Asphalt Materials Research Articles

Synchronous method and mechanism of asphalt-aggregate separation and regeneration of reclaimed asphalt pavement

The objective of this paper is to propose a separation technology for asphalt and aggregates of reclaimed asphalt pavement (RAP) materials with bio-oil as a solvent, which could significantly improve the recycling rate and quality of RAP. The byproducts of asphalt-aggregates separation of RAP are the stripped aggregate and the blends of bio-oil and old asphalt (BBOA). The stripped aggregates could be used as new aggregates. Based on the superior compatibility of bio-oil and asphalt, and the regeneration effect of bio-oil on old asphalt, the BBOA could be used as raw material for asphalt or liquid asphalt production. Through 60 °C viscosity, Fourier transforms infrared spectroscopy (FTIR), fluorescence microscope (FS), scanning electron microscope (SEM), contact angle, and adhesion test, established the relationship between the separation effect and the temperature, time, the mass ratio of RAP to bio-oil. The results show that the optimum temperature for asphalt-aggregate separation is about 110 °C, and the optimum mass ratio of RAP to bio-oil is 4:1 ∼ 5:1. The residue on the stripped aggregate surface is consistent with the characteristic peak of BBOA. BBOA can form pre-coating on the stripped aggregate and improve the bonding performance of asphalt and stripped aggregate. The stripped aggregate obtained after asphalt-aggregate separation has no false particle size phenomenon, and the coarse aggregate remains intact. The residue on the surface of stripped aggregate increases with the decrease in aggregate particle size. The stripped aggregate becomes oil sand when the aggregate particle size is less than 1.18 mm.

Heat Transfer Analysis of Warm Guss Asphalt Concrete for Mini-Trench Overlaying.

Conventional hot mix asphalt overlaying on trench infrastructure typically necessitates extended cooling times for further works and can have adverse effects on buried components, such as electricity cables and hot water pipes. Therefore, this research aims to investigate the use of warm guss mastic asphalt (at an installation temperature of 160 °C) as an overlaying material for mini-trenches, which can reduce the cooling time required for traffic opening and improve the efficiency of the construction process. This research involved two stages: first, lab testing and related research results were used to generate the thermal conductivity and specific heat necessary for simulation work. Second, a finite element model analysis was conducted to evaluate the thermal transmission of the overlaying surface and the buried conduit based on the summer pavement temperature distribution through the Korean Pavement Research Program. Afterward, the field test bed was constructed to verify the simulation. The results indicate that the optimal thickness of the overlaying material and the concrete covering should be designed to ensure thermal durability and meet traffic opening requirements. The overlaying depth of the mini trench using warm mix guss mastic asphalt should be less than 100 mm to meet with the traffic opening time, while the thickness of the concrete covering should be designed to be more than 100 mm to ensure thermal durability. Additionally, the findings suggest that the application of warm guss asphalt could reduce the opening time by 30 min to 1 h and 25 min compared to conventional hot guss asphalt materials. When the pavement surface temperature for the traffic opening is controlled at 50 °C, the asphalt mixture requires at least 2 h to 5 h to meet the cooling criteria for traffic opening, respectively. Overall, this research confirms the potential benefits and optimal use of warm guss mastic asphalt in the construction process of mini-trenches.

Viscoelastic characterisation of warm asphalt mixtures

ABSTRACT The characterisation of the visco-elasto-plastic properties of asphalt materials are important for a better understanding of the pavements’ mechanical behaviour and performance. The complex modulus aims to characterise the linear viscoelastic properties of the material present in the domain of small deformations. This article aimed to characterise the viscoelastic properties of hot and warm asphalt mixtures, by adding surfactant additive to the latest. Four asphalt concrete mixes with basalt aggregate and the following binders: conventional 50/70 penetration, polymer-modified SBS 60/85, rubber asphalt (AB 8) and modified asphalt with Trinidad Lake Asphalt (CAP TLA) were designed for this study. In addition, the parameters of adhesiveness and resistance to hot and warm mixtures were obtained. Through the study it was observed that mixtures with conventional binder presented similar behaviour both in conventional hot and warm mixes. Modified binder mixes show important variations both in viscous and elastic phases, comparing hot and warm production methods, with greater differences found in the polymer-modified mixtures.

