Conventional Asphalt Research Articles

Optimization of asphalt cold recycling containing ordinary and waste additives based on life cycle assessment considering the road traffic level- case study: Coal preparation plant

In recent years, extensive research has been conducted on the use of second-hand or waste materials in the road pavement construction layers. Most of these studies evaluated the mechanical properties of materials and emphasized the environmental benefits of using waste materials for use in road construction projects, regardless of the environmental consequences. The present study intends to compare the life cycle of waste materials with standard materials and determine the optimal conditions for the selection of waste materials based on environmental criteria by considering life cycle assessment (LCA) and several environmental indicators. The analysis considered emulsified cold recycled asphalt with different types of activator fillers including cement, coal waste+lime and coal waste ash+lime. Also, the recycled pavement was compared with that of conventional asphalt pavement in this environmental assessment. The LCA analysis was performed for pavements with design traffic of 0.1–100 million equivalent single axle loads (ESALs). In order to design the pavements structure, 96 resilient modulus tests were done for 32 recycled mixes. Environmental indicators under study included energy consumption, abiotic depletion potential (ADP), global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP). The collected data for the studied functional unit was undergone an environmental analysis in SimaPro software. Apart from a standard case, parametric study was accomplished to analyze the effect of activator additive content. Accordingly, it was concluded that for the standard case, the traffic level or in other words the highway grade is of the main importance criterion in choosing the rehabilitation method based on environmental indicators. Emulsified cold recycled pavement with waste additives can be environmentally justified only in projects with low to medium traffic levels of less than 5–10 ESALs. For projects with medium to high traffic levels, only the ordinary recycling method with cement was comparable to conventional reconstruction.

Effect of Multiple-Walled Carbon Nanotubes (MWCNTs) on Asphalt Binder Rheological Properties and Performance

Growing traffic loads, soaring summer temperatures, and moisture damage will render conventional asphalt binder insufficient to maintain the performance standards of asphalt concrete pavement. Thus, it is necessary to modify the virgin asphalt using various polymers or nanomaterials. The primary goal of this research was to examine the rheological effects of combining multiple-walled carbon nanotubes (MWCNTs) and styrene butadiene styrene (SBS) in an asphalt binder. In this study, MWCNTs and SBS were mixed with virgin asphalt at concentrations of 1%, 3%, and 5% by weight. The performance grade (PG) and asphalt binder qualities were determined through Superpave system testing. The addition of 1% MWCNTs had no effect on the (PG) of virgin asphalt, whereas the addition of 3% and 5% MWCNTs resulted in increases of 2° and 4°, respectively. When 1% SBS is added to asphalt, the PG rises by an average of 1°; when 3% and 5% SBS are used, the PG rises by an average of 2° and 3°, respectively. The results also showed that the rutting parameter (G ∗ /sin) increased by 10%, 73%, and 208% when asphalt was changed with 1%, 3%, and 5% of SBS, and by 18% and 130% when MWCNTs were applied.

Effect of different waste plastic modifiers on conventional asphalt performance: optimal preparation parameters determination and mechanism analysis.

The typical treatment of waste plastics has become a global environmental problem. In light of recent developments, waste plastics used as asphalt modifiers offer an efficient approach to solve this problem. This paper studied the effects of three kinds of waste plastic-modified asphalts (WPMA), with polypropylene (PP), polyethylene (PE) and ethylene-vinyl acetate copolymer (EVA) as their respective modifiers, on the conventional asphalt performance. Furthermore, an orthogonal experimental design (OED) was used to determine the preparation parameters of WPMA. Thereafter, thermogravimetric-differential scanning calorimetry (TG-DSC) and Fourier transform infrared spectroscopy (FTIR) were employed to expound the mechanism of WPMA. It was then subsequently ascertained that the optimum preparation parameters of PP-modified asphalt (PPMA) and PE-modified asphalt (PEMA) were 170 °C, 3000 rpm, and 30 min, while the optimum preparation parameters of EVA-modified asphalt (EVAMA) were 180 °C, 3000 rpm, and 30 min. In addition, WPMA displayed better high-temperature performance and are inherently more suitable for pavement in high-temperature regions. Ultimately, this study will effectively solve the disposal of waste plastic and promote the research and application of WPMA in the future.

