Recycled Waste Materials and Technologies in Asphalt Pavements: Comparison
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Please note this is a comparison between Version 2 by Jason Zhu and Version 1 by Nura Shehu Aliyu Yaro.

Given the prevailing concerns about greenhouse gas emissions, global warming, and the growing demand for renewable resources, the pavement industry, among others, is actively engaged in researching and exploring low-carbon materials and technologies. Despite the growing interest in low-carbon asphalt pavement, there is still a significant knowledge gap regarding the use of various waste materials and technologies to achieve this goal. 

  • recycled waste materials
  • CO2 emission
  • low-carbon road
  • waste materials

1. Introduction

The significance of pavement construction cannot be overstated, especially as populations grow. Raw resources and materials used in the asphalt pavement sector, on the other hand, are depleting, with immediate socioeconomic and environmental consequences [30][1]. Recently, there is much emphasis on the importance of incorporating low-carbon technologies into the manufacturing of pavement materials, particularly those that contribute significantly to greenhouse gas emissions, such as asphalt binder, aggregates, and cement [3][2]. The primary source of CO2 emissions from these materials has been identified during the production phase. Thus, to reduce these emissions, measures such as using materials with lower emission factors and reducing overall material use must be implemented. Therefore, the application of low-carbon-emitting recycled waste materials and technologies is critical in reducing the environmental impact of asphalt pavement. Because of the pavement industry’s continued growth and the corresponding increase in material demand, it is critical to prioritize the development of sustainable and low-carbon alternatives to conventional materials and technologies [8][3].

2. Waste and Reprocessed Materials

Generally, the utilization of mineral aggregates and the hauling of constituents in pavement-laying activities have a significant impacts on CO2 emissions [3][2]. As a result, academics have investigated the feasibility of implementing resource-efficient economy practices in the pavement sector to address this issue. Furthermore, various geographical areas have implemented guidelines and strategies to promote the implementation of circular economy practices. One prevalent method for employing circular economy practices in pavement production is to use waste materials as a substitute for non-renewable resources or raw materials [31][4]. This strategy has the viability to decrease carbon emissions during material production and transportation [11,32][5][6]. Also, these wastes and reprocessed materials are utilized to achieve sustainable development goals, and they are biodegradable and cost-effective [33][7]. There are numerous sources from which the waste materials utilized in asphalt pavement can be sourced; for instance, agricultural waste can be processed and utilized as a replacement for conventional asphalt paving materials [34][8]. Also, construction and demolition waste materials obtained from tearing down old structures and roads, such as concrete, asphalt, and bricks, can be recycled into new asphalt pavement. Furthermore, industrial waste products from sectors including metal casting, tire manufacture, and roofing can be utilized in place of conventional asphalt paving components [35][9]. Moreover, municipal solid waste can also be processed and used as a replacement for conventional asphalt pavement materials, including glass, plastic, and paper. Additionally, waste materials produced by other industries, such as fly ash obtained from coal-fired power stations, can be utilized as alternatives to conventional asphalt paving materials [9,11][5][10]. By utilizing these waste products in asphalt paving, these sectors produce less waste and help harness sustainability. Below are some of the available literatures on various waste materials employed in asphalt pavement to reduce carbon emission.