A novel resourcezation strategy for the alkylphenol distillation residues: From hazardous wastes to high-valued epoxy asphalt materials

The treatment of industrial organic wastes is always a challenge for both the production companies and the environmental protection organizations due to their complexity and hazardousness. Take the alkylphenol distillation residues (APDRs) as an example, it was largely produced in petroleum industry every year but traditionally disposed by incineration or landfill, leading to not only the waste of resources but also the potentially secondary pollution. Herein, a novel sustainable way has been proposed to convert the APDRs into high-valued asphalt additives to replace the commercial cardanol for road construction. Generally, APDRs was added into asphalt, mixed with curing agent, and then reacted with epoxy resin to produce epoxy asphalt. Results showed that, compared with cardanol, the APDRs performed more evenly in dispersing the epoxy resin and asphalt binder, increasing the compatibility between epoxy and asphalt. According to the measurements by fluorescence microscopy and toluene etching-SEM hybrid tests, it is found that the addition of APDRs would cause the phase transition of the epoxy asphalt materials with different concentrations. Under the optimal addition of APDRs (15%), the most improved mechanical properties (the tensile strength was 2.09 MPa and elongation at break was 261.58%) of the epoxy asphalt system are obtained, much higher than the national standards. The mechanistic studies showed that the alkylphenol distillation residues play important roles in reacting with epoxy and asphalt by alkylation and cross-linking during the curing process of epoxy asphalt. In this way, the epoxy and asphalt could be well mixed and interacted, improving the mechanical properties and thermal stability of epoxy asphalt for the road construction. Finally, the economic evaluation for this strategy has been preliminarily conducted, which further proves the feasibility of conversion of APDRs to high-valued asphalt additives. These findings would also shed lights on the development of reproducible and scalable resourcization methods for other similar industrial organic wastes.

Rapid and Direct Assessment of Asphalt Volatile Organic Compound Emission Based on Carbon Fiber Ionization Mass Spectrometry.

Due to the complicacy of asphalt fumes, the analytical methods for investigating volatile organic compounds (VOCs) are very limited. In this study, a direct and real-time analysis method based on carbon fiber ionization mass spectrometry (CFI-MS), an ambient mass spectrometric technique, was established and successfully applied in the analysis of asphalt VOCs. The asphalt VOCs can be directly detected in the open atmosphere without the collection step of asphalt fumes, and the mass spectra of one asphalt sample can be obtained in a few seconds in both positive and negative ion modes. By investigating the mass spectral changes of asphalt fumes at different heating temperatures ranging from 50 to 200 °C, the temperature factor of asphalt fume emission was demonstrated in this work. The research results demonstrate that the complexity of asphalt fumes is positively related to the applied temperature. Moreover, the VOCs of saturates, aromatics, resins, and asphaltenes fractions were also analyzed by the direct analysis method. The result shows that aromatics contribute most to the emission of VOCs. In addition, the obtained mass spectra combined with the principal component analysis method show the great potential to quickly screen VOC inhibitors of asphalt materials.

The Photo-Oxidation of CO from Ambient Air Using Catalytic Asphaltic Pavement

Road transportation in urban areas may be considered a major source of environmental pollution. The purpose of this study is to determine the effectiveness of the oxidation of carbon dioxide gas emitted by an internal combustion engine. This is achieved using an asphaltic pavement coated with Cu/TiO2 nanoparticles by spraying and irradiating with white light under ambient conditions to reduce the air pollution problem (carbon monoxide) caused by vehicles. Using electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy, we determined the physicochemical and morphological characteristics of the photocatalyst. Following the characterization study, the photo-catalytic activity of the asphalt materials was determined. Experimental results showed that CO conversion positively depends on different conditions, including Cu loading, light intensity, and relative humidity. However, the gas flow rate showed a different trend. The optimal operating parameters were determined as follows: Cu loading (3.6% by weight), a flow rate of gas (1 L/min), relative humidity (30%), and light intensity (35 W/m2) to ensure the best photo-oxidation efficiency of 56.4% after three hours of operation. A mathematical correlation related to CO2 removal as a function of different operating conditions was found with a correlation factor of 0.975 and a variance equal to 0.964. Moreover, a kinetic pathway for photo-oxidation of CO at various oxygen concentrations was presented.

