Styrene-butadiene-styrene Modified Asphalt Binder Research Articles

Investigating the rheological behaviour of styrene–butadiene–styrene modified asphalt

The rheological properties of the styrene–butadiene–styrene modified asphalt (SBSMA) binder have not been thoroughly investigated yet. In this study, SBSMA binders with various SBS contents and base asphalt types were prepared and analysed. Fluorescence microscopy, temperature sweeping, and multiple stress creep recovery (MSCR) tests were conducted to analyse the phase structure and rheological behaviour of SBSMA. The results indicate that the special rheological behaviour of a decreasing phase angle value in SBSMA as the temperature increases is a result of the gradual dominance of the network structure over SBSMA’s rheological behaviour. Results from MSCR tests indicate that with the increase in stress levels, the elasticity of the network structure gradually diminishes, signifying a significant stress sensitivity in the network structure. Consequently, due to the stress sensitivity of the network structure, traditional rheological indicators measured at low stress levels (such as phase angle, elastic recovery rate) may overestimate the elasticity of SBSMA at high temperatures (40–80°C).

Study on the properties of polydopamine/hexadecyltrimethoxysilane co‐deposition functionalized modified graphene oxide and composite styrene–butadiene–styrene modified asphalt binder

AbstractA composite graphene oxide (GO) modifier was prepared by co‐deposition of polydopamine (PDA) and hexadecyltrimethoxysilane (HDTMS) with hydrophobic function to enhance the interfacial interaction between GO and asphalt. Dopamine as a medium enhances the adhesion of the hydrophobic functional material HDTMS on the surface of GO. And the long alkyl chains of HDTMS molecules greatly reduce the surface free energy and ensure the dispersion stability of composite GO modifier in styrene–butadiene–styrene (SBS) modified asphalt. The physical properties of modified asphalt show that the ductility, high‐temperature stability, and viscosity of asphalt can be improved by the addition of PDA/HDTMS composite GO modifiers (DH‐GO). Among them, 0.04% DH‐GO composite SBS modified asphalt binder (DH‐GO/SBSMB) has the best mechanical properties. Compared with 0.05% GO composite SBS modified asphalt binder (GO/SBSMB), the softening point of 0.04% DH‐GO/SBSMB increased by 8.3%, the penetration degree decreased by 9.7%, and the elongation increased by 18.2%. Dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR) and rotational viscosity (RV) tests show that 0.04% DH‐GO/SBSMB has higher high‐temperature stability, plasticity, and viscosity than 0.05%GO/SBSMB, which meets the requirements of asphalt construction specifications.

Nonlinear viscoelastoplastic kinetics for high-temperature performance of modified asphalt binders

Modified additives are widely used to improve the high-temperature performance of asphalt binders. However, the high-temperature performance of modified asphalt binders cannot be well evaluated by the existing methods. To address this issue, this study aims to develop a new nonlinear viscoelastoplastic kinetics method to evaluate the high-temperature performance of modified asphalt binders. Styrene-butadiene-styrene (SBS), rubber modified asphalt binders and their aged materials are employed. First, the non-recoverable creep compliance from the standard and modified Multiple Stress Creep and Recovery (MSCR) tests are used to evaluate the high-temperature performance of asphalt binders. Then, the viscoplastic strain and activation energy from creep-recovery tests are adopted to evaluate the high-temperature performance of asphalt binders based on nonlinear viscoelastoplastic kinetics method. Results show that the high-temperature performance results from the standard and modified MSCR tests are inconsistent. The viscoplastic strain of unaged SBS modified asphalt binders shows different trends compared with other asphalt binders. It rapidly increases at the initial loading stage, then follows by a reinforcement period, and finally maintains a steady growth rate, while the reinforcement period will disappear after aging. The viscoplastic activation energy from the nonlinear viscoelastoplastic kinetics method can characterize the stable high-temperature performance of asphalt binders, avoiding controversy caused by the number of cycles in MSCR tests.

