Conventional Asphalt Mixtures Research Articles

Coal gangue in asphalt pavement: A review of applications and performance influence

The comprehensive utilization of coal gangue is low, and this causes serious environment problems and security risks. The physical and chemical properties of coal gangue were analyzed in this paper, and the estimated value of different chemical components of coal gangue was counted. The physical properties of coal gangue aggregate were analyzed, and performance and its influencing factors of base course mixture with coal gangue aggregate were studied. The influence of coal gangue powder and coal gangue aggregate on performance of asphalt mortar and asphalt mixture was analyzed, and possible influencing factors and function mechanism were discussed. The results showed that heavy metal elements of coal gangue applied into asphalt pavement is not seeped out. The crushing value, water absorption and flat elongated particles content of coal gangue aggregate are generally high, but the compressive strength of base course with coal gangue aggregate is verified to meet the strength requirement. The performance, volume stability and durability of base course with coal gangue aggregate are closely related to aggregate gradation, the type and dosage of cementations materials and aggregate. The high temperature performance, temperature susceptibility and viscosity of asphalt mortar are improved by the addition of different coal gangue powder, and improvement effect of activated coal gangue powder on asphalt mortar performance is better. The low temperature performance and adhesion property of asphalt mortar with chemical activated coal gangue powder are improved. The physical reaction between asphalt and different coal gangue powder is only taken place. The temperature stability of asphalt mixture with coal gangue coarse aggregate has achieved the specification requirement. The water stability and low temperature fracture performance of asphalt mixture with fine aggregate replaced by coal gangue are improved. However, the high temperature performance of above mixture is lower than conventional hot mix asphalt mixture. The research results will provide reference for coal gangue applied into asphalt pavement.

Bio-graded recycling for hot asphalt mixtures with high RAP content considering freeze-thaw

This paper investigates the effects of freeze-thaw cycles on the performance of asphalt mixtures containing 60% rejuvenated asphalt pavement (RAP). Two rejuvenation processes, traditional and bio-graded recycling, are compared regarding high-temperature performance, low-temperature performance, dynamic stability, flexural tensile strength, split tensile strength, water stability, and fatigue performance after various freeze-thaw cycles. The results indicate that bio-graded rejuvenation, compared to traditional rejuvenation, effectively enhances the high-temperature performance, low-temperature performance, water stability, and fatigue performance after freeze-thaw cycles. Both rejuvenations initially meet the dynamic stability requirements but show a decreasing trend with increasing freeze-thaw cycles, with traditional rejuvenation exhibiting more severe degradation. The flexural tensile strength initially exceeds that of conventional asphalt mixtures but decreases significantly with freeze-thaw cycles, especially in traditional rejuvenation. Additionally, freeze-thaw action increases the internal void ratio, affecting water stability and anti-freezing ability, particularly in traditional rejuvenated mixtures. These findings underscore the impact of freeze-thaw cycles on rejuvenated asphalt mixtures and emphasize the importance of innovative rejuvenation techniques for sustainable pavement.

Performance Comparison of Conventional and Biopolymer-modified Asphalt Mixtures for Airport Pavement

Raising the temperature of airport pavement softens its surface, leading to rutting or thermal cracking. As aircraft manufacturers lean toward heavier planes with higher tire pressures, challenges arise. To tackle these problems, incorporating polymers like high-density polyethylene into asphalt binders has emerged as a solution. This study investigates biopolymer-modified asphalt, blending conventional asphalt with highdensity polyethylene and pine resin. This study aims to compare the performance of asphalt mixtures using both conventional and biopolymer-modified asphalt binders. Various tests‒physical, Fourier transform infrared, energy dispersive X-ray, dynamic shear rheometer, volumetric properties, Marshall stability, retained stability, indirect tensile strength and Cantabro loss-were conducted. The results highlighted that integrating pine resin and high-density polyethylene increased the performance grade (PG) of the conventional asphalt from PG 64 to PG 82. Asphalt mixtures using biopolymer-modified binders exhibited superior stability, stiffness and resistance to moisture damage compared to those with conventional asphalt. These properties aligned with the specifications outlined in Item P-401 of the Federal Aviation Administration Advisory Circular 150/5370-10H. Keywords: Pine resin, High-density polyethylene, Biopolymer-modified asphalt, Performance grade 64, Performance grade 82

