Evaluation and optimization of the engineering properties of polymer-modified asphalt

Polymers are increasingly being used to modify asphalt and enhance highway pavement performance. This paper reports the development of a procedure to evaluate and optimize a polymer-modified asphalt (PMA). Two asphalt cements and two styrene-butadiene-styrene (SBS) copolymers were mixed at ten concentration levels. The engineering properties and morphologies of the binders were investigated using a dynamic shear rheometer, scanning electron microscopy (SEM), and other rheological techniques. The morphology of the PMA was characterized by the SBS concentration and the microstructure of the copolymer. Polymer modification increased the elastic responses and dynamic moduli of asphalt binders. As the SBS concentration increased, the copolymer gradually became the dominant phase, accompanied by a change in engineering properties. Results from SEM demonstrated that, up to 6% concentration, good compatibility exists between SBS and asphalt binder. The modified binders show either a continuous asphalt phase with dispersed SBS particles or a continuous polymer phase with dispersed asphalt globules, or two interlocked continuous phases. The optimum SBS content was determined based on the formation of a critical network between asphalt and polymer.     

Thermo-rheological behavior and compatibility of modified asphalt with various styrene–butadiene structures in SBS copolymers

The knowledge of the morphological structure or effect of polymer structure on the performance of polymer-modified asphalt (PMA) is not systematic and completed yet. In this paper, SBS-modified asphalts were prepared by asphalts with different compositions and styrene–butadiene–styrene (SBS) copolymers with various styrene–butadiene structures, which in turn were subjected to frequency sweep tests, viscous measurements and fluorescence microscopy. The results revealed that the SBS-modified asphalt containing 30 wt.% styrene had the optimal viscoelastic functions and the highest viscosity, indicating enhanced viscoelastic characteristics and less sensitivity to temperature changes. Furthermore, it is less susceptible to shear forces for asphalts as the increase of styrene content because larger and stronger aggregated polystyrene domains can render deformation and movement more difficult. For system studied, the compatibility becomes poorer as the increase of styrene contents and polymer phase sizes decrease with the enhancement of styrene contents as well as their volume proportions. The scope of distribution curves becomes narrower and the swelling degree is lower as the increase of styrene contents by image analysis. As a conclusion, there is a moderate styrene content for SBS to acquire equilibrium between the compatibility and viscoelastic characteristics.     

Photoinitiator grafted styrene–butadiene–styrene triblock copolymer

Grafting of photoinitiator-4-maleimidobenzophenone (4-MBP) onto styrene–butadiene–styrene (SBS) triblock copolymer was carried out by free radical polymerization. The grafting ratio was evaluated by varying initiator concentrations, and the structure of grafted copolymer (SBS-g-MBP) was characterized by attenuated total reflectance infrared Fourier transform spectroscopy (ATR-FTIR), proton nuclear magnetic resonance (¹H NMR) and X-ray photoelectron spectroscopy (XPS). The results confirmed that 4-MBP was successfully grafted onto the SBS backbone. Thermal gravimetric analyzer (TGA), dynamic mechanical thermal analysis (DMTA), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to study the thermal properties and morphology of the SBS-g-MBP. From the data of TGA, the SBS-g-MBP had better thermal stability compared with that of SBS. DMTA testing indicated that the glass transition temperature (T_g) of SBS-g-MBP was higher than that of SBS. With the aid of SEM and AFM, the structure of micro-phase separation can be observed obviously. What is more, the aggregates become smaller compared with those of pure SBS. The experiment of UV-crosslinked SBS-g-MBP revealed that the gel fraction could be facilely controlled by adjusting grafting ratio and exposure time. The results suggested that this novel grafted copolymer could be attractive for its application in biomedical materials such as medical pressure-sensitive adhesive.     

Study on viscosity of conventional and polymer modified asphalt binders in steady and dynamic shear domain

This study focuses on evaluating the flow behavior of conventional and polymer modified asphalt binders in steady- and dynamic-shear domain, for a temperature range of 20–70 °C, using a Dynamic Shear Rheometer (DSR). Steady-shear viscosity and frequency sweep tests were carried out on two conventional (VG 10 and VG 30) and two polymer (SBS and EVA) modified asphalt binders. Applicability of the Cox–Merz principle was evaluated and complex viscosity master curves were analyzed at five different reference temperatures. Cross model was used to simulate the complex viscosity master curves at different temperatures.It was found that asphalt binders exhibited shear-thinning behavior at all the test temperatures. The critical shear rate increased with increase in temperature and was found to be lowest for plastomeric modified asphalt binder. The Cox–Merz principle was found to be valid in the zero-shear viscosity (ZSV) domain and deviated at higher frequency/shear rate for all the binders. Results from the study indicated that the ratio of ZSV can be successfully used as shift factors for construction of master curves at different reference temperatures. Cross model was found to be suitable in simulating the complex viscosity master curves at all the test temperatures. Analysis of model parameters indicated that a strong relationship exists between ZSV and the critical shear rate. ZSV and critical shear rate varied exponentially with temperature. This relationship was used to propose a simple equation for assessing the shift factors for construction of master curves.     

