Unmodified Asphalt Binder Research Articles

Exploring the physicochemical and rheological properties of sustainable asphalt binders modified with lignin and high-viscosity additive

The primary objective of this investigation is to evaluate how the incorporation of lignin and high-viscosity modifiers impacts the performance of asphalt binders. Lignin-modified asphalt binder (LBA) and lignin-high viscosity modifier composite-modified asphalt binder (LHA) were created by blending 5 % and 15 % lignin, respectively. To understand the physicochemical interactions, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) were employed to analyze functional groups, thermal properties, and phase changes. Additionally, the linear rheological behavior and nonlinear rheological behavior were evaluated through frequency sweep and multiple stress creep recovery tests. The findings suggest that lignin blends physically with the asphalt binder and high-viscosity modifier without a chemical reaction. Although the onset pyrolysis temperature of lignin is significantly lower than that of asphalt binders, due to its relatively low content, the thermal decomposition of lignin-modified asphalt binders is primarily controlled by the asphalt binder itself and still exceeds the construction temperature. However, lignin incorporation increases the asphalt binder's glass transition temperature, potentially affecting low-temperature performance. Lignin significantly enhances the modulus in the high-frequency region of both unmodified and high-viscosity modified asphalt binder. However, it has a negative effect on the modulus in the low-frequency region of high-viscosity modified asphalt binder. Furthermore, nonlinear creep recovery test results demonstrate that lignin positively contributes to the deformation resistance of unmodified asphalt binder in a content-dependent manner, whereas it reduces the elastic behavior and deformation resistance of high-viscosity modified asphalt binder. In addition, low levels of lignin increase the stress sensitivity of binders, while high levels of lignin decrease it. Despite these effects, the performance of lignin and high-viscosity additive composite-modified asphalt binder remains superior to that of unmodified asphalt binder. These findings offer valuable insights into the combined use of lignin and polymers in asphalt binder modification.

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.

Incorporating Environmental Impact Analysis into Louisiana’s Balanced Asphalt Mixture Design

To meet the asphalt pavement industry’s net zero carbon emission goals, increasing reclaimed asphalt pavement (RAP) levels to greater than 25% is considered a critical tactic. However, many state departments of transportation are cautious in adopting high RAP content into their designs because of durability issues resulting from aged RAP binders. This paper assesses the effectiveness of using the Lewis acid catalyst, FeCl3, in improving the cracking resistance of high-RAP asphalt mixtures to meet Louisiana’s balanced mixture design (BMD) criteria, and lower embodied carbon of asphalt mixtures. Four asphalt mixtures were designed and tested against permanent deformation, intermediate- and low-temperature cracking, and durability. Mixture 1 is conventional, which contains performance grade (PG) 76-22 polymer-modified asphalt binder with no RAP. Mixture 2 is unmodified PG 67-22 and 30% RAP without catalyst. Mixtures 3 and 4 incorporated an unmodified asphalt binder PG 67-22, a catalyst, and 30% and 50% RAP, respectively. A life cycle assessment (LCA) analysis was conducted on asphalt mixtures that complied with Louisiana’s BMD specifications to quantify global warming potential improvements. Because the performance of both mixtures is expected to be similar, the scope of the LCA analysis was limited to only those life cycle stages that are expected to be different, modules A1–A3 (i.e., cradle-to-gate stages). Results showed that the use of FeCl3 can improve asphalt mixtures’ cracking resistance containing high RAP contents, whilst it did not have a negative impact on permanent deformation resistance. Further, the addition of FeCl3 to asphalt mixtures with 30% and 50% RAP levels showed a reduction in greenhouse gas emissions by 28% and 43.4%, respectively.

