Abstract

To evaluate influence of external environment and material composition on skid-resistance durability of high viscosity modified asphalt (HVMA) mixture, the accelerated abrasion test was selected to simulate decay of skid resistance for asphalt mixture by setting different test conditions. The influence of aggregate gradation, asphalt type, ambient humidity and overload on skid-resistance durability of asphalt mixture was discussed, and the significant effect of selected factors on skid-resistance durability of asphalt mixture was revealed. The results show that the skid-resistance durability of SMA-13 (Stone Mastic Asphalt) mixture is better than OGFC-13(Open Graded Friction Course) and PA-13 (Porous Asphalt) mixture under different conditions, and attenuation rate of different indexes of SMA-13 mixture is 1.6–2.2% and 0.8–2.1% lower than compared with OGFC-13 and PA-13 mixture. The attenuation rate of texture depth for asphalt mixture is closely related to aggregate gradation and asphalt, but the attenuation rate of british pendulum number for asphalt mixture with the same mineral aggregate is only significantly affected by the asphalt. The skid resistance of SMA-13 and PA-13 mixture is improved slightly by addition of high viscosity modified asphalt. The attenuation rate of texture depth of SMA-13 and PA-13 mixture with HVMA is reduced about 0.6–3.0% and 2.2–4.2% than SBS modified asphalt, but the attenuation rate of british pendulum number of above mixtures is increased about 1.2–1.6% and 0.3–1.7%. The skid-resistance durability of asphalt mixture with TPS (TAFPACK-Super) and SINOTPS high viscosity agent is better than HVA (High viscosity additive). The skid-resistance durability of asphalt mixture based on texture depth is improved under wet condition. However, the skid-resistance durability of asphalt mixture for british pendulum number gets worse due to water intrusion. The skid-resistance durability of asphalt mixture is rapidly decreased under overload condition. The influence of overload and SBS modified asphalt on skid-resistance durability of asphalt mixture is higher than ambient humidity and HVMA. This paper will provide foundation for high viscosity modified asphalt applied in asphalt pavement.

Introduction

The surface layer of asphalt pavement is directly contact with tire, and automobile stability during running is affected by skid resistance of asphalt pavement. The skid resistance of asphalt pavement is inevitably degraded under the synthetic effect of vehicle load, natural environment and asphalt aging, so the traffic accident is occurred frequently [1]. The skid resistance of asphalt pavement remains at a high level, and it is conducive to reduce traffic accident rate. Now, the skid resistance of asphalt mixture is required to evaluate in the quality acceptance of asphalt pavement. But the skid resistance of asphalt pavement in the early stage is inconsistent with skid-resistance durability. The skid-resistance durability of different asphalt mixture needs a long term to test. Zhu et al. [2] has evaluated the long-term skid resistance of SAS-16, GAC-16 and AC-16 mixture with SBS modified asphalt, and found that the long-term skid resistance of asphalt mixture is affected by the oil-stone ratio (asphalt-aggregate ratio), gradation type and coarse aggregate type. Besides the initial and final values as well as the attenuation trend of texture depth for AC-16, SAS-16 and GAC-16 mixture is different, which is related to that the 4.75 mm sieve passage rate of AC-16 is higher than SAS-16 and GAC-16. Huang et al. [3] has studied that frictional coefficient of AC-13I, SAC-13 and SMA-16 mixture with different coarse aggregate is little difference at the initial stage, but the BPN of AC-13I, SAC-13 and SMA-16 mixture is 15.5, 25 and 27 after repeated loading of 70 × 104 circles, which is related to surface feature and polish value of coarse aggregate. Tan et al. [4] has found that skid-resistance durability of SMA-10 mixture is lower than UTAC-10 mixture, but the initial BPN of SMA-10 mixture is better. The aggregate gradation of above mixture is fundamentally the same, but the optimum asphalt content of UTAC-10 mixture is relatively low. So it is necessary to study the skid-resistance durability and influencing factors of asphalt mixture. Besides, the skid-resistance durability of asphalt mixture is closely related to mechanical property of aggregate, volume ratio of mixture, nominal maximum aggregate size[5], [6], [7]. But the influence of external conditions on skid-resistance durability of asphalt mixture has been paid little attention.