2.1. Biochar-Based Materials

Asphalt pavement biochar-based materials come from renewable resources like vegetable oil, biomass materials, and bio-based polymers. These materials can be used as alternative asphalt binders or admixtures to enhance the durability of asphalt pavements. The application of bio-based asphalt pavement materials has the potential to lower greenhouse gas production while also promoting the utilization of green energy sources [36][11]. Biochar is a type of material created by pyrolyzing organic materials such as agricultural waste and wood chips. Biochar is also being researched for its ability to reduce carbon footprint gas emissions by adsorbing volatile organic compounds (VOCs) from asphalt and carbon dioxide from industrial processes [37][12]. The Intergovernmental Panel on Climate Change (IPCC) has recognized biochar as a low-carbon technology [38][13]. The average carbon footprint of biochar, on the other hand, varies depending on factors such as raw material source, characteristics, and proposed utilization. The standard carbon emissions of biochar range from 2.0 to 3.3 kg of CO2 equivalent per kg [39][14]. Despite these, biochar applications can substantially cut down greenhouse gas emissions, with estimates ranging from 3.4 to 6.4 Pg CO2 equivalent. Also, the CO2 extraction of biochar from the atmosphere accounts for 1.7 to 3.7 Pg CO2 equivalent, or 49–59% of this reduction [37][12]. Ghasemi, et al. [40][15] examined the use of biochar made from algae as a potential carbon capture strategy for absorbing CO2 from the atmosphere. The biochar was created through pyrolysis, and the researchers discovered that it has the potential to absorb CO2, showing its viability as a low-cost and sustainable method of reducing carbon emissions. The study emphasizes the potential of algae-based biochar for reducing CO2 levels in the atmosphere and reducing greenhouse gas emissions. Also, the potential of biochar to reduce volatile organic compound emissions from asphalt mix was studied in a study conducted by Zhou et al. [41][16] Because of its inherent porosity and carbon negativity, biochar was found to effectively reduce VOC emissions by up to 50% in the study. Interestingly, the adsorption mechanisms were found to be influenced by the type of biochar used, with biochar produced from swine droppings exhibiting physical adsorption and biochar made from wood or straw exhibiting chemical adsorption. Another significant advantage of using biochar as a CO2 adsorbent is its low cost, with the study revealing that it is nearly ten times less expensive than other CO2 adsorbent materials [41,42][16][17]. These findings highlight the potential of biochar as a long-term and low-cost solution for carbon reduction.

2.2. Palm Oil Waste

These refer to the waste and residues of palm oil cultivation and processing, which are classified as solid waste and liquid waste, respectively [43][18]. Because of its negative environmental impacts, waste is a significant environmental issue, but there is growing interest in using it in asphalt pavement [44][19]. The use of palm oil waste also has the potential to help reduce carbon emissions, which is a major concern associated with conventional materials. According to Kanadasan and Razak [45][20] and Alnahhal et al. [46][21], replacing cement with palm oil fuel ash and palm oil shells can result in significant reductions in CO2 emissions of up to 61% and 52%, respectively. Furthermore, palm oil ash and powder geopolymers can lower CO2 emissions by up to 64%. These findings show palm oil waste releases notably lower CO2 − e than conventional cement [47][22]. It is important to note that the total CO2 − e was determined by considering the resources required for processes such as recycle, dumping, and hauling of resources within a 100-km distance [46][21].

2.3. Crumb Rubber

Crumb rubber is a recycled material made from used tires that has desirable properties such as elasticity, durability, and weathering resistance, making it useful for a variety of applications [3][2]. Crumb rubber is incorporated into asphalt binder through both wet and dry processes, with wet processes using a carrier oil to blend the crumb rubber and dry processes directly adding crumb rubber to the asphalt binder. The incorporation of crumb rubber into bituminous mixtures represents a promising sustainable asphalt pavement [48][23]. Various studies have emphasized the possibility of incorporating CR into asphalt mixtures using wet technology to reduce carbon emissions and promote sustainability in the construction industry. Farina et al. [49][24] examined the efficacy of incorporating crumb rubber into asphalt mixtures using the wet manufacturing method, as well as the impact on carbon reduction. When compared to the conventional mixture, the asphalt mixture with 18% CR had a carbon reduction potential of 36% to 44%, according to the findings. It suggests that incorporating 18% CR into asphalt mixtures using the wet technology method is the best way to improve mixture properties while lowering carbon emissions. Also, White et al. [50][25] studied the ecological effects of utilizing crumb rubber in asphalt mixtures. The study discovered that, while the use of crumb rubber increased CO2 emissions during the mixture production phase, it also reduced emissions from natural material production. The apparent contradiction in the study stems in part from the fact that the production and use of crumb rubber have both positive and negative environmental consequences. According to the study, the utilization of crumb rubber in the pavement industry can provide a net environmental benefit, but more research is required to better comprehend the environmental impacts and identify strategies for mitigating the adverse effects while optimizing the positive ones. Furthermore, Wang et al. (2020) performed a comparison study on the environmental impacts of crumb rubber modified mixes and styrene-butadiene-styrene modified mixes and discovered that crumb rubber modified mixes decrease CO2 emissions by 17% when compared to styrene-butadiene-styrene modified asphalt. The reduction can be attributed to tire recycling and the balance of the generated and prevented effects of reprocessing and co-product recovery. The study recommends optimizing crumb rubber content and manufacturing processes to maximize environmental benefits, emphasizing the need for additional research in this area.