Development of a new rejuvenator for aged SBS modified asphalt binder

The objective of this study is to evaluate the effectiveness of active reagents (i.e., methylene-bis(4-cyclohexylisocyanate) (HMDI) and 1,6-hexanediol diglycidyl ether (HDE)) and epoxidized soybean oil (ESO) in rejuvenating aged styrene-butadiene-styrene (SBS)-modified asphalt binder (SBSPAV) by promoting the interaction of aged binders with virgin asphalts. To achieve this objective, a multidisciplinary approach combining chemical and engineering methods was adopted. The chemical characterization of asphalt binders includes SARA fractionation (saturates, aromatics, resins and asphaltenes) and Fourier transform infrared spectroscopy (FTIR) tests. Rheological evaluation of the asphalt binders was utilized assessing fatigue, rutting, and thermal cracking resistance. The results indicated that the addition of ESO helped to adjust the low temperature performance of SBSPAV. Compared to SBS-modified asphalt (SBSMA), the low temperature relaxation modulus of ESO-rejuvenated asphalt has a 35.8% reduction. Whereas the addition of ESO alone could did not restore the performance of the SBSPAV. The addition of HMDI and ESO could improve the high-temperature performance of SBSPAV. Compared to SBSMA at 52 °C, the rutting factors of HMDI-rejuvenated asphalt with 0.5% and 1.0% were improved by 43.12% and 97.86%, respectively. According to the MSCR results, with a 1.0% content, the recovery rates of HDE-rejuvenated asphalt and HMDI-rejuvenated asphalt increased by 8.2% and −23.4%, respectively. The rejuvenated binders with HMDI showed better elastic recovery properties and permanent deformation resistance than the other studied binders. HMDI can increase the asphaltene content in rejuvenated asphalt, while HDE can increase the aromatic fraction content in rejuvenated asphalt, according to the SARA fraction results. The asphaltene content of 1.0% HMDI-rejuvenated asphalt increased by about 2.13%, and the aromatic content of 1.0% HDE-rejuvenated asphalt increased by about 3.46%. The FTIR results showed that HMDI chemically reacted with SBSPAV to form carbamate bonds with a stable chemical structure, and both HMDI and HDE could partially restore the broken chain structure of SBS. Overall, the results indicated that HMDI and HDE (combined with ESO) have the potential to be used to rejuvenate SBSPAV and that the recommended optimum contents for HMDI and HDE are 0.5%–1.0%.

Effect of glutaraldehyde-chitosan crosslinked graphene oxide on high temperature properties of SBS modified asphalt

Composite material using glutaraldehyde (GA) cross-linked chitosan (CTS) and graphene oxide (GO-CTS-GA) was designed applying electrostatic interaction strategy under strong alkali environment. GO-CTS-GA was in turn applied to prepare styrene butadiene styrene (SBS) GO-CTS-GA/SBS composite modified asphalt (MA)_binder. The effect of GO-CTS-GA on the physical properties of SBS modified asphalt binder was investigated and its mechanism of action was analyzed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy tests confirmed the retainment of GO flakes microscopic dimensions while compensating for the chemical structural defects and mechanical property damage of GO. The results of dynamic shear rheometer and multi-stress creep recovery tests indicated that the GO-CTS-GA/SBS-MA binder exhibited better viscosity performance and elasticity performance, rutting resistance and high temperature thermal stability. At 64 °C, the loss modulus of 0.10 % GO-CTS-GA/SBS-MA was 29.5 % and 25.2 % higher than that of SBS-MA and GO/SBS-MA, respectively. SEM and TEM analyses of the four components of asphalt binder before and after modification revealed that the change of asphaltene microscopic morphology seriously affects the stability of asphalt colloidal system. Fourier transform infra-red analysis of the MA binder revealed that the change of saturation fraction and colloidal polarity by GO-CTS-GA is responsible for the dispersion and cross-linking of SBS chain segments in the asphalt binder phase. This study provides important reference information for nanomaterials to change the macroscopic mechanical properties by modulating the microstructure, physical and chemical properties of asphalt binder at the micro and nano-scale.

