Determination of zero shear viscosity of warm asphalt binders

With the increasing awareness of the warm asphalt technology, it is imperative to study the properties of the binders containing the warm asphalt additives thoroughly, especially since not much research has been conducted on warm asphalt binder properties to date. Also, in the recent years, researchers have observed that the SHRP rutting parameter G¹/sin δ is not very effective in predicting the rutting performance of binders, especially in case of modified binders. Zero shear viscosity (ZSV) has been evaluated to determine its effectiveness in predicting the rutting behavior of asphalt binders. Thus, in this paper, the ZSV of five asphalt binders with and without the warm asphalt additives, Asphamin^® and Sasobit^®, were calculated using the different models and test methods available in literature. From the test results, it was observed that the addition of the warm asphalt additives increased the ZSV of all the five binders used in this study. It was also observed that the different test methods gave different ZSV values, and that the selection of the test methods and the testing parameters are crucial parameters.     

聚合物改性沥青低温性能指标研究

研究了4类聚合物改性沥青的常规性能与低温流变性能,并对其混合料进行了低温弯曲试验.结合灰色关联理论,对聚合物改性沥青的多个低温性能指标与混合料低温弯曲试验结果进行了相关性分析.结果表明:聚合物改性沥青的玻璃态转变温度、低温流变性能指标、低温测力延度试验的黏韧性指标与沥青混合料低温弯曲试验结果均具有良好的关联性,其中的玻璃态转变温度关联度最高,能较好地反映聚合物改性沥青的低温性能,其次是低温流变指标和黏韧性指标.     

SBS改性沥青热储存及运输过程中的降解研究

通过室内模拟低空气浓度(或相对绝氧)环境下苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)改性沥青的热降解过程,测试和分析了不同条件下SBS改性沥青的性能.结果表明:在热降解过程中,SBS改性沥青低温抗裂能力随时间的延长或温度的升高而逐渐降低;与低空气浓度下热降解对SBS改性沥青微观结构的影响相比,SBS改性沥青在高空气浓度下热降解过程中有更高的羰基和更低丁二烯含量.在生产、储存和运输SBS改性沥青时,需要充分考虑时间、温度以及空气浓度对其性能的影响.     

Comprehensive analysis of surface free energy of asphalts and aggregates and the effects of changes in pH

Moisture damage is a major factor in the deterioration of asphalt pavements. In order to combat this problem, it is essential to understand the effects of moisture on the adhesive and cohesive bonds in asphalt concrete mixtures. These effects can be quantified through the use of surface free energy, which is a thermodynamic material property that has been successfully used to select asphalt binders and aggregates that have the necessary compatibility to firm strong bonds and resist moisture damage.This study aimed at understanding the effects of material characteristics and additives on surface energy and the resulting bond between asphalt binders and aggregates. As such, the study involved measuring the surface free energy of 37 neat and polymer modified asphalt binders and 11 aggregates were measured. In addition, the surface free energy was measured for three asphalt binders after two anti-strip agents were added separately (six binder-anti-strip agent combinations) and for nine asphalt binders that were both short and long-term aged. The study also examined the effect of water pH on surface energy and water-aggregate adhesive bond. It was found that anti-strip agents, in general, reduced the cohesive bond energy of asphalt binder, allowing better wetting and adhesion to aggregates and increase in resistance to moisture damage. Aging of the asphalt either increased or decreased the cohesive bond depending upon the chemical composition of the unaged asphalt binder. Statistical analysis was conducted to rank the moisture resistance of asphalt binders and asphalt–aggregate combinations, respectively. The results showed that the pH of the water increased slightly due to contact with the aggregates, but did not significantly alter the total surface tension of the water or surface free energy components of the asphalt binder.     