Evaluation of the state of practice asphalt binder and mixture tests for assessing the compatibility of complex asphalt materials

The present study aims to evaluate binder and mixture testing methods for capturing the compatibility of complex asphalt materials consisting of different virgin binder sources, reclaimed asphalt pavement (RAP) materials and recycling agents (RA). Binder evaluation methods include the saturate, aromatic, resin and asphaltene (SARA) fractionation, advanced polymer chromatography (APC) analysis, differential scanning calorimeter (DSC) and rheological measurements. Mixture performance tests include the complex modulus (E*), direct tension cyclic fatigue (DTCF), disk-shaped compact tension (DCT) and semi-circular bending (SCB) fracture tests. The results from the testing and analysis indicate that the rheological characterisation of asphalt binder or mixture may not capture the incompatibility between virgin binder, RAP and RA. Binder DSC analysis as well as mixture fracture tests have shown promise to evaluate the compatibility of complex asphalt materials with different virgin binders, RAP and RA, as well as the effect of incompatibility on mixture performance.

Evaluation of high percentage of alternative aggregates for the production of hot mix asphalt surface layers

In the last decades, recycling of hot mix asphalt (HMA) materials became one of the major issue concerning the world of pavement engineering. As required by Italian technical specifications, pavements surface layers must be produced using high-quality aggregates, in order to meet performance in terms of mechanical and anti-skid properties. Inevitably, the extraction of virgin mineral aggregates and their decreasing availability encourage the use of recycled alternatives, such as electric arc furnace steel slag and municipal solid waste. This study evaluates the possibility to implement recycled aggregates, and others sustainable solutions, in the production of HMA surface layers. In particular, eleven mixtures were produced combining the use of recycled aggregates to polymers obtained from plastic waste recycling and basalt fibres obtained from mineral deposit productions. Laboratory and field results confirmed the validity of the ecological solutions proposed in terms of fundamental properties for surface layers, such as fatigue resistance, rutting and skid resistance.

Ultrasonic characterisation of the elastic properties of mineral aggregates used in asphalt mixtures

Mineral aggregates are the main constituent of asphalt mixtures by volume, having a significant influence on the performance and durability of asphalt materials and flexible pavements, but their elastic stiffness properties are rarely investigated in the scientific literature. Nevertheless, these properties represent important input to micromechanical models which are aimed at providing a better understanding of the behaviour of asphalt mixtures as the basis for optimising their design. Herein, the elastic properties of 55 cylindrical specimens representing six types of rock from two quarries are investigated using ultrasonic testing, in order to assess the variation of the results between different rock types and between different samples of the same rock type as well as the sensitivity to specimen length (50–150 mm) and frequency (0.05–5.00 MHz). Most of the elastic stiffness values of the investigated rocks are found to be larger than stiffness values frequently used as input to micromechanical models.

