Innovative Pavement Solutions: A Comprehensive Review from Conventional Asphalt to Sustainable Colored Alternatives

Abstract

Climate change significantly impacts transportation infrastructure, particularly asphalt pavements. Similarly, the heat absorption of paved surfaces, especially conventional black pavements, significantly intensifies the urban microclimate. Paved surfaces, including asphalt pavements, account for over 30% of the covered surfaces and are vulnerable to rising temperatures, which cause not only pavement distress, such as rutting and cracking, but also urban heat islands (UHI). Sustainable pavement solutions, specifically colored pavements, have been investigated for their potential to mitigate these effects. This review presents an extensive overview of current pavement technologies, emphasizing conventional asphalt’s economic, environmental, and functional characteristics. A discussion of the benefits and challenges of colored pavements is also provided, including their ability to reduce UHI, enhance safety, and contribute to sustainable urban growth. This paper discusses advancements in pavement material science, the use of recycled materials, and the application of reflective coatings, providing insights into sustainable infrastructure development. Transitioning from conventional black pavements to sustainable colored alternatives is not merely a matter of material choice but a strategic transition toward resilient urban planning. Increasing demand for environmentally friendly infrastructure could prompt the construction industry to adopt colored pavements as a tool to promote environmental stewardship.

1. Introduction

Climate change significantly threatens human life, ecosystems, and the built environment in general [1]. Transportation infrastructure, which includes roads, bridges, railroads, and hydraulic structures, is susceptible to these effects and can be significantly impacted by them. This infrastructure is crucial in facilitating the efficient, safe, and dependable transportation of people, products, and services.

The United States has more than 2.7 million miles of roadways, with approximately 94% being constructed using asphalt as a binder. All of these roads are vulnerable to the elements and hence classified as ecologically sensitive infrastructure. Extreme high temperatures significantly affect flexible pavements, leading to a drop in the viscosity of bitumen. This might aggravate distress, like rutting (permanent deformation), or cause a degree of roughness and cracking. The primary climatic issue for flexible pavements is the rising temperatures, as indicated by climate estimates for future changes [2,3,4,5].

In 2015, the Federal Highway Administration (FHWA) published a comprehensive 450-page reference paper titled “Towards Sustainable Pavement Systems” [6]. The study focused on defining sustainability in the context of pavements and provided examples of sustainable practices across many stages, including design, materials, construction, use, maintenance, preservation, end of life, and assessment. The collaborative efforts of the federal authorities and other organizations to create such a project exemplify the broader mindset of the pavement sector and its players, who enthusiastically support the imperative of establishing a sustainable transportation network. A sustainable infrastructure encompasses both environmental impacts and economic expenses [7].

Roads are crucial transportation infrastructure components, as people increasingly depend on vehicles for everyday commuting. The extensive road network has significant adverse environmental effects, including contributions to global warming, increased energy consumption, alteration of landscapes, and acidification of the soil [8]. The production of materials used in road construction and maintenance involves carbon-intensive and energy-demanding procedures [9].

Furthermore, the global road networks constitute a substantial contributor to the loss of biodiversity. This is primarily due to the migration of species, the fragmentation of habitats, and the increased human presence in natural ecosystems [10,11]. Transportation authorities strongly promote using environmentally friendly practices, concepts, and procedures in the road sector to reduce adverse environmental effects [12].

1.1. Rationale for This Review Study

The development of emerging countries requires the expansion of paved surfaces, and it is crucial to prioritize and adopt sustainable and environmentally friendly infrastructure development practices. However, this transformation from soil land into artificially paved surfaces made of concrete or asphalt alters the thermal characteristics of the area. The larger latent heat capacity of natural ground, compared to paved surfaces, can be linked to moisture and small pores [13,14].

Paved surfaces have higher thermal inertia, which means they can store more thermal energy. This leads to an increase in the pavement surface’s temperature, which raises the surrounding air’s temperature [15]. The rise in air temperature in metropolitan areas with paved surfaces has formed urban microclimates. Urban microclimates experience higher temperatures than the surrounding rural areas, leading to the urban heat island (UHI) effect [16].

Roads are crucial for various human activities, and they are considered one of the most significant transportation facilities. They play a decisive role in facilitating the national and international expansion of the economy, the transportation of products, cultural interchange, and the transmission of technology. Despite their notable contribution to the advancement of society, the substantial environmental effects that occur throughout the life cycle of a road cannot be disregarded [17]. Pavement engineering is part of an industry that consumes a significant amount of energy. Road infrastructures substantially impact the environment due to the required quantity of raw materials, earthworks, and maintenance activities [18,19].

1.2. Significance of Sustainable Colored Pavements

Pavements generally fall into three main varieties based on their constituent materials: concrete and rigid pavements, bitumen or flexible pavements, and composite pavements. Concrete pavement is commonly constructed using concrete made from Portland Cement Concrete (PCC), while asphalt pavement is built using hot-mixed asphalt (HMA). On the other hand, composite pavement is a combination of both materials which are built by combining asphalt and concrete layers that work together as one material. Flexible pavement offers better ride quality, and rigid pavement provides better strength. Although composite pavements offer advantages, a cost comparison with flexible and rigid pavement disqualifies the broader use of this type of pavement. Moreover, the focus of this review article is colored pavement, which is an offshoot of flexible pavements. Composite pavements are infrequently utilized in construction due to their excessive pricing and intricate analysis requirements [20]. Approximately 83% of the roadways in the United States are composed of flexible pavements [21].

Asphalt or bituminous pavement is the most prevalent and extensively utilized road type worldwide due to its superior riding quality, shorter construction time, and easier maintenance [22]. The flexible and viscoelastic properties of asphalt pavement are derived from bitumen. Bitumen’s great tinting power gives it color dominance, making the asphalt seem black. Black is widely recognized for its high heat absorption capacity and low heat conductivity [15].

In the summer, the dark color of asphalt absorbs and accumulates a significant amount of heat, causing surface temperatures to reach 70 °C during the day [23]. The viscoelastic properties of asphalt make it susceptible to rutting and aging when exposed to high temperatures [24,25,26]. The extent of pavement degradation can be reduced by lowering the ambient temperature of the pavement’s framework [27,28]. To address the significant obstacles posed by limited resources, the effects of climate change, and environmental pollution, it is crucial to prioritize advancing transportation and energy systems and driving industrial transformation. These measures have been identified as fundamental strategies for tackling these challenges [29,30,31,32].

Developing a green, resilient, self-sustained, and sustainable energy-efficient transportation integration system is a vital future direction for the road engineering sector. It is essential to explore technology that integrates renewable energy and transportation to enhance the efficiency and sustainability of transportation. In addition, optimizing the energy structure in transportation has emerged as a prominent area of research, leading to the development of various pavements that attach clean energy [33].

The term ‘sustainability’ refers to utilizing the Earth’s resources to meet the demands of the present generation without compromising the needs of future generations. This concept is closely associated with the 21st-century Millennium Development Goals (MDG) [34]. When discussing the transportation sector, particularly pavements, environmental sustainability means considering the effects on the environment, economics, and society at every stage, including material choice, design, construction, and preservation methods. Pavement sustainability, in essence, encompasses the triptych, commonly known as the triple bottom line, which has distinct sides [6]. The three key factors are the environment, economics, and society. Figure 1 illustrates the triple bottom line of environmental sustainability.

Aggregates used on paved surfaces have more thermal inertia than the natural ground. Therefore, substituting soil ground with concrete surfaces leads to the assimilation of a larger quantity of ultraviolet radiation during daylight hours. This scenario can lead to a substantial disparity in temperature between the Earth’s surface and paved surfaces, particularly black asphalt roadways [35]. Approximately 20–40% of metropolitan land is occupied by asphaltic pavements [28]. As a result, heat absorbed by the pavement is transferred through convection to the surrounding areas, contributing to and exacerbating the urban heat island (UHI) effect [35,36].

Research has demonstrated that decreasing the surface temperature of pavement materials directly helps to mitigate the UHI effect [36,37,38]. On the other hand, the elevated temperature of pavements leads to the deformation of plastic materials when vehicles are driven over them [39]. Reducing the temperature of the pavement surface is a potentially effective method for mitigating rutting and aging [27,40,41]. In addition, the elevated surface temperature of asphalt pavement leads to thermal–oxidative aging, which subsequently impacts the water susceptibility and the low-temperature performance of the asphalt [42].

The entire phenomenon leads to a growth in temperatures worldwide concerning the UHI effect, as well as irreversible distortion of the pavement. Consequently, researchers are focusing their efforts on addressing these concerns. Several studies have tried to solve this issue by utilizing cool roofing and pavement materials with a high albedo/solar reflectivity value [43,44]. Berg et al. [45], investigating the thermal stability of paving materials, found that in mid-summer, pavements painted white (with a solar reflectance of approximately 0.55) have temperatures nearly identical to the surrounding environment. Nevertheless, there was a notable temperature difference of approximately 11 °C between the unpainted roadways (with a solar reflectance of around 0.15) and the natural surroundings.