Influence of the epoxidation degree of a polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer on the compatibilization with an organomodified nanoclay

In this work, the addition of organophilic-modified montmorillonite into polystyrene–polybutadiene–polystyrene (SBS) triblock copolymers was investigated with and without the use of epoxidized SBS as a compatibilization agent. The nanocomposites were prepared by melting mixture at 60 rpm and 130 °C. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), tensile tests, and dynamic-mechanical analysis (DMA). XRD and TEM showed the formation of an intercalated dispersion of clay platelets oriented on the SBS surface. The AFM showed the typical lamellar microstructure of the styrene and butadiene phases of SBS. The estimation of the average distance between the styrene lamellae by AFM analysis showed that the platelets are anchored between the phases, and this structural feature caused an increase in elastic modulus. DMA analysis showed that the T _g of butadiene decreased in the nanocomposites. The decrease of the T _g and the increase in the elastic modulus are correlated to mechanisms at the micro- and the macro-scales, respectively. The decrease in the T _g indicates flexibilization at the interface, whereas the intercalation of the platelets restricted the interphase macroscale deformation.     

考虑水-温循环的SBS改性沥青复数剪切模量预估模型

为探寻季节性冻土区多次水-温循环后沥青胶结料特征官能团变化与复数剪切模量之间的关系,联合FTIR和动态剪切流变（DSR）试验,对经0、3、6、9、12、15和18次水-温循环后的苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）改性沥青进行测试,探明了多次水-温循环下SBS改性沥青复数剪切模量和特征官能团的变化规律;采用灰色关联熵分析理论数学模型,明确了复数剪切模量与特征官能团含量变化的关联程度;基于麦夸特法和通用全局优化算法对不同温度和频率下DSR测试的SBS改性沥青复数剪切模量G*及FTIR测试官能团变化指数进行多元统计回归分析,提出了SBS改性沥青复数剪切模量的预估模型。结果表明:多次水-温循环使沥青发生了水-温老化,但SBS改性剂对沥青水-温老化具有抑制作用;随着水-温循环次数的增加,沥青FTIR图谱中亚砜基与羰基呈现出明显的增大趋势;SBS改性沥青特征官能团变化对复数剪切模量影响程度由大到小的排序为脂肪族化物 > 非对称脂肪族化物 > 芳香族化合物 > SBS含量（苯乙烯+丁二烯） > 亚砜基 > 羰基;多次水-温循环后SBS改性沥青复数剪切模量随着特征官能团含量变化呈现出多元线性关系。      

Dynamic mechanical characterization of asphalt concrete mixes with modified asphalt binders

The primary objective of this work is to characterize and compare the dynamic mechanical behavior of asphalt concrete mixes with styrene butadiene styrene (SBS) polymer and crumb rubber modified asphalt binders with the behavior of mixes with unmodified viscosity grade asphalt binders. Asphalt binders are characterized for their physical and rheological properties. Simple performance tests like dynamic modulus, dynamic and static creep tests are carried out at varying temperatures and time. Dynamic modulus master curves constructed using numerical optimization technique is used to explain the time and temperature dependency of modified and unmodified asphalt binder mixes. Creep parameters estimated through regression analysis explained the permanent deformation characteristics of asphalt concrete mixes. From the dynamic mechanical characterization studies, it is found that asphalt concrete mixes with SBS polymer modified asphalt binder showed significantly higher values of dynamic modulus and reduced rate of deformation at higher temperatures when compared to asphalt concrete mixes with crumb rubber and unmodified asphalt binders. From the concept of energy dissipation, it is found that SBS polymer modification substantially reduces the energy loss at higher temperatures. Multi-factorial analysis of variance carried out using generalized liner model showed that temperature, frequency and asphalt binder type significant influences the mechanical response of asphalt concrete mixes. The mechanical response of SBS polymer modified asphalt binders are significantly correlated with the rutting resistance of asphalt concrete mixes.     