Study on Thixotropic Properties of Asphalt Mastics Based on Energy Viewpoint

An asphalt mastic has thixotropic characteristics that significantly influence its fatigue and healing performance. Therefore, understanding the thixotropy of an asphalt mastic is clearly of great importance. However, research in this area is still in the early stages. This study focuses on self-heating as one of the biasing performances of asphalt material by analyzing the viscosity, stress, and hysteresis loops the of asphalt mastics under cyclic shear loading. Twelve types of asphalt mastics fabricated with asphalt, as well as different types of mineral filler, were selected to examine thixotropy. In addition, the filler/asphalt ratio was examined via the hysteresis technique to analyze the hysteresis loop and the viscosity–shear rate. The thixotropic potential function was also studied from the energy viewpoint. The results show that asphalt mastics with different asphalt binders, mineral fillers, and filler volume fractions showed hysteresis loops for shear stress versus shear rate diagrams. With an increase in the loading times of the cyclic load, the area of the hysteresis loop gradually decreases, and the hysteresis area most likely features a relatively stable value. The thixotropy of the asphalt can be significantly reduced by adding filler, and different types of mineral filler can slightly influence the thixotropy. The viscosity decreases with an increase in the shear rate, and it gradually recovers with a decrease in the shear rate. The greater the filler/asphalt ratio, the greater the viscosity, and the faster the viscosity’s descent is with the prolongation of time. Due to the existence of a higher amount of filler content, the recovery of a viscosity crack is more difficult. For asphalt mastics with high filler/asphalt ratios, the thixotropic mechanism can be explained via particle agglomeration and the depolymerization theory. For asphalt mastics with low and medium filler/asphalt ratios, the thixotropic mechanism can be explained via the particle chain theory. The damage and recovery of the internal structure of an asphalt mastic can be characterized by the structural failure potential function and the structural recovery potential function, respectively.

Influence of Waste Toner on Asphalt Binder: Chemical and Rheological Characterization

The growing amount of waste toner (WT) has posed a significant environmental challenge. Meanwhile, researchers are interested in the feasibility of utilizing waste toner as an asphalt binder modifier because its primary chemical components (Styrene-acrylic copolymer and carbon black) are known to improve asphalt properties. The objective of this study was to evaluate the chemical and rheological properties of the waste-toner-modified asphalt binder and hence determine the suitability of integrating waste toner for asphalt modification. The waste-toner-modified asphalt (TMA) binders were produced by blending base asphalt with two types of waste toners of different gradation sizes. Microscopic tests such as x-ray fluorescence (XRF), attenuated total reflectance transform infrared spectroscopy (ATR-FTIR), and scanning electron microscopy with energy dispersive X-ray (SEM-EDS) and fluorescence microscope, as well as rheology tests such as multiple stress creep recovery (MSCR) tests, oscillation tests, and bending beam rheometer tests were performed. The FTIR results showed that there was a chemical reaction between waste toners and base asphalt binder. A fluorescence effect was observed on the binders produced with different toners used in this research. The binder modified with an optimal content of 8%WTs revealed better high and low-temperature properties. Additionally, 8%WTs used in this research could change the PG70-22 binder to PG76-22 binder. The rutting properties of asphalt material were improved for its improved elasticity. In addition, the 200-mesh TMA binders were desirable with respect to waste toner particle size. Overall, there is a benefit to using waste toner in the asphalt industry.

Surface modification of fly ash by waste engine oil under mechanical activation enhanced the sustainable service life of asphalt

Oxidative aging of asphalt leads to changes in its molecular structure and chemical composition, deteriorating the properties. Therefore, extending the service life of asphalt materials is essential for environmental protection and sustainable development. In this study, waste engine oil (WEO) with similar components and chemical composition to asphalt was used to modify the fly ash (FA) surface by a high-energy ball grinding process to produce a well-compatible compound fly ash modifier (CFAM). This process achieved ultra-refinement and surface modification in one step, enhancing the chemical bonding and anchoring force between FA and asphalt, thereby effecting the ageing resistance of the asphalt. Dynamic light scattering tests showed that the oil grinding process enhanced the stability of CFAM, whose median particle size (654 nm) increased by only 103 nm after four months of storage. Thermogravimetric (TG), BET tests showed that the FA surface was grafted with a large amount of WEO, and the CFAM after de-oiling and rinsing had a WEO content of 1.39 wt%, which gave it excellent compatibility with asphalt. The nano-indentation and Fourier transform infrared spectroscopy (FTIR) experiments showed that CFAM reduced the changes in micro hardness, modulus of elasticity, carbonyl content and sulfoxide group content of asphalt before and after ageing and provided an excellent anti-ageing effect. The oil grinding process activated the reactivity of the FA that could chemically bond with the carboxylic acids in the asphalt, stabilizing the chemical components of the asphalt and delaying the ageing of the asphalt, thus achieving sustainable service of the asphalt.