Santamouris et al. [46] found an almost 18 °C disparity in surface temperature between traditional bitumen and white pavements during the hottest part of the summer. A study [47] found that increasing the albedo by 0.1 may lead to a decrease in the pavement surface temperature of 2.1 °C. Albedo refers to the ratio of reflected solar radiation, where each of the incoming and reflecting radiation sources are measured on a plane horizontal to the surface and integrated over the entire spectral angle of solar radiation [48]. Pavement textures exhibiting greater solar reflection indexes or albedo ratings can effectively reduce the UHI effect and alleviate issues associated with high surface temperatures [22].

Xu et al. [49], with the same objective, found that pigments, when incorporated into the wearing course of pavements, exhibit a high level of reflectivity to both visible and infrared light. In addition, they have the ability to efficiently emit an enormous quantity of retained heat to the surroundings through long-wave radiation without requiring any energy consumption. Furthermore, the degree of thermal conductivity, solar reflectivity, and infrared radiation emittance values of the pavement structure are enhanced when it is modified with bright or light-colored materials [50]. The resulting change in the paving substance leads to a cooler pavement surface, in contrast to traditional black surfaces. The phenomenon of an increased solar reflectance ratio or albedo rating is not solely restricted to pavements.

Several studies have found that using highly reflecting and light-colored materials in roofing can substantially reduce the temperature, up to 30 °C, compared to typical roofing materials during the hottest part of summer [51,52]. Solar reflectance is the surface’s ability to reflect solar radiation back to the hemisphere where the solar source is located, integrated over the entire solar spectrum and encompassing specular and diffuse reflection components [51]. Research has demonstrated that increasing the solar reflectance by 0.25 can lead to a direct decrease in the pavement surface temperature by 10 °C [53]. Elevated surface temperatures can have a negative impact on the durability of pavement infrastructure. A reduction of 5 °C in the temperature of the pavement structure has the potential to increase its lifespan by up to 5 years [15]. However, this effect is not strictly linear and may reach a practical limit depending on environmental conditions and material properties.

1.3. Objectives and Scope of This Review

The primary focus of this review paper is to investigate and evaluate novel pavement solutions that shift past conventional asphalt to sustainable colored alternatives. The objective of the study is to offer an extensive overview of the present condition of pavement technologies, with a specific emphasis on the economic, environmental, and functional characteristics of conventional asphalt.

Furthermore, this review seeks to draw attention to the growing patterns in colored pavements, particularly those intended to improve sustainability by utilizing environmentally friendly materials and methods. This involves evaluating the potential benefits of colored pavement with the aim of mitigating UHI, enhancing safety and aesthetics, and supporting overall sustainable urban development. Additionally, the research aims to determine the challenges and limitations related to the practical application of these alternatives, thus providing a critical evaluation of their sustainability and effectiveness in various atmospheric circumstances.

The scope of this study covers an evaluation of the characteristics, efficiency, and effectiveness of conventional asphalt pavements, along with an in-depth examination of several sustainable materials and methods used in colored pavements. The experimental method of this review paper is illustrated in Figure 2, which shows the detailed layout. This paper will address current progress in the field of pavement material science, including the integration of recycled materials and the application of photoreactive and reflective coatings. Furthermore, it will focus on the impact of colored pavements on urban climates, traffic safety, and energy consumption. It comprises various case studies and research findings from different regions to offer a comprehensive perspective on advancements in paving solutions. This study proposes significant insights for researchers, policymakers, and practitioners on the subject of sustainable infrastructure development by analyzing the existing literature and highlighting specific areas.

2. An Overview of Conventional Asphalt Pavements

Asphalt pavements consist of several layers, including the subgrade, the unbounded subbase, and the base, and wearing courses. These materials exhibit a multifaceted reaction to applied force and alterations in the environment. Every location or country may adhere to a specific pavement design guide, but they must all adhere to the same fundamental design concepts. These principles include taking into account the number of times the pavement will be subjected to loads and environmental changes, as well as understanding how materials and structures behave in theory versus reality [54].

2.1. Brief History of Asphaltic Pavements

Asphalt is found naturally in asphaltic reservoirs and in rock asphalt, which is a combination of sand, limestone, and asphalt.

Table 1. Historical development of asphalt.

Date	Event
Ancient Times	Asphalt was utilized by Mesopotamians for waterproofing, Phoenicians employed it to seal ships, Egyptians utilized it as mortar to prevent erosion, and Moses’ basket was made waterproof by using asphalt.
625 B.C	The earliest documented utilization of asphalt as a material for constructing roads was observed in Babylon. Asphalt was also utilized by the Greeks and Romans for a variety of applications.
1595	Europeans encountered naturally bituminous deposits in the new continent. Sir Walter Raleigh employed it for the purpose of ship recaulking.
Early 1800s	Thomas Telford and John Loudon McAdam revolutionized road construction by introducing the use of crushed stone and tar, resulting in the development of “tarmacadam” pavements.
1870	Edmund J. DeSmedt, a chemist from Belgium, constructed the initial authentic asphalt pavement in the United States in Newark, New Jersey. The Cummer Company established the first concentrated facility for producing hot mix asphalt. Nathan B. Abbott was the first person to submit a patent on asphalt.
1900	Frederick J. Warren obtained a patent for the “Bitulithic” pavement, and Warren Brothers constructed the initial contemporary asphalt production in East Cambridge, Massachusetts.
1907	Production of refined petroleum asphalt exceeded that of natural asphalt. The process of mechanization and the introduction of new technologies in the production and laying of asphalt commenced.
1942	The advancements in asphalt materials for military plane runways were driven by the impact of World War II.
1956	The implementation of the Interstate Highways Act by Congress resulted in the advancement of larger and more advanced machinery for the purpose of road construction.
1970	The energy crisis prompted a rise in the utilization of recycled asphalt. Asphalt pavement emerged as the most extensively recycled material in the United States.
1986	The National Centre for Asphalt Technology (NCAT) was founded at Auburn University and has since become the primary organization for conducting research on asphalt.
2002	The Environmental Protection Agency (EPA) excluded asphalt facilities from the roster of significant contributors to dangerous airborne contaminants.
Today	Asphalt pavement is the most recycled material in America, exceeding the recycling rates of newspaper, aluminum cans, and glass.

provides a summary of the historical development of asphalt [55].

2.2. Composition and Construction Methods

Approximately 95% of the world’s road infrastructure comprises flexible pavements [56]. The composition of the structure consists of four distinct layers, subgrade, subbase, base, and surface course [12,57], as illustrated in Figure 3.

The subgrade refers to the underlying natural soil on which additional layers are placed. Frequently, it is discovered that the current subgrade is weak or has expansive properties, meaning that even a small change in moisture levels can result in significant volume changes in a short amount of time [58]. In such instances, the subgrade is altered by using specific additives. The altered foundation layer is referred to as the sub-base. The base course, located above the sub-base, is a load-bearing layer mostly consisting of high-quality aggregate of varying sizes. Located above it is the surface course, which consists of a combination of aggregates, fines, filler material, and binder. The layer on top is in close touch with the traffic load, so it is imperative to use a high-quality material.

Pavements have a geotechnical challenge as they are constructed on the ground using resources derived from it, including untreated substances, such as soils and rocks, as well as processed hydrologic and asphalt binders. Individuals constructed pavements over the landscape, including on excavated areas, raised banks, and even within human-made tunnels or at the base of artificial ponds. Pavement materials consist of both natural and artificial components, such as rocks, soil, lime, Portland Cement, bitumen, polymers, geo-synthetics, and various chemical products, that are used to improve their inherent properties. While pavement collapse often does not pose a threat to life or property, pavements are complex constructions that necessitate a comprehensive strategy encompassing all aspects of study, design, construction, and surveillance. Pavement management systems, or contemporary asset management systems, also encompass the economic dimensions of roadway engineering [59].

Pavement design encompasses two main categories: (a) the design of mixes of asphalt and hydraulic-binder-treated materials and (b) the structural design of pavement components. The latter differs from the structural stability design of bridges and buildings due to the significant impact of environmental factors on the pavement’s structure. The primary considerations in developing a pavement construction are its serviceability and intended use [60]. When designing pavements, it is important to consider the requirements of the users. This is because the way vehicles interact with the pavement has a significant impact on how people perceive and value the structure. When designing functional pavements, it is crucial to prioritize user satisfaction by considering five essential factors: speed, evenness, safety, maintenance, and cost. Hence, a logical approach to pavement design should consider the “optimization of the pavement” when all the elements possess equal physical reliability, including their overall reaction to environmental circumstances. The design problem incurs expenses related to reliability, which in turn impact construction, maintenance, operations, and contingency costs throughout the project’s life cycle [61].