Conclusions

The skid resistance of OGFC and PA mixture is better than SMA mixture, but SMA mixture has the good skid-resistance durability. The attenuation rate of different indexes for SMA-13 mixture is 1.6–2.2% and 0.8–2.1% lower than compared with OGFC-13 and PA-13 mixture. The mixture and asphalt type have significant influence on the attenuation rate of texture depth for asphalt mixture, but the attenuation rate of british pendulum number for asphalt mixture with the same mineral aggregate is only significantly affected by the asphalt type.

The skid resistance of SMA-13 and PA-13 mixture is improved by the addition of high viscosity modified asphalt, and skid-resistance durability of SMA-13 mixture with different asphalt is better than PA-13 mixture. The evaluation index of skid-resistance durability of asphalt mixture is affected by the asphalt.

The skid-resistance durability of asphalt mixture with SINOTPS additive is better. The attenuation rate of texture depth for asphalt mixture with SINOTPS additive modified asphalt is lower than TPS additive and HVA. The attenuation rate of british pendulum number for asphalt mixture with SINOTPS additive is in the middle of selected high viscosity modified asphalt.

Abstract

     Frost and thawing damage asphalt in cold climates. Water that enters the pores of asphalt at low temperatures may accelerate its degradation. Water can expand into pores, altering the void content and shape, thus affecting the asphalt’s internal structure and fracture properties. We can develop more durable asphalt types if we understand how void topology changes with freeze–thaw cycles. The purpose of this study is to establish a correlation between the mechanical properties of asphalts and the topological properties of voids. To determine their internal structure, various asphalt types representing dense asphalt and asphalt with voids were made and X-rayed before and after each freeze–thaw cycle. We also obtained the mechanical properties of asphalt and correlated them with the void properties. It was found that dense asphalt has the lowest degradation rate in wet conditions characterised by non-connected gaps, which was approximately constant with freeze–thaw cycles; however, dense asphalt was least durable under dry conditions compared with asphalts with more voids. Due to its high water retention rate, asphalt with a 10% void content degraded at an accelerated rate during the initial cycles. As a result of bigger voids, asphalt with a higher pore content plateaued in later cycles due to reduced water retention.

Introduction

     Asphalt mixture is a heterogeneous material made of aggregates, mineral filler, and a bituminous binder. It is compacted at temperatures ranging between 135 °C and 155 °C; asphalt mixtures may also include voids, up to more than 20 % of the total asphalt’s volume, depending on the gradation and compaction methodology. Asphalt is the most used material to build pavement surfaces. Asphalt undergoes different mechanical loads and environmental conditions during its lifetime, leading to crack and damage and reducing its lifespan [1], [2]. In particular, the extreme environmental condition in cold regions with large temperature fluctuations [3] and the water permeation are some of the most harmful deterioration mechanisms that may affect asphalt, leading to thermal stress [4], loss of adhesion at the interface between aggregate and bitumen [5], and loss of cohesion of the binder [6].

Conclusions

     Several types of asphalt with acceptable air void contents ranging from 3% to 14% were examined for their influence during freeze–thaw cycles, where a correlation between differences in air void topology and changes in mechanical properties was established. According to the results in this study, the topological properties evolution under freeze–thaw cycles was influenced by three different phenomena: (1) volume increase of the existing voids and formation of small cracks, (2) voids coalescence, and (3) cracking and new voids formation. The voids were analysed using X-ray CT scans after every freeze–thaw cycle, and the mechanical properties were measured from 3-point bending tests. The following conclusions were obtained:

     The three different asphalts had different behaviours when exposed to freeze–thaw cycles, attributed to the different aggregate size distributions and air void topologies. Hence, the durability of asphalt to freeze–thaw cycles could be controlled by carefully selecting the aggregate gradation, aggregate morphology and air void topologies.