2.4. Recycled Asphalt Materials

The recycled asphalt materials include reclaimed asphalt pavement (RAP), which is made by milling and crushing existing asphalt pavement and recycled asphalt shingles which are obtained from roof membranes and incorporated into the asphalt mixture. The application of recycled materials in asphalt pavement decreases the demand for natural raw materials while lowering the environmental impact of disposal. The application of reclaimed asphalt pavement in road rehabilitation can substantially decrease ecological footprint as well as carbon dioxide emissions [3][2]. As a low-carbon technology, recycling RAP materials is becoming increasingly significant in pavement construction. Because of their environmental and economic benefits, hot recycled asphalt mixtures are gaining popularity in pavement engineering. The degree of mixing between the virgin and RAP asphalt binders in these mixtures is critical in influencing the overall performance of the pavement [51][26]. Understanding the blending state of virgin and RAP asphalt binders during the design and manufacture of recycled asphalt mixtures is critical for optimizing their performance. This understanding allows for the optimization of blending procedures and binder formulas, resulting in improved durability, rutting resistance, and fatigue life. Understanding the mixing condition is important for constructing high-performance recycled asphalt mixtures, both in terms of environmental advantages and cost savings [51][26].
Giani et al. [52][27] discovered that incorporating RAP with asphalt can reduce carbon emissions by up to 6.8%. Additional research has found that increasing RAP content can result in significant reductions in carbon emissions. Furthermore, based on the research of Gulotta et al. [53][28], the use of RAP with warm mix asphalts (WMA) has been shown to have substantial advantages for minimizing CO2 emissions (2019). Other studies, conducted by Farina et al. [49][24] and Saeedzadeh et al. [54][29], have discovered that the use of RAP does not always result in improvement, and in some cases, a higher RAP content may even result in higher environmental burdens. This could be because of the greater energy required for the mixing and compaction processes of conventional asphalt mixture when RAP is used. To account for the increased rigidity of RAP, further heating energy and extra intensity must be applied during compaction, resulting in increased energy consumption. Lime stabilization “in situ” and RAP can significantly reduce CO2 emissions and contribute to sustainable construction practices in embankment construction. By reducing the need for virgin materials, lime stabilization alone can reduce emissions by 10.96%, while the integration of RAP and lime stabilization can reduce emissions by 48.27%. RAP is a low-cost, long-term alternative to traditional materials that can reduce the need for virgin materials while also lowering material-production emissions [55][30]. Furthermore, steel industry development is heavily reliant on electricity or coal, which contributes significantly to greenhouse gas emissions. According to Karlsson et al., using recycled steel reinforcement steel could potentially reduce emissions by 5% to 27% [56][31]. Recycling steel uses less energy, produces less waste, and emits less pollution than traditional steel production. The use of recycled steel in reinforcement bars has the viability to considerably lower the environmental impact of steel production.