Static and cyclic performance of polyurethane foam adhesive bound soil–rubber mixtures under drained conditions

The major drawbacks of a railway track include noise, vibration, and aggravated track degradation. Resilient mats and asphalt have been increasingly used in recent years to mitigate this noise and vibration. However, these materials are quite expensive. Conventional asphalt is very stiff and brittle, making it more prone to cracking. The present work aims to develop a novel material that can be used as a base layer in ballasted and slab tracks. The current research proposes a sustainable and resilient base course layer comprising ground rubber (GR) and polyurethane foam adhesive (PFA). In this study, the performance of GR embedded in the sand is investigated. The use of PFA-treated sand with and without GR is then explored. The optimum dosage of PFA for soil and GR for treated and untreated soil is recommended based on static direct simple shear (SDSS) and cyclic direct simple shear (CDSS) tests. SDSS tests were performed to evaluate the monotonic performance of all mixtures. CDSS tests were performed to assess the long-term performance of these different mixes under repeated cyclic loading (50,000 load cycles) and varying cyclic shear stress amplitude. It is shown that PFA helps reduce the settlement and enhance soil shear strength, while GR increases the damping ratio of the soil. The optimum dosage of PFA is recommended 10%. The optimum GR content for untreated and PFA-treated soil is recommended 5 and 10%, respectively.

Effect of Fine Aggregates and Mineral Fillers on the Permanent Deformation of Hot Mix Asphalt

Conventional asphalt pavement is the dominant mode of passenger and freight traffic in Pakistan. As a result, asphalt pavements suffer from various failures, where rutting, corrugation, and fatigue cracking are significant. Fine aggregates and mineral fillers play a pivotal role in providing structural integrity in asphalt pavements when subjected to traffic and the environment. The current study aims to examine the effects of various locally accessible fine aggregate and mineral filler materials on the interlocking properties of asphalt mixtures in relation to internal friction angle, rutting resistance, and controlling environmental pollution as an indirect benefit, thereby reducing wastes. Four distinct asphalt samples were prepared using cinders, stone dust, natural sand, and surkhi as fine aggregates and mineral fillers, as a full replacement, as per ASTM D1559, confirming the Asphalt Institute’s gradation for asphalt wearing course. Optimum binder contents (OBC) of 4.40%, 4.1%, 6.57%, and 6.63% by weight of Marshall specimen were concluded for asphalt samples containing stone dust, natural sand, cinder, and surkhi, respectively. The results revealed that surkhi, natural sand, stone dust, and cinder all showed a diminishing tendency in developing interlocking properties in asphalt mixtures at internal friction angles of 35°, 33.7°, 32°, and 28.4°, respectively. The wheel tracking test results revealed that the asphalt samples made with surkhi as fine aggregates and fillers have the highest rut resistance, whereas samples made with cinders as fine aggregates and fillers have the lowest rut resistance. The direct shear test showed that fine aggregates with a larger angle of internal friction are significantly more stable in terms of rut resistance than fine aggregates with a smaller angle of internal friction. The current research will help to prevent pavement rutting and corrugation by adding surkhi into asphalt pavements, with the reduction in brick kiln waste providing an indirect benefit.

Effect of Recycled Aggregates and Polymer Modified Bitumen on the Marshall Properties of Hot Mix Asphalt- A Case Study

The main objective of this study was to assess the performance and physical properties of hot mix asphalt mixes incorporating recycled aggregates from demolished concrete and compare them with an unmodified hot mix asphalt mixture. Using recycled aggregates offers potential environmental benefits by reducing the load on landfill sites associated with demolished concrete waste. Hot mix asphalt mixes were prepared using the Marshall mix-design technique, with varying proportions (0%, 25%, 50%, and 75%) of recycled aggregates replacing the coarse virgin aggregates. The resulting mixes were compared to a control sample. It was observed that with an increase in the proportion of recycled aggregates, the stability of the mixes decreased. Additionally, the number of air voids and voids filled by mineral aggregates increased. However, laboratory tests indicated that the recycled aggregates modified mixes exhibited comparable performance to conventional hot mix asphalt mixes while providing improved environmental advantages through the recovery and reuse of waste concrete aggregates. These findings highlight the potential of utilizing recycled aggregates in hot mix asphalt as a sustainable approach in asphalt pavement construction.