Hot-mix asphalt pavement recycling is widely practiced for its economic and environmental benefits. Existing studies are mainly focused on the engineering properties of reclaimed asphalt pavement (RAP) materials, without considering their impacts on the generated asphalt fumes—a widely recognized environmental hazard. The effects of using RAP on asphalt fumes are systematically studied in this research. Asphalt binders from different sources were used to create RAP materials in three aging conditions. Asphalt fumes were generated and collected from non-aged asphalt materials as well as RAP materials, followed by gravimetric and chemical analysis of the collected asphalt fumes. RAP materials were found to generate greater amount of particulates in asphalt fumes as compared with non-aged ones. RAP materials are also associated with increase in the types and concentrations of polycyclic aromatic hydrocarbons (PAHs) in asphalt fumes, especially those PAHs with more than three aromatic rings. PAHs increase in asphalt fumes is particularly noticeable for RAP created in the natural aging condition. It is reasonable to conclude that asphalt fumes generated from RAP become more hazardous, hence deserving more attention from researchers and practitioners. The mechanisms of the increase in PAHs are discussed, in addition to field exposure studies and mitigation measures.

Introduction

The majority of paved roads around the world are surfaced with hot-mix asphalt (HMA) pavements (Mallick et al., 2017), which are also widely used for the construction of airport runways, parking lots, and other facilities. It is estimated that about 1.6 trillion metric tons of asphalt mixtures are produced annually for the construction, rehabilitation, and maintenance of the paved civil infrastructures (NAPA and EAPA, 2011). The life expectancies of HMA pavements range from a few years to several decades. At the end of their service lives, HMA pavements need to be demolished, creating a large amount of wastes. In the United States alone, for instance, about 100 million tons of asphalt pavements are milled off annually in road resurfacing and widening (MAPA, 2019). The demolished pavements, however, still contain valuable aggregate and asphalt binder. If unattended, they form a significant source of inert solid wastes. Therefore, asphalt pavement recycling has become a common practice for cost saving and environmental conservation (Alam et al., 2010; Wang, 2016).

1- Introduction

2- Materials and Testing

3- Testing

4- Results and discussion

5- Conclusions

References

Abstract

Recycled Concrete Aggregate (RCA) is considered to be a potential substitute for natural aggregates in asphalt mixtures. Despite some contradictory results achieved by researchers, it is believed that RCA treatment can improve quality of recycled asphalt mixes considerably. In this research, a two-stage treatment was applied on coarse RCA materials in order to improve their properties. The treatment was consisted of first soaking RCAs in Hydrochloric Acid (HCl); second impregnating the treated RCAs into Calcium Metasilicate (CM). The pores of RCAs were filled with CM particles. Substituting virgin aggregates with different amounts of coarse RCA materials into HMA resulted in increased tensile properties of mixes as tested in indirect tensile fatigue test (ITFT). The treatments resulted in reduced moisture sensitivity of mixes. The improvements were mostly attributed to the reduced water absorption of RCA materials. Moreover, morphological characteristics of the treated coarse RCA materials were determined using Scanning Electron Microscopy (SEM) photography.

Introduction

Over the past decades, the growing amounts of Construction and Demolition Waste materials (CDW) have been a great concern for the environmental protection agencies [1]. Unlike the proper actions of recycling these materials and also re-using in different applications, the general trend is to use virgin mineral aggregates for constructing roads and other civil engineering projects. This trend will certainly have adverse effects on the environment [2]. However, lack of adequate landfill areas for damping CDW materials, and the detrimental environmental issues have conducted highway agencies to perform research works so that to find alternative solutions for recycling CDW materials [3]. In fact, road construction projects, that require huge amounts of aggregates are proper sites for using these recycled materials [4]. Production of mineral aggregates in quarries, not only have negative impacts on the environment, but it results in emission of large amounts of CO2 gases during the processing phases [5].