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.

Optimizing Regenerant Content of Aged SBS Modified Asphalt Binder Based on High- and Low-Temperature Performance

The performance of the recycled asphalt pavement is directly influenced by the content of the used regenerant (i.e., rejuvenator and/or unaged asphalt binder). The goal of this study is to optimize regenerant content of aged styrene-butadiene-styrene (SBS) modified asphalt binder based on high-temperature creep and low-temperature relaxation performance tests. Initially, penetration, ductility, softening point, multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) tests were carried out to investigate the rheological behavior of the aged SBS modified binder (AMB) regenerated with different contents of the rejuvenator and unaged SBS modified binder (UMB). A method is proposed, based on the rheological behavior of the regenerated AMB, to determine the optimum contents of the regenerants (i.e., rejuvenator and UMB). To reach a successful trade-off between low- and high-temperature properties of the regenerated AMB, the relaxation rate VR and nonrecoverable creep compliance J3.2 (at 3.2 kPa) were selected as the evaluation indices to settle the optimum contents of the rejuvenator and UMB. The results showed that the ductility of regenerated AMB is on par with the UMB when the contents of rejuvenator and UMB are 4% and 70%, respectively. The nonrecoverable creep compliance and relaxation rate of the regenerated AMB tended to increase with the increase in the content of the rejuvenator and UMB, whereas the recovery rate and relaxation modulus decreased. It indicated that the low-temperature performance increased while the high-temperature performance was adversely affected by the increase in the content of the regenerants. The VR and J3.2 of the regenerated AMB were comparable to those of unaged state, when the contents of the rejuvenator and UMB in the aged binder were 5% and 70%, respectively. It indicated that the high-temperature creep and low-temperature relaxation performance of the AMB reach a balance.

Using molecular dynamics and experiments to investigate the morphology and micro-structure of SBS modified asphalt binder

The study aimed at investigating the compatibility between styrene-butadiene-styrene (SBS) and asphalt, and the influence of SBS on morphology and micro-structure of asphalt through molecular dynamics (MD) and experiments method. In this work, the solubility parameter and molecular structure parameters of SBS modified asphalt were calculated by Materials Studio software, and its morphology of were investigated by microscope techniques. The results showed that solubility parameter of SBS and asphalt fluctuated along with simulation temperature, and the difference between SBS and asphalt is around 10.5 (J/cm3)0.5, which means these two materials cannot reach a total miscible state, and the scanning electron microscope (SEM) and fluorescence microscope (FM) results on the compatibility between asphalt and SBS corresponding with the simulation results. The interaction simulation on SBS and asphalt indicated that van der Waals interaction makes a significant contribution to non-bond interaction and plays a dominate role in the miscibility between asphalt and SBS. The structure parameters of radial distribution function (RDF) and radius of gyration showed that SBS had an a evident influence on the structure of asphalt molecule, for it increased the tightness of the asphalt and reinforced the ractility of branched-chain of asphalt components. Through AFM test results, we also found that SBS increased the bee-like phase of asphalt, and bring asphalt a better physical properties.

Compatibility and Storage Stability of Asphalt Binder Modified by Styrene-Butadiene-Styrene (SBS) Graft Copolymer

A styrene-butadiene-styrene triblock copolymer (SBS) was grafted with an unsaturated polar monomer (monomer A) composed of maleic anhydride (MAH) and methoxy polyethylene (MPEG) via a ring-opening reaction after epoxidizing styrene-butadiene-styrene triblock copolymer (ESBS). The microscopic changes of SBS before and after grafting has been characterized with Fourier transform infrared spectrum (FT-IR), X-ray photoelectron spectroscopy (XPS) and gel permeation chromatography (GPC). The results revealed that the monomer A was successfully grafted on SBS backbone, and the maximum graft ratio (GR) was 20.32%. To verify the compatibility between SBS and asphalt, solubility parameters and surface free energy (SFE) of SBS, grafted SBS and asphalt were measured. It was found that the solubility parameter and SFE of grafted SBS were closer to asphalt compared with SBS. It also has been confirmed from storage stability that the temperature susceptibility of grafted SBS modified asphalt was reduced in compare with SBS modified asphalt binder. As consequence, the use of grafted copolymer can be considered a suitable alternative for modification of asphalt binder in pavement.