Research on the preparation and self-healing performance of microwave-induced functional steel slag asphalt mixture

This study explores the potential applications of steel slag and tire pyrolysis oil (TPO) in creating self-healing road construction materials, aiming to address environmental concerns related to industrial waste and to extend the service life of roadways. A novel functional steel slag asphalt mixture was developed, utilizing steel slag as the aggregate and TPO as a healing agent. This agent permeates the pores of the steel slag, with microwave induction facilitating its controlled release. The research embarked on identifying the optimal process for preparing the functional steel slag aggregate through orthogonal experiments. It puts forward the optimum parameters of microwave induction based on the results of the low-temperature bending beam test and evaluates the effectiveness of the microwave-induced asphalt mixture’s self-healing. The study revealed that the recommended process for preparing functional steel slag aggregates is vacuuming the steel slag submerged in TPO for 30 minutes, followed by a soaking period of 10 minutes under standard atmospheric pressure, and concluding with a 48-hour standing period after removal from the TPO. Under this process, the absorption rate of TPO by steel slag reaches its maximum. Employing the Marshall test design method, the optimal asphalt-aggregate ratio was determined to be 5.15%. Significantly, the microwave heating rate of the functional steel slag asphalt mixture was found to be 3.25 times that of a conventional limestone asphalt mixture. The recommended microwave induction parameters were established at 700 W of power for a duration of 80 seconds. Initially, the crack healing rate reached 64.6%, which decreased to 47.6% after five microwave cycles. Remarkably, the healing rate of the functional steel slag asphalt mixture outperformed that of the ordinary steel slag asphalt mixture without TPO by 69.5% after the same number of cycles. These findings offer valuable contributions to the development of self-healing road construction materials, presenting a promising path for enhancing the durability of road infrastructures while addressing environmental challenges posed by industrial waste.

Influence of Petroleum-Based and Bio-Derived Recycling Agents on High-RAP Asphalt Mixtures Performance

Reclaimed asphalt pavement (RAP) has been utilized as a potential partial substitute for virgin asphalt binder in asphalt mixtures. However, a primary concern with increasing RAP content in asphalt mixtures is the cracking potential, attributed to the aged RAP asphalt binder (RAP-binder). To address this, the use of petroleum-based and bio-derived recycling agents (RAs) in enhancing the cracking resistance of high-RAP asphalt mixtures has been explored. The objective of this study is to ascertain the effectiveness of six RAs in mitigating cracking in high-RAP asphalt mixtures. The RAs considered include petroleum-crude-oil-derived aromatic oil, soy oil, and four types of tall-oil-derived phytosterol (industrial by-product, intermediate, purified, and fatty acid-based). The RAs’ dosages were optimized, based on RAP-binder and unmodified asphalt binder properties, to produce target PG 70-22 asphalt binder when incorporated in asphalt mixtures containing 30% RAP. To assess the engineering performance of these 30%-RAP asphalt mixtures for each RA, a conventional asphalt mixture incorporating styrene-butadiene-styrene (SBS)-modified PG 70-22 asphalt binder without RAP or RAs was benchmarked for comparison. Mechanical tests performed included Hamburg wheel-track testing (HWTT), intermediate-temperature fracture tests (semi-circular bend, Illinois flexibility index, and IDEAL cracking tolerance), and thermal stress-restrained specimen tensile strength test to evaluate permanent deformation, intermediate-temperature cracking resistance, and low-temperature cracking resistance, respectively. Results showed that petroleum-crude-oil-derived aromatic oil and tall-oil-derived fatty-acid-based oil RAs were able to rejuvenate RAP-binder as measured by the cracking tests performed. Further, the use of these RAs did not adversely impact the asphalt mixtures’ permanent deformation performance.

Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt

Abstract Recently, researchers have been moving toward using local waste as an alternative for construction materials. Using these wastes to pave roads is one of the essential recycling methods, which aims to reduce the consumption of natural resources and environmental pollution resulting from the difficulty of decomposing these wastes. In the Middle East, especially in Iraq, Date Palm fiber is widely available as a local waste material. The aim of this research is to evaluate the performance of a developed asphalt mixture with palm leaf powder (PLP) as a partially substituted mineral filler. The Marshall mix design method produced the asphaltic mixes with ordinary Portland cement and PLP as mineral fillers. PLP was included in three rates denoted by 10, 20, and 30% by the weight of the mineral filler. Marshal stability, flow, bulk specific gravity, air voids, voids in mineral aggregates, voids filled with the binder, the indirect tensile strength, and the indirect tensile strength ratio of the PLP mixture were measured and compared with those of the conventional asphalt mixture. Based on the findings of this study, 20% of the Portland cement could be replaced with PLP, at which all of the properties of the enhanced mixture met the requirements of the Iraqi specifications. Then, the asphalt mix with 20% PLP was tested to assess its resistance against fatigue cracks. The results support the usage of waste PLP in pavement construction, enhancing its properties, which would also be very effective as an eco-friendly material.

Induction heating and induced healing evaluation of the asphalt concretes incorporating conductive aggregates exposed to microwave radiation

This study investigates the application of aggregate-based conductive additives, including steel slag, Iron slag, and ferrosilicon, in asphalt concretes for induction heating and induced healing purposes. The research focuses on evaluating the mechanical properties, induction heating capabilities, induced crack healing, environmental impacts, and cost of various conductive asphalt concretes. The Gray Relation Analysis (GRA) technique is then employed to determine the sustainability ranking of these mixtures based on the aforementioned criteria. The mechanical properties of the asphalt concretes were evaluated through the Indirect tensile strength at intermediate temperature and semi-circular bending tests at intermediate and low temperatures. The homogeneous induction heating rate of the mixtures was also examined. Additionally, the healing indices for the breaking-healing cycles were investigated. The environmental impacts and fabrication cost of conductive asphalt concretes were compared to identify the most sustainable conductive mixture with optimal performance and durability. The results demonstrate that the addition of aggregate-based conductive additives significantly improves the mechanical properties and homogeneous heating rates under microwave radiation. Furthermore, the conducted tests indicate that the introduced conductive asphalt concretes possess the ability to heal and restore their mechanical properties after damage or cracking. Moreover, the sustainability analysis reveals that the mixtures incorporating steel slag, especially asphalt concrete incorporating fine steel slag, are more sustainable and cost-effective compared to conventional asphalt mixtures. These findings provide valuable insights for road infrastructure and pavement design, aiming to incorporate innovative and environmentally friendly materials and methods to enhance the healing competencies and performance of flexible pavements.

A novel foaming additive derived from waste polyethylene terephthalate (PET) for low-carbon warm mix asphalt

Plastic pollution is growing relentlessly due to the careless disposal of waste plastic products. This study focuses on converting waste plastic bottles into a foaming additive for the production of eco-friendly warm mix asphalt (WMA) for paving purposes. The additive, namely PET-TETA, was synthesized from waste polyethylene terephthalate (PET) via an aminolysis process. Its chemical and physical properties were characterized by the scanning electron microscope (SEM), X-ray diffractometer (XRD), and thermogravimetry-differential thermal analyzer (TG-DTA) tests. The WMA mixtures were prepared using PET-TETA and a commercial foaming additive, and their properties were studied and compared to a conventional hot mix asphalt mixture. The performances of the asphalt mixtures were characterized through the indirect tensile stiffness modulus, moisture susceptibility, and immersion Hamburg wheel-tracking tests. The findings revealed that PET-TETA was a semicrystalline material containing approximately 26 % hydration water, which could be released gradually during the preparation of asphalt pavements. The performance of the WMA mixture utilizing PET-TETA was comparable to the other two asphalt mixtures, and it exhibited higher strengths and better resistance to stripping. Therefore, it is promising to apply PET-TETA as a sustainable and effective WMA additive for paving purposes, providing a solution to the issue of waste plastic disposal.