Effects of aging on the properties of modified asphalt binder with flame retardants

Effects of aging on the properties of asphalt binders modified by incorporating Styrene–Butadiene–Styrene (SBS) and flame retardants (FR) were studied. Asphalt binders were artificially aged in the rolling thin film oven (RTFOT) and Pressure Aging Vessel (PAV). The flame retardancy of modified asphalt binders were characterized using limited oxygen index (LOI), and the effects of aging on the properties of asphalt binders were studied using Brookfield viscometer test and dynamic shear rheometer test. Experimental results indicated that the flame retardancy of asphalt binder was increased after aging. But the increasing amount of LOI is low when the modified asphalt binder containing more flame retardants. The variation of the LOI, softening point, penetration, ductility and viscosity of asphalt binder decreased with flame retardant content increasing, meaning the flame retardants can improve the thermo-oxidative aging resistance of asphalt binder. Furthermore, the G^*/sin δ, stiffness and m-value of flame retardant modified asphalt binders display smaller changes after two different aging.     

High temperature properties of rubberized binders containing warm asphalt additives

Several studies have been conducted evaluating the properties of warm mix asphalt (WMA), and it is observed that warm asphalt additives work in different ways to either reduce the viscosity of the binder or to allow better workability of the mix at lower temperatures. In terms of rubberized asphalt mixtures, they are compacted at a higher temperature than conventional mixtures, based on the field experience. If the technologies of warm mix asphalt are incorporated, it is expected to reduce the mixing and compaction temperatures of rubberized asphalt mixtures to those of conventional mixtures. This paper presents the high temperature properties of rubberized binders containing warm asphalt additives. Rubberized binders were produced at 10% by binder weight using five binder sources, and the binders with the additives were produced using two (i.e. Aspha-min^® and Sasobit^®) of the available processes and artificially short-term aged through the rolling thin film oven (RTFO) method. Tests were conducted on the binders using the rotational viscometer and the Dynamic Shear Rheometer. The results indicated that the viscosity properties of rubberized binders can be changed significantly through the use of warm asphalt additives. Also, the addition of the additives was found to improve rutting resistance of the rubberized binders.     

基于重复蠕变的改性沥青非线性黏弹响应分析

对4种改性沥青和1种基质沥青进行高温条件下较宽应力范围的重复蠕变试验,计算不同温度和应力水平下的不可恢复蠕变柔量Junr,分析改性沥青黏弹响应从线性到非线性的变化规律,再选择夏季沥青路面典型高温下沥青非线性响应区域内的Junr值,与沥青混合料车辙试验结果进行相关性分析.结果表明：随着温度升高,沥青的线性范围明显减小;进入非线性响应区域后,Junr值迅速增大,沥青抗永久变形能力明显降低;改性沥青的高温性能在不同温度和应力水平下存在差异,在较高温度和应力下,高强改性沥青的高温性能最优;有限样本条件下,沥青在非线性响应区域内的Junr值与沥青混合料车辙试验结果相关性较好,说明沥青混合料永久变形与沥青非线性黏弹响应关系密切.     

Effect of polyester resin additive on the properties of asphalt binders and mixtures

The properties of AC-5 control asphalt binder, mixture containing the same asphalt were compared with the properties of AC-10 asphalt binder modified by 0.75%, 1%, 2%, and 3% of polyester resin (PR), mixture containing pure AC-10 and AC-10 modified by 0.75% of PR, respectively.Initial research was done to determine the physical properties of unmodified and PR modified asphalt binders. The AC-10 asphalt binder modified by 0.75% of PR had good results compared to AC-5 control asphalt binder and all other modified binders, and hence this modified binder as well as unmodified binders were used to prepare Marshall samples for Marshall stability and flow, indirect tensile stiffness modulus (ITSM), indirect tensile strength (ITS) and creep stiffness tests.The results of investigation indicate that AC-10 + 0.75% PR binder has better physical properties than AC-5 control asphalt binder and, at the same time, PR improves mechanical properties of asphalt mixture.     