2.3. Performance Attributes and Constraints

Pavement performance pertains to the capability of the pavement to adequately satisfy transportation needs during a specified length of time. The major components of this process include ride comfort, wear and tear, surface damage, and structural strength [62]. Performance metrics are commonly employed in pavement performance modeling to assess the performance of the pavement [63,64,65]. Performance measures can be categorized into two types: non-comprehensive measures and comprehensive measures. Non-comprehensive measures are used to evaluate certain aspects of pavement performance, while comprehensive measures assess the entire state of the pavement.

Table 2. Commonly used pavement performance measures.

Publication	Classification	Considered Factors	Pavement Performance Measures
[66,67]	Non-compressive performance measures	Surface distresses	Crack Index (CI)
[68]			Alligator Deterioration Index (ADI)
[69]			Pervious Concrete Distress Index (PCDI)
[70]			Distress Rating (DR)
[71]			Pavement Structural Condition Index (PSC)
[72]			Pavement Distress Condition Index (PDCI)
[72]			Transverse Cracks Rating Index (TCEI)
[73]			Surface Distress Index (SDI)
[74,75]		Ride quality	Ride Quality Index (RQI)
[74,76,77]			Rutting Depth Index (RDI)
[72,78,79,80,81,82]			Rutting Depth (RD)
[78,79,83,84,85,86,87,88,89,90,91,92,93,94]			International Roughness Index (IRI)
[95,96,97]		Friction	International Friction Index (IFI)
[74]			Skidding Resistance Index (SRI)
[98]			Skid Number (SN)
[72,98,99]			Sideway Force Coefficient (SFC)
[100,101,102,103]			Mean Summer SCRIM Coefficient (MSSC)
[104,105,106]		Structural Capacity	Deflection
[74]			Pavement Structural Strength Index (PSSI)
[107]			Surface Curvature Index (SCI)
[108,109]			Structural Number (SN)
[110]	Compressive performance measures	Surface distresses, ride quality	Urban Pavement Condition Index (UPCI)
[64]			Pavement Serviceability Rating (PSR)
[111,112,113,114,115,116]			Pavement Serviceability Index (PSI)
[117]			Pavement Quality Index (PQI)
[118,119,120,121,122]			Pavement Condition Rating (PCR)
[93,123,124,125,126,127,128,129]			Pavement Condition Index (PCI)
[130]			Overall Performance Index (OPI)
[131]			Overall Pavement Condition (OPC)
[132]			Future Pavement Surface Condition (FPSC)
[133]			Composite Condition Index (CCI)

summarizes the performance measures as well as classifies them into comprehensive and non-comprehensive performance measures.

Various elements influence the condition of the pavement and any resulting damage. These elements can pertain to materials, construction, transportation, or the interplay among distresses and the natural environment.

Pavements often degrade over time due to a combination of factors, including materials, vehicle traffic, and environmental conditions [83,134]. This deterioration can have negative impacts on road safety and result in increased expenditures for users. Therefore, it is necessary to implement timely and suitable repair and maintenance treatments in order to enhance the performance of the pavement and prolong its lifespan. Pavement performance models are crucial tools for pavement managers to make up-to-date decisions on pavement maintenance and rehabilitation. These models enable managers to forecast future pavement conditions, choose appropriate maintenance activities, and establish the optimal time for maintenance interventions [135,136]. Therefore, it is crucial to have a reliable pavement performance model that can precisely forecast pavement performance for efficient pavement management.

Pavement performance models primarily depict the correlation between the pavement’s efficiency and pertinent influential components. These models are utilized to investigate the degradation process and forecast forthcoming roadway conditions [118,137,138]. In general, pavement performance models can be categorized into three fundamental types: mechanistic models, empirical models, and mechanistic–empirical models [139]. Mechanistic models typically rely on mechanistic concepts to examine how pavements react to pressures, strains, and deflections. Empirical models primarily depend on data from observations to investigate the correlation between the performance of pavement and different influencing elements.

Mechanistic–empirical models integrate mechanical principles and empirical investigation to examine the correlation between response variables and pavement performance. The empirical models are more often utilized in pavement management than the other two. Empirical pavement assessment models can be further classified in other ways. The Pavement Management Guide of the American Association of State Highway and Transportation Officials (AASHTO) [140] categorizes pavement performance models into deterministic models, probabilistic models, Bayesian models, and subjective models (also known as expert-based models). Uddin [141] classified them as statistical regression models, artificial neural network simulations, and probabilistic models.

Justo-Silva et al. [142] introduced a framework for categorizing pavement performance models. These models can be classified based on their formulation type, with deterministic models and probabilistic models being the two main categories. They can also be classified based on their application levels, with project-level performance approaches and network-level performance models being the two main categories. Furthermore, they can be classified based on the types of dependent variables they consider, with globally dependent variable models and parametric-based variable models being the two main categories. Lastly, they can be classified based on the types of independent variables they consider, with absolute independent variables models and, when compared, independent variable models being the two main categories.

According to a bibliometric analysis, the formation of pavement performance models has been recognized as a significant subject in the field of pavement management [143]. Several empirical pavement performance models have been established through numerous studies [84,144,145]. The deterioration of pavement performance is a multifaceted process characterized by dynamic changes. Therefore, it is imperative to frequently update pavement performance models to accommodate these new changes. The progress of science and technology has led to the utilization of advanced data collection techniques [146,147] and analysis approaches [148,149,150] in pavement management. This has improved the inspection of pavement conditions and shaped possibilities for updating performance models. Furthermore, effective road management also necessitates the need for adaptable upgrading of research-based performance models.

2.4. Environmental Impacts

Typically, the life cycle of pavements can be divided into five stages: material manufacturing, construction, service, maintenance, and end of life [151]. Energy consumption and emissions occur during every phase, as depicted in Figure 4. The primary stages encompass material production and construction. The material production stage encompasses the acquisition of raw materials, the transportation of these commodities, and the manufacturing process [152,153]. The pavement construction process involves the transportation, paving, and compaction of mixtures [154].

Horvath et al. conducted a life cycle inventory analysis to examine the environmental effects of pavements constructed from asphalt and steel-reinforced concrete using publicly accessible data [156]. Research indicates that asphalt pavement has greater energy input, lower requirements for ore and fertilizer input, and lower toxic emissions compared to steel-reinforced concrete pavement. However, it does generate a higher volume of hazardous waste.

Kim and colleagues conducted a series of research studies on greenhouse gas (GHG) emissions associated with road construction projects. The researchers developed a systematic approach to estimate GHG emissions using data from the pavement project at the design stage. A total of 23 standard highway construction projects in the Republic of Korea were subjected to the framework [157]. The research also examined the GHG emissions resulting from the use of onsite equipment during road building. It provided a summary of the eight main activities that contribute to GHG production during the construction process [158,159]. Hong et al. conducted an analysis of the GHG emissions that occur during the constructing of the structure in China. They used extensive onsite process data and considered an extended systems boundary [160]. During the development of urban roadways, the primary factors contributing to energy consumption and greenhouse gas emissions are the construction materials, building activities, and transportation [161,162,163,164].

Santero and Horvath conducted a study on the impact of pavement on global warming. They divided the construction process into eight elements: material extraction and manufacturing, transportation, worksite equipment, traffic delays, the carbonation process, the lighting, the albedo, and rolling resistance. The potential impact ranges for every aspect were computed and compared. The results encompassed both the range of variations in pavements and the lack of assurance in the facts. Two ranges were established: a likely range of values according to the most accurate predictions and a broad range of values depending on outlier data and fewer logical possibilities [165].

The overall emissions of greenhouse gases in the United States amounted to around 6.8 billion tons of equivalent carbon dioxide (CO₂-eq) in 2010. The transportation sector accounted for almost 1.8 billion tons of carbon dioxide emissions, which is equivalent to 27.1% of the total GHG emissions. The transportation industry is the primary source of carbon dioxide (CO₂) emissions in the United States, making it the largest contributor to the Earth’s atmosphere. It is responsible for approximately 31.1% of the total emissions of CO₂ [166].

Huang created a model to examine the entire life cycle of asphalt pavement, including its construction and maintenance. Information is provided regarding the process and data collection in the United Kingdom. The model is utilized in an asphalt pavement project to compare the environmental consequences of using virgin aggregate, waste glass, incineration bottom ash, and recycled asphalt roads [154,167]. Zapata et al. [168] studied the energy utilization and environmental effects of asphalt and reinforced concrete pavement, including the materials used and the construction process. The study reveals that the primary energy consumption in the process of extracting and placing asphalt is predominantly attributed to the blending and drying of aggregate, accounting for 48% of the energy consumed for pavement construction. Furthermore, the manufacturing of bitumen constitutes around 40% of the overall energy use.

