommended to determine the optimal percentages of recycled PET content in pavements [19]. The addition of polyethylene terephthalate (PET) in hot modified asphalt mixtures (HMA) improves mechanical properties such as Marshall, indirect tensile strength (ITS), and retained Marshall stability (RMS) [20]. The addition of glass fragments as aggregate material in a flexible bituminous pavement can have positive effects on both the stability and the flow value of the design mixture [21]. Furthermore, mining activity generates a large amount of waste that negatively affects the environment. Thus, it is necessary to find alternatives for the use of this waste in the construction industry [22]. This is the case of blast furnace slag which has chemical and physical properties that make it suitable for use in the construction, maintenance, and rehabilitation of roads [23]. On the other hand, the use of industrial waste powders as substitutes for standard limestone filler in the composition of asphalt mixtures is a viable option [24]. Regarding this, the incorporation of steel slag can be used as a suitable substitute for coarse aggregate in road surface layers as it has a high resistance to permanent deformation and damage caused by moisture, as well as good mechanical properties [25].

The objective of this review is to analyze and collect the most relevant information on the use of waste materials in the manufacture of sustainable pavements. The advantages and disadvantages of each material are identified, as well as its environmental impact and technical feasibility. In addition, current advances and trends in this field are outlined to enable the identification of further research areas on the use of waste materials in the manufacture of sustainable pavements.

2. Plastic Waste

Polyethylene Terephthalate (PET)

PET is a plastic waste that is abundant in the world due to its versatility in application for the packaging industry [26]. Recycling is a third option (Figure 1) in the treatment of plastic waste that is deposited in the open or incinerated, releasing components harmful to the mammalian reproductive system [27]. The reuse of PET is on trend to improve the properties of traditional bitumen, harmonize it with the environment, and point out the reduction of production costs inherent in asphalt concretes [28]. PET is a binder additive capable of meeting the expectations of asphalt cement [29]. The British company MacRebur made a mixture of binders for paved roads that contains the equivalent of eighty thousand plastic bottles per ton. These volumes represent a considerable reduction in the discharge of plastic into the soil which allows it to interact with the environment as an inert pollutant [30]. If the PET goes through an aminolysis treatment where its flakes and Triethylenetetramine (TETA) react chemically, it becomes an additive, which improves the adhesion between the asphalt cement and the aggregates, reducing the moisture-induced damage of the asphalt mixture [31]. In addition, PET combined with a silicon nanomaterial forms a sustainable hybrid additive that makes SMA (Stone Mastic Asphalt) mixtures more rigid, improving resistance to deformation and traffic; with a reduction of up to 0.04% in the infiltration rate (drain-off) [32]. On the other hand, due to the high melting point of PET, it is also considered as a substitute aggregate for asphalt mixtures after a mechanical reduction process [33]. PET is cut into small flakes, which are integrated into the hot asphalt mix, as physical recycling; capable of improving resistance to detachment and rutting with a proportion between 2% to 10% of the weight of the mixture [34]. Mixtures containing crushed PET flakes have high porosity, and the texture is similar to semi-dense asphalt mixtures (SDA) that reduce road traffic noise [35]. Crushed PET, with particles between 0.1 mm and 2 mm, is a replacement for sand in semi-dense asphalt mixtures (SDA) that makes them more ductile, but difficult to compact; They also present a reduction in cracking due to low temperature and resistance to permanent deformation at high temperature [36]. Therefore, exposing PET to gamma radiation increases its mechanical and thermal properties with a positive impact on its resistance; showing a Marshall stability with a range of 4.5% to 5.5% for an asphalt mixture with a content between 0.2% and 0.8% of PET fibers; considering a linear relationship between the increase in asphalt or PET content that increases the Marshall flow value [37]. Additionally, the use of plastic waste as a partial replacement for fine aggregates in concrete pavements can improve the compressive strength and durability of the pavement [38]. The incorporation of polyethylene terephthalate plastic waste as an aggregate in concrete can reduce porosity and improve the compressive strength of the material [39]. On the other hand, the addition of thermoplastics such as high-density polyethylene and polypropylene in the hydraulic concrete with a replacement percentage of up to 12% does not negatively affect the corrosion behavior in the reinforcing steel [40]. Therefore, the use of recycled plastics in concrete pavements contributes to environmental sustainability by reducing the amount of plastic waste in landfills [41].