Chemical and rheological characteristics of accelerate aged asphalt binders using rolling thin film oven

The SUPERPAVE (Superior Performance Pavements) system and design method uses a rolling thin film oven (RTFO) test in the laboratory to simulate short-term ageing. The accelerated asphalt ageing method to simulate the long-term ageing. Whereas the method accelerated asphalt ageing using a pressure ageing vessel (PAV) takes an extended period of time to prepare the samples. In this case, the present study is an attempt to achieve accelerated long-term aged binder similar to that of PAV by running multiple cycles of RTFO maintained at 163 °C for a duration of 85 min per cycle. To achieve this, two unmodified binders of PG 70-XX were obtained from two different sources, and a styrene–butadienestyrene (SBS) modified binder of PG 64-XX was selected. The rheological characteristics such as viscosity at elevated temperature using rotational viscometer (RV), rutting and fatigue parameters using dynamic shear rheometer (DSR), the chemical characteristics such as carbonyl and sulfoxide indices using Fourier transform infrared spectroscopy (FTIR) are used to compare between the RTFO and PAV aged binders. The rheological results suggest that, to produce an accelerated aged binder using RTFO for unmodified and SBS modified asphalt binder with respect to G*sinδ, the RTFO duration of 5 h 20 min and 6 h can be used as alternative for ASTM D6521 respectively. In additions, the rutting parameter G*/sinδ shows to match its PAV aged binder properties at 256 ± 6 min for both PG 70-XX, and 269 min for PG 64-XX modified binder. Further, the variations in functional group concentration and changes in volatile mass are limited the achievement of specific RTFO duration.

Compound modification of asphalt with styrene-butadiene-styrene and waste polyethylene terephthalate functionalized additives

The modification of asphalt binder using recycled plastics such as polyethylene terephthalate (PET) may improve its rheological characteristics while providing secondary environmental benefits. In this study, the chemical recycling of PET was conducted to synthesize additives and used in conjunction with styrene-butadiene-styrene (SBS) to modify asphalt binder. The properties of the modified asphalt binder (PS-MB) were characterized through both conventional binder tests, including penetration, softening point, viscosity, and storage stability tests, and Superpave binder tests, such as multiple stress creep recovery (MSCR), rutting factor (G∗/Sinδ), fatigue factor (G∗Sinδ), and low temperature creep stiffness tests. These properties were then compared with those of the unmodified asphalt binder and asphalt binder modified with SBS (S-MB). To study the effects of PET additives on the physical and chemical structures of S-MB, additional analyses were done using scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The outcomes of the laboratory investigation indicated that using waste PET derived additives as modifiers for SBS modified asphalt binder not only provides a functioning way to recycle waste PET, but also enhances the rheological properties of SBS modified asphalt binder as a paving material.