Researchers have studied the GHG emissions associated with roadways and cars for decades [169,170,171,172,173,174]. The highway construction business significantly contributes to economic development and is a major source of carbon emissions. The GHG emissions resulting from the heating of aggregates, the refining of bitumen, and the mixing of the mixture have been assessed [169]. The overall emissions are calculated by aggregating the emissions from several construction processes associated with different types of projects, including subgrade, roads, bridges, and tunnels [174].

Internationally, many tools, such as LEEDS and GreenRoad in the United States and CEEQUAL in the United Kingdom, can be utilized to quantify CO₂ emissions or assess sustainability. Additional tools can be found in Australia and Germany. Furthermore, numerous studies have assessed the GHG emissions associated with roadway infrastructure construction.

3. The Need for Sustainable Solutions for Pavements

Presently, road pavements are essential infrastructure for the economic development of any nation, leading to significant funds being committed to their construction. In the past, the focus in designing these structures was to build them using the least expensive materials while ensuring their structural integrity and safety [175]. Nowadays, evaluating investments includes considering the environmental viewpoint and analyzing all potential outcomes (such as those related to the economy and environment, social, or other effects) linked to these investments. Multiple interpretations of the concept of sustainable development have been proposed. The prevailing definition of sustainable growth was established in 1987 in the publication “Our Common Future” [176], sometimes referred to as the “Brundtland Report”. Sustainable development is defined as the ongoing process of meeting present demands while safeguarding the ability of future generations to meet their requirements without making any concessions.

3.1. Environmental Aspects

At first, the pavement construction process has obvious and easily noticeable environmental aspects. However, over time, the significance of elements like energy usage and the release of greenhouse gases into the atmosphere became far more important. Currently, “sustainability” is widely used to describe nearly every aspect of existence. However, it is increasingly being used specifically concerning the sustainability of humans on Earth, with a particular emphasis on the factors contributing to global warming and environmental degradation [177].

Sustainable development implies a balance between economic and social development and environmental protection, i.e., between human activities and the natural world. Thus, as the perception of the world’s limited resources (minerals, fossil fuels, etc.) increases, the search for solutions to reduce their dependence is intensified. Installation activities, particularly road pavements, have a substantial environmental impact. Construction activity directly impacts the environment by consuming energy and natural resources and releasing gaseous emissions into the atmosphere. Nevertheless, the impact on the environment persists throughout the lifespan of the infrastructure, intensifying during specific activities, such as maintenance, refurbishment, and demolition [175].

Nevertheless, the energy used for traffic over the lifespan of a road accounts for approximately 95–98% of the total amount of energy used, whereas the energy utilized for constructing, maintaining, and operating the road constitutes less than 2–5% of the overall energy usage [178]. Perez et al. [179] state that road transport is a significant contributor to emissions in the economic sectors, responsible for around 30% of total utilization of energy and CO₂ emissions.

The World Bank defines road sector energy consumption as the utilization of petroleum products, natural gas, electricity, renewable fuels, and trash. Figure 5 illustrates trends in paved and unpaved roads, urban population, road sector energy consumption, and CO₂ emissions across several countries. The dataset shows that China and the United States lead in both paved road length and CO₂ emissions, with high road sector energy consumption, indicating a strong correlation between road infrastructure development and environmental impact. In contrast, countries like Canada, Australia, Brazil, and Mexico have lower paved road lengths, unpaved roads, and significantly lower CO₂ emissions and road sector energy consumption. Despite these differences in road infrastructure, all countries exhibit consistently high urban population percentages, indicating a shared trend of urbanization.

3.2. Social and Economic Advantages Offered by Sustainable Pavements

Communities’ quality of life and livability are interchangeable concepts that refer to how communities enhance people’s overall quality of life. Transportation has a significant role in the livability of small and large communities, alongside other contributing variables [181]. Rural communities rely heavily on public transit to offer essential lifeline services to persons who lack mobility options, enabling them to access crucial medical services, learning institutions, employment opportunities, and other significant activities [182].

A community’s overall well-being can directly impact an individual’s level of contentment with their own life. Although numerous studies have established a correlation between factors, such as income, health, employment status, and other individual characteristics, and satisfaction with life [181,183,184,185], there is a scarcity of research examining the link between community livability and life satisfaction.

3.3. Latest Advancements and Innovative Techniques

Resilient and environmentally friendly pavement infrastructure is paramount in addressing current economic and environmental concerns. Over the past decade, the pavement infrastructure has played a crucial role in facilitating the fast growth of the global economy. New theories, methodologies, technologies, and materials are emerging in pavement engineering. The degradation of pavement systems is a common issue that involves multiple branches of physics. Due to the interplay between traffic patterns and environmental factors, accurately predicting pavement lifespan has grown increasingly complex and necessitates a thorough understanding of pavement material analysis [186].

Table 3. Sustainable asphalt solutions [187].

Category	Solution	Description	Benefits
Sustainable Asphalt Solutions	WarmMix Asphalt [188]	Asphalt mixed and laid at a lower temperature	Reduced energy consumption Extended paving seasons Improved working condition
	Recycled Asphalt Pavement (RAP) [189]	Recycling old asphalt into new mixtures	Resource conservation Cost saving Environmental impact
	Bio-Based Binders	Binders derived from renewable energy sources, such as plant oil	Renewability Lowered emissions Enhanced performance
Technological Advancement	Intelligent Compaction	Advanced rollers with sensors and GPS for real-time compaction data	Improved quality Efficiency Data collection
	Perpetual Pavement	Multi-layer approach to pavement design for indefinite lifespan	Long service life Reduced maintenance Sustainability
	Self-Healing Asphalt [188]	Asphalt that can repair itself when minor cracks occur	Extended lifespan Cost-effective Enhanced durability
Smart and Connected Infrastructure	Smart Pavements	Pavements with integrated sensors and communication systems	Real-time monitoring Predictive maintenance Enhanced safety
	Electric Vehicle Charging Roads	Pavements with embedded wireless charging system for EVs	Convenience Sustainability
	Solar Roadways	Pavements with integrated solar panels to generate renewable energy	Energy generation Reduced carbon footprints Innovative uses
Advanced Materials	Polymer-Modified Asphalt (PMA)	Asphalt enhanced with polymers	Increased durability Enhanced performance Weather resistance
	Nanotechnology in Asphalt	Use of nano-sized material to improve asphalt properties	Improved strength Increased service life Self-healing properties
	Geopolymer Asphalt	Asphalt using industrial byproducts like fly ash or slag as binders	Sustainability Environmental impact

is the illustration of sustainable asphalt pavement solutions along with their benefits.

4. Introducing Colored Pavements

4.1. Definition of Colored Pavement

Colored pavements are road surfaces constructed using clear binders blended with pigments other than conventional asphaltic pavements. Colored pavements not only enhance the aesthetics but also improve visibility and reduction in surface temperature in comparison to black asphaltic pavements. Different colors with varying albedo significantly enhance the thermal performance of colored surfaces, which is a major effort in urban heat island mitigation strategies [190].

Colored pavements are constructed by using various roadway construction materials, including colored concrete or asphalt, paint, or other marking substances, which are placed on the top of a roadway or island to resemble a colored pavement. Non-retroreflective colored pavement, such as bricks and patterned surfaces, is not considered a traffic control device if it is used only for aesthetic purposes and does not convey regulating caution or guidance messages to road users. This applies even if the colored pavement is positioned between the lines of a crosswalk [191].

Colored pavement is classified as a traffic control device when used in the traveled way, on flushing or raised islands, or on the shoulders to control, warn, or guide traffic. If a retroreflective colored roadway is used, it must adhere to the following colors and uses:

• The yellow pavement color is only designated for flush or elevated median islands that separate traffic flow in opposite directions and for the left-hand shoulder of roads on divided highways, one-way streets, or ramps.
• The color of the pavement on flush or elevated channelizing islands, where traffic travels on each side in the same general path or on right-hand shoulders, shall be white.

4.2. Description and Types of Colored Pavements

Colored asphalt consists of material identical to regular asphalt, including a colored pigment. Colored asphalt can be applied as a thin overlay on top of regular asphalt to lower expenses. Colored asphalt pavements consist of two main types: light-colored pavements and pigment pavements [192]. In some methods, the aggregates are coated and secured with translucent bitumen instead of the conventional black bitumen. Transparent bitumen is used in regions with notable landscapes or locations of significance to culture and history to highlight the natural color of mineral aggregates. In the second form, translucent bitumen is combined with pigment in asphalt mixes or artificially colored particles and added to the mix to achieve the desired visual effect [192].