3. Waste Materials

3.1. Tire Recycling

The polluting waste of tires at the end of their useful life reaches 3.9 million tons per year in Europe [42]. This growing problem requires studies aimed at recycling rubber through sustainable methods [43]. The application of crumb rubber (CR) in the manufacture of asphalt pavements offers an opportunity to reduce its negative impact on the environment while improving the properties of asphalt mixtures [44]. Rubber is obtained from tires with a consumed service life by reducing it by crushing it to fragments whose size allows them to be incorporated into an asphalt mixture as aggregates [45]. Kim et al., (2019) mention two processes for adding crumb rubber to an asphalt mixture: the wet one that integrates the rubber fragments into the asphalt binder and the dry one that replaces crumb rubber a part of the aggregate destined for the mixture with the advantage that the latter does not require additional equipment concerning that used for conventional mixtures [46]. In addition, acoustic properties are improved for an AC11 asphalt concrete tread (Asphalt Cement 11) with the addition of crumb rubber using the dry process compared to an SMA 11 mix tread (Stone Mastic Asphalt 11) [47]. Incorporating modified crumb rubber (CRM) in the hot asphalt mixtures (HMA), the cost of road maintenance, and the improvement of abrasion resistance with a partial elastomeric recovery will be a function of the type and size of the particle, the mixing process and the rubber content in the mixture [48]. The asphalt mixtures with contents of 5%, 7%, and 10% of crumb rubber within a temperature range between 46 °C and 82 °C applying the response surface methodology (RSM), suggests that the content of crumb rubber impacts more than the temperature on the complex modulus (G*) and phase angle (δ), both rheological properties of the asphalt mixtures [49]. In addition, it was found that for contents of 12% and 15% of crumb rubber, it was necessary to modify it with an increase in temperature above 200 °C in their respective samples. The degradation and expansion of the rubber particles allows the agile absorption of the binder of the mixture reducing the formation of cracks in the asphalt concrete modified with this material [50]. However, through the Analytic Hierarchy Process (AHP), two types of asphalt cement were classified by their performance grade (PG), and a third cement was classified by its viscosity (AC), with particle sizes of the crumb rubber at room temperature defined by the meshes no. 20 and no. 40, it was observed that the recommended amount of rubber for the mix with PG64-16 asphalt cement is 15% with particles passing mesh no. 20. Furthermore, for mixtures with asphalt cement PG58-28 and AC20 are 10% and 15%, respectively, with particles passing the mesh no. 40 [51]. In contrast, blends with a maximum of 15% crumb rubber under temperature ranges between–15 to 40 °C have a lower stiffness modulus than blends that do not include this material, where the void content is significant for establishing differences, even changing the trend described [52]. Consequently, the higher the content of crumb rubber in the asphalt mixture, the lesser the risk of cracking and fracture in the asphalt mixture; therefore, a high fatigue strength implies a lower deformation and, thus, a lower phase angle [49]. Total X-ray reflection spectrometry (TXRF) quantifies the rubber content in asphalt mixtures and represents an alternative with a greater sustainable range, guaranteeing good rheological properties that inhibit the formation of rust and reflection cracks [53]. The Indirect Tensile Strength (ITS) test at 60 °C for SMA blends shows that higher rubber content by wet process reduces chafing and presents a high percentage of voids per mineral aggregate favoring resistance to cracking [54]. Finally, mixtures with high-content crumb rubber modified asphalt (HCRMA) such as 50% of this reach a complex modulus (G*) that exceeds 100 MPa when the temperature is 34 °C, while its phase angle (δ) is maintained below 60 °C by increasing the temperature up to 88 °C showing good resistance to the formation of grooves; considering that its ordering modulus (G* sinδ) indicates up to 2956.10 kPa within different wear conditions according to the linear amplitude sweep test (LAS), presenting a decrease in fatigue resistance [55].

Table 1. Impact of the amount of crumb rubber on asphalt mixtures.

Blend Type	Replacement Value	Method/Test	Effect	Author
HMA       PG64-16       PG58-28       AC20	15% 10% 15%	AHP	Improves resistance to deformation	Khalili et al., (2019) [51]
SMA	20%	ITS	Decreases tensile strength	Noura et al., (2021) [54]
HCRMA	50%	LAS	Decreases fatigue resistance	Wang et al., (2022) [55]

shows the consequences of replacing a percentage of aggregates with crumb rubber on different asphalt mixtures.