2.5. Industrial Waste Ash and Powder

In recent years, there has been increased demand in the pavement sector to lower its carbon footprint and contribute to global resources to alleviate climate change. The production of Portland cement, a key component in concrete, is a major contributor to carbon emissions in the pavement industry. Researchers have been investigating various methods, including the use of alternative materials, to decrease the carbon footprint of concrete production. The partial substitution of Portland cement clinker with industrial waste such as fly ash or palm oil fuel ash is one example of this. Using this method, carbon emissions can be significantly reduced throughout the manufacturing process. Less energy is required to produce cement by utilizing industrial waste and by-products, resulting in lower carbon emissions. This method is regarded as a viable strategy for achieving sustainability in the pavement industry. Choudhary et al. [57][32] researched to study the viability of using construction waste materials as fillers in asphalt concrete mixtures to reduce GHG emissions. The researchers compared four construction waste materials to conventional stone dust: concrete dust, glass waste, brick dust, and granite dust. The study discovered that limestone dust mixtures had the lowest carbon emissions, reducing them by 7% when compared to conventional stone filler. White et al. [50][25] investigated the feasibility of using fly ash as a replacement for Portland cement for concrete production. The researchers discovered that by substituting fly ash for a portion of Portland cement, they were capable of lowering CO2 emissions by 29.6%, which is attributed to the fly ash having a lower carbon intensity than Portland cement. Overall, these alternatives provide environmental benefits by lowering the need for natural materials and lowering emissions from material production, resulting in a more durable and long-lasting structure.
Other benefits of employing recycled waste materials in asphalt pavement include lower environmental impact, because using recycled materials instead of virgin ones minimizes the environmental and carbon footprints of pavement construction. It also leads to cost savings, because recycled waste materials minimize the requirement for virgin resources and landfill waste management, resulting in long-term cost reductions. Furthermore, the use of recycled waste materials can increase pavement performance while reducing the frequency of maintenance and repairs. Finally, choosing recycled waste materials contributes to the circular economy by lowering the need for fresh resources and preventing waste from ending up in landfills.

3. Mixing and Production Technology

3.1. Warm Mix Asphalt (WMA)

WMA is a form of asphalt production technology in which asphalt pavement is produced at lower temperatures than standard hot mix asphalt (HMA), leading to lower energy intake, lower greenhouse gas emissions, and greater construction workability [63][33]. WMA is made with a variety of additives that reduce the viscosity of the asphalt binder as well as the amount of energy needed to make and lay the mix. WMA has been demonstrated in studies to provide considerable environmental benefits over HMA, including lower energy use, greenhouse gas emissions, and pollutants like nitrogen oxides. WMA’s lower production temperature can potentially result in cost benefits for pavement construction [19,63][33][34]. WMA technology has gained popularity in recent years, with several publications emphasizing its ability to mitigate CO2 emissions. WMA has been studied as an effective strategy to minimize greenhouse gas emissions [64,65][35][36]. These studies have emphasized the advantages of WMA technology, including lower production temperatures and lower energy usage, which can result in significant CO2 emissions reductions when compared to conventional technologies. WMA technology makes use of additional additives that can be made at lower temperatures varying from 110 °C to 140 °C. According to Vidal et al. [66][37], this temperature reduction can result in a significant reduction in energy usage, estimated at 15% to 16%. Furthermore, as compared to conventional HMA, the utilization of these additives can lower the processing temperature, resulting in energy savings and perhaps lower carbon emissions connected with the manufacturing process. Different compounds reduce CO2 emissions to varying degrees. Also, Sharma and Lee [67][38] investigated the influence of employing Ca(OH)2 integrated zeolite modifier in asphalt mixture production and discovered it can greatly decrease CO2 production from heating the pavement mixture, as well as decreasing fuel usage during the production process. Furthermore, studies by Vaitkus et al. [68][39] and Bueche [69][40] also reported a 30% to 40% reduction in CO2 emission when the warm mix technology was utilized for pavement construction compared to the conventional mix.
Another type of warm asphalt technology is half-hot mix asphalt (HWMA). While the production temperature of WMA mixes is in the range of 100–150 °C, HWMA technology permits asphalt pavement production at a reduction temperature of less than 100 °C [70,71][41][42]. HWMA technology employs chemical additives and foaming processes to minimize HMA mixing and compaction temperatures [70][41]. This method has been found to decrease energy usage and greenhouse gas emissions during the manufacturing process. Additionally, del Carmen Rubio et al. [72][43] assessed the environmental impact of HWMA and discovered that it can reduce CO2 emissions by 58% when compared to HMA throughout the production process. Lower manufacturing temperatures and the application of chemical additives to improve workability and lower viscosity are responsible for the considerable reduction in CO2 emissions. Overall, the WMA technology is a potential solution to lowering the environmental impact of asphalt production and construction while retaining the desired engineering features of the pavement.