Study of Factors Influencing Moisture Susceptibility of Warm-Mix Asphalt Using the Surface Free Energy Approach.

The application of warm-mixing technology brings considerable economical and environment benefits by decreasing the mixing temperature during warm asphalt mixture (WMA) production. However, the possible water residue also generates concerns for moisture susceptibility. For deep investigation on the influencing factors and mechanisms of the moisture susceptibility of WMA, surface free energy (SFE) tests and laboratory tests are applied in this research. A novel indicator based on SFE, namely, effective adhesion work, is proposed to assess the asphalt-aggregate adhesion with different moisture contents. Then, given the mixing procedure of the dry-mixing method, an advanced three-phase model as a form of asphalt-aggregate-warm mixing additive is introduced, improving the conventional two-phase asphalt-aggregate model for better reflecting the separate addition of warm-mixing additives during mixing. Afterwards, the influence of aggregate type, asphalt type, aggregate moisture content, warm-mixing agent type, and the warm-mixing process on the moisture susceptibility of WMA is analyzed utilizing the models and indicators proposed. Finally, the validity of the SFE indicator is verified by comparing the calculation of effective adhesion work with freeze-thaw splitting test results. The results show that all of the above factors impact the moisture susceptibility of WMA by influencing the interfacial adhesion, with the effect of moisture content being the most significant. Meanwhile, effective adhesion work and the three-phase model brought out in this research are proven to be feasible to characterize the adhesion properties of WMA, offering theoretical support to the research on warm-mixing technology.

Load response and fatigue life of cement-stabilized macadam base structure considering dynamic and static load differences and tension-compression modulus differences

The conventional semi-rigid base asphalt pavement (SRBAP) construction is designed with the classical theory of linear elastic mechanics. There is a significant discrepancy between the calculation results of the pavement structure load response and the measured results, which leads to inaccurate structural resistance and load response calculations. For this reason, this work depended on the actual structure of the SRBAP, took the linear elasticity theory as a contrast, and considered the difference between dynamic and static loads or the difference between the compressive and tensile modulus of pavement materials. Thus, the pavement structure response to load under three conditions is calculated, and five mechanical indexes are selected for comparative analysis. Furthermore, based on the calculated mechanical response, the structural fatigue life of the cement-stabilized macadam (CSMB) was then calculated, replacing the design index in the fatigue cracking model with the underside tensile stress or equivalent stress. The results demonstrated 20–30% variations between the calculated mechanical responses to dynamic and static stresses. Additionally, there is a substantial discrepancy between the strain computed using the bimodulus theory and the traditional linear elasticity theory, with a maximum divergence of 40%. In the meantime, the fatigue life of the CSMB produced using various design indices is noticeably different, and the fatigue life achieved using equivalent stress as the design index is significantly higher than that obtained using underside course tensile stress. Following is a relationship between the CSMB's fatigue life calculated by underside course tensile stress: viscoelastic theory (dynamic load) > bimodulus theory (tension–compression modulus difference) > classical linear elastic theory; The relationship of fatigue life represented by equivalent stress is as follows: viscoelastic theory > classical linear elastic theory > bimodulus theory.

Engineering properties, microplastics and emissions assessment of recycled plastic modified asphalt mixtures

The use of recycled plastic in asphalt is raising interest since contributing to increase the sustainability of roads pavements. The engineering performance of such roads are commonly assessed but scarcely correlated to the environmental impacts of incorporating recycled plastic in asphalt. This research encompasses an evaluation of the mechanical behaviour and environmental impact of introducing low melting point recycled plastics, low density polyethylene and commingled polyethylene/polypropylene, to conventional hot mix asphalt. While this investigation reveals a reduction in moisture resistance between 5 and 22 % contingent on the plastic content, the benefits include a significant 150 % enhancement in fatigue resistance and 85 % improvement in rutting resistance when compared with conventional hot mix asphalt (HMA). From an environmental perspective, high-temperature asphalt production with higher plastic content resulted in decreased gaseous emissions for both types of recycled plastics up to 21 %. Further comparison studies indicate that microplastic generation from recycled plastic-modified asphalt is comparable to that from commercial polymer-modified asphalt products, long employed by the industry. Overall, the use of low melting point recycled plastics as an asphalt modifier is promising since offering both engineering and environmental benefits when compared to conventional asphalt.