3.2. Waste Glass (WG)

Waste glass (WG) can be recycled and applied as a sustainable building material capable of mitigating greenhouse gas emissions and reducing environmental risks [56]. The construction industry has uncontrollably consumed natural resources, which have simultaneously been contaminated with waste glass, a non-biodegradable material, however, this can act by totally or partially replacing sand [57]. WG can be used as a coarse aggregate (Figure 2a) or fine (Figure 2b) in the production of hydraulic concrete mixtures [56]. Spraying waste glass to a particle size of less than 100 mm is used for the manufacture of clinker due to its pozzolanic reactivity, improving the plastic properties of hydraulic concrete, with an increase in its resistance between 28 and 90 days of setting [58]. Asphalt mixtures that integrate 10% waste glass as a fine aggregate reduce thermal sensitivity, improving its fatigue response compared to conventional mixtures for tensile stress of 250 kPa at both 5 °C and 25 °C [59]. Glass fiber (GF) is predominantly composed of oxides of calcium, silica, aluminum, and iron [60]. Glass fibers for making concrete are used to a lesser extent than steel fibers [61]. However, waste glass as an aggregate, combined with milk can fiber increases the compressive strength of hydraulic concrete from 1% at 7 to 28 days and up to 20% at 56 days [62]. The compressive strength of hydraulic concrete increases as long as the combination of glass fibers and the condensed milk cans do not exceed 20% and 1%, respectively, of the aggregate in the mixture, avoiding the decrease in the settlement and density of hydraulic concrete at early ages [63].

4. Waste in Civil Engineering

4.1. Reclaimed Asphalt Pavement (RAP)

Roads are essential infrastructure for the economic growth of nations and global technological exchange; however, their construction and maintenance require an enormous amount of natural resources that negatively impact the environment [64]. For instance, the rehabilitation of civil structures generates large volumes of solid waste by demolishing elements that have met the design lifespan, destined for open-air landfills, putting humanity’s habitat at risk [65]. The rehabilitation of asphalt pavements generates a large amount of removed material called RAP (reclaimed asphalt pavement) capable of being reprocessed [66]. According to the US EPA IWEM transport and destination model, the negative environmental effects of RAP leaching on pavement construction report a low risk to human health [67]. The main source of RAP is the milling process, which reduces the size of fragments (Figure 3) of the removed pavement when the machine speed is slow at high milling depth [68]. The depth of the milling is determined by the condition of the binder and the original level to be rehabilitated [69]. The RAP contains residual asphalt binder which increases the viscosity of the mixture improving the tensile response [70]. The RAP content in hot asphalt mixes (HMA) should not exceed 30% for good performance [71]. Warm mix asphalt (WMA) exhibits the same low-temperature behavior and fatigue as HMA with a recycled RAP content of up to 40% [72]. The low-temperature crack resistance decreases if the RAP content increases in the mixture [73]. However, the higher the RAP content in the mixture, the greater its stability, reducing the asphalt content and increasing resistance to transit loads [74]. Marshall stability improves with lower asphalt cement demands for 75% RAP content in HMAs registering 29.32 kN [75]. In turn, 60% of RAP in hydraulic concrete mixtures presents 6.13% savings in its manufacturing cost and a 10% increase in compressive strength [76]. Additionally, Cold Recycled Mixtures (CRM) consume higher compaction energy to increase their stiffness when the content of air voids increases due to the decrease of the rated maximum RAP size [77]. The homogeneity of the asphalt layers improves when the rigidity of the mixture is reduced with rejuvenating additives [78]. The incorporation of RAP in warm blends with polyethylene wax-based additive (RH-WMA) equates to the indirect tensile strength (ITS) of hot mix asphalt (HMA), favoring a lower consumption of compaction energy [79]. Blends with RAP that include rejuvenating additives increase fatigue resistance and, therefore, increase pavement life [80]. Incorporating polypropylene fibers negatively affects the mechanical properties of the mixtures combined in a ratio of 70/30 aggregates of RAP and rock powder, r [81]. Nevertheless, asphalt mixtures with RAP at 50% of their weight report a Marshall stability value equal to 21.4 kN that allows a depth in the formation of grooves of 9.89 mm and a crack resistance of 1750 kPa using hydrated lime as a filler; while its fatigue resistance decreases with high deformation; however, it reaches a resilient modulus equal to 4200 Mpa [82]. Finally, the incorporation of optimal amounts of additives improves the mechanical properties of the mixtures, increasing stability and reducing wear loss, which extends the durability of the pavement [83].