For sustainable pavement construction, this research paper aims to investigate the feasibility of using Waste Cooking Oil (WCO) and Waste Engine Oil (WEO) as rejuvenators on the rheological properties of aged bitumen extracted from Reclaimed Asphalt Pavement (RAP). The aged bitumen was extracted from milled RAP recruited from an old pavement. The rheological characteristics of the rejuvenated bitumen were determined by penetration, softening point, Brookfield viscosity, Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR) tests. In addition, the chemical composition of virgin (control), aged and rejuvenated bitumen by WCO, and WEO was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray (EDX). The quality of the rejuvenated bitumen was also evaluated by the Scanning Electron Microscopy (SEM) imaging technique. Based on penetration and softening point testing results, the optimum percentages of the waste oils were found to range from 3.5 to 4.0% for the WCO and from 5.5 to 6.0% for the WEO. The aged bitumen properties were significantly improved by rejuvenators as evidenced by the chemical analysis (FTIR and SEM/EDX) along with the ratio of asphaltenes to maltenes. Furthermore, the surface morphology was renovated as well as the fundamental physical properties of the rejuvenated aged bitumen. Additionally, the rejuvenated bitumen showed less tendency to short-term aging as confirmed by the DSR results. BBR results of rejuvenated aged bitumen samples exhibited comparable performance to those of the control samples at different low temperatures having a performance grade of PG 64-28. Moreover, rejuvenated 100% RAP mixes were found to cope with Egyptian requirements for heavy traffic as binder courses and medium traffic as wearing courses in terms of Marshall stability and flow. Finally, Indirect Tensile Strength (ITS) results were within the specification limits.

Introduction

Despite the limited resources, about 110 million tons of bitumen are used annually in the highway industry worldwide [1]. Bitumen is an organic hydrocarbon material with high thermal sensitivity. Exposure to elevated temperatures during mixing and placement of the Hot Mix Asphalt (HMA), and the environmental conditions throughout the pavement service life, lead to aging of the asphalt binder. The loss of volatiles and oxidation of bitumen (as bitumen is a hydrocarbon material) are the main causes of aging, which result in higher viscosity and stiffer bitumen [2]. Aged bitumen tends to lose its flexibility and turns into a brittle material that is prone to crack easily [3]. There has been an enormous increase in the use of Reclaimed Asphalt Pavement (RAP) worldwide as an economic and environmentally sound alternative for sustainable pavement construction [4–6]. However, some road authorities are hesitant in encouraging the use of RAP in pavement construction on a large scale due to some limitations. The barriers that limit the use of high RAP percentages (more than 15%) are the high variability in milling processes, mixing RAP from different sources, different properties of aged bitumen than required for virgin bitumen, in addition to one more additional material to care about during HMA manufacturing [6,7].

Icing on asphalt pavement may lead to potential hazards for driving safety. To reduce the security risk, this paper aims at preparing a hydrophobic emulsified asphalt coating on asphalt pavement by adding a hydrophobic agent (HPA, Polytetrafluoroethylene powder) to emulsified asphalt. Considering the factors influencing hydrophobic effect, such as roughness of hydrophobic agent, dosage and incorporation method, the ice-repellency of hydrophobic emulsified asphalt coating was characterized by means of contact angle. It was found the hydrophobic properties of emulsified asphalt were significantly affected by roughness, dosage and incorporation methods of HPA and the highest contact angle was 94.3
when the HPA with 1250 meshes and dosage of 15% was added by the external addition method. Through the interlayer shear test and the indoor anti-icing test, hydrophobic asphalt pavement could reduce the bond strength between pavement and ice so that the ice layer could be easily broken and cleared, and the bond strength could be reduced by about 40% at 0.3 kg/m2 dosage of hydrophobic emulsified asphalt. It was proved that the skid resistance performance of the hydrophobic emulsified asphalt coating could conform to the requirements of the specification. The addition of interfacial agent can significantly improve the adhesion between emulsified asphalt and aggregates. These findings demonstrated the potential of using hydrophobic emulsified asphalt coating on highways in adverse weather to provide better anti-icing performance and contribute to traffic safety in winter.