Microstructural Characteristics of Fly Ash Geopolymer Modified Asphalt Binder

The incorporation of by-product materials, such as fly ash geopolymer, has a significant influence on the properties of asphalt binder. This results in a reduction in binder viscosity and an increase in binder stiffness. This, in turn, promotes enhanced aggregate-asphalt binder bonding. Geopolymer refers to a class of inorganic materials characterized by the formation of a long-range, covalently bonded non-crystalline skeleton. The aim of this study was to explore the potential of incorporating waste and by-product materials, specifically fly ash geopolymer additive, in order to influence the microstructure of asphalt binder. The focus was on examining how the inclusion of fly ash geopolymer could alter the internal arrangement and composition of the asphalt binder, leading to potential improvements in its properties and performance. Laboratory experiments were performed to analyze the microstructure of 60/70 and 80/100 asphalt binder samples using Scanning Electron Microscope (SEM) imaging. These samples were modified with various concentrations (3%, 5%, 7%, 9%, and 11%) of fly ash geopolymer additive. The SEM images were obtained to examine the morphological changes and assess the distribution of the fly ash geopolymer particles within the asphalt binder matrix at different additive concentrations. The NOVA NANOSEM 230 equipment was utilized to determine the morphological characteristics of the asphalt binders. The results showed notable variations in the properties of the asphalt binders modified with fly ash geopolymer compared to the unmodified control asphalt binder. The morphological evaluation revealed thorough blending of the fly ash geopolymer additive. Notably, the micrographs demonstrated a denser structure with increased percentages of fly ash geopolymer, indicating a presence of fly ash and alkaline activator promotes the rapid formation of polymerization. These findings emphasize the promising potential of fly ash geopolymer as an additive in asphalt binder. The significant effect it has on viscosity when incorporated into modified asphalt binder makes it a valuable candidate for application in the field.

Molecular dynamics simulation and experimental analysis on fluidity improvement of liquid rubber modified asphalt binder

Liquid styrene-butadiene rubber (LSBR) has been used as a modifier to improve high-temperature storage stability and cracking resistance of asphalt binder. However, the interaction mechanism between LSBR and asphalt binder at both micro and macro scales has not been well understood. In this study, the intermolecular dynamics, rheological and chemical properties of liquid rubber modified asphalt (LRMA) binder by laboratory experiments and molecular dynamics simulation. Five LSBR dosages (0, 0.5, 1.0, 1.5, 2.0, and 2.5% by weight of asphalt binder) were applied to prepare the LRMA binders. Frequency sweep, performance grading, and multiple stress creep recovery (MSCR) tests were conducted to assess the intermediate- and high-temperatures rheological properties of modified asphalt binders. Fourier transforms infrared (FTIR) spectroscopy was applied to evaluate the chemical properties. Molecular dynamics (MD) simulation was performed to evaluate compatibility and molecular mobility during self-healing process. The results indicated that the addition of LSBR improved the fluidity of asphalt binder at intermediate- and high- temperature, and also enhanced the susceptibility to temperature changes. FTIR results showed that LSBR could effectively delay aging of asphalt binder and ameliorate the service performance degradation. The MD simulation results indicated that the addition of LSBR could improve the solubility of different components in asphalt and the homogeneity of asphalt system. LRMA had a better capability to heal micro-crack than the unmodified asphalt binder. LSBR could improve the fluidity of base asphalt and aged asphalt. It is feasible and appropriate to use liquid styrene-butadiene rubber to improve fluidity of asphalt to meet the requirements of construction and production. Keywords: asphalt fluidity, molecular dynamics simulation, liquid styrene-butadiene rubber, self-healing, rheological property.

Rheological, Mechanical, Microscopic, and Chemical Characterization of Asphalt Binders at Extended Aging Levels

This study aims to connect asphalt binder mechanical properties to their dynamic microscopic morphology and chemical indices to provide a more thorough and fundamental picture of aging and cracking phenomena. Unmodified and modified asphalt binders were aged to five levels for a comprehensive representation of the asphalt binder service life. Rheological indices used covered linear viscoelastic cracking indicators and nonlinear parameters including fatigue life obtained by the linear amplitude sweep test. A recently validated asphalt binder cracking test, the poker chip test, was used to provide new insight into the mechanical performance of asphalt binders as they stretch into the nonlinear regime and experience cavitation damage. Rheological and mechanical properties were compared to static surface topography from atomic force microscopy (AFM) and time-sensitive asphalt binder microstructure based on electron beam loading using an environmental scanning electron microscope (ESEM). Results indicated that the parameters based on linear viscoelastic analysis and fatigue life derived from the linear amplitude sweep (LAS) test are not adequate to delineate the evolution of asphalt binder behavior with aging among different asphalt binders, due to poor ranking based on known phenomena. However, it was confirmed that the poker chip test was sensitive to longer aging cycles and could capture the total degradation of the asphalt binder’s ductility for both modified and unmodified asphalt binders. The consistency between ESEM and AFM was ensured by observing static surface structures; however, quantification of the fibril formation in ESEM images was the most critical morphological observation when it came poker chip results, because both sharing similar deformation mechanisms. Chemical characterization using Fourier transform infrared spectroscopy was also able to capture asphalt binder aging well, and could be best related to the strength of the asphalt binder. Overall, it was established that the surface microstructure has some relationship to mechanical properties, but not a definitive one, and that using ESEM as an energy absorption indicator was most similar to the comprehensive results from mechanical and chemical testing.