Layered Viscoelastic Analysis with Moving Loads of Low-Volume Roadway Pavement Response

Low-volume roads (LVRs) are typically not expected to withstand large amounts of traffic, consequently they have relatively thin pavement structures. However situations can occur when traffic loading rapidly increases, resulting in rapid structural deterioration of the pavement. Examples include resource exploration and production, new industrial facilities, and military operations. Improved evaluation procedures, including computation of pavement structural responses, are needed to accommodate these scenarios. This paper reports recent advances in methods for computing the structural response of LVRs that incorporate viscoelastic asphalt material behavior and accommodate moving loads. Application of layered elastic analysis, using a Hankel transform with numerical integration methods, is popular in several mechanistic-empirical pavement design procedures. This paper describes an application of the collocation method for approximating the creep compliance and viscoelastic solution, which removes the necessity for approximating the Laplace transform inversion. This was coupled with Boltzmann’s superposition principle for moving loads. Comparisons showed that the proposed approximate method matched well with the viscoelastic solution, and with the full-scale instrumented test data of highway pavements. The measured near surface response of a thin LVR test pavement subjected to military truck loads was then modeled to determine the suitability of the approach for LVR. The modeled results for asphalt strain and vertical pressure in the granular layers showed generally good agreement with the measured instrumentation data. The developed structural response model provided a more realistic simulation of flexible pavement viscoelastic material behavior and accommodation of moving loads with similar computational speed to a conventional layered elastic approach.

Evaluation of long-term oven aging protocols on field cracking performance of asphalt binders containing reclaimed asphaltic materials (RAP/RAS)

This study compared two loose mixes’ long-term oven aging (LTOA) protocols (i.e., 5-day at 95°C and 8-hour at 135°C) based on asphalt binder rheological and chemical properties. The protocols were then correlated with field aging conditions. Extracted and recovered asphalt binders from four asphalt mixtures were tested in the Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Double-Edge-Notched-Tension (DENT) Test, and Fourier Transform Infrared Spectroscopy by Attenuated Total Reflectance (FTIR-ATR). Based on the research results, the loose mix aging protocol of 5-day at 95°C replicates the effects of 2- and 3-year field oxidative aging on the rheological and chemical properties of the binders. The laboratory protocol of 8-hour at 135°C yielded a higher level of aging to the binders compared to the 5-day at 95°C protocol. Additional testing is planned to determine if these loose mix LTOA protocols can simulate 4–5-year field aging in Alabama.

Research progresses of fibers in asphalt and cement materials: A review

Research progresses of fibers in asphalt and cement materials: A review

Influence of Thermo-Oxidative Aging on the Properties of SBS-Modified Asphalt Binders

The superior performance of styrene-butadiene-styrene (SBS) modified asphalt makes it widely used in asphalt pavement construction. However, SBS-modified asphalt pavement still faces an aging problem. Aging causes the performance of asphalt materials to decline and many pavement diseases. The dosage of SBS commonly used in industry is generally between 3% and 4.5%, and the performance of SBS with a high dosage needs to be explored. Therefore, in this paper, 12 modified binders were prepared with blending amounts of 3%, 5%, and 7% and the type of modifiers as linear and star. The softening point increment (SPI), viscosity aging index (VAI), rutting factor index (RFI), complex modulus aging index (CMAI), and phase angle aging index (PAAI) were used to study the antiaging performance of SBS-modified asphalt. Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were used to study the microscopic and structural changes that occur during the aging process of modified asphalt. The result shows that when the amount of the same type of modifier is 3%–7%, the higher the amount of modifier, the better the performance of the modified asphalt. At the same content, a star modifier is not necessarily better than a linear modifier. For the same type of modifier, the larger the amount, the better the antiaging performance of the modified asphalt. Given an increase in aging time, the deterioration of the asphalt performance will deepen. Aging leads to the enhanced high-temperature performance of asphalt. The macroscopic performance of asphalt aging can be explained by the microscopic view. The aging process of modified asphalt is the cumulative process of oxidation products.