Introduction

After the rain and snow in winter, the accumulated water or snow on asphalt pavement is easy to freeze in the lowtemperature environment, resulting in a sharp decline in the anti-skidding performance of the pavement [1]. On the pavement with ice and snow, the emergency braking distance is greatly increased which poses a serious threat to the safety of life and property of pedestrians and vehicles even causes serious traffic congestion inducing a series of traffic accidents [2]. In view of the icing problems on asphalt pavements, the frequently-used methods of removing ice currently include artificial mechanical snow removal, spraying chloride ice-melting agents, thermal melting technology include microwave heating, thermal cables, solar energy collection technology, and electrically conductive pavements [3–11]. Nevertheless, the methods above will either aggravate pollutants, corrode metal structures, reduce the performance of asphalt binders or be quite expensive. A large number of literatures have shown that hydrophobic surfaces have good hydrophobic and anti-icing properties [12,13]. The larger contact angle and the smaller wetting lag angle can effectively make the droplets rolling and sliding on the surface of the object, thus making it difficult to freeze.

The effects of cement and emulsified asphalt contents on the performance of cement-emulsified asphalt mixture were systematically evaluated, including the indirect tensile strength, compressive strength, modulus of resilience, tensile strength ratio, dynamic stability, maximum bending strain, and Cantabro loss. In addition, the mesoscopic images and void characteristics of cement-emulsified asphalt mixtures with different material compositions were obtained, using scanning electron microscopy (SEM) and computed tomography (CT). The results indicated that at a constant cement content of 3%, when the emulsified asphalt content increased from 6% to 9%, the indirect tensile strength, compressive strength, and modulus of resilience first increased and then decreased. At a constant emulsified asphalt content of 8%, when the cement content increased from 0% to 4%, the indirect tensile strength first increased and then decreased, and the compressive strength and modulus of resilience each reached its maximum at a cement content of 3%. The addition of cement significantly improved the high-temperature stability and moisture stability of the asphalt mixture but was not conducive to its low-temperature performance. In addition, a minimum Cantabro loss was observed at a cement content between 2% and 3%. The mesoscopic void structures formed in different cement and emulsified asphalt contents also significantly affected the mechanical properties and mixture performances.

Introduction and literature review

A cement-emulsified asphalt mixture contains cement, emulsified asphalt, and aggregates, and is mixed at a normal temperature. In the mixture, the emulsified asphalt aggregates and demulsifies, and the cement hydrates, crystallizes and solidifies, forming a new engineering material [1,2]. Emulsified asphalt is liquid at normal temperature, and the process of mixing, paving and compacting with aggregate and cement would cause emulsion asphalt to demulsification [3,4]. Part of the moisture produced by the demulsification was consumed by the hydration reaction of the cement, and the other part was lost by evaporation. The asphalt and aggregate heating process were avoided throughout the construction process, thus avoiding the emission of asphalt smoke from heating, thereby greatly reduced energy consumption and carbon emissions during construction [5,6]. Therefore, it has been applied more and more in civil engineering, especially in pavement engineering. Because a cement-emulsified asphalt mixture contains both cement and emulsified asphalt, which have different engineering properties, the properties of the mixture are thus between those of cement and emulsified asphalt [7–9].

Mechanical characteristics of the asphalt binders and mixtures were enhanced by utilising modifiers. The crumb rubber modifier has been introduced to the asphalt modification as an environmentally friendly procedure of scrap tires, to improve the mechanical characteristics of the asphalt. This study aims to modify the dry method for mixing crumb rubber modifier with asphalt and aggregate based on the binder mix design. To achieve this goal crumb rubber modified asphalt mixtures were prepared and tested by applying various tests such as Marshall Stability test, indirect tensile strength test, and wheel tracking test. Three mixing methods of CRM were studied regarding evaluating the stability, rutting, and moisture susceptibility. The crumb rubber modifier dry mixing method was modified and named the complex process. Better results were achieved for enhancing mechanical properties.

Introduction

To reduce the environmental effects of roads building and maintenance, necessary to find solutions capable of increasing the performance of the pavement while decreasing the negative impacts. In this context, the utilisation of recycled materials appropriate for other re-uses must be progressed and enhanced [1,2]. The fields of application of CRM in road constructions are miscellaneous. The previous researchers validate them are as numerous as the number of positive results achieved in recycling this material [1]. The usage of the recycled rubber from the End of Life Tires into the bitumen concretes was began in the 1960s. The technology that has spread more is the so-called Asphalt Rubber (AR) one. AR binders produced with the manufacturing process innovated by Charles McDonald, and that is at the foundation of the wet process. This method began with the mix of the end of life tire ground rubber with the asphalt binders utilising mechanical stirring systems, operating at temperatures ranging between 190 and 218 C, for a time interval of 45–60 min [3–6].