Performance based binder type selection using mixed integer programming technique

The rationale behind an asphalt mix design is optimizing the binder content for the desired aggregate gradation to satisfy the specified volumetric and strength requirements. The designed asphalt mix should be durable and cost effective. The mechanical behavior of a designed asphalt mix is affected by the traffic loading and climatic variations. To improve the mechanical properties of asphalt mixes, additives are added to the base asphalt binder. These binders are called modified asphalt binders. The objectives of the present study are to compare the performance of asphalt mixes with different binders by two different mix design methods and to optimize the asphalt binder type to achieve the desired performance. Two methods of mix design namely, Marshall and Superpave mix design methods are considered. The performances of asphalt mixes viz., tensile strength, moisture damage, densification and rutting resistance were compared. The results indicated a statistically significant difference in the optimum asphalt binder content from the two mix design methods. The Marshall method of asphalt mix design is found to yield lower optimal asphalt binder content when compared to the Superpave method of mix design. The moisture susceptibility and construction densification index of asphalt mixes designed using Superpave method were found to be significantly lower than that of the mixes designed by Marshall method. Optimization using a Mixed Integer Linear Program (MILP) indicated that the polymer modified asphalt binder outperforms the requirements of engineering properties when compared to other commercial binders used in the study.     

高模量沥青胶结料路用性能流变学分析

以基质沥青、高模量改性沥青和SBS改性沥青的路用性能为研究对象,通过常规流变学试验方法,对比研究了高模量外掺剂和SBS改性剂对基质沥青黏弹特性的定性影响,并量化分析了不同外掺剂种类对基质沥青路用性能的影响;通过多应力重复蠕变恢复试验,对比研究了高模量外掺剂和SBS改性剂在提高基质沥青抗车辙能力上的差异和提高效果;基于加速疲劳试验方法对上述三大类沥青胶结料的疲劳损伤及失效特性进行对比研究,分析比较了不同沥青胶结料在疲劳损伤演化和疲劳寿命方面的差异.结果表明:RA(resin alloy)和PR(PR plasts)这2种常用高模量外掺剂在提高沥青胶结料劲度模量方面具有相近的效应;三大类沥青胶结料在相同试验温度条件下的永久变形抵抗能力排序为:高模量改性沥青SBS改性沥青基质沥青;三大类沥青胶结料疲劳寿命的排序为:SBS改性沥青高模量改性沥青基质沥青;此外,在使用相同基质沥青的条件下,掺加RA的高模量改性沥青比掺加PR的高模量改性沥青具有更好的抗疲劳性能.     

Aging analysis of rubberized asphalt binders and mixes using gel permeation chromatography

This study was initiated to investigate the aging characteristics of binders due to the reaction with the crumb rubber. For this laboratory study, the crumb rubber modified (CRM) and control binders were aged using an oven aging method. Also, asphalt mixtures with CRM or control binders were made and subjected to short-term and long-term aging treatments. The properties of these aged binders were evaluated using gel permeation chromatography (GPC) test procedures. The results from this study showed that: (1) the higher CRM percentage resulted in the higher large molecular size (LMS) value of asphalt binder under the binder aging conditions, and the rate of increase in the LMS value was found to have a relation to the CRM percentage. The asphalt binders with higher CRM percentages (15% and 20%) had a trend the LMS values decrease after a certain level. This finding is thought to be related to the required time for the rubber to be fully digested; (2) after subjecting to the long-term oven aging, the asphalt mixtures with the control and CRM modified binders were found to have statistically insignificant differences in aging level, measured using the LMS values. The very thin film thickness of binder in asphalt mixture and the aging temperature of 100 °C insufficient to enable a reaction were considered to be the main reasons that no differences were observed from the standpoint of the aging effect.     