Relationship between absolute viscosity of polymer-modified bitumens and rutting resistance of pavement

New polymer-modified bituminous binders require verification of the relationship between binder properties and road pavement performance, formerly found for conventional road bitumens. The paper deals with one particular problem of polymer-bitumen (PB) viscosity and bituminous mixture rutting resistance. Non-Newtonian, shear-dependent behaviour of PB in a viscosity meassurement has been characterized by a new equation proposed by the author. This equation enables calculation of the absolute (zero shear rate) viscosity of PB and is applied for evaluation of test results at 60and 90°C. The absolute viscosity of PB at 60°C has been correlated with the bituminous mixture's rutting resistance at 45°C. Correlation with other rheological properties of PB is also examined by means of multiple regression analysis.     

Mechanical property and failure mechanism of 3D Carbon–Carbon braided composites bolted joints under unidirectional tensile loading

In this paper, the mechanical property and failure mechanism of Carbon–Carbon braided composites (C–Cs) bolted joints structure subjected to unidirectional tensile load were studied by the experimental method and numerical analysis. The braided C–Cs bolted joints with the single-bolt single-lap (SBS) and double-bolt single-lap (DBS) were tested. The dominant failure modes for both C–Cs SBS and DBS joint configurations were bearing failure and net-tension. Additionally, the finite element method (FEM) was utilized to study the mechanical property and failure mechanism of the joints. The FEM results have a good agreement with the test values. Parametrics studies were implemented by finite element (FE) analysis to classify the effects of geometric parameters including the joint width (W), edge distance (e) and the bolt pitch (p) on the SBS and DBS joint configurations. It can be found that present numerical model can be used to predict the experimental mechanical behaviors and failure modes of bolted C–Cs joints with different geometric parameters and joint configurations.     

Performance evaluation of WMA plant and field trial mixes

Warm mix asphalt (WMA) technology is still in its infancy, with significant scope for further exploration of the benefits of incorporation of higher percentages of recycled asphalt RA as well as modified binders for performance enhancement. The objective of this study was to evaluate three different WMA technologies, namely chemical and organic additives as well as foamed technology, within different mix compositions. The variables in mix composition included 10–20 % RA in surfacing mixes and 20–40 % RA in base layer mixes. The binder variables included two base binders, control mixes (no modifier) and ethylene vinyl acetate (EVA) or styrene butadiene styrene (SBS) with or without WMA technologies. A partial factorial experimental design based on the above variables was developed. Full-scale plant mixes and field (construction) mixes were produced and beams were prepared from compacted slabs and tested under 4 point loading to provide master curves and fatigue relations. Comparative results show inconsistent trends between different technologies. control mixes (HMA) can provide both higher and lower flexural stiffness than their WMA counterparts. EVA or SBS modification can provide either superior or inferior mixes to their WMA counterparts depending on the WMA technology. Generally the fatigue results of both the HMA surfacing and base layer mixes at both RA contents are superior to their equivalent WMA counterparts. The implications of these differences are explored in the publication.     

Fatigue and healing performance assessment of asphalt binder from rheological and chemical characteristics

The fatigue and healing performance of asphalt binder affect the durability of asphalt concrete and by extension, asphalt pavements. The objectives of this paper are to (1) estimate the fatigue and healing characteristics of asphalt binder by newly developed linear amplitude sweep (LAS) and LAS-based Healing (LASH) protocols, and (2) investigate the relationship between chemical composition of asphalt and engineering performance. Three neat asphalt binders (Pen-30, Pen-50 and Pen-70) and one SBS modified binder are selected for this study. Experimental results indicate that the SBS binder has advanced fatigue resistance among all tested binders and the softer neat binder with a higher penetration grade generally displays better fatigue performance. The fatigue failure occurrence is a significant threshold for healing potential comparison. The rate of healing (H^R) results suggest that the best healing potential is with Pen-70 binder in pre-failure conditions followed by the SBS binder, Pen-50 and Pen-30 binders. However, the SBS binder presents better healing performance than Pen-70 binder in post-failure condition. Further solvency fractionation, into saturates, aromatics, resins and asphaltenes, indicates that the asphaltene content is negatively proportional to the quantified binder fatigue life whereas the H^R index is found to be well correlated to the weight percents of saturates and ratio of saturates to aromatics (S/Ar). The combined use of LAS and LASH tests is recommended for effectively distinguishing and designing the fatigue-healing performance of neat and modified asphalt binders. Limiting the contents of asphaltenes would be of help to improve the binder fatigue resistance and either saturates percent or S/Ar parameter should be considered to assure the self-healing potential of asphalt binder.     