Design and experimental evaluation of reflective grouting asphalt concrete for durable cooling asphalt pavement

Based on grouting asphalt concrete, titanium dioxide (TiO2) and magnesium phosphate cement materials were selected as reflective grouting materials (RGM) to prepare reflective grouting asphalt concrete (RGAC), which was used to improve the reflective capacity, mechanical strength and cooling effect of pavement. The reflectance and mechanical properties of RGM were characterized through color characteristic, mechanical strength, reflectance and bonding strength tests. The results show that the spectral reflectance of RGM was 4.61 times higher than that of asphalt, but the addition of TiO2 reduced its mechanical and bonding strength. The visual and cooling effects of RGAC were analyzed by digital image processing technology and indoor irradiation test. The addition of TiO2 improved the visual uniformity and lightness of the surface, which had a good reflection effect. Compared with conventional asphalt mixture, the maximum surface temperature of RGAC reduced by 20.2 ℃. RGAC is a potential material of thermal reflective asphalt pavement construction.

Influence of Wetting-Drying cycles on the linear viscoelastic properties of asphalt mixtures

The top asphalt layers of pavement structures are subjected to loading demands and multiple environmental factors. Even though existing studies on moisture damage in asphalt mixtures have demonstrated the deleterious effects of water on different mechanical properties of these materials, the impact caused by changes in the partial saturation during the application of wetting–drying cycles on the linear viscoelastic properties of the mixture is an unexplored field. This study quantifies, for the first time, the changes in these properties (i.e., dynamic modulus, |E*|, and phase angle, ϕ) of a conventional asphalt mixture subjected to multiple wetting–drying moisture vapour cycles. The testing specimens were conditioned at five different relative humidity (RH) environments that were increased (wet path) or reduced (dry path) gradually, causing different saturation levels within their microstructures. The magnitude of |E*| and ϕ of the specimens was measured after reaching a steady state condition at each individual RH environment. In total, the specimens were subjected to five wetting–drying cycles and to a total of 41 dynamic modulus tests. The results corroborate that the degree of saturation impacts the linear viscoelastic properties of the mixture and show the irreversible effect of wetting–drying cycles on these properties. Since the dynamic modulus is an input parameter in the design of flexible pavements, the results also suggest that the degradation of this property due to changes in the partial saturation under field conditions could be included as part of existing mechanistic-empirical design methodologies.

Characteristics and properties of asphalt mortar containing FO filler

As a preventive maintenance method, microwave self-healing is an effective method for early repairing small cracks in asphalt mixture, reducing maintenance costs and prolonging service life. However, asphalt mixtures containing aggregate-type wave-absorbing agents have a common problem of uneven heating. Asphalt mixture was prepared by partially replacing the limestone filler with ferroferric oxide (Fe3O4, FO), and the healing performance under microwave heating was studied. The rheological properties of asphalt mortars with FO and the fluidity of conventional asphalt mortars were studied by dynamic shear rheometer (DSR). Then, the magnetostatic properties and electromagnetic parameters of FO fillers were analyzed by vibrating sample magnetometer (VSM) and vector network analyzer (VNA). Finally, the semicircular bending (SCB) samples were studied by the breaking-microwave healing experiment. The results show that FO fillers have obvious ferromagnetism, and they mainly rely on magnetic loss for energy conversion. FO is beneficial to the improvement of high temperature rheological properties of asphalt mortar but not to low temperature rheological parameters; the replacement ratio of FO to limestone filler should not exceed 50%. The flow healing behavior of asphalt mortar is greatly affected by temperature, which is the fundamental reason for the self-healing of asphalt mixture. The heating efficiency of the asphalt mixture containing FO filler is significantly improved under microwave irradiation; the FO filler has a slightly negative effect on the initial strength of SCB samples but can significantly improve the healing rate after microwave.