Microwave deicing properties and carbon emissions assessment of asphalt mixtures containing steel slag towards resource conservation and waste reuse

A large amount of solid waste, such as steel slag (SS), is generated annually. At the same time, the shortage of road construction materials is becoming a concern. In this study, to recycle and reuse SS as a substitute for natural aggregates to achieve resource conservation and sustainable development of roads were conducted. First, the electromagnetic performance of SS was explored to evaluate its wave-absorbing properties. Next, the effect of different SS contents on heating properties, surface temperature, heating uniformity, and ice melting time (IMT) were investigated. Finally, the carbon emissions assessment (CEA) of conventional asphalt mixture (CAM) and steel slag asphalt mixture (SSAM) was compared. Results indicated that SS has ferromagnetic behavior and higher electromagnetic parameters, showing better wave-absorbing properties than limestone. There were three stages during microwave heating (MH): ice melting, moisture emitting, and stabilization. In addition, heating uniformity tends to be poor with the increase of SS, and samples with 100 % content of SS have the highest standard deviation of 21.04 °C and 20.77 °C after 270 s at −10 °C and − 20 °C. Samples containing 50 % SS have the best microwave deicing properties, which can reduce the IMT by 28.57 % to 46.18 % at different initial freezing temperatures and ice thickness compared to CAM. Furthermore, CEA revealed that CAM and SSAM's carbon emissions over road construction's life cycle are similar (around 27,000 kg) and originate mainly from the mixing and raw material extraction phases. However, SSAM leads to better environmental and economic benefits and provides an exemplary resource conservation and waste reuse solution.

Development of improved porous asphalt mixtures with high porosity levels

Porous asphalt (PA) mixtures are gaining wider acceptance in pavement construction due to their benefits in terms of road safety, noise mitigation and stormwater management. Increasing demands, such as those imposed by climate change, require the design of mixtures that provide enhanced functional properties, while keeping the same durability of conventional porous asphalt mixtures. This study proposes different experimental PA mixes with higher air voids content and suitable structural capability than a conventional PA mixture. The functionality of the mixtures was evaluated in accordance with total and interconnected air voids, while the mechanical performance was assessed in terms of raveling resistance both in dry and wet conditions, tensile strength, and moisture sensitivity. The binder drain down was also verified. In a first stage, the experimental results were analyzed through descriptive and inferential statistics tests. As multiple responses were obtained, principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) were applied to explore the association pattern among the test results and experimental designs. The study concluded that PA mixes with air voids content of up to approximately 28% and admissible values of resistance can be designed. The use of polymer modified binder (PMB) and the inclusion of fibers and hydrated lime (HL) was essential for the formulation of the mixes.

Micro-structural characteristics of asphalt mixture and its effect to mechanical performance based on two-stage mixing method

Conventional asphalt mixtures are prone to material separation during mixing, causing rutting, loosening, and cracking of the pavement. This study proposes a two-stage mixing method to address these problems. The theoretical asphalt film thickness is calculated, and a physical index of the mixture for aggregates with different specific surface areas is used to determine the optimal asphalt mixing ratio. The microstructural characteristics and mechanical properties of the mixtures are evaluated using digital image processing, laboratory experiments, and correlation analyses. The results show that the two-stage mixing process mixes the aggregate more thoroughly, resulting in a uniform asphalt film with sufficient contact between the asphalt particles, improving the mixture’s mechanical performance. The results of this study can be used to improve the design of asphalt mixtures and reduce the use of petroleum asphalt.