Solution blow spinning: parameters optimization and effects on the properties of nanofibers from poly(lactic acid)/dimethyl carbonate solutions

Solution blow spinning (SBS) is a process to produce non-woven fiber sheets with high porosity and an extremely large amount of surface area. In this study, a Box–Behnken experimental design (BBD) was used to optimize the processing parameters for the production of nanofibers from polymer solutions consisting of poly(lactic acid) (PLA) dissolved in dimethyl carbonate. In addition, a comparative study between SBS fibers and cast film was performed to verify the influence of the SBS process on the crystallinity and thermal properties of PLA. The PLA concentration in polymer solutions was the most significant parameter affecting fiber diameter. The BBD analysis revealed that small diameter fibers were best obtained by a combination of 8 % w/v PLA concentration, 80 psi air pressure, and a feed rate of 50 µL min^?1. The comparative study showed that both the SBS and the film casting processes increased the PLA crystallinity. However, the PLA films had a higher degree of crystallinity compared with the fibers made by the SBS process (39 and 17 %, respectively), which was attributed to the high shear created at the SBS nozzle inducing orientation and chain alignment. During the fiber formation, crystals formed with varied morphology including the α′-crystals, which have a less ordered structure and lower thermal stability compared to the α-crystals. The lower thermal stability of SBS fibers compared to the films can be explained by the lower degree of crystallinity and also by the higher surface area which can accelerate the weight loss process.     

A study of short-beam-shear and double-lap-shear specimens of glass fabric/epoxy composites

Two experimental methods for determining the inter-laminar shear strength (ILSS), are compared: the short-beam-shear (SBS) and the double-lap-shear (DLS) test method. Specimens with a constant ply angle for all layers are considered. The experimental results show a significant difference (up to 50%) in the obtained ILSS. A finite element analysis shows that both test methods underestimate the real ILSS and demonstrate that the standardized ILSS evaluation procedures are more or less valid for the SBS test, but require modifications in the case of the DLS test. Acoustic emission measurements and numerical investigations were performed to determine the real ILSS from the DLS results. The real ILSS cannot be obtained from the SBS test without an extended analysis. It is, however, possible to determine bounds for the real ILSS from the SBS results.     

反应性弹性体三元共聚物改性沥青及其混合料性能与机制

采用黏度试验和动态剪切流变试验研究了反应性弹性体三元共聚物（RET）对基质沥青与苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）改性沥青性能的影响,通过原子力显微镜（AFM）分析了SBS改性沥青和RET-SBS改性沥青的表面形貌特征,并采用车辙试验、低温弯曲试验、弯曲疲劳试验及加速加载试验评价了RET改性沥青混合料的各项技术性能,最后通过Weibull分布,分析了不同RET改性沥青混合料在不同失效概率下的疲劳性能。结果表明：RET的掺入提高了沥青的黏度和抗车辙因子,对沥青的高温性能有较大改善;通过掺入RET-SBS,增加了改性沥青中的黏性成分;相较于SBS改性沥青,RET-SBS改性沥青的表面粗糙度显著增大;RET改性剂能够明显改善沥青混合料的高温稳定性;RET与SBS改性剂复配,可有效弥补RET对沥青混合料低温性能的不足,明显改善沥青混合料的疲劳性能和高温长期稳定性。     

Effect of waste plastic bottles on the stiffness and fatigue properties of modified asphalt mixes

Nowadays, the use of recycled waste materials as modifier additives in asphalt mixes could have several economic and environmental benefits. The main purpose of this research was to investigate the effect of waste plastic bottles (Polyethylene Terephthalate (PET)) on the stiffness and specially fatigue properties of asphalt mixes at two different temperatures of 5 and 20 °C. Likewise, the effect of PET was compared to styrene butadiene styrene (SBS) which is a conventional polymer additive which has been vastly used to modify asphalt mixes. Different PET contents (2–10% by weight of bitumen) were added directly to mixture as the method of dry process. Then the resilient modulus and fatigue tests were performed on cylindrical specimens with indirect tensile loading procedure. Overall, the mix stiffness reduced by increasing the PET content. Although stiffness of asphalt mix initially increased by adding lower amount of PET. Based on the results of resilient modulus test, the stiffness of PET modified mix was acceptable and warranted the proper deformation characteristics of these mixes at heavy loading conditions. At both temperatures, PET improved the fatigue behavior of studied mixes. PET modified mixes revealed comparable stiffness and fatigue behavior to SBS at 20 °C. However, at 5 °C the fatigue life of SBS modified mixes was to some extent higher than that of PET modified ones especially at higher strain levels of 200 microstrain.     