3.2. Cold Mix Asphalt (CMA)

CMA is an asphalt production technology in which asphalt pavement is produced at a much lower temperature. It is made by combining aggregates and asphalt binder emulsion without the use of heat, which considerably minimizes dangerous volatile component emissions and fuel usage. Unlike HMA, the interaction between the aggregate and leftover asphalt binder occurs at room temperature [73][44]. However, CMA has some drawbacks, such as hurdles during compaction, the high air-void percentage in compacted mixtures, reduced initial strength, and the prolonged time required to generate completely cured specimens for best performance. Despite these constraints, CMA’s lower environmental effect makes it an appealing option to HMA in some applications [74][45]. Several studies have found that cold mix outperforms hot mix in terms of resource usage and greenhouse gas emissions during the production and placing stages. These benefits have been established in studies [73,74,75][44][45][46]. Goyer et al. [76][47] conducted a comparison study between cold mix and standard hot mix procedures and observed that the amount of energy demand and greenhouse gas emissions for producing a 10 cm layer of pavement material were roughly double for hot mix manufacturing compared to cold mix manufacturing. These data imply that using cold mix asphalt pavement construction can greatly lower the carbon footprint of asphalt pavement construction. Also, Chappat and Bilal [77][48] conducted a study to assess CO2 emissions from cold mixes, which were discovered to emit less CO2 than other forms of asphalt. This is mostly attributed to the use of emulsion asphalt binder and that the mixing materials do not require heating, leading to lower energy demand and emissions throughout the manufacturing process. According to other studies, CMA uses less energy and emits less CO2 during the production process than HMA. HMA has an energy consumption and CO2 emissions of 132.3 kWh/ton and 35.5 kg CO2/ton asphalt mix, respectively, while CMA has just 37.4 kWh/ton and 7.1 kg CO2/ton asphalt mix, respectively [73][44]. Furthermore, the usage of cationic asphalt binder emulsion for asphalt pavement construction was discovered to have 15% to 20% less emission than conventional asphalt binder [73][44]. CMA has also been proven to be more energy-efficient and produces fewer emissions than HMA for the paving and maintenance of rural pavements, which account for a large fraction of the paved surface and are exposed to lower traffic loads. Because of its decreased environmental impact and cost-effectiveness, CMA appears to be an appealing solution for sustainable pavement construction [77][48].