4.2. Recycled Concrete Aggregate (RCA)

With urban growth, waste concrete is generated (Figure 4) which adds up from 35% to 50% of the solid waste of the construction industry [84]. Aggregates occupy the largest volume of concrete, between 60% and 75%, causing a demand that accounts for up to 48.3 billion tons a year of natural resources, therefore, recycled concrete aggregate (RCA) is a globally accepted option in the sustainable construction industry with the responsibility of verifying its mechanical properties and its percentage of replacement [85]. The hydraulic pavement that replaces 40% of its coarse aggregates with RCA generally achieves compressive strengths greater than 29 N/mm² at 28 days, reporting good durability of the concrete [86]. Hydraulic pavement concrete achieves a compressive strength of 50 MPa at 28 days and a bending strength equivalent to 4.72 MPa with 50% replacement of its conventional aggregates by recycled concrete aggregate [65]. When the aggregates of the semi-dense asphalt mixtures (SDA) are replaced at 60% by recycled concrete aggregate (RCA), a fracture energy of 12 kPa is reached through the indirect tensile strength (ITS) test, favoring the resistance to the formation of grooves, but with a potential propagation of cracking once initiated [87]. Marshall stability increases for hot mix asphalt (HMA), incorporating RCA in their coarse fraction due to the hexahedral and angular shape of this aggregate, however, the optimal asphalt content also increases [88]. The resilient modulus of samples with RCA compacted as unbound granular pavement layers reaches up to 247 MPa [89]. Partial replacement of coarse aggregates for warm mix asphalt (WMA) by RCA in a range of 15% to 45% directly increases the optimal asphalt binder content by 2.3% to 18.2%, related to negative environmental impact [90]. However, warm mix asphalt (WMA), incorporating RCA, reduces the consumption of natural aggregates and decreases the thermal energy for their elaboration, presenting a low yield and an increase of the optimal asphalt content [91]. An optimal replacement by industrial sludge requires 4% fine aggregate and 10% cement, allowing 100% coarse aggregate to be replaced by RCA with compressive strength at 28 days, which is equal to 18.9 MPa [92].

5. Industrial and Mining Waste

5.1. Mining Waste

The increase in the extraction of mineral resources increases the accumulation of industrial waste from mining and the metallurgical industry [93]. Globally, the mining industry generates around 20 to 25 billion tons of mining waste annually [94]. Mining causes a large environmental impact by releasing harmful substances into the air, dumping contaminated wastewater, and accumulating large amounts of waste on land [95]. The mining waste is economical, with stable physical and mechanical properties; as well as a uniform granulometry, useful for applied geotechnology, capable of replacing the conventional aggregate of artificial filler masses, lowering the operating costs of the mining industry [96]. The high production of asphalt mixtures in Europe demands a considerable amount of natural aggregates and asphalt binders [52]. The properties of the aggregate are essential to ensure good performance in pavement construction [97]. Examining the characteristics of iron waste aggregates is the starting point for evaluating whether they can be used in asphalt mixtures [98]. The mechanical strength of aggregates generated from degraded soils (Figure 5) by mining is suitable for concrete mixtures in civil structures [22]. Applying mining waste treated with an activator decreases the cement in the hydraulic mixture by 40%, increasing the resistance in a range of 25% to 30% [99]. The combination of mechanical activation and leaching processes can lead to efficient mining of target components, which may contribute to the environmental safety and economic viability of their disposal [100]. If efficiency in the mineral extraction and processing industry improves, environmental safety does as well [101].