Research on aging performance of hot mix fully recycled epoxy asphalt mixture with 100% RAP utilization-Take the surface course as the application target

With the continuous development of concepts such as “environmental protection” and “sustainable development”, it is difficult for the existing technology of asphalt pavement recycling to meet the needs of efficient utilization of Recycled Asphalt Pavement(RAP). The purpose of this research is to explore the application potential of the fully recycled epoxy asphalt mixture(FREAM), which achieves 100% utilization of RAP, in asphalt pavement. By testing the dynamic modulus, the difference between FREAM and conventional asphalt mixture was explored, and the problems that need to be paid attention to when FREAM is used as the surface course were analyzed. Through two aging methods with different mechanisms, the pavement performance of FREAM before and after aging was studied, including high-temperature performance, low-temperature performance, moisture sensitivity, and fatigue performance. Through this research, it is found that the dynamic modulus of FREAM is higher than that of conventional asphalt mixture, and it has better deformation resistance. However, the influence of the difference in modulus between layers needs to be paid attention to when used as a surface course structure. The FREAM has strong resistance to long-term thermal oxidation aging, and the road performance before and after aging meets the application requirements of the surface course. However, the anti-ultraviolet aging ability of the FREAM is weak, and it is not suitable for the surface of the surface course and more suitable for the middle course and lower layer.

Stiffness evaluation of Forta Fibre Reinforced Asphalt Concrete (FRAC) mixture under different pulse repetition load

Pavement structure can be designed either as a flexible or a rigid pavement based on its structural behaviour, with flexible pavements being frequently favored due to its advantages. One of the major problems that normally occurred in road construction was pavement distresses due to the quality of the materials. Numerous studies were carried out to explore sustainable ways to improve the pavement performance especially on modification of the asphaltic concrete in construction phases. This paper investigates the effect of Forta-Fi fiber on stiffness performance of hot mix asphalt mixture (HMA). In this respect, conventional asphalt binder grade 60/70 and Nominal Maximum Aggregate Size (NMAS) 12.5mm were used in the preparation of asphalt mixture specimens as specified in Superpave mix design method. Performance of modified samples incorporating 0.3, 0.5 and 0.7% of total mixture were evaluated for resilient modulus accordance to ASTM D4123 using Universal Testing Machine (UTM). The samples were tested at 25°C and 40°C with pulse repetition period 1000ms, 2000ms and 3000ms to simulate low, medium and high volume of traffic. As a result, the resilient modulus values of modified asphalt mixture improved 38% with 0.3% additive of Forta-Fi at 25°C with 3000ms pulse repetition period, while at 40°C with 3000ms pulse repetition period improved 23% with 0.5% additive of Forta-Fi. Based on these studies, the addition of fibers reinforcement into the asphalt mixture has a significant effect on resilient modulus of fibers reinforced asphalt mixture.

Comparison of Asphalt Concrete-Wearing Course (AC-WC) characteristics using 60/70 asphalt penetration and Elvaloy modified asphalt

The performance of the asphalt mixture is affected by the asphalt characteristics and the gradation of the aggregate. Polymer-modified asphalt has been widely used to overcome road pavement damage such as cracking, spalling, yielding, and damage due to deformation due to grooves, curling, or rutting. Polymer-modified asphalt has been widely used, both from plastomers and elastomeric types. Elvaloy modification asphalt resulted from the conventional asphalt mixing process of 60/70 with Elvaloy additives from Dupont that are elastomer using RET (Reactive Elastomer Terpolymer) technology. This study aimed to compare the characteristics of the AC-WC mixture using 60/70 penetration asphalt and Elvaloy modified asphalt. The study began by making a paved mixture using 60/70 penetration asphalt with the middle-graded aggregate. The Elvaloy modified asphalt has three aggregate gradations: lower limit, middle, and upper limit gradation. Test objects were made as many as 156 test objects to obtain Optimum Asphalt Content (OAC) values, then using OAC values, made 36 test objects for the Marshall test; 4 test objects for Wheel Tracking Machine (WTM) testing. The Marshall and WTM tests determine the performance of 60/70 penetration asphalt and Elvaloy modified asphalt on the AC-WC mixture. The research results of the properties test showed that Elvaloy modified asphalt has a better penetration value, softening point and ductility than 60/70 penetration asphalt. Marshall’s test results provided the highest Stability and flow value in the Elvaloy modified asphalt mixture. From the results of the WTM test, only the middle grade of Elvaloy modified asphalt meets the specification.