Determination of time-temperature superposition relationship of SBS modified asphalt based on special rheological phenomenon caused by SBS-formed structure in asphalt matrix

The time-temperature equivalency theory is an important component in asphalt rheology and has been extensively applied in asphalt rheological characterization. The presence of phase angle plateau region shown by styrene–butadiene–styrene (SBS) modified asphalt binder are tightly related with time-temperature conditions, which can be utilized to develop a new potential method for determining time-temperature superposition relationship of SBS modified asphalt (SBSMA). In this paper, the relationship between SBS modifier dosage and its formed morphology structure in asphalt matrix was revealed by fluorescence microscope test. Then, the characteristics and the cause of rheological behaviors for SBSMA with different SBS dosages were described and analyzed, respectively. Further, in terms of different SBSMA binders, the specific ways to determine the time-temperature superposition relationship based on their respective special rheological phenomena were put forward and validated. The results indicate that the structures formed by SBS in asphalt matrix transform from dispersed phase to continuous phase as the SBS dosage increases. SBSMA binders with more than 2% dosage of SBS can all show plateau regions concerning phase angle, while the type of plateau region is varying for different SBS dosages. For SBSMA containing 4% dosage of SBS, the time-temperature conditions that correspond to the end point of every “concave” plateau region are equivalent. For SBSMA containing 6% and 8% dosage of SBS, time-temperature conditions that correspond to the middle point of “convex” plateau region are equivalent.

Influence of different high viscosity modifiers on the aging behaviors of SBSMA

High viscosity modifier (HVM) is a polymer material that has been widely employed in the porous pavement. However, its road performance deteriorates as the use of time increases. One of the main reasons for the deterioration of road performance is the aging of polymer materials. The purpose of this article was to investigate the influences of four different HVMs on the aging resistance of styrene-butadienestyrene modified asphalt (SBSMA). Composite SBSMA binders were prepared by using different HVMs. The functional groups of HVMs and SBSMA binder with and without HVMs before aging were characterized by Attenuated total reflection (ATR)-Fourier transform infrared (FTIR). All the samples were tested with thin film oven test (TFOT) and pressure aging vessel (PAV), respectively. Physical and rheological properties were tested on all samples of SBSMA binders with and without HVMs, and chemical properties were characterized by ATR-FTIR. FTIR spectroscopy test result shows that HVMs have good compatibility with SBSMA binder and the aging resistance of the SBSMA can be improved through HVMs, but the improvement effect is reduced with the increase of aging degree. With the addition of HVMs, the high-temperature stability and low temperature properties of SBSMA binders are improved. After two aging methods, blending HVMs into SBSMA binder shows lower aging indices, indicating their good anti-aging properties. Moreover, on the basis of correlation analysis, the aging degree of high viscosity modified asphalt could be predicted by softening point increment and viscosity aging index.

Partially replacing Styrene-Butadiene-Styrene (SBS) with other asphalt binder modifier: Feasibility study

Although a number of studies indicated that the addition of Styrene-Butadiene-Styrene (SBS) brings a lot of benefits on properties of asphalt binder, some studied did report that SBS had some drawbacks as asphalt modifier, such as poor storage stability. The primary objective of this study is to investigate the feasibility of partially replacing SBS with APAO as asphalt binder modifier. The storage stability, workability, physical and rheological properties, aging properties, and the chemical properties of the SBS-APAO compound modified asphalt binders were investigated. The results indicated that the SBS-APAO compound modified asphalt binders with APAO content of 3% or higher showed better storage stability, high- and intermediate-temperature properties than the SBS modified asphalt binder. In addition, the SBS-APAO compound modified binders showed comparable workability and low-temperature properties in comparison to the SBS modified asphalt binder. Overall, it has potential to improve the storage stability and rheological properties of SBS modified asphalt binder without raising the material's cost by partially replacing 2% of SBS with 3% of APAO (by weight of asphalt binder).

Characterization of Recovery in Asphalt Binders.

The recovery property of asphalt binders plays an important role in the performance and service life of asphalt pavements. Since the internal stress is the driving force for the recovery of asphalt binders, the accurate measurement of the internal stress is full of significance. Based on this rationale, this paper aims to measure the internal stress of asphalt binders using a creep and step-loading recovery (CSR) test and characterizing the recovery behaviors by the internal stress. One base asphalt binder and one styrene–butadiene–styrene (SBS)-modified binder are selected in this study. The key elements of the CSR test are carefully designed and its accuracy is verified in three aspects, including the loading conditions, the effect of disturbance by step-loads, and accuracy of measured internal stress. Then, a kinetics-based recovery model is proposed to evaluate and predict the recovery properties of asphalt binders from its causal relationship. The constant-rate recovery activation energy indicates a major difference with nondestructive and destructive loading conditions, while the fast-rate recovery activation energy keeps almost constant regardless of the loading conditions. After that, the healing activation energy is calculated by using the kinetics-based recovery model and the results indicate that SBS modified asphalt binder shows better healing abilities than a base binder.