5.2. Waste Foundry Sand (WFS)

Industrial processes deliver waste foundry sand (WFS) to the environment through open-air reservoirs polluting soil and groundwater; therefore, plant recovery (Figure 6) of this waste in civil engineering has become relevant in hot mix asphalt (HMA), hydraulic concrete, and pavement subbases [102]. The implementation of sustainable concrete with industrial waste has potential in pavements due to its non-structural volumes [103]. The WFS consists mostly of fine grains of adhered quartz sand that constitute the mold for the liquid metal and that after the casting process is disintegrated and discarded [34]. Foundry sand is classified according to the type of binder used when manufacturing the molds, sand agglomerated with clay or green sand and sand agglomerated with chemicals [104]. Waste foundry sand (WFS) is incorporated with alternative processes to concrete and asphalt for implementation in the construction industry such as pavements [105]. The workability of a hydraulic concrete mixture is not committed to the partial replacement of sand by WFS; however, the demand for water gradually and steadily increases as the percentage increases to a maximum equal to 30% replacement of this solid waste in concrete [106]. When the percentage of WFS as a fines substitute does not exceed 20%, the flexural and compressive strength does not vary significantly against an equal control mixture of respective 4.087 N/mm² and 40 MPa values; however, the abrasion resistance increases if the WFS content in the hydraulic concrete increases [107]. In addition, WFS is part of the alternative stabilizing materials for subgrade floors with expansive soil problems as they improve their resistance [108]. On the other hand, concrete formed with 30% WFS as a fine aggregate, 40% ground granulated blast furnace slag (GGBFS) cement mix, and 30% crumb rock as a coarse aggregate achieve an unconfined compressive strength of 12.7 MPa after 90 days of curing, with the limiting use in areas undergoing constant flooding or extreme droughts [109]. However, additives for hydraulic concretes with WFS that reduce their high pozzolanic activity at 28 days should be applied [15]. Thus, the reuse of WFS in road projects could generate significant environmental and economic benefits worldwide [110].

6. Analysis and Discussion

One of the most relevant aspects of the use of substitute aggregates is the replacement percentage in pavement mixes. Reviewed studies have shown that it is possible to replace a certain percentage of traditional aggregates with recycled materials without compromising the mechanical performance of the mixes. However, it is important to consider that the optimal replacement percentage may vary depending on the specific characteristics of each recycled material and the pavement mix in question. For example, in the case of RAP, it has been observed that it is possible to replace up to 30–40% of traditional aggregates in asphalt mixes without significantly compromising the strength and durability of the pavements. On the other hand, recycled tire rubber has proven to be an effective substitute aggregate in asphalt mixes, allowing for the replacement of up to 10–20% of conventional aggregates. In the case of foundry sand, mining waste, PET, glass waste, and recycled hydraulic concrete, the optimal replacement percentages may vary depending on the specific application and the characteristics of the recycled materials. Additionally, the review compiles studies with promising results in terms of compression, bending, and fatigue strength, as well as wear and erosion resistance. However, it is important to note that the mechanical performance of the mixes may vary depending on the amount and type of recycled material used, as well as the application and service conditions they are exposed to.

It is necessary to understand that each recycled material has unique properties that can influence the mechanical performance of pavement mixtures. RAP may have higher stiffness and fatigue resistance than recycled hydraulic concrete, while recycled tire rubber may have greater flexibility and abrasion resistance. Therefore, the combination of these materials in different percentages can lead to significant variations in the mechanical performance of the mixtures. Additionally, the lack of comparability of results is due to the absence of standardized and unified methodologies for evaluating the performance of pavement mixtures with recycled materials. Each research or study may use different evaluation methods and acceptance criteria, making direct comparisons of results between studies difficult. Furthermore, the lack of compatibility of results refers to the interaction between different recycled materials and their effect on the mechanical properties of the mixtures. For example, the addition of recycled tire rubber can affect the adhesion between aggregates and asphalt binder, which may result in a decrease in the mix’s skid resistance. Similarly, the presence of mining residues can alter the particle size distribution in the mixture, which may affect compaction resistance and durability.

7. Recommendations

Solid waste is a potential alternative to partially replace natural aggregates in the construction of flexible and rigid pavements. However, waste can occur physically with significant process differences in their collection, storage, improvement, and/or application as an aggregate. Thus, special studies should be carried out to gain more knowledge on the mechanical behavior in mixtures incorporating them.

Sustainable aggregates incorporated into pavement construction mixtures perform well as fractions of the total content, but when combined with other materials such as fibers or additives the percentage of replacement increases; hence, the need to carry out more studies to replace conventional aggregates in a greater proportion with solid waste in hydraulic and asphalt concretes.

Having identified the key aspects that have been studied, the findings, the methodologies used, and the emerging trends about the use of recycled materials in pavements, the following suggestions can be made:

The evaluation of the methodology used, the validity of the findings, and the limitations of the investigations allow an abundance of knowledge; however, it is necessary to further investigate the effects on the environment of the new waste of recycled materials when the lifespan of the works that applied them is met.