Effect of Stress Levels and Temperatures on Creep Compliance of Asphalt Binders

Abstract: Mostly, the laboratories in Pakistan use DSR (Dynamic Shear Rheometer) Test AASHTO T 315 for quality control purposes but it was designed for unmodified asphalt binders, and it gives inadequate results of modified binders. On the other hand, AASHTO T 350 called as multiple stress creep recovery (MSCR) test gives better result for modified binders. MSCR grades of mostly modified binders with additives, nano composites, viscous fluids is determined in this research paper. The effect of these modified as well as unmodified binders on the Creep Compliance factor is also evaluated. To characterize Creep Compliance factor along with Stress Sensitivity and Traffic Loading this test is now used. For evaluating the Stress Sensitivity of modified binders there is development of new factor called as JNR Slope instead of JNR Difference. Jnr Slope gives vast representation of asphalt binders and there is no congestion left between them. The binders which fail in JNR Difference might get satisfactory results from JNR Slope Which gives better results than the conventional way of testing. For determining the rutting behavior of modified as well as unmodified asphalt binders there is usage of peak strain factor at stress level of 100 Pascal, and 3200Pascal relatively. The values of JNR at the stress levels 25 Pascal to 25600 Pascal gives almost linear variation between modified as well as unmodified binders. This research paper is developed to determine Peak strain values, Creep Compliance factors, Stress Sensitivity Factors, And MSCR grading according to the Traffic Loading.

Rheological Properties of Asphalt Binder Modified With Reactive/Non-Reactive Polymer and Polyphosphoric Acid

This paper investigated the rheological performance of the combination of ethylene methyl acrylate and glycidyl methacrylate—EMA-GMA (reactive polymer)—and high-density polyethylene (HDPE) associated with polyphosphoric acid (PPA116%) in the modification of an asphalt binder (PG 64-XX). Tests such as performance grade (PG), multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), and master curve vary the EMA-GMA and PPA116% contents to obtain an ideal composition to provide a high-performance asphalt binder and thus compare with an unmodified asphalt binder and a styrene-butadiene-styrene (SBS) modified asphalt binder. The results showed that the asphalt binder stiffness improved as the EMA-GMA and PPA116% content increased. The PG temperature increased with the addition of PPA116% content in the asphalt binder samples, being most significant with the use of 1.8% of EMA-GMA. The addition of the combined polymers decreased the susceptibility to rut and improved the elastic recovery of the asphalt binder PG 64-XX, but only the samples with 1.8% EMA-GMA showed higher elastic recovery than the SBS-modified binder. PPA116% provided benefits in damage resistance at all strain levels; however, more was observed in samples subject to minor strains. The incorporation of 1.8% EMA-GMA, 0.3% HDPE, and 0.5% PPA116% was the one that presented the most improvements, without presenting gelation, in the performance of the asphalt binder in relation to stiffness and elasticity with increasing temperature. Thus, the use of these polymers in this composition can be a good alternative to regions with high temperatures, such as the northeast region of Brazil.

Aging Characterizations of Modified Asphalt Binders Based on Low Field Nuclear Magnetic Resonance (LF-NMR).