High temperature in asphalt pavements often leads to rutting of asphalt pavements and heat island effects in urban areas. In this study, to improve the thermal resistance of asphalt pavement, hollow glass microspheres (HGM) modified asphalt and HGM/Styrene-Butadiene-Styrene (SBS) modified asphalt were used to prepare asphalt concrete (AC) and stone mastic asphalt (SMA) respectively. The effects of HGM on the penetration, ductility, softening point and rheological properties of asphalt binder and the cooling performance, mechanical property, high temperature stability, low temperature resistance, water stability and other properties of asphalt mixture were investigated. Finally, the composition of the thermal resistance surface layer was recommended. Results showed that, adding HGM increased the high temperature stability of both matrix asphalt and SBS modified asphalt while the low temperature performance of both the two types of asphalts decreased. For the asphalt mixture, the addition of HGM improved the cooling performance of the AC-13 mixture but had no effect on the cooling performance of the SMA-13 mixture. HGM also showed positive effects on the pavement performance of the asphalt mixtures. For the AC-13 mixture, it improved the mechanical property, high-temperature stability, low-temperature cracking resistance and immersion residue stability but had no effect on the thaw-splitting strength ratio (TSR). For the SMA-13 mixture, it improved the Marshall stability, high-temperature stability, immersion residue stability, scattering resistance while impaired the low-temperature crack resistance, TSR and anti-drainage ability. Finally, it was recommended to use 5% HGM modified AC-13 mixture as the thermal resistance surface layer.

Introduction

Due to its dark color, asphalt mixture has a high solar radiation absorption rate in the natural environment. Long sunshine exposure causes the asphalt pavement to absorb a large amount of heat, resulting in the continuous increase of the road surface temperature and rutting. As one of the most typical and extensive forms of distress, rutting reduces the comfort and safety of driving, affects the performance of asphalt pavement [1]. Besides, the high temperature of road surface also causes urban heat island effect in cities [2]. The heat accumulated due to heat island effect also leads to urban heating, aggravates air pollution and causes harm to residents’ health [3]. In order to reduce the negative impact of high temperature on the road surface, many measures have been taken.

Abstract

The objective of this study is to investigate the micro-mechanical characteristics of High Modulus Asphalt Concrete (HMAC) pavement structure under loads. The Discrete Element Method (DEM) was employed in this study to build the models for HMAC pavement and conventional asphalt pavement structures. The laboratory tests and DEM simulations of uniaxial compression tests were conducted on the materials of HMAC pavement structure layers. To simulate the mechanical behavior of the asphalt mixture, micro-parameters were adjusted to fit with the strain–stress curve results from lab-test. The displacement and stress distribution in vertical and horizontal directions, and the shear stress in the horizontal direction were analyzed for the HMAC pavement and conventional asphalt pavement. The results showed that the maximum vertical displacement of HMAC pavement (0.25–0.293 mm) was less than that of the conventional asphalt pavement (0.3–0.324 mm). The application of HMAC decreased the vertical stress in all structural layers except the upper surface layer. The HMAC decreased the horizontal stress in the subbase layer. Though the HMAC pavement had a slightly greater horizontal shear stress in the upper and middle surface layers than the conventional asphalt pavement, its shear resistance was. Therefore, the results indicated HMAC layer can enhance the resistance to deformation and reduce the rutting potential in asphalt pavement.