Research has shown that transparent binders and asphalt manufactured with transparent binders have equivalent performance to traditional bitumen and the related asphalt mixes (HMA) [193,194]. Furthermore, a recent study has demonstrated that transparent binders and the accompanying asphalt have a higher capacity to disperse heat quickly and a lower ability to absorb heat than traditional black bitumen [195]. Furthermore, research has demonstrated that adding metal oxide pigments to standard binders and asphalts can raise the heat transfer capacity of the pavement. This, in turn, leads to a notable improvement in the efficiency of the wearing surface under high temperatures [196].

In addition, scientists have examined the practicality of using novel combinations of transparent and colorful substances on road surfaces to reduce the UHI impact. This is achieved by increasing the reflectivity (albedo) and lowering the temperature of the surface [22,197,198]. Research has demonstrated that transparent mixtures effectively lower the temperature to a large extent when compared to traditional black surfaces. Research has demonstrated that the color of the surface has an impact on the thermal response. Additionally, mixtures changed with oxide show potential for strong mechanical qualities. This suggests that these mixtures could be used in residential regions with low levels of traffic [199]. Therefore, changing the color of traditional black binders to any color other than black or only employing a transparent binder could lead to a long-lasting and cooler pavement structure.

In sunny and hot seasons, colorful pavements have a higher reflectivity level than ordinary asphalt pavements [199]. Therefore, those surfaces have a reduced tendency to absorb solar radiation and consequently maintain lower temperatures when exposed to light. Consequently, the air temperatures in the nearby regions fall due to reduced heat transmission from the road surface to the air [50,200]. The pavements are extremely reflective, which decreases the chances of overheating in the summer. This, in turn, enhances the durability of the pavement and minimizes damage [201]. Research has shown that translucent bitumen can reduce the amount of lighting required, resulting in lower electricity expenses [192]. Colored asphalt pavements can be utilized as a proficient traffic management scheme component to designate bus lanes, sidewalks, pedestrian crossings, and pedestrian zones [193].

4.3. History of Development and First Application

Colored asphalt pavements are becoming more commonly utilized in expansive public spaces and high-risk locations, such as crossroads, roundabouts, or pedestrian crossings. In the previous application, the colored pavement is typically used to provide a specific aesthetic quality to the area or to blend it with its environment seamlessly. The primary purpose of the later application is to increase the safety of users by boosting visibility and making the road easier to understand. Nevertheless, colored pavements are equally exposed to the pressures caused by traffic and the environment, and, as a result, they must have comparable mechanical performance to their uncolored equivalents. Specific ingredients, such as colored aggregates, pigments, and clear binders, are used to obtain the desired colors [202]. Different techniques are used to colorize asphalt pavement, ranging from traditional methods like dry pigment addition to more advanced techniques, such as acrylic-based coatings and synthetic binder emulsions. Each method has different advantages and disadvantages, as shown in

Table 4. Overview of different methods for preparing colored pavements.

Method	Description	Advantages	Disadvantages
Dry Pigment Addition	Adding dry pigment directly to the hot asphalt blacktop mix	- Simple method - Direct color integration	- High cost - Limited color range - Low reflectivity, affecting nighttime visibility and safety - Environmental concerns due to limited reflectivity
Acrylic-Based Color Coatings	Applying an acrylic-based color coating on top of the asphalt pavement	- Allows for exact color - Can reflect colors, improving visibility and reducing heat absorption - High UV and weather resistance, enhancing durability	- Requires additional coating steps - May require reapplication over time, increasing maintenance
Inorganic Pigments	Introducing inorganic pigments like oxides of chromium, manganese, iron oxide, and cobalt into binder formulation	- High resistance to temperature, oxygen, and UV radiation, improving durability - Environmentally safe (non-toxic pigments) - Helps reduce the heat island effect by allowing lighter colors	- Can be more costly than organic pigments - Limited to specific metal oxide inorganic pigments
Incorporation of Light Mineral Components	Using light mineral fillers (sand, crushed stone, gravel) or colored minerals (granite crumb)	- Enhances reflectivity, improving visibility and heat reduction - Adds texture and durability to the surface, improving safety	- Limited to lighter colors - Can affect the pavement’s structural properties, potentially impacting the durability
Synthetic Binder Emulsion	Applying a thin colored coating made from emulsions of synthetic binders stabilized in water with fatty alcohols, alkylpolyamines, etc.	- Versatile application - Lower temperature required for application, reducing energy consumption - Can produce various colors, enhance safety and aesthetic appeal	- Requires surfactants, and there are potential environmental concerns with surfactants - Limited long-term durability, especially under heavy traffic

[203,204].

Utilizing colored pavements for bicycle amenities is an intriguing approach to facilitate the establishment of a top-notch cycling network. The unique coloring of dedicated lanes, tracks, or shared walks creates a marked route, enhancing the appeal and ease of navigation of the infrastructure, particularly at crossings and junctions. The increased emphasis caused by the coloration enhances a shift in the behavior of road users. Still, its success in promoting safety appears to be closely linked to the individual contextual features at each location. Various red, green, and blue colors are universally recognized, yet there is no standardized global usage of a particular color for similar circumstances [205].

Furthermore, various innovative implementations, including a diverse array of hues not specified in official records, are actively experimented with, resulting in a partially disordered setting and causing perplexity among drivers. Certain states, regions, or municipalities may only specify the basic color without considering other factors, such as brightness, lightness, color intensity, or nuance. In contrast, others require a specific color based on an internationally recognized color chart (such as the British standard–BS 381 C [206], Australian standard–AS2700: 1996 [207], and Swedish natural color system–NCS [208].

The Federal Highway Administration (FHWA), a division of the U.S. Department of Transportation, classifies green-colored pavements as traffic control devices. These pavements must meet specific requirements for their color, which is measured using four (x, y) coordinates in the CIE 1931 color space, as well as their luminance factor. The mention of the primary color gives a designer or project leader limited flexibility to tailor the modification to the surroundings [207] more effectively. In rural environments, such as parks and towpaths, as well as in historic settings, the use of bright colors can have a negative impact by being intrusive and harmful to the adjacent landscape or streetscape. One should consider a harmonious equilibrium between the advantages and the appearance [209]. This approach is well-suited to asphalt and resin-based treatments for high-friction surface and wearing courses. The ultimate color of these treatments is determined by the chromatic interactions among aggregates, binder, and pigment and the mix design process [210]. The Dutch practice of coloring bikeways red throughout their entire length is primarily due to the ability to achieve pavement with high color accuracy by using standard black asphalt mixed with small amounts of iron oxide pigmentation and/or naturally red-colored aggregates. This approach is preferred over other colors, which require more expensive synthetic binders [211]. Below is a description of the common coded colors used for bicycle facilities, as shown in the

Table 5. Coded colors for bicycle facilities.

Study	City	Nation	Continent	Color System	Hue	Code
[212]		Korea	Asia	Munsell- HV/C KS L*, a*, b* SRGB CMYK	Red	5R ¾ 0075 30.25, 20.68, 8.56 105, 58, 59 0, 45, 44, 59
[213]		Singapore		RAL		3011-brown red
[214]		USA	America	CIE 1931	Green	Daytime chromaticity (x,y): (0.230, 0.754), (0.266, 0.500), (0.367, 0.500), (0.444, 0.555) Nighttime chromaticity (x,y): (0.230, 0.754), (0.336, 0.540), (0.450, 0.500), (0.479, 0.520)
[205]		Chile		RAL	Blue	5012-light blue
[215]		Iceland	Europe	NCS	Green	S 0506-G40Y
[216]	Zaragoza	Spain		RAL	Green	6002-leaf green
[217]	Moscow	Russia		NCS	Ochre	S 3060-Y20R/S 3060-Y30R/S 3060-Y40R
					Pink	S 4030-Y40R/S 4030-Y50R/S 4030-Y60R
					Red	S 1580-Y80R
[218]		Italy		RAL	Red	3003-ruby red
[219]		Slovakia		RAL	Green	6018-yellow green
[220]	South Australia	Australia	Australia			G13-emerald green G27-homebush green
[205]	Western Australia					G13-emerald (crossing in shared path)

.

4.4. Construction Methods and Applications of Colored Pavements

To enhance road safety, the Netherlands and other countries are implementing colored pavements, such as red, blue, or yellow cycling lanes, crossroads, and plateaus. There is not a singular technique for forming pavements with color. Several approaches can be identified:

• Surface treatment using colored crushed stone;
• Application of colored epoxy resin coating;
• Colored asphalt with black bitumen;
• Colored asphalt with clear binders that are unaltered (without polymer);
• Colored asphalt with clear binders that are treated with polymer.