Styrene-butadiene-styrene block copolymer (SBS) and crumb rubber modifier (CRM) are commonly used modifiers to modify asphalt binders. The aging of modified asphalt binders is an important factor affecting their performance. In this paper, the effects of the two modifiers (i.e., SBS, CRM) on the aging of modified asphalt binders were studied by using low field nuclear magnetic resonance (LF-NMR) technology and dynamic shear rheological (DSR) tests. Test results showed that when T2, a parameter of relaxation time from NMR test, was within 2.2 milliseconds, the relaxation peak of both modified and unmodified asphalt binders tested showed two peaks (i.e., "M" shape), and when it was greater than 2 milliseconds, extra peaks appeared only in the modified asphalts. These extra peaks gradually disappeared with increased aging; the modifiers carried signal intensities of their own. The addition of a modifier changes the law of "the greater the viscosity of asphalt, the shorter the T2 relaxation time". With the aging process, the normalized peak area (NPA) from NMR decreased, and rutting resistance factor from DSR increased. However, the NPA of modified asphalt increased after the PAV test, which may be related to the change of H semaphore. The rheological properties of the asphalt binders before and after aging were well-correlated with the NPA of T2.

Correlation Analysis of Linear Viscoelastic (LVE) Properties, Damage Resistance and Microstructure of Unmodified Asphalt Binders with the Same Penetration Grade.

The penetration grade system is still widely adopted for selecting asphalt binder with desired paving performance. However, the initial material compositions of asphalt binder with the same penetration level are still different, and vary with the crude oil source and essentially result in different rheological performance. This study aimed to assess the linear viscoelastic (LVE) properties, and high- and intermediate-temperature and microscale characteristics of seven unmodified asphalt binders from different sources and countries with the same penetration level of 70. The LVE parameters were firstly evaluated followed by comparisons to various damage-based indexes. The microstructure of asphalt binders was further investigated followed by correlations between morphology and performance parameters. Experimental results indicate the |G*|/sin δ is well related to the MSCR-based non-recoverable creep compliance; furthermore, the R and |G*|·sin δ can generally represent the LAS-based failure strain and fatigue life, respectively. The viscoelastic nature of tested binders was clearly distinguished and related to rheological performance by atomic force microscopy (AFM). The roughness parameters and the phases' content derived from AFM images showed significant correlations with LVE characteristics and fatigue resistance nature, respectively. This research provides theoretical foundations for further investigating the rheological performance and microstructure characteristics, and their correlations with asphalt binders.

Influence of Styrene-Butadiene-Styrene Polymer on Local Asphalt Characteristics

In this study the effect of Styrene-Butadiene-Styrene (SBS) polymer on local asphalts was investigated by comparing the performance of unmodified asphalt binder and hot mixture with binder and mixtures modified by SBS polymer modified asphalt (SBS-PMA) and its hot mixture. The comparison was made by evaluating the effectiveness of using different percentages (dosages) of this modifier to produce SBS-PMA. The penetration, ductility, elastic recovery, softening point, flash point, penetration and loss on heat tests for the asphalt binder was used. While, Marshall, indirect tensile strength (ITS), and index of retained strength (IRS) tests for the mixture was used in this study as they are the most available and economic. SBS polymer modifier was added to asphalt binders from Kirkuk governorate (KAT) and LANAZ refineries in Erbil governorate-Kurdistan region- Iraq in four percentages 3%, 5%, 7% and 9% by weight of the asphalt binder. The results showed that SBS polymer modifier significantly enhances the performance of asphalt binder and its hot mixture resulting in enhanced flexible pavements. However, adding 5% SBS leads to the best results of the Marshall test properties, and the moisture damage resistance, which increases the pavement performance against the environmental effects. Comparing the experimental results for both unmodified and 5% SBS polymer modified asphalts, showed that the replacement of the unmodified asphalt by 5% SBS polymer modified asphalt increased the stability by 26.00% for KAT asphalt and 21.34 % for LANAZ asphalt. Also, it increased the TSR by 15.63 % for KAT asphalt and 7.95 % for LANAZ asphalt and the IRS by 11.92% for KAT asphalt and 7.11 % for LANAZ asphalt. The regression analysis technique was applied to fit the mathematical relationship between the SBS polymer percentage and the Marshall stability of the hot mixture. Based on this investigation, the polymer modified asphalt is recommended to be used in new constructed roads to help reduce the amount of deterioration and maintenance cost in the region.

Study on Adhesion Property and Moisture Effect between SBS Modified Asphalt Binder and Aggregate Using Molecular Dynamics Simulation.