Effect of styrene-butadiene-styrene (SBS) on the rheological behavior of asphalt binders

The binders in pavement could support the loading in either linear or nonlinear regime. The linear viscoelasticity of asphalt binders was well established, however, a few of researches focused on the nonlinear viscoelasticity of asphalt binders. Here, this paper deals with the effects that SBS exerts on the linear and nonlinear rheological behavior of asphalt binders. The nonlinear rheological behavior of one kind of neat asphalt binder and the corresponding SBS modified asphalt binders under large amplitude oscillatory shear stress (LAOS stress) is analyzed by Fourier Transform (FT)-rheology and strain decomposition methods. The linear viscoelastic measurements show that the elastic proportion and the complexity of rheological behavior of the asphalt binder increases with increase in SBS content. The nonlinear viscoelastic measurements reveal that the relative nonlinearity of asphalt binders increases with increase in stress and decrease in frequency; the relationship between I3/I1 and stress amplitude can obey the sigmoidal function; the intrinsic nonlinearity Q0 decreases with increase in frequency and increases with the increase of SBS content. Both the FT analysis and decomposition results show that the nonlinearity of SBS modified asphalt binder is more obvious than neat asphalt binder and increases with the increase of SBS content. SBS could increase the nonlinearity and the elastic proportion of asphalt binder and decrease its fluidity. All the studied binders exhibit stress softening and stress thinning under all the studied test conditions.

Microstructure of neat and SBS modified asphalt binder by small-angle neutron scattering

The microstructure of asphalt binders is believed to have a significant impact on the performance of binders used in roadway constructions. However, there are only limited studies of their nanoscale to microscale structures. Here, small angle neutron scattering (SANS) is used to study the nanoscale structure of neat asphalt binder, styrene-butadienestyrene (SBS) block copolymers and SBS modified asphalt binder. The SANS pattern for asphalt binder demonstrates that it exhibits a colloidal structure comprised of asphaltenes surrounded by resins dispersed in saturates and aromatics. Fractal-core-shell model fits to these patterns indicate that the asphaltene core size decreases with increasing temperature. Both SANS and rheology confirm that SBS modified asphalt has a thermo-reversible phase transition around 110 °C, where the SBS micelles swell and lose scattering contrast above this temperature. The thermo-reversibility of this phenomenon indicates that the mechanism of SBS modification is mostly a physical modification of the nanoscale structure as proposed in the colloidal model of asphalt. Modeling of the SANS patterns shows that neat SBS and SBS dispersed in asphalt binder have a lamellar structure surrounded by a shell. These results are useful for understanding the relationship between the nanoscale structure of asphalt binder and pavement performance, as well as potentially developing new types of modified asphalt binders.

Evaluation of Degradation of SBS Modified Asphalt Binder Because of RTFO, PAV, and UV Aging using a Novel Extensional Deformation Test