Performance of Hybrid Asphalt Mixture through the Stability and Tensile Strength

Introduction: The stability and tensile strength of asphalt mixtures play a crucial role in pavement durability, primarily due to the challenges associated with cracking. This study investigates the utilization of a hybrid asphalt mixture comprising hybrid materials: Palm Oil Fuel Ash (POFA), garnet waste and sawdust to enhance the modified asphalt performance. Aims: The objective is to examine the hybrid materials’ influence towards the mechanical properties of the hybrid asphalt mixture, specifically focusing on the Indirect Tensile Strength (ITS) as well as the Marshall stability test. Methods: To achieve this, hybrid materials were finely ground and sieved to 25µm before being incorporated into the mixture. The Marshall mix design procedure was conducted, utilizing hybrid binders at concentrations of 0% (control), 3% 6%, and 9%. The effects of the hybrid asphalt mixture on stability, flow, stiffness, and ITS were assessed at the optimal binder content. Results: The findings indicate that the hybrid asphalt mixture reveals enhanced Marshall stability, stiffness, flow, and ITS values compared to conventional asphalt mixtures. Notably, hybrid asphalt mixtures with 6% binder concentration demonstrate the most significant enhancement in terms of Marshall stability and ITS. Conclusion: This correlation suggests that the incorporation of POFA, garnet waste, and sawdust as hybrid materials in the hybrid asphalt mixture possesses a positive effect on the overall mechanical properties of the pavement. Highlights: • POFA, garnet waste, and sawdust increased the stability of the hybrid asphalt mixture. • POFA, garnet waste, and sawdust increased the tensile strength of the hybrid asphalt mixture. • Hybrid asphalt mixture performs positively towards flow and stiffness.

Effect of Ceramic Waste Powder on Rutting and Dynamic Modulus of Asphalt Mixture

Abstract: Aggregates, asphalt binder, and mineral filler are blended in appropriate proportions to guarantee the desired characteristics of asphalt. Besides from aggregates and bitumen, the role of filler material in HMA is critical since it affects the mechanical characteristics and serviceability particularly when subjected to wheel load. The current research investigated the effect of Ceramic Waste Powder (CWP) used as filler in terms of rutting, and dynamic modulus of asphalt mixtures when used in different proportions 20%, 40%, 60%, 80% and 100% by weight of Marshall Specimen, and the results were compared to conventional mixture employing stone dust as a filler. The performance testing revealed that the rut resistance increases with the increase in CWP content from 40 % to 60 % in asphalt mixtures and showed 21 %, and 58 % decrease in rut depth value to that of conventional asphalt mixture at 55 ℃ respectively. While dynamic modulus increases as the frequency of the applied load increases from 0.1 Hz to 25 Hz and it decreases when the temperature of the dynamic modulus test increases from 4.4 °C to 54 °C. Higher values of Dynamic Modulus are observed at 21.1°C and 37.8 °C temperature for all frequencies. Therefore, using CWP as filler in asphalt not only increases the mechanical properties of HMA but also be a suitable approach towards reducing ceramic waste pollution.

Development and evaluation of cenospheres/polyethylene glycol composite microcapsule for temperature-regulation of asphalt pavements

ABSTRACT In this study, a phase change material microcapsule was produced by using cenospheres as the microcapsule shell, polyethylene glycol 2000 as the phase change material, and silica sol as the sealing material. The produced CenoPCM microcapsule was analyzed using scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The thermal properties and stability of the CenoPCM were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and a thermal cycling test. The results showed that the phase change temperature and enthalpy of the CenoPCM were 55.7°C and 101.4 J/g, respectively, with a mass loss of 2.35% at 200°C. After 200 thermal cycles, the mass change remained stable at 2.05%. An outdoor test was conducted to assess the impact of CenoPCM on the thermal performance of asphalt mixtures. In comparison with conventional asphalt mixture specimens, the maximum temperature differences at depths of 2, 5, and 8 cm below the surface of the phase change asphalt mixture specimens were 4.9°C, 6.4°C, and 5.9°C, respectively. Finally, the influence of CenoPCM on the performance of asphalt mixtures was evaluated, revealing a promising future for its use in asphalt pavements.