In this project, the adhesion property and moisture effect between styrene–butadiene–styrene (SBS) modified asphalt binder and aggregate were studied to reveal their interface adhesion mechanism. The influence of SBS contents on adhesion property and moisture effect between binder and aggregate phases were investigated using molecular dynamics simulation. Moreover, the double-layer adhesion models of asphalt binder–aggregate and triple-layer debonding models of asphalt binder–water–aggregate were constructed and equilibrated, and the adhesion property and the moisture effect were evaluated numerically. The results indicate that the built SBS-modified asphalt binder models show favorable reliability in representing the real one. The variation in the work of adhesion for SBS modified asphalt binder–quartz is not remarkable with the SBS content when its content is relatively low. However, the work of adhesion decreased significantly when the content was higher than 6 wt.%, which is consistent with the experimental results. The adhesion between SBS-modified asphalt binder and quartz is derived from Van der Waals energy. The modified asphalt binder with a high SBS modifier content (8 wt.% and 10 wt.%) shows much better moisture resistance (nearly 30% improved) than the unmodified asphalt binder from the work of debonding results. According to the Energy Ratio (ER) values, asphalt binders with high SBS content (8 wt.% and 10 wt.%) present a good moisture resistance performance. Therefore, the SBS content should be seriously selected by considering the dry and wet conditions that are used to balance the adhesion property and debonding properties. The content of 4 wt.% may be the optimal content under the dry adhesion and moisture resistance.

To study the Effect of Organophilic Nano-clay on Creep Stiffness of Asphalt Binder at Low Temperatures

Abstract: The asphalt binder must be modified to extend the service life of flexible pavements. As the temperature outside drops, the pavements shrink and develop internal stresses. The pavement may break if this contraction happens quickly enough because it won't have time to relax these stresses. Due to the cracking's orientation with respect to the flow of traffic, this form of fracture is frequently referred to as a "thermal crack" or a "transverse crack.". The purpose of this article is to assess how adding nanoclay to asphalt binder changes its performance at low temperatures. The stiffness and stress relaxation time of a material can be measured with a Bending Beam Rheometer (BBR). It is ideal for asphalt binders to be able to release built-up tensions and not become overly stiff at low temperatures. The BBR test was carried out to investigate the low-temperature behaviour of asphalt binder. Test samples were prepared by adding varying nanoclay content and test temperatures were defined. Three small beams of each percentage were prepared and tested after conditioning at defined test temperatures. Results of modified asphalt binder were assessed and contrasted to unmodified asphalt binder to optimize the nanoclay content. The study revealed that increment in nanoclay amount increased the creep stiffness of asphalt binder. İt was concluded from the study that improvement of creep stiffness played a key role towards the low-temperature performance. The maximum increase in creep stiffness was found by the addition of 5 % nanoclay at -16 °C

Rheological Properties of Cement-Modified Asphalt Binders

Asphalt pavements are subjected to major distresses like fatigue, rutting, and low-temperature cracking due to repeated traffic loading and climatic conditions. The modification of the asphalt binder (a major component of an asphalt paving mixture) using additives helps in minimizing the possibility of pavement distresses. The cement additive was used in this study at cement-to-asphalt (C/A) percentages of 0, 10, and 20% by volume. The main objective of the study was to investigate the impact of C/A percentage, temperature, and loading frequency on the rutting resistance of asphalt binders using statistical analysis. Two aging conditions were also used: unaged condition and short-term aging condition in the rolling thin-film oven (RTFO). The dynamic shear rheometer (DSR) test was used to characterize the asphalt binders at ten loading frequencies (0.1, 0.3, 0.6, 1, 1.59, 3, 5, 7, 8, and 10 Hz) and four temperatures (58, 64, 70, and 76°C). These combinations were used to cover a wide range of combined conditions and to follow the high-temperature range for the Superpave performance grade (PG) system. Multiple statistical analyses [the one-way analysis of variance (ANOVA) and correlation tests] were performed to identify the relation between the tested variables and the rutting parameter (G*/sinδ). Findings of the study have shown that the loading frequency has a significant effect on the rutting parameter for unaged and RTFO-aged asphalt binders under different temperatures and using different C/A percentages. Regression analysis was conducted to depict an accurate model that can predict the rutting parameter (G*/sinδ) for each aging condition. Based on the regression analysis, nonlinear power models were developed for the rutting parameter of four groups: unaged unmodified, unaged cement-modified, RTFO-aged unmodified, and RTFO-aged cement-modified asphalt binders with the coefficient of determination (R2) values of 0.986, 0.986, 0.996, and 0.992, respectively. The ANOVA test results showed that the cement addition (represented by the C/A percentage) had a significant impact on the rutting parameter of cement-modified asphalt binders for both aging groups. Furthermore, the correlation tests conducted in this study showed that the temperature and loading frequency had significant effects in the predictive models of the rutting parameter of unmodified asphalt binders and that the temperature, loading frequency, and C/A percentage had significant effects in the predictive models of the cement-modified asphalt binders.