Introduction

High-modulus asphalt concrete (HMAC) was originated from France in 1980s to increase the rutting mitigation resistance and the stiffness of asphalt base layers [1]. Generally, there are three methods to obtained high modulus binders which contributes the most of the higher stiffness of HMAC: use hard-grade asphalt binders that have low penetration and high softening points [2]; use polymer modifier, such as SBS and lake asphalt [3–5]; use high-modulus agent [3,6,7]. HMAC shows evident higher stiffness when compared with conventional asphalt concrete. Pavements with HMAC base layers were reported to have good resistance to rutting and fatigue with the context of climate in France [7]. By applying HMAC, the thickness of the base layer can be greatly reduced while the performance remains the same. However, researchers still have great concerns on the mechanical performance of the HMAC in more inclement climate condition, especially its low temperature performance. Researchers from Spain carried out the repetitive loading axial tests at high temperature (40–45 C) and found the permanent deformation resistance of HMAC was highly related with the asphalt grade and voids contents [2,7].

Safe highway operations are one of the major concerns of pavement engineers and authorities. The reduction of skid resistance during rainy weather poses high risk for safe driving. Wet skid resistance varies under different rainfall intensities and is influenced by many factors such as permeability of asphalt material, pavement geometric design, and tire operating conditions. Empirical studies could offer useful understanding of mechanisms of wet skid resistance and its influencing factors, however, the applicability of the empirical relationships are restricted as soon as there is a change in one of the relevant factors. In recent years, the advancement of the finite element tools has enabled researchers to simulate the tirefluid-pavement interaction in a more realistic way. However, to the best of the authors’ knowledge, the current available numerical models either do not include the real microstructures of the pavement or ignore the water infiltration through the pavement voids in the simulations. Therefore, this paper aims to providing a numerical tool to evaluate the wet skid resistance at various rainfall intensity conditions considering the effects of pavement geometric design, tire tread design and tire operating conditions. The surface characteristics and porous microstructures of the pavement are included in the model in a way that both the vertical water flow into the asphalt concrete and surface flow on the pavement can be captured in the simulation. The effects of several pronouncing influential factors as mentioned above are quantified. Such a model upon validation is expected to provide an easy and reliable tool for pavement engineers to evaluate wet skid resistance under rainy weather more accurately which can be incorporated into pavement management systems for safety highway operation.

Introduction

Safe highway operation is of prime importance for most of the road agencies, road institutions and road organizations. According to the reports, approximately 14% of the fatal road accidents occur under wet weather conditions [1,2]. During wet weather driving conditions, the water on the pavement acts as a lubricant which reduces the contact area at the tire-pavement interface [3,4]. As a consequence, skid resistance decreases or in other words chances of skid related traffic accidents increases on wet pavements as compared to dry pavements. The adverse effect of the presence of a water film on skid resistance has been highlighted in many research studies [5,6]. In general, higher rainfall intensity results in greater water accumulation over the pavement [7,8]. . Further, a combination of critical water film thickness and vehicle speed may result in significantly low skid resistance, which has been widely reported as the main cause of wet weather-related accidents [9,10]. Hence, it is necessary for road authorities and organizations to evaluate wet skid resistance at different rainfall conditions more accurately.

Previous studies showed that Mg-Al layered double hydroxides (Mg-Al LDHs) had well anti-ultraviolet (anti-UV) aging properties when used in the asphalt materials, but it cannot contribute to improve the self-healing properties to repair cracks caused by UV aging under the microwave radiation. Fe3O4 has well microwave absorption and based on the layered structure and large surface area of Mg-Al LDHs, the primary objective of this work was to synthesize Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets, to envisage that the added bitumen modifier has both enhanced anti-UV aging properties and microwave absorption properties. Three modifiers were obtained by the adhesion of Fe3O4 magnetic particles on the surface of Mg-Al LDHs nanosheets, and named as L1F1 (the mass ratio of LDHs: Fe3O4 = 1:1), L2F1 (the mass ratio of LDHs: Fe3O4 = 2:1) and L1F2 (the mass ratio of LDHs: Fe3O4 = 1:2). Morphology, phase composition, chemical structure, anti-UV aging properties, static magnetic properties and microwave absorption properties of them were detected by different analytical methods. Results demonstrate that all magnetic nanosheets present the ferromagnetic behavior, L2F1 shows the lowest MS value among three types of magnetic nanosheets, and the value increases from 28.67 emug1 to 56.78 emug1 with augmented Fe3O4-LDHs ratio. Additions of Fe3O4 significantly enhance the anti-UV aging properties and microwave absorption properties of Mg-Al LDHs. The maximum RL value of L1F2 is recorded as more than two times of that of LDHs, and L1F2 shows the best anti-UV aging properties and microwave absorption properties among all magnetic nanosheets.