It is essential to collect information on the advantages and disadvantages of using recycled materials in pavements. This includes technical, economic, environmental, and social aspects. This information is crucial to understanding the benefits and potential limitations of using these materials in road works for all types of traffic.

It is vitally important to focus a thorough study of the existing gaps in the use of recycled materials for pavements and their global economic impact. To provide a basis for further research in a more exhaustive way, which may contribute to sustainable pavements.

Carrying out a study that supports the take for global policymaking related to recycled materials in pavements. This will facilitate appropriate strategies to encourage the use of waste effectively and sustainably.

8. Conclusions

The objective of this review was to describe the alternatives currently available for sustainable aggregates for the construction of pavements. This review has revealed materials with environmental benefits, good mechanical responses to traction, appropriate fatigue strength, and qualities that cause low deformation to rolling surfaces.

PET presents various reuse opportunities that not only reduce its environmental impact by reducing its discharge to the ground but also improve the properties and durability of asphalt mixtures used on roads. From its use as a binder additive to its incorporation as a substitute for aggregates and sands, PET proves to be a viable and sustainable option for the construction of road infrastructures, offering benefits such as the reduction of traffic noise, greater resistance to deformation, and improvement in the thermal and mechanical stability of asphalt mixtures. These innovations not only contribute to mitigating plastic pollution but also promote efficiency and sustainability in the road construction sector.

The use of rubber improves the properties of asphalt mixtures. From reduction of rutting to resistance to crack formation, modified comminuted rubber offers significant benefits in terms of durability and track performance. The amount and particle size of rubber have a crucial impact on the rheological properties of the mixtures, and methods such as X-ray reflection spectrometry ensure their long-term quality and performance. Despite the challenges, such as the possible decrease in fatigue strength, the integration of high percentages of modified crushed rubber in asphalt mixtures shows great potential to improve the sustainability and efficiency of road infrastructures.

By partially or totally replacing sand in rigid pavements, Waste Glass (WG) not only reduces the demand for natural resources but also improves the plastic properties and strength of concrete. In addition, its use as a fine aggregate in asphalt mixtures contributes to the reduction of thermal sensitivity and improves the response to road fatigue. The combination of glass scrap as an aggregate with condensed milk can fibers even significantly increasing the compressive strength of hydraulic concrete, without compromising its density or slump. These applications demonstrate the potential of glass scrap as a valuable resource in sustainable construction, offering both environmental and structural benefits for the infrastructures of the future.

The RAP, which contains residual asphalt binder, can be reprocessed and reused in hot or warm asphalt mixtures, thus reducing the demand for natural resources and improving road stability. Although the optimal RAP content varies depending on the type of mixture between 30% and up to 50%, its incorporation can generate significant savings in manufacturing costs and improve the compressive strength of hydraulic concrete. The addition of rejuvenating additives and the optimization of the RAP ratio can further improve the mechanical properties of the mixtures, increasing their stability and durability.

RCA improves the mechanical properties of hydraulic concrete and asphalt mixtures, allowing the manufacture of more durable and resistant pavements. Despite some challenges, such as increased asphalt content in warm asphalt mixes and the need for adjustments in asphalt binder proportions, the use of RCA presents tangible benefits in terms of performance and sustainability. In addition, the partial or total replacement of conventional aggregates by RCA offers a viable alternative to reduce the environmental footprint of construction, while preserving the quality and integrity of structures.

The use of treated mining waste reduces the operating costs of the mining industry, in addition to improving the properties of concrete and asphalt mixtures, increasing their strength and stability. In addition, the combination of mechanical activation and leaching techniques can improve the efficiency in the extraction of valuable components, thus contributing to the environmental safety and economic viability of mining waste disposal.

The incorporation of waste foundry sand (WFS) in concrete and asphalt offers advantages in terms of both sustainability and performance. In hydraulic concrete, the partial replacement of sand by WFS does not compromise the workability of the mixture, although it may require greater water consumption. In addition, the flexural and compressive strength of concrete is not significantly affected up to a 20% replacement of WFS, while abrasion resistance tends to increase with a higher content of this residue. In pavement subbases, WFS acts as an alternative stabilizer for expansive soils, improving their resistance. However, it is important to consider limitations such as the high pozzolanic activity of the WFS and its suitability in environments subject to extreme floods or droughts.