Investigation of Surface Micro-Mechanical Properties of Various Asphalt Binders Using AFM

The microstructure of asphalt affects the micro-mechanical properties. In this study, atomic force microscopy (AFM) was used to investigate the surface elastic modulus and nanohardness of asphalt binder. Relevant mechanical indexes were quantitatively evaluated by contact mechanical model. Five types of asphalts, including different grades, oil sources, and before and after modification, were selected as test objects, and the effects of asphalt binder type, aging, water, and anti-stripping agent on the asphalt micromechanics were explored. The results showed that the micromechanical properties of asphalt binder are affected by grade, oil source, and modification. The aging resistance of modified asphalt binder is better than that of unmodified asphalt binder. Water immersion reduces the surface micromechanical properties of the asphalt binder. The effect of the anti-stripping agent on the modified asphalt binder is greater than that of the unmodified asphalt binder.

Effects of Aggregate/Filler Characteristics on Semi-Circular Bend Fracture Parameters of Asphalt Concrete Mixtures Subject to Moisture Damage

The binder–aggregate adhesiveness plays an important role in preventing asphalt concrete adhesive fracture and it is greatly influenced by the chemical, physical, morphological, and mineralogical properties of aggregates. Many studies have attempted to assess fracture resistance of asphalt mixtures by evaluating parameters found from different laboratory fracture tests. Those parameters are related to the mixture components, and they can change when moisture conditions are induced. This study aims to investigate the effects of aggregate/filler characteristics on mixture fracture resistance including the effect of moisture damage. Two aggregates and four fillers with varied chemical compositions were selected and combined with one unmodified asphalt binder to design five different asphalt mixtures. Each aggregate and filler was tested to characterize physical, chemical, and morphological properties. Asphalt concrete mixtures samples, with and without being subjected to moisture conditioning, were submitted to the semi-circular bend (SCB) fracture test. Statistical analyses were performed to determine the level of significance on the parameter change resulting from the properties of particles and moisture conditioning. The results indicated that the type of aggregates did not present significant influence on the SCB fracture results when moisture conditioning was not involved. Also, the type of filler presented different trends on the parameter’s change when the samples were subjected to moisture. However, it was observed that the effects of aggregates and fillers on the fracture resistance of asphalt mixtures were pronounced when the SCB samples were subjected to moisture conditioning, because of the material-specific binder–aggregate adhesion in the presence of moisture.

Using the Dynamic Shear Rheometer for Low-Temperature Grading of Asphalt Binders

Abstract The Superpave Performance Grading (PG) framework or a variation of this framework is often used as a purchase specification in the United States and as a tool to evaluate the expected performance of modified and unmodified asphalt binders in many countries around the world. A cornerstone of the PG framework is the low-temperature grade of the asphalt binder that is assessed using a bending beam rheometer (BBR) using maximum stiffness and a minimum rate of deformation as criteria. Several previous studies from other researchers have demonstrated the feasibility of using the dynamic shear rheometer (DSR) with a 4-mm parallel plate geometry to measure the rheological properties of asphalt binders at low temperatures. This article builds on these studies to evaluate the feasibility of using a DSR to replace the use of a BBR for low-temperature grading of the asphalt binder using two different approaches. The first approach was to measure complex shear modulus of different asphalt binders using the DSR, convert these measurements to BBR equivalent stiffness and m-value using principles of linear viscoelasticity, and compare the two pairs of parameters from each method. The second approach was to use the complex shear modulus and phase angle measured using the DSR in lieu of using the stiffness and m-value measured using the BBR. Although the results from both methods show feasibility of using the 4-mm plate with the DSR to estimate low-temperature properties, the second approach of measuring and using the DSR-based complex shear moduli and phase angle is a more viable alternative for routine use.