Study on the influence mechanism of recycled concrete aggregate on strength of asphalt mixtures

Recycled concrete aggregate (RCA) has great potential use in pavement. However, unclear characteristics of RCA and its relationship with the properties of asphalt mixture hinder severely its promotion. The objective of this study is to characterize the microscopic morphology and structure of RCA, further investigate its impact on the strength of asphalt mixture and associated mechanisms, by means of various test method. Results showed that cement mortar was the vital factor to affect the properties of RCA. Hence, the asphalt mixtures with RCA had characteristics of higher air voids (VV) and voids in the mineral aggregate (VMA), lower asphalt saturation (VFA), compared with conventional asphalt mixtures (CAM). In addition, according to the results of Micro-Scratch (MS) test, the compression depths of aggregate, interfacial transition zone (ITZ) and asphalt mortar in RAM are larger than that in CAM. Therefore, the influence of RCA on the performance of asphalt mixture is mainly in the following two aspects: reducing the strength of asphalt mortar; decreasing the skeleton strength of asphalt mixtures.

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.

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.

A Top-Down Approach Based on the Circularity Potential to Increase the Use of Reclaimed Asphalt

Resource depletion and climate change, amongst others, are increasingly worrying environmental challenges for which the road engineering sector is a major contributor. Globally, viable solutions that comply with the principles of circular economy (CE) are being investigated that can replace conventional asphalt mixtures in a post-fossil fuel society. The use of reclaimed asphalt (RA) is a widely used and well-established method to reduce the environmental and economic impacts of asphalt mixtures while increasing their circularity. However, RA’s market supply and demand have not yet been systematically analyzed and established. Moreover, the actual circularity potential and the opportunity of re-circulating RA in a closed-loop model have not yet been methodically defined. To address this, a three-layered framework to quantify and assess the circularity potential (Ω) of RA has been developed. To give stakeholders and legislative bodies a simple method to assess the opportunities available to them to become “more circular”, a novel equation has been formulated. This takes the form of a three-level indicator that considers: technical aspects, the effect of the RA market, and the legislative restrictions. A case study in Germany was structured and undertaken to develop and verify the proposed approach. The results indicate that the available RA is insufficient to cover the needs of asphalt mixture production; even though RA production is significantly lower than the actual need of asphalt mixtures, it is not utilized in its entirety. An impactful step forward is the alteration of the regulations to support the higher utilization of RA in asphalt mixtures, and subsequently, the increased circular opportunity and potential of RA. Thus, Circularity potential (Ω) is a composite indicator that can support stakeholders, designers, and asset managers during the process of decision-making, to follow more circular operational, design, and asphalt pavement management patterns.

Enhanced Induction Heating and Self-Healing Properties of Steel Slag Powder Based Asphalt and Asphalt Mixture under Microwave Irradiation.

This paper aims to study the application feasibility of steel slag powder (SSP) in replacing limestone powder (LP) to enhance the heat release and self-healing properties of asphalt and an asphalt mixture. First, the microwave-heating characteristics of SSP and LP asphalt mortar were analyzed, and the differences in the microstructure and chemical composition between SSP and LP were compared. Secondly, through the DSR frequency sweep test, the optimal healing temperature of the two asphalt mortars was determined. Finally, asphalt mixtures with different SSP contents were prepared by replacing part of LP in the mixture in a gradation with SSP. Under microwave radiation, the temperature distribution of the mixture was explored, and the self-healing properties and factors affecting the healing were analyzed. Results demonstrated that there are metal oxides with high electromagnetic parameters such as Fe2O3 and CaO in SSP, therefore, asphalt and a mixture containing SSP were seen to have excellent microwave absorption capacity. The healing temperature of the two kinds of asphalt mortar was between ~50 °C and 60 °C. Under microwave radiation, the temperature of the asphalt mixture increased with the increase in SSP content, and the temperature difference decreased with the increase in SSP content. Asphalt mixtures with an LP content of 30%, 40%, 50%, 60%, and 70% replaced by SSP increased the healing index by 8.7%, 17.3%, 22.1%, 26.9%, and 27.7% compared with conventional asphalt mixtures. Temperature is the most important factor affecting the healing behavior of the asphalt mixture. With the increase in the damage times of the asphalt mixture, the overall healing index of the asphalt mixture showed a downward trend. However, the healing index of an asphalt mixture containing SSP can still be maintained at more than 50% after repeated mechanical damage.