3.3. Cold Recycling

Cold recycling includes removing an existing asphalt pavement, crushing it, and then mixing it with a recycling agent to create a new base material for road construction [78][49]. Cold recycling, unlike typical HMA procedures, does not require the materials to be heated to high degrees, making it a more ecologically friendly and cost-effective alternative [79][50]. Cold recycling technologies are classified into two types: cold in-place recycling (CIR) and cold central plant recycling (CCPR). Cold in-place recycling includes milling existing asphalt pavement, mixing it with a recycling agent, and then laying it back down and compacting it in situ. The cold central plant recycling strategy, on the contrary, requires transporting milled material to a central plant for processing, where it is combined with the recycling agent and then returned to the construction location for placement [79][50]. Cold recycling has major advantages over hot recycling in terms of lowering CO2 emissions. One of the fundamental benefits of cold recycling is that most materials may be recycled on-site, reducing the requirement for significant vehicle travel, and thus lowering emissions [3][2]. Furthermore, because heat is not required for the asphalt mixture, the procedure greatly lessens energy consumption, resulting in lower fossil fuel usage and CO2 emissions. According to Santos et al. [80][51], cold in-place recycling can decrease carbon dioxide emissions associated with raw material collection and mix manufacture by approximately 75% when compared to typical recycling procedures. Furthermore, because there is no energy demand in the production and aggregate sections, cold in-place recycling with emulsion has the lowest energy usage [3,81][2][52]. Cold recycling can also be used with other measures to lower CO2 emissions from asphalt pavement; for example, reducing emissions may occur by optimizing pavement roughness by employing low rolling resistance combinations and further pavement restoration. Improving waste concrete carbonation and surface albedo can also assist in decreasing CO2 emissions [3][2].

4. Energy Saving and Reduction Technology

High-energy-consuming sectors such as the asphalt pavement industry are currently promoting energy conservation and emission reduction [82][53]. Implementation of new energy-efficient and environmentally friendly technologies may increase construction costs, but an examination of the benefits of energy sustainability and emissions mitigation should prioritize emission reduction before taking economic reasons into account [82][53]. According to Liu et al. [83][54], the adoption of renewable energy sources, using electrical energy to power and hybrid fuel systems, are the key decarbonization approaches for road production machinery and equipment. These approaches are widely used to lower carbon emissions in the transportation industry.

4.1. Energy Reduction through Moisture Content

Moisture content, in addition to energy type, has an important influence on carbon emissions throughout the aggregate heating process, and it is relatively easy to adjust. Peng et al. [82][53] investigated how moisture content affected the aggregate heating procedure and carbon emissions when the asphalt binder-aggregate ratio was 5.1%, the mineral filler content was 4%, the mixing plant’s output ability was 300 t/h, and the aggregate heating temperature was 175 °C. According to the findings, the moisture content of aggregates affects the carbon emissions during the heating process. It was also revealed that the impact of moisture content on the aggregate heating process and carbon emissions increased linearly with moisture content. Thus, reducing aggregate moisture content by 1% reduces carbon emissions by 8.92%, saves energy by 9.12%, and lowers construction costs in the making of one tonne of asphalt mixture.

4.2. Energy Substitution and the Material Heating Process

The energy type utilized in asphalt pavement construction makes up for more than 60% of entire carbon emissions, making it an important topic for energy-saving and emission-reducing research. Converting traditional fuels to biomass-based fuels is one effective approach for reducing emissions in construction equipment. Karlsson et al. [56][31] discovered that using biomass-based fuel can result in a substantially higher proportion of emissions reduction, up to 90%. Another effective technology that has the potential to reduce emissions by 67% to 95% is electrified construction equipment. Similarly, a study by Fernández-Sánchez et al. [84][55], was conducted where a 20% biofuel blend named B20 was employed instead of diesel for off-road equipment and transportation machinery. From the studies, it was observed that biofuel reduced CO2 emissions by 13%. Furthermore, the type of energy used has a significant impact on carbon emissions. As a result, more focus is given to altering the energy type and analyzing the consequences on energy savings and emission reduction [82,85][53][56]. Heating asphalt binder leads to about 15% of total carbon emissions because many asphalt mixture mixing units utilize coal for this purpose. Table 1 shows the benefits of switching the energy source for asphalt binder and aggregate heating and using various alternative energy sources. The table demonstrates that using alternative energy sources can significantly reduce carbon emissions during the heating process. While switching from coal to alternative energy sources would increase expenses, it would also cut sulphur dioxide and dust generation, as well as carbon emissions. Also, Table 1 demonstrates that heating the aggregate with natural gas can reduce carbon emissions. Based on the research of Peng et al. [85][56], the asphalt binder factory generates a large portion of CO2 emissions due to the use of fossil fuels to heat and dry aggregates and the acquisition of power to operate the facility. Natural gas, as a replacement for heavy oil, can cut emissions by roughly 27.68% in heating aggregates and by 40.82% when compared to coal. Similarly, moving from electricity to natural gas can reduce CO2 emissions by 65% [86][57]. However, [87][58] claims that plants that rely purely on electricity release more CO2 than gas-powered plants, although this is dependent on the type of electricity generation. Effective CO2 reduction strategies for cement industries include the utilization of bio-based fuel, waste as fuel, and electrical energy [56][31].
Table 1.
The effect of material heating on the emissions reduction.
Parameters Heating of Material
Asphalt Binder Asphalt Binder Aggregate Asphalt Binder Aggregate
Energy Substitution Coal to Oil Coal to