Styrene-butadiene-styrene (SBS) modified PG 64-22 and PG 76-22 binders are studied to investigate the degradation of polymer because of aging applied by: rolling thin film oven (RTFO), pressure aging vessel (PAV), and ultraviolet (UV). Upon observing the temperature increment of unmodified binder during high shear mixing, a polymer mixing procedure has been established. SBS (2%, 4%, and 6%), polyphosphoric acid (PPA) (0.5%, 2%, and 3.5%), and PPA (2%)-SBS (0.5%, 2%, and 3.5%) are mixed with PG 64-22 binder. Sentmanat extensional rheometer, based on dynamic shear rheometer, is used to investigate the extensional deformation characteristics in which SBS modified binders exhibit both first peak elongation force, F1, and second peak elongation force, F2, whereas, unmodified binders and PPA modified binders exhibit no F2. SBS is the most effective in increasing F2 with an increasing rate of 1.16N/% of SBS polymer. At 12°C and 16°C, F2 of RTFO aged SBS modified binder reduces, which indicates the polymer is degrading. In the case of PAV aged SBS modified binder, no F2 is found at 12°C and 16°C. With the increment of temperature, the PAV aged sample shows F2, but the value is less than the F2 of the original and RTFO aged binder of similar stiffness (F1). A normalized parameter, F2/F1, also shows that RTFO and PAV aging degrade SBS. Evaluation of UV aged SBS modified binder shows no F2 at any temperature while oven aged binder shows F2 value at similar aging temperature, duration, and thickness, indicating SBS completely degrades because of UV aging.

Critical matters in using Attenuated Total Reflectance Fourier Transform Infrared to characterize the polymer degradation in Styrene–Butadiene–Styrene-modified asphalt binders

Styrene–Butadiene–Styrene (SBS) polymer is widely employed as an outstanding asphalt modifier. However, inevitable field aging will cause degradation of SBS polymer and consequently shortened pavement lifespan. To characterize the SBS degradation of SBS-modified asphalt (SBSMA), infrared spectroscopy is frequently utilized and the infrared intensity of 966 cm−1 peak is usually employed as an SBS content indicator. However, in this study, Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), which is a promising alternative to conventional transmission-FTIR, yielded an abnormal 966 cm−1 peak intensity growth after asphalt aging. To investigate this phenomenon, two types of SBSMAs (radial and linear) were laboratorial aged and their infrared spectra obtained by ART-FTIR and transmission-FTIR were compared. It was found that aging significantly reduced the SBS polymer particle size and facilitated SBS dispersion, and a more uniform SBS dispersion combined with the relatively shallow scanning depth of ATR-FTIR (2 μm) caused the different result between ATR-FTIR and transmission-FTIR. A mathematical model was presented to explain this phenomenon. Moreover, a novel infrared index specially developed for ATR-FTIR was proposed to assess the degradation of SBS polymer.

Investigation of sodium stearate organically modified LDHs effect on the anti aging properties of asphalt binder

The layered double hydroxides (LDHs) has been widely used as the anti-aging modifier to improve the anti aging performance of an asphalt binder, but for the different chemical and physical properties of LDHs with asphalt binder, the compatibility of them is not very well, therefore the best modification effect can not be obtained. The sodium stearate was designated to organically modify the LDHs to enhance its improvement effect on the anti aging performance of asphalt binder. The modern test instruments such as Fourier transform infrared spectroscopy, X-ray diffractometer, scanning electron microscopy, ultraviolet visible spectrophotometer were used to investigate the sodium stearate effect on the characteristics of LDHs. In addition, the LDHs modified styrene–butadienestyrene modified asphalt (LDHs/SBS MA) and sodium stearate organically modified LDHs (SS-LDHs) modified styrene–butadienestyrene modified asphalt (SS-LDHs/SBS MA) were prepared by the melt blending method, the thin film oven test and UV aging test were conducted to simulate the short term thermo-oxidative aging and UV aging of asphalt binder respectively. Finally, the chemical structure, viscosity, and complex modulus of LDHs/SBS MA and SS-LDHs/SBS MA before and after aging were tested respectively. The results show that the sodium stearate can improve the compatibility of LDHs with styrene–butadienestyrene modified asphalt binder (SBS MA). Both LDHs and SS-LDHs can improve the anti thermo-oxidative aging and anti UV aging performance of SBS MA. Notably, the improvement effect of SS-LDHs on the anti aging performance of SBS MA is much better than that of LDHs.