Influence of polymer modification on low temperature behaviour of bituminous binders and mixtures

Effects of polymer modification on low-temperature properties of bituminous binders and mixtures were studied. Three bitumens were blended with 6% SBS, SEBS, EVA or EBA. Dense graded asphalt mixtures were prepared using a gyratory compactor. The low-temperature properties of the binders were characterised using dynamic shear rheometer and bending beam rheometer, and the low-temperature cracking of the mixtures evaluated by tensile stress restrained specimen test. The results indicated that low-temperature parameters were greatly dependent on the base bitumen, and in most cases, polymer modification did not show significant benefits as compared to the corresponding base bitumen. The mixture cracking temperature was found to correlate with the limiting temperatures (in bending beam rheometer) of the binders, weakly with Fraass breaking point, but not with parameters obtained using dynamic shear rheometer. Upon isothermal storage at low temperatures, the bitumens displayed physical hardening, and effect of polymer modification was small. However, physical hardening as measured by TSRST (tensile stress restrained specimen test) was not observed for the mixtures studied.     

Shear strength of palm oil clinker concrete beams

This paper presents experimental results on the shear behavior of reinforced concrete beams made of palm oil clinker concrete (POCC). Palm oil clinker (POC) is a by-product of palm oil industry and its utilization in concrete production not only solves the problem of disposing this solid waste but also helps to conserve natural resources. Seven reinforced POCC beams without shear reinforcement were fabricated and their shear behavior was tested. POCC has been classified as a lightweight structural concrete with air dry density less than 1850 kg/m³ and a 28-day compressive strength more than 20 MPa. The experimental variables which have been considered in this study were the POCC compressive strength, shear span–depth ratio (a/d) and the ratio of tensile reinforcement (ρ). The results show that the failure mode of the reinforced POCC beam is similar to that of conventional reinforced concrete beam. In addition, the shear equation of the Canadian Standard Association (CSA) can be used in designing reinforced POCC beam with ρ ⩾ 1. However, a 0.5 safety factor should be included in the formula for ρ < 1.     

Mechanism of a vegetable waste composite with polymer-modified cement (VWCPMC)

In search for improved construction materials and techniques, two main factors must be taken into account: ecological impact and production costs. The incorporation of recycled materials originating from renewable sources into cementitious cores is a feasible alternative that has gained ground in civil construction. This study investigated the matrix of a vegetable waste composite with polymer-modified cement. Several mixtures composed of Slag-Modified Portland cement, treated vegetable residue, wood from the Pinus caribaea species, latex type polymer, styrene–butadiene rubber (SBR) and an adequate water ratio for the mixtures were studied. The composite was characterized based on mortar tests carried out according to ABNT norms to determine its mechanical behavior, workability and water absorption by capillarity. Some of the essential properties of mortars, such as workability, mechanical strength and durability were substantially altered by the addition of polymers when compared to mortars without this addition. The effect of reduced capillary pores resulting from the action of the polymer contributed to decrease in the permeability of the material, preventing the penetration of aggressive agents due to the phenomenon of water transport. The composite containing vegetable residues and SBR-modified core presented the best mechanical behavior, and an increase of the polymer content resulted in greater water retention in the fresh mixture and a significant reduction in porosity.     

Moisture absorption of unidirectional hybrid composites

Unidirectional hybrid composite rods were conditioned in humid air to investigate the sorption kinetics and the effects of moisture on mechanical and physical properties. Sorption curves were obtained for both hybrid and non-hybrid composite rods to determine characteristic parameters, including the diffusion coefficient (D) and the maximum moisture uptake (M_∞). The moisture uptake for the hybrid composites generally exhibited Fickian behavior (no hybridization effects), behaving much like non-hybrid composites. A two-dimensional diffusion model was employed to calculate moisture diffusivities in the longitudinal direction. Interfaces and thermally-induced residual stresses affected the moisture diffusion. In addition, the effect of hygrothermal aging on glass transition temperature (T_g), short beam shear strength (SBS), and tensile strength was determined for hygrothermal exposure at 60 °C and 85% relative humidity (RH). Property retention and reversibility of property degradation were also measured. Microscopic inspection revealed no evidence of damage.