Natural Gas		 Awning Oil to Natural Gas Oil to Natural Gas
Energy saving (MJ) - 12.24 20.44 7.36 34.55
Reduction in emission (mg) 955,180 2,126,377 1,259,370 1,171,197 6,120,587
Reduction in emission (%) 18.34 40.82 5.9 27.53 28.2
Reference [82][53] [3,85][2][56] [82][53] [3,82][2][53] [82][53]

4.3. Emerging Technology and Recycled Waste Materials

Emerging technology and recycled waste materials are critical for lowering carbon emissions in asphalt pavement construction. Technological advancements have resulted in the development of new materials and heating technologies that can promote the use of clean energy and boost energy efficiency. Superconducting heating, solar heating, and infrared radiation heating are some of the new technologies being investigated, all of which increase the application of clean energy and enhance energy efficiency. Furthermore, the usage of environmentally friendly materials such as bio-based fuels, waste-based fuels, and biomass-based fuels can significantly cut carbon emissions. It is possible to efficiently reduce carbon emissions and promote green road construction by using these innovative technologies and materials in asphalt pavement construction [82,84][53][55]. Other types of emerging technology are permeable, perpetual, and smart pavement. A study conducted by Brown [88][59] compared the carbon footprint of perpetual pavement with that of conventional pavement. The study discovered that while perpetual pavement had a greater carbon footprint during its initial construction than conventional pavement, it had lower GHG emissions during its service life. This suggests that, despite greater initial construction emissions, permanent pavement is a more sustainable alternative for decreasing carbon footprint in the long run. Also, a study on a smart road conducted by Guerrieri et al. [89][60] combines technologies like recycled asphalt pavement, lime stabilization, safety restrictions, and cooperative transportation function to demonstrate a considerable reduction in CO2 emissions when compared to traditional methods for road construction. The study calculated the smart road’s life cycle CO2 emissions and its potential for global warming, demonstrating that smart asphalt roads could be an effective strategy for lowering carbon emissions. Moreover, Liu et al. [90][61] conducted a study that compared the CO2 emissions produced by porous asphalt pavement with conventional impermeable asphalt pavement. The study observed that the use of porous pavement greatly lowered CO2 emissions. Also, the porous pavements were discovered to have a cooling impact and might be employed to decrease urban warming.
Furthermore, changing the asphalt pavement construction techniques can also help to reduce carbon emissions during the mixing and paving of asphalt pavement; it is critical to consider using bulk asphalt binder rather than bottled asphalt [82][53]. This is because removing the bucket from bottled asphalt before use is a required step that can contribute to higher carbon emissions. To bypass this process, several asphalt binder mixing stations have begun to use bulk asphalt. Additionally, contemporary asphalt heating tanks use waste heat to heat barrelled asphalt, improving energy utilization efficiency. In conclusion, employing bulk asphalt binders throughout the heating process can significantly cut energy usage and carbon emissions. Using bulk asphalt instead of bottled asphalt will decrease energy usage and carbon emissions by roughly 11.36% [82][53].

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