Generalised Kelvin contact models for DEM modelling of asphalt mixtures

ABSTRACT Rigid particle models based on the discrete element method (DEM) have been adopted to model creep, fracture, and the viscoelastic behaviour of asphalt mixtures considering an irregular micro-structure and particle contacts. Within a DEM framework, the Burgers contact model, which is known to have a narrow frequency and temperature range, is usually adopted to model viscoelastic properties. In this study, a new explicit three-dimensional generalised Kelvin (GK) contact model formulation for the DEM model is proposed for asphalt materials. The model is implemented following two different methodologies (GK 1 and GK 2 ). The models are validated in uniaxial tension-compression sinusoidal tests for predicting the dynamic modulus ( | E ∗ | ) and phase angle (ϕ) of these composites at a frequency range of 1–10 Hz at 20 ∘ C. Four mixtures are investigated based on the modelling of their mastic. The influence of the GK contact parameters on the dynamic response of mastics is assessed. Results show that κ m has an important influence on both rheological properties and that η m can be used for small adjustments focussing on the predicted phase angle. Moreover, it is shown that a viscoelastic contact model should be adopted to simulate aggregate-to-mastic contacts in mixtures. As expected, the response obtained for both GK models is the same but the simulations with the GK 1 are 14% faster. In addition, the response predicted with the proposed GK contact model is compared with the response predicted with a Burgers contact model. The DEM predictions obtained for the GK model are more accurate. For mastics, the average errors for | E ∗ | and ϕ when adopting the GK model (Burgers) are 2.40% (3.46%) and 3.64% (4.17%), respectively. For mixtures, the average errors for | E ∗ | for the GK model (Burgers) are 7.00% (7.92%). The proposed contact model greatly enhances the DEM ability to simulate the viscoelasticity of asphalt materials.

Chemical fingerprinting of volatile organic compounds from asphalt binder for quantitative detection

Asphalt material is an irreplaceable material in road construction. However, it releases VOCs (Volatile Organic Compounds), which do cause pollution to the surrounding environment, during its full life cycle, especially in high-temperature paving stage and summer service time. Asphalt VOCs release mechanism and effective emission reduction technologies are therefore urgently needed. The chemical analysis of VOCs from asphalt binder always invariably excludes a vast number of compounds of unknown relevance, making the quantitative analysis lower data accuracy. In order to address this problem, fingerprint database was developed and introduced in this study, with the detected VOCs data from 104 kinds of asphalt binders. The analysis parameters, including fingerprint components and calibration curves were optimized through quantitative study. With the help of a self-developed fingerprint database, the calculation formulas of single VOC and total released VOCs were established for quantitative analysis of VOCs from asphalt binder. In addition, the influencing mechanism of heating temperature and asphalt types on VOCs volatilization characteristic were explored to achieve emission reduction in asphalt industry.

MASAI: sustainable, automated and intelligent asphalt materials. The way to the next generation of asphalt pavements

Despite the efforts made during decades, pavement construction still uses essentially the same traditional model as that employed one hundred years ago. This makes road construction actions less efficient, thereby affecting the productivity and the possibilities of economic growth of the sector. To help establish a model based on the circular economy, but also to promote the implantation of the new technologies, the Laboratory of Construction Engineering of the University of Granada has created the conception of sustainable and smart asphalt materials named MASAI, which enable the combination of the most important sustainable techniques developed in last decades in a single material. This paper describes the main characteristics of MASAI and presents several of the experiences carried out in Spain that demonstrate their viability and great potential regarding the minimisation of the environmental impact of asphalt pavements and their adaptation to the future needs of users and administrators.

Fatigue damage evolution and self-healing performance of asphalt materials under different influence factors and damage degrees

This paper determines the self-healing performance and damage accumulation process of asphalt materials under different damage degrees and influence factors by the fatigue-healing-fatigue (F-H-F) time sweep test. A comprehensive index HF is proposed to characterize the fatigue-healing performance of asphalt materials. The results show that with the increase of rest time and temperature, the HF value of asphalt materials increases. The newly proposed fatigue damage factor DR fully considers the energy dissipation history in the fatigue test process, and the mathematical model of damage accumulation based on DR can better characterize the nonlinear evolution process of asphalt material fatigue damage.