Introduction

Layered double hydroxides (LDHs) is a type of multifunctional inorganic supramolecular materials, which is formed by the orderly assembly of positively charged metal cation twodimensional laminate and interlayer anions [1–3]. The nanometer two-dimensional laminates of LDHs are arranged in a longitudinal order to form a three-dimensional crystal structure, which mainly composed of Mg2+ and other metal cations [4,5]. The chemical formula of LDHs can be represented by [M2+ 1xM3+ x (OH)2] x+(An)x/n- mH2 O, where M2+ and M3+ represent divalent and trivalent metal cations, respectively [6–9]. Studies have shown that the layered structure of LDHs has well shielding effect on ultraviolet rays, and can effectively improve the anti-ultraviolet (anti-UV) aging properties of the asphalt materials [5,10]. Zeng added 3% of Mg-Al layered double hydroxides (Mg-Al LDHs) into AH-90, AH-90 and SBS modified bitumen as anti-UV aging agent. The comparisons of equivalent brittle point and fatigue parameters showed that LDHs could effectively reduce the photo-oxidative aging rate of bitumen [11]. This is because when ultraviolet light passes through LDHs, the main layer of metal hydroxide can reflect and absorb ultraviolet light for multiple times. To a certain extent, it can also absorb ultraviolet rays, and the physical shielding effect of the layers on ultraviolet rays is dominant.

Ultraviolet (UV), light-activated, self-healing polymers are an emerging technology that was proposed to enhance the elastic behavior of asphalt binder, while improving its self-healing properties. The objective of this study was to evaluate the effects of self-healing polymer on the rheological properties of binder blends prepared with or without recycled asphalt materials. Binder blends were prepared with two different binders (PG 67-22 and PG 70-22M), with or without recycled asphalt materials, and 5% self-healing polymer (Oxetane-substituted Chitosan-Polyurethane). High-Pressure Gel Permeation Chromatography (HP-GPC) results showed an increase in High Molecular Weight (HMW) components in the binder with an increase in stiffness through the addition of recycled materials. A further increase was observed with the addition of self-healing polymer. Fourier Transform Infrared Spectroscopy (FTIR) confirmed HighPressure Gel Permeation Chromatography (HP-GPC) results with an increase in the carbonyl index. Furthermore, the addition of recycled materials led to an increase in the high-temperature grade and the low-temperature grade of the binder blends, while the self-healing polymer did not have a significant effect on the PG-grade. Overall, the addition of self-healing polymer led to an increase in stiffness and an improvement in the rutting performance, while it did not have a positive effect on low-temperature cracking performance. For unmodified binder (PG 67-22), self-healing polymer incorporation improved the elastic and fatigue cracking properties of the binder. However, when it was added to a polymermodified binder (PG 70-22M) and/or binder blends containing recycled asphalt materials, the potential of this material was low to negative on the low temperature and fatigue cracking performances.

Introduction

Asphalt binder is a viscoelastic material with self-healing abilities, which can restore its original properties by healing the micro-cracks and providing an asphalt mixture with higher durability. Yet, the rate of asphalt mixture’s crack healing process is slow for conventional asphalt binders at ambient temperature and under continuous loading [1]. On the other hand, the application of recycled asphalt materials such as Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingle (RAS) has received considerable attention due to its economic and environmental advantages. Various studies have been conducted in recent years with the aim to produce asphalt mixtures with high percentages or even 100% of recycled materials [2–5]. Even with these advantages, the use of high content of recycled asphalt materials is challenging as the recycled binder is subjected to oxidation and aging during its service life. A severely aged binder is hardened and brittle, and as a result, it may increase the cracking susceptibility of the newly constructed mixture. In addition, the increase in the binder’s viscosity and the loss of relaxation can negatively affect the selfhealing properties of the binder, possibly causing premature failure of the pavement.