An Investigation into the Behavior of Disposable Face Masks in Modified Bitumen for Sustainable Transportation Pathways

Since December 2019, COVID-19 infection rates have risen considerably, and the virus is currently widespread around the world. Following the COVID-19 outbreak, the production of medical waste has skyrocketed. Disposable face masks are considered medical waste. Alternative measures must be implemented to assist in reducing medical waste disposal, which can result in serious public health problems and have a negative influence on the environment. In this regard, this research was conducted to investigate the effect of disposable face mask (DFM) ash with varied rates ranging from 5% to 20% by weight on bitumen with a 5% increment to be utilised as an alternative material in asphalt pavement. A series of physical and rheological tests were conducted on the bitumen samples to study the behavior of the DFM ash in bituminous material. Overall, the physical and rheological test results revealed that introducing 20% DFM ash to the modified bitumen was unable to achieve the same properties as with the conventional SMA14 asphalt binder. However, the modified bitumen penetration grade PEN 60/70 has improved the properties and quality of the asphalt in the flexible pavement. In addition, utilising the DFM waste in road construction would be a sustainable technique for protecting the environment by minimising face mask waste caused by the COVID-19 epidemic while lowering the pavement’s construction cost. These research findings may be commercialised to generate revenue in the construction industry for sustainable transportation pathways.

Using Cement as Filler to Enhance Asphalt Mixes Performance in Hot Climate Regions

This paper investigates the addition of different percentages of ordinary Portland cement as a filler in conventional asphalt concrete for a range of heavy traffic. Road pavement agencies in hot areas face the daunting challenge of preserving their pavements in a fair to good condition to increase their lifespan. This challenge is due to the high occurrence of permanent pavement deformation via rutting, which is one of the major distress factors influencing pavements. This is a particularly serious issue in hot and arid countries which are closely associated with various aggravating factors. These aggravating factors include the choice of bitumen binder viscosity, the type of bitumen, the available low-quality materials, and the high environmental temperatures. Ultimately, poor performance will show within the first few years of service as permanent deformations such as rutting, shoving, and depressions. The examined properties include the resilient modulus and the resistance to rutting. Findings indicate that the resistance to rutting and the rigidity of the asphalt concrete are both substantially increased as the cement content is increased. Moreover, to meet the heavy traffic spectrum requirements, increasing the embedded cement content in the asphalt concrete improves pavement structural capacity. Finally, based on the rigidity expected for different cement levels, design curves are provided for pavement design in hot climates using low quality aggregate materials.

Preliminary optimization design of inverted asphalt pavement structure using response surface method

Inverted asphalt pavement (IAP) has the advantage of maintaining good performance under the condition of thin asphalt concrete (AC) layer compared with conventional flexible asphalt pavement. The stress-dependent property of unbound aggregate base (UAB) plays an important role in mechanistic responses of IAP. The focus of this paper is to quantitatively analyze the function of UAB’s stress-dependent property on the structure combinations design of IAP using response surface method (RSM). In this paper, an improved UMAT subroutine was developed to characterize the stress-dependent stiffness of UAB. The three-dimensional FE pavement model was established and validated against KENLAYER calculation and field FWD test deflection data. The critical mechanical response, maximum principal strain and bulk stress, were selected to evaluate the fatigue performance of AC layer and stress-dependent property of UAB. The significance analysis was conducted to describe the relationship between input variables (thickness and stiffness of structural layers) and the critical mechanical response variables. An optimization design method to balance the fatigue performance and stress-dependent property was proposed to obtain the optimal structure combinations of IAP. Research results demonstrate that the thickness and stiffness of the AC and UAB layers present a clearly significant impact on the maximum principal strain at the bottom of AC layer and the bulk stress in UAB, particularly during the summer season, whereas the thickness and stiffness of CTB and stiffness of subgrade have a minor impact. The responses of bulk stress and maximum principal strain can be empirically predicted by 2FI and Quadratic models. Optimal structure combinations (13.6 cm AC layer and 10 cm UAB) were recommended after quantifying the stress-dependent properties of UAB. The recommended structural combination has good fatigue resistance and can also efficiently minimize AC and UAB layer thickness.