Colored road surfaces have multiple applications in addition to promoting road safety; light-colored road surfaces (yellow/white) help reduce CO₂ emissions by minimizing the need for artificial lighting and reducing heat buildup in urban areas. Nevertheless, there are growing uncertainties in the industry over the continued usability of these synthesized pigmentable clear binders, primarily due to problems related to handling and health and safety. However, this particular sort of colored asphalt does provide optimal outcomes in terms of both color and durability. Recent research indicates that these fears are baseless and that a transparent binder may be utilized responsibly to create a top-notch hot-mix asphalt (HMA) [221].

4.5. Construction Techniques

The various methods for attaining a colored road surface vary in terms of both quality and expense. The most cost-effective option would be to apply a bituminous surface treatment using colored crushed stone. The weather patterns will mostly influence the service life of the construction during its execution. If crushed stone fails to adhere effectively to the emulsion, the durability of the pavement will be significantly reduced, mainly when it is laid under unfavorable weather conditions. This principle also extends to the application of an epoxy resin coating, which needs to be applied to a surface devoid of moisture.

Colored asphalt, made by combining conventional black bitumen with significant quantities of color pigment, is commonly utilized due to its reduced starting expenses compared to bitumen with a transparent binder. One drawback is that the color is significantly darker than what can be achieved with a transparent binder. For example, in the instance of red-colored asphalt, it appears purple instead of red. Moreover, the abundance of pigmentation in black bitumen leads to a decline in quality, particularly in terms of its resistance to aging, compared to normal black asphalt. The potential reason for this issue is the incompatibility between the colors utilized and specific varieties of bitumen. This may even become evident shortly after applying asphalt, appearing as an almost non-compressible ‘dry’ combination of asphalt.

Colored asphalt with transparent binders typically yields the highest quality. Clear binder serves distinct functions compared to conventional binder. The application of a specific binder depends on the requirements of the project. Both have various properties. Clear binders are remarkably effective aesthetically, but they may not provide performance characteristics like conventional binders in terms of strength, flexibility, adhesion, and durability. A clear binder (unmodified) is a low-grade binder that will perform worse than the conventional binder due to less durability, long-term stability, and performance under load. This makes them less suitable for applications in pavement construction where durability and reliability are considered. This will subsequently result in premature unraveling. Due to the limited research conducted on laboratory-scale properties, visual inspections are currently the main means of assessing performance [221].

4.6. Functional and Aesthetic Benefits

Using synthetic pigmentable transparent binders can achieve vibrant-colored asphalt with minimal pigment usage. Unlike traditional black bitumen, which requires a 5% (powder) pigment to achieve a dark color, this alternative does not. Clear binders do not adhere to any established models in the Netherlands. Consequently, readily available binders in the market may exhibit subpar performance and are utilized inappropriately. COPRO has formulated criteria for the Belgian market, documented in PTV 858 [222].

Synthetic pigmentable transparent binders often have petrochemical constituents obtained from petroleum, similar to conventional bitumen. By carefully selecting the appropriate combination of elements in a synthetic transparent adhesive, it is possible to replicate the characteristics of typical (polymer-modified) bitumen while achieving a light brown hue [223]. The qualities of the bitumen might vary depending on the provider and the product type, ranging from low-quality normal bitumen to high-quality polymer-modified bitumen. According to the type of binder used, the temperature for asphalt mixing and processing should be adjusted proportionately. The type of binder plays a significant role in determining the appropriate mixing and processing temperature of asphalt. Several types of binders require different temperatures; for example, warm mix asphalt operates at a reduced temperature, while conventional bitumen and polymer-modified bitumen often demand elevated temperatures. The desired workability can be achieved by adjusting the mixing and processing temperature according to the binders’ type. This also helps in improving durability and long-term performance of the pavement [224].

4.7. Financial Comparison with Conventional Pavements

The Life Cycle Assessment (LCA) is a widely used and effective tool for making decisions based on the demand for environmental sustainability [225]. The LCA method has frequently been utilized to assess the cost-effectiveness of marking materials. Two distinct Life Cycle Assessments (LCAs) were conducted on thin-layer pavement marking systems in accordance with ISO 14040 [226] procedures. The analytical results showed that the primary factor influencing the outcome was the general durability of the marking materials rather than the specific choice of materials [227,228].

5. Performance Evaluation of Colored Sustainable Pavements

Colored asphalt pavements are becoming more commonly utilized in expansive public spaces and high-risk locations, such as crossroads, roundabouts, or pedestrian crossings [229]. In the previous application, the colored asphalt pavement is typically used to provide the space with a specific aesthetic quality or to blend it with its environment seamlessly. In contrast, its primary purpose in the later application is to increase the safety of users by boosting visibility and the clarity of the road.

Nevertheless, colored pavements are equally exposed to the pressures caused by traffic and the environment, and, as a result, they must demonstrate comparable mechanical performance to their uncolored counterparts. Specific ingredients like colored aggregates, pigments, and clear binders are used to achieve desired colors [230].

Yet, utilizing these latter components can impact the effectiveness and longevity of colored asphalt mixtures. As an initial phase, BRRC (Belgian Road Research Centre) identified the specific properties of these materials, including the flow characteristics of transparent binders at both high and low temperatures and the hardening impact of pigments acting as fillers. Afterwards, the influence of the material properties on the quantitative mix design was examined. Subsequently, these substances’ impact on the mechanical properties of colored mixtures was investigated in a laboratory setting. The evaluation of the latter performance involved conducting tests to assess water sensitivity, rutting resistance, and low-temperature cracking [202]. The moisture damage of asphalt mixtures can be assessed by using different methods depending on loose coated asphalt mixture or compacted asphalt mixture. The rolling bottle test was found to be more reliable in comparison with other tests on loose coated asphalt mixtures while in compacted asphalt mixture, and the modified Lottman test as well as the Hamberg wheel track test were found more suitable for the determination of moisture susceptibility [231].

The wheel tracking test is used to determine the rutting performance of various asphalt mixtures in the laboratory. The solid rubber tire runs on the specimen under a constant-temperature environment and the loading pressure and rutting performance of the asphalt mixture are evaluated using a dynamic stability indicator [25]. Pavement life is highly affected by low-temperature cracking distress, thus reducing pavement service life. Various methods can be used to assess low-temperature cracking resistance of asphalt mixtures, but the most used methods are the bending beam rheology (BBR) test, the direct tensile (DT) test, and the dynamic shear rheometer (DSR) test [232].

5.1. Comparison of Conventional Versus Colored Pavements

In a tropical climate, the pavement surface can become hotter than the air temperature due to the absorption of solar radiation throughout the day [233]. Colored road areas, such as those observed on walkways for pedestrians, parking lots, and bicycle paths, can reduce the heat absorption of pavements. This study examines the thermal performance of five different color coatings added to the surface of concrete and asphalt pavement. The thermal characteristics and solar reflectivity of the colored coated pavement were assessed using an infrared thermometer, a solar-powered meter, and a thermal imaging approach.

The statistical analysis indicated that adding a colorful overlay to both asphalt and concrete samples resulted in lower surface temperatures than standard or without-coating asphalt and concrete. The asphalt sample with a white coating exhibited the most significant drop in surface temperature, experiencing a fall of 17 °C. Additionally, it had a solar reflectance value of 0.61. In contrast, the concrete sample with a white coating exhibited a temperature reduction of 10 °C and a solar reflectivity of 0.78. The ENVI-met simulation is used to evaluate the thermal impacts of incorporating the specimens in a site inquiry. This study can assist in choosing more appropriate colored coatings for the pavement of urban areas, such as streets, parking lots, and streets. Consequently, it can decrease the air temperature by reducing heat transmission and improve the comfort of being outside and the attractiveness of the cityscape [234].

In the experiment, the thermal performance of five color coatings was investigated by examining their effect on the surface temperatures of asphalt and concrete.

Table 6. Mean surface temperature of the tested samples.

Sample	Concrete		Asphalt
	Mean Surface Temperature (°C)	Mean Surface Temperature Reduction (°C)	Mean Surface Temperature (°C)	Mean Surface Temperature Reduction (°C)
Uncoated	48.52	0.00	58.95	0.00
Green	46.04	2.49	57.69	2.49
Brown	44.26	4.26	56.45	4.26
Red	43.72	4.81	55.85	4.81
Yellow	39.99	8.54	48.09	8.54
White	38.15	10.38	41.52	10.38

summarizes the mean surface temperature and mean temperature reduction statistics for each coating when compared to unmodified asphalt and concrete [235].