Study on macroscopic properties and microstructure of thermosetting polyurethane asphalt binder (PAB) based on curing kinetics

Recently, novel thermosetting polyurethane asphalt binder (PAB) has been studied by more researchers. This paper investigated the curing mechanism, microstructure and macroscopic performance of PAB. The mechanical properties, rheological properties, and elastic recovery performance of PAB were evaluated. Fourier transform infrared spectroscopy (FTIR), fluorescence microscopy (FM) and gel permeation chromatography (GPC) were adopted to confirm the chemical reaction and microstructure, curing process was studied combined with kinetics. Results showed PAB was the first-order curing reaction system and slow curing progress was conducive to mixing application, polyurethane particles changed from granular to the reticular structure during curing. The ratio of large molecular weight showed an increasing trend as temperature/time up. Furthermore, multi-stress creep recovery demonstrated that elastic recovery performance of PAB-50 (0.1 kPa) can be improved to 2.2 times, 8.1 times approximately compared with styrene–butadienestyrene block copolymer asphalt binder (SBSMA) and unmodified asphalt binder (MA). The tensile strength of PAB-30 (cured at 4d-130 °C) was 3.1 times that of 2 h (130 °C). Viscosity temperature index (VTS) value gradually increased implied that temperature sensitivity was habited by curing time. Pearson correlation coefficient illustrated that the mechanical property of PAB was positively related to the large molecular weight and conversion rate of the isocyanate group. The non-recoverable creep compliance reduction positively relied on polyurethane content and microstructure.

Albedo Change Mechanism of Asphalt Concrete Surfaces

Albedo, or average solar reflectance, is an important property affecting the development of temperature profiles within asphalt concrete (AC) pavements. It influences material durability and has an urban heat island effect. The albedo of new AC pavements ranges from 0.05 to 0.10 but rises rapidly to a stable value ranging from 0.15 to 0.25 within the first year of service. The mechanism of this rapid increase has typically been associated with oxidation of the asphalt binder, loosely referred to as “aging,” but has never been verified in the laboratory. To test this hypothesis, AC mixtures, prepared using PG 64-22 unmodified asphalt binder and aggregates, were subjected to accelerated aging using various techniques. The albedo of the AC mixtures was found to have statistically the same value of about 0.05 regardless of the extent and method of aging. An alternate hypothesis introduced is that the albedo increases as a result of abrasion loss of the surface binder, which has been tested in the laboratory. When this new abrasion procedure was applied to four field cores, the albedo increased in the same way observed in the field. This laboratory study confirmed that abrasion and loss of surface binder is the primary mechanism for the rapid increase in albedo of AC pavements.

Demonstration Project for Ground Tire Rubber and Post-Consumer Recycled Plastic-Modified Asphalt Mixtures

Research has demonstrated that asphalt pavements can be a strategic destination for some of the major streams of waste materials around the globe, such as scrap tires and plastics. Ground tire rubber (GTR) from scrap tires has been used in asphalt pavements since the 1960s but has yet to approach its full potential in relation to market adoption. The heightened restrictions imposed by China in relation to waste stream contamination in 2018 have catalyzed research on incorporating post-consumer recycled (PCR) plastics into asphalt pavements. A field demonstration project was carried out in Columbia, MO to evaluate modern recycled plastic and GTR additives in an asphalt pavement overlay. The demonstration focused on dry-process modification, which requires minimal alterations to an existing asphalt plant and allows a higher amount of recyclates to be utilized. The project was also designed to assist in the Missouri Department of Transportation’s early roll-out of balanced mix design asphalt design and quality assurance specifications. The results of the study indicated the viability of dry-process GTR and PCR plastic additives used with neat (unmodified) asphalt binder as an alternative to binders modified with virgin polymers, chemical treatments, or both, in a wet process. The results of the study also suggest the viability of hybrid wet polymer-modified binder with dry-process PCR plastic as a greener alternative to binders modified with virgin polymers, chemical treatments, or both. Future studies will be needed to examine additional PCR plastic streams, especially mixed polymer streams.