Feasibility of Pellet Material Incorporating Anti-Stripping Emulsifier and Slaked Lime for Pothole Restoration

Climate change has caused a surge in abnormal weather patterns, leading to a rise in cracks, plastic deformation, and pothole damage on road surfaces. In order to fabricate a ready-mix admixture of warm asphalt mixture (WMA) for pothole restoration, this study aimed to develop a neutralized anti-stripping material in pellet form by extruding a combination of slaked lime and a liquid emulsifier additive. Slaked lime (1% by weight of aggregate) was chosen for its ability to enhance moisture resistance, while a liquid emulsifier (wax + vegetable oil + surfactant + water) was added to create a pellet-type stripping inhibitor for WMA. After successfully fabricating the pellet admixture, this study evaluated the performance of two asphalt mixtures: conventional Slaked Lime Hot Mix Asphalt (LHMA) and the Pellet-Type Anti-Stripping Warm Mix Asphalt (PWMA). Several compatibility tests were conducted to evaluate the quality of the developed material. The results showed that the fatigue resistance of the developed material (PWMA) improved by over 20%, indicating an extended fatigue life for the pavement. The LHMA and PWMA met the quality standard for asphalt mixtures, with a TSR value of approximately 83%. Both mixtures demonstrated improved rutting resistance compared to HMA. The PWMA required 16,500 cycles, while the LHMA required 19,650 cycles to reach a settlement of 20 mm, indicating better moisture resistance than the control mix (13,481 cycles). The modified mixture performed properly in the Cantabro test, with loss rates below 20%, indicating their ability to retain their aggregate structure. The PWMA also showed superior resistance to plastic deformation, with a 12.5% lower phase angle (35°) at a reduced frequency of 10−3. In general, the application of PWMA not only prolongs the pavement lifespan but also reduces the production temperature by over 20 °C, leading to lower emissions and energy consumption. This makes it an environmentally friendly option for pavement applications and contributes to sustainable road construction practices.

Biomass valorization toward sustainable asphalt pavements: Progress and prospects

To cope with the global climate crisis and assist in achieving the carbon neutrality, the use of biomass materials to fully or partially replace petroleum-based products and unrenewable resources is expected to become a widespread solution. Based on the analysis of the existing literature, this paper firstly classified biomass materials with potential application prospects in pavement engineering according to their application and summarized their respective preparation methods and characteristics. The pavement performance of asphalt mixtures with biomass materials was analyzed and summarized, and the economic and environmental benefits of bio-asphalt binder were evaluated. The analysis shows that pavement biomass materials with potential for practical application can be divided into three categories: bio-oil, bio-fiber, and bio-filler. Adding bio-oil to modify or extend the virgin asphalt binder can mostly improve the low temperature performance of asphalt binder. Adding styrene-butadienestyrene (SBS) or other preferable bio-components for composite modification will have a further improved effect. Most of the asphalt mixtures prepared by using bio-oil modified asphalt binders have improved the low temperature crack resistance and fatigue resistance of asphalt mixtures, but the high temperature stability and moisture resistance may decrease. As a rejuvenator, most bio-oils can restore the high and low temperature performance of aged asphalt and recycled asphalt mixture, and improve fatigue resistance. Adding bio-fiber could significantly improve the high temperature stability, low temperature crack resistance and moisture resistance of asphalt mixtures. Biochar as a bio-filler can slow down the asphalt aging process and some other bio-fillers can improve the high temperature stability and fatigue resistance of asphalt binders. Through calculation, it is found that the cost performance of bio-asphalt has the ability to surpass conventional asphalt and has economic benefits. The use of biomass materials for pavements not only reduces pollutants, but also reduces the dependence on petroleum-based products. It has significant environmental benefits and development potential.