All five color coatings (white, yellow, red, brown, and green) reduce surface temperatures of both asphalt and concrete when compared to uncoated surfaces, while the white coating performs the best, followed by the yellow coating. The data provided for the other colors (yellow, red, brown, and green) correspond with the overall trend that higher solar reflectance leads to lower surface temperatures, even if the degree of improvement varies between coatings.

In the investigation of the optical characteristics of the specified asphalt during daylight hours, the optical properties of samples are primarily influenced by their surface solar reflectance [236]. This is because surface solar reflectance refers to the portion of the total solar energy that is reflected back. The incident solar irradiance and reflected solar irradiance measurements were utilized to compute the solar reflection of each sample. Compared to the uncoated reference samples, the optical characteristics of the coated asphalt and concrete samples demonstrate that the application of an appropriate color coating can greatly enhance the solar reflectivity of the samples. All five color-coated concrete and asphalt samples exhibit more solar reflectivity than the bare asphalt and concrete samples. Higher solar reflectance results in lower surface temperature due to reduced absorption of solar energy by the sample.

Reflectance has a greater impact compared to emissivity. This study, which references ENERGY STAR guidelines [126] and Lawrence Berkeley National Laboratory studies [127], discovered that a sample must have a solar reflectance of 0.25 to 0.40 to be considered a cool pavement. Reflectance has a greater impact compared to emissivity. This study, which references ENERGY STAR guidelines [237] and Lawrence Berkeley National Laboratory studies [238], discovered that a sample must have a solar reflectance of 0.25 to 0.40 to be considered a cool pavement.

The solar reflectance values (SRs) and reflectance values in the ultraviolet (UV), visible (VIS), and near-infrared (NIR) parts of the spectrum were measured for five tested samples and a sample of standard black asphalt. The SR values were measured across the 300–2500 nm range, while the UV, VIS, and NIR reflectance values were measured across the ranges of 300–400 nm, 400–700 nm, and 700–2500 nm, respectively [50].

The reflectivity of the colored thin-layer asphalt specimens was consistently higher than that of the traditional black asphalt in all circumstances, as shown in

Table 7. Solar reflectance of the conventional and colored asphalt [235].

Sample	SR (%)	SRNIR (%)	SRUV (%)	SRVIS (%)
Conventional black asphalt	4	4	4	3
Off-white thin-layer asphalt	55	63	10	45
Yellow thin-layer asphalt	440	51	8	26
Green thin-layer asphalt	27	39	8	10
Beige thin-layer asphalt	45	56	10	31
Red thin-layer asphalt	27	40	6	11

. The samples exhibit a solar reflectance that varies from 27% (for red and green samples) to 55% (for the off-white sample), while the solar reflectance of the traditional black asphalt is only 4%. In addition, all samples exhibit a significantly high absorptance level in the UV range (300–400 nm), with values varying from 90% to 96%.

5.2. Mechanical Properties and Performance under Normal and Severe Conditions

The black hue of conventional asphalt binding material results in a significant absorption of solar light [239]. The elevated surface temperature of asphalt pavement in the summer leads to the acceleration of rutting, the deterioration of long-term durability, and the occurrence of unwanted environmental consequences, such as heat island effects and emissions of volatile gases. Asphalt’s dark surface has a strong thermal emissivity and quickly drops in temperature during extreme cold weather. Thermochromic materials are substances that have the ability to modify their color in response to changes in temperature, and this shift is reversible. Li et al. introduce a novel thermochromic asphalt binder with many functions. The binder is specifically developed to control the surface temperature of the asphalt pavement. It can lower the surface temperature of the asphalt during hot summers and enhance it during freezing winters.

Optical analysis is performed on the thermochromic asphalt binders, revealing that they have a higher level of reflectivity than traditional asphalt binders. Furthermore, the reflectance of the thermochromic binder increases as the temperature rises. These characteristics were discovered to greatly decrease the temperature of the pavement surface on a normal, hot day in Cleveland, Ohio. To examine the impact of thermochromic materials on the mechanical properties of asphalt binder, the thermochromic asphalts are evaluated using Superpave binder performance tests. Usually, asphalt binders have been tested at three different stages: unaged, after being subjected to the rolling thin-film oven (RTFO), and after being subjected to both the RTFO and pressure aging vessel (PAV). The addition of thermochromic powder to conventional asphalt binder resulted in a decrease in the penetration, phase angle, and creep rate, as well as an increase in the softening point, viscosity, complex modulus, rutting parameter, fatigue parameter, and stiffness of the asphalt binder, as indicated by the experimental results. Moreover, enhancing the quantity of thermochromic powder results in a decrease in the depth of penetration and the rate of deformation over time, while causing an elevation in the temperature at which softening occurs, the resistance to flow, the ability to withstand shear stress, the parameter that measures the tendency to form ruts, the parameter that measures fatigue resistance, and the rigidity. In addition, the performance at elevated temperature grades of the asphalt binder was improved by using 3–6% black, 6% blue, and red thermochromic powder. Hence, the integration of thermochromic substances into asphalt pavement has the potential to enhance its performance and longevity, particularly in hot climates [240].

This study aims to create a practical solar-heat-reflecting layer for asphalt surfaces. The cooling properties of 10 coats designed by the user and a type of paint from Japan were examined and assessed through laboratory and field experiments. Ceramic particles and machine-made sands were utilized to improve the coat’s anti-skid function. The results indicate that some schemes had superior indoor cooling effects compared to the other schemes, resulting in a reduction of 30 °C in the surface temperature of the specimens. Furthermore, the observed changes in cooling efficiency over time were consistent amongst different experimental setups, both in the field and in the laboratory. However, it is worth noting that the cooling impact of each coating was less effective outside than indoors. The results of the anti-skid experiment indicated that the application of 160 g/m² resulted in 1.18 mm of machine-produced sands, which resulted in the highest increase in the British Pendulum Number (BPN). Ultimately, three optimal designs were suggested for practical implementation based on their effectiveness in cooling outdoor environments and their influence on reducing driving glare [224].

5.3. Durability and Lifespan of Colored Pavements

A study conducted by [241] proposed a color-durable asphalt pavement; the solution involves addressing the issues of low color durability and the absence of study findings on color asphalt pavement by applying an anti-tire traces seal resin emulsion on the surface. The color stability was assessed using the RGB tool in Photoshop and the trace residue rate algorithm after extensive rolling and aging tests.

The test results demonstrated that the evaluation approach was straightforward and efficient. After prolonged rolling, the coloring of the pavement surface eventually stabilizes at a constant value. Applying the emulsion over the roadway surface can effectively prevent the formation of tire marks. Following an extended aging test, the tire’s resistance to traces grew by 26.6% compared to the conventional type. Furthermore, the former exhibited a 44.1% higher resistance to traces than the latter without undergoing long-term aging. Using resilient asphalt pavement enhances the color asphalt pavement’s resistance to tire marks and greatly improves its color life expectancy [242]. In a recent study [243], Badin et al. utilized a clear asphalt binder instead of a conventional one to prepare non-black samples. They added three different colored pigments into the clear binder to produce the desired asphalt color. The results of the colored asphalt samples and the asphalt prepared with a neat clear binder exhibited significant resistance to temperature absorption. The colored samples were also efficient in heat dissipation. Moreover, the resistance to permanent deformation was also significant in the performance testing of the study.

5.4. Real-World Application from the Existing Literature, Including Global Implementation Examples

Global utilization of cool pavements (CPs) can be categorized into reflecting and evaporative CPs, as shown in Table 7. Gaitani et al. [200] implemented the use of photocatalytic bitumen and colored concrete with a high level of infrared reflection in a specific area in the center of Athens, Greece. The area covered a total of 4160 square meters. In March 2009, they conducted multiple daylight monitoring campaigns. The researchers demonstrated through experimentation that the CPs maintained a temperature up to 4.8 °C lower than traditional asphalt. Additionally, numerical analysis indicated that CPs can potentially reduce the mean near-surface air temperature by up to 1.6 °C.

A single scientific team conducted multiple large-scale public space rehabilitation projects in Athens, comprising about 61,660 m². The projects were documented in various studies by [37,244,245,246]. The numerical study of the applied control points revealed that their position can decrease near-surface air temperatures of up to 2 °C. In recent times, many CP projects have been implemented in the urban areas of Los Angeles [247], Makkah [197], and Doha [197] by putting a reflective coating on the existing pavements. Initial results from these applications indicate a decrease in ambient temperature of 0.5 °C due to the applied CPs.

Table 8. Research on the large-scale implementation of cooler pavement construction through field testing.

Type of Cool Pavement	Base Material (BM)	Albedo of Base Material	Cool Pavement Application	Albedo of Cool Pavement	Area	City	Study
Evaporative	-	-	Water retention pavement	-	Public square	Minato, Japan	[248]
Evaporative	-	-	Water retention pavement	-	Small park	Mitaka, Japan	[248]
Evaporative	Dense graded asphalt	-	Water retention pavement	-	Parking lot	Tokyo, Japan	[249]
Reflective	White concrete, black asphalt	0.45 (concrete)	Photocatalytic, colored infrared reflective concrete	0.68	4160 m2	Athens, Greece	[200]
Reflective	Dark concrete, black asphalt	0.15–0.2	Colored infrared reflective concrete	0.65–0.75	25,000 m2	Tirana, Albania	[250]
Reflective	Dark concrete, black asphalt	<0.4	Colored infrared reflective concrete, marble	0.70–0.78	16,000 m2	Athens, Greece	[244]
Reflective	Concrete, black asphalt	0.35–0.45 (concrete), <0.2 (asphalt)	Colored infrared reflective concrete	0.60	4500 m2	Athens, Greece	[37]
Reflective	Grey concrete, black asphalt	0.04 (asphalt)	Colored infrared reflective asphalt, photocatalytic concrete	0.35–0.66	37,000 m2	Athens, Greece	[245]
Reflective	-	-	Marble cement	0.69	-	Athens, Greece	[246]
Evaporative	Black asphalt, gray concrete	-	Porous brick, porous asphalt	-	200 m sidewalk, 200 m bike lane	Taipei, Taiwan	[251]
Reflective	Dark asphalt	0.06–0.08	Reflective coating	0.18–0.25	13,000 m2	Los Angeles, CA, USA	[247]
Reflective	Dark asphalt	0.12	Reflective coating	0.33–0.38 (initially), (0.19–0.30) (after 10 months)	57,936 m2	Phoenix, AZ, USA
Reflective	Black asphalt		Reflective coating	-	3500 m2	Makkah, Saudi Arabia	[197]
Reflective	Black asphalt		Colored cryogenic material with hallow ceramic microspheres	-	200 m road, 200 m sidewalk/bicycle lane	Doha, Qatar	[197]
Evaporative	-	-	Semi-permeable asphalt, fully-permeable asphalt	-	850 m2	Pingtung, Taiwan	[252]

provides an illustration of the research on large-scale implementation of cooler pavement construction through comprehensive field testing.

Numerous large-scale uses have been implemented for evaporative cooling systems. However, only a few have been monitored and assessed regarding their cooling efficiency [253]. Furumai et al. [248] and Takahashi and Yabuta [249] conducted studies on creating water-retaining pavements in several locations in Tokyo, including a public space, a park, and a parking area. These pavements resulted in a significant decrease in surface temperature, ranging from 13 to 19 °C. Recently, Cheng et al. [251] and Yang et al. [252] discussed using permeable brickwork and porous asphalt to construct bike lanes and sidewalks in Taipei and Pingtung, Taiwan. The previous study documented a decrease in surface temperatures of up to 6.6 °C in the summer and up to 0.7 °C in the winter.

5.5. Challenges in Adopting Colored Pavements

The solar reflection of pavements is a significant characteristic of the pavement associated with climate change’s influence. Increased albedo results in a reduction in the heat island effect and a reduction in net radiative forcing (RF) [254]. A study has demonstrated that a 1% increase in solar reflectance reduces 2.55 kg and 1.27 W/m² of CO₂ and RF, respectively, per square meter of pavement [255]. These estimations do not consider the variation in albedo over time. Conversely, certain researchers incorporated time-varying characteristics when estimating the quantity of CO₂ produced [256]. The model created by Yu and Lu [257] allows for estimating time-dependent CO₂ levels and enables calculations to be performed in both deterministic and probabilistic manners. Akbari et al. [258] have recently found that aging significantly impacts albedo. The implementation of various scenarios and tactics for pavement maintenance would have a significant impact on the albedo over the lifespan of the pavement. The impact of albedo changes over time is significant, especially due to weathering, material degradation, and surface wear, which result in reduced reflective properties in pavements. The long-term effects of albedo are the absorption and retention of more heat by reducing the overall efficiency [259].

Further investigation should be conducted in future pavement life cycle assessments to determine the albedo in relation to maintenance and rehabilitation strategies. Furthermore, technological advancements will impact the long-term reflection of sunlight, such as the development of photocatalytic surfacing and pavements coated with cool paints that reflect infrared light [253]. The potential environmental effects of applying these emerging technologies have not yet been considered in the life cycle assessment of pavements.

6. Future Trends and Directions

The field of pavement engineering is developing rapidly, driven by the demand for road surfaces that are environmentally friendly, durable, and economical. Recent progress in materials and building processes facilitates the development of innovative pavement solutions, such as the transition from traditional asphalt to environmentally friendly colored alternatives. A significant focus in road pavement engineering nowadays is the development of environmentally friendly and sustainable infrastructures. This includes minimizing environmental effects, enhancing traffic safety, and improving transportation efficiency [17].

6.1. Recent Advancements in Materials and Construction Techniques

Smart building materials encompass a variety of substances, such as self-healing materials, innovative materials, and shape-shifting materials that regain their original form after deformation, among others. These materials exhibit the latest innovations designed to improve construction techniques’ durability, sustainability, and effectiveness. The study of green construction methods focuses on implementing sustainable practices and employing environmentally friendly materials. Advanced insulation products, solar-integrated construction, and new waste reduction measures support environmentally responsible building practices. With the increasing importance of sustainability, these technologies aim to reduce the environmental impact of construction projects [260].

6.2. Amalgamation of Smart Technologies

The advancement of technology has significantly improved the field of construction. Digitization has enhanced the efficiency, accuracy, and streamlining of processes. Construction technologies encompass a broad range of tools and techniques, including Building Information Modelling (BIM) for accurate project visualization and generative AI for enhancing design and resource allocation. These tools enhance their productivity and accuracy, indicating a transition towards eco-friendly construction. Integrating sustainability into the building industry is of great significance. Corporations are actively attempting to reduce the emissions produced over the whole lifespan of their projects by utilizing all accessible technology. This is essential for creating a more ecologically sustainable future, and every effort contributes to attaining this objective [260].

7. Conclusions

In comparison to conventional black pavements, modern infrastructure can be transformed using colored pavements, which underscores the superiority of these environmentally friendly materials. While conventional black pavements are cost-effective and easy to use, colored pavements offer several compelling advantages, making them a prominent choice in many contexts. The significance of colored pavements is highlighted in the following paragraphs.

Enhanced Aesthetic Appeal and Effective Urban Design: Out of 95% of flexible pavements, only 4.5% comprise colored pavements. The remaining 91.5% of asphaltic black pavements absorb and retain heat during extreme hot weather. One of the main advantages of using colored pavements is enhancing the aesthetic appeal by improving urban spaces and making them more vibrant for society. Also, these pavements are attractive and pedestrian-friendly because the combination of colors enhances the identity of neighborhoods, highlights pedestrian zones, and supports creative urban planning, making public spaces more enjoyable and engaging for residents and visitors alike.

Better Safety and Visibility: Colored pavements have reflectivity ranging from 0.2 to 0.6 compared to newly constructed asphaltic pavements, which have reflectivity of 0.1. Another outstanding feature of colored pavements is enhanced safety by improving visibility and highlighting specific areas, such as crosswalks, bike lanes, and traffic islands. The contrast between colors increases awareness of these features for drivers and pedestrians, which can lead to reduced accident rates and improved traffic management.

Thermal Performance and Energy-Efficient Materials: Lighter-colored pavements reduce the frequency of heat waves by 41%, and one of the most significant advantages of colored pavements is their impact on UHI effects. Unlike conventional black pavements, which absorb and retain excessive heat, colored pavements, particularly those with lighter or reflective colors, reduce surface temperatures. The significant reduction in ambient temperature increases thermal efficiency in urban areas. Also, it decreases the need for air conditioning in surrounding buildings, leading to substantial energy savings and reduced greenhouse gas emissions.

Longevity and Durability: A well-maintained asphaltic pavement can last 15–30 years. Due to advancements in material testing, durable and sustainable colored pavements can withstand heavy traffic loads and harsh environmental conditions while maintaining their aesthetic qualities over time. This durability translates into longer maintenance intervals and reduced life cycle costs.

Environmental Benefits: Sustainable and resilient pavements align with broader environmental goals by reducing the carbon footprint associated with urban infrastructure. The reduced heat absorption mitigates the UHI effect, and the potential use of eco-friendly materials in producing colored pavements contributes to a more sustainable construction practice.

The superiority of colored pavements over conventional black pavements is manifest in their aesthetic, safety, environmental, and societal benefits. As cities and municipalities prioritize sustainable and efficient infrastructure solutions, the adoption of colored pavements represents a modern approach that addresses both practical and ecological challenges. Implementation of colored pavements can lead to more sustainable urban development, enhanced quality of life, and a positive impact on the environment.