Laboratory evaluation of antioxidants for asphalt binders

A laboratory study was carried to investigate whether certain antioxidants could be used to reduce age-hardening in asphalt binders. Several additives including: Vitamin E, Irganox 1010, Irgafos P-EPQ, carbon black, hydrated lime, and DLTDP/furfural, were evaluated. The modified asphalt binders were subjected to two accelerated oxidative aging regimes in the laboratory. Short-term oxidative aging of the binders was simulated using a rolling thin film oven while long-term aging was performed using a pressure aging vessel. The effects of aging on the binders were evaluated based on changes in rheological properties of asphalt binders undergoing oxidative aging. Binders modified with a combination of furfural and DLTDP was found to posses the lowest aging index. The antioxidant-treated binders exhibited improved performance at both high and low pavement temperatures.     

Low-temperature tensile behaviour of asphalt binders: Application of loading time–temperature–conditioning time superposition principle

Thermal cracking of bituminous layers is one of the main modes of failure for asphalt pavements. This distress is highly related to the rheological properties of asphalt binders. The purpose of this study was to investigate the low-temperature behaviour of asphalt binders by performing Direct Tension Tests (DTTs) according to Superpave specification. The DTT results were analyzed and compared in terms of trend of stress–strain curve instead of conventional failure stress or failure strain values. Through the analysis of stress–strain diagram, it was possible to evaluate the effects of temperature, elongation rate and conditioning time on the rheological properties of binders. Particular attention was paid to the conditioning time variable as it was observed that the stiffness of the binder changes with time when it is stored isothermally at low temperature due to the physical hardening phenomenon.To this end, a modified superposition effects principle, which also includes the conditioning time in addition to the temperature and elongation rate variable, has been proposed. Finally, this principle allowed the authors to find an analytical model capable of describing the rheological properties of asphalt binders as functions of the three considered test variables.     

国内改性沥青的研究与使用

分析了我国改性沥青的使用现状和改性机理,指出了改性沥青具有广阔的发展前景,总结了多年来的研究成果与使用经验,并对改性沥青的研究工作提出了较为客观实际的建议。     

The effects of using lime and styrene–butadiene–styrene on moisture sensitivity resistance of hot mix asphalt

This study focuses on determining the effects of styrene–butadiene–styrene (SBS) and using mineral filler with lime on various properties of hot mix asphalt especially moisture damage resistance. The asphalt cement was modified with 2%, 4% and 6% SBS. The lime treated mixtures containing 2% lime by weight of the total aggregate as filler. The physical and mechanical properties of polymer modified binder and binder–aggregate mixes were evaluated through their fundamental engineering properties such as dynamic shear rheometer (DSR), rotational viscosimeter (RV) for binders, Marshall stability, stiffness modulus, indirect tensile strength and moisture susceptibility for mixes. The retained Marshall stability (RMS) and tensile strength ratio (TSR) values were calculated to determine the resistance of mixtures to moisture damage. To investigate clearly the effective of SBS and lime seven freeze–thaw cycle was applied to specimens at TSR test. The results indicate that application of SBS modified binders and lime as mineral filler one by one improves the stability, stiffness and strength characteristic of hot mix asphalt. According to retained Marshall stability it is concluded that addition of only 2% lime have approximately same effect with addition of 6% SBS. Using lime together within the SBS modified mixes exhibit high accordance and exacerbates the improvement of properties. Specimens containing both 2% lime and 6% SBS, have the highest stiffness modulus which is 2.3 times higher than those of the control mixture and showed the least reduction in tensile strength ratio while maintaining 0.70 tensile strength ratio after seven freeze–thaw cycle.     

SBS改性沥青中SBS含量测试方法研究

对基质沥青、SBS和6种SBS含量的SBS改性沥青进行了红外光谱测试.结果表明,SBS改性沥青红外光谱中966,699 cm-1处SBS基团特征吸收峰和810 cm-1处沥青基团特征吸收峰,可作为SBS定性和定量分析依据;单因素方差分析和多重均值比较表明,SBS含量对699 cm-1与810 cm-1处特征峰吸收面积比(A699/A810)具有显著性影响,且不同SBS含量的A699/A810值之间存在显著差异;A699/A810与SBS含量呈现良好线性关系(相关系数0.9983),可将A699/A810作为SBS含量定量分析指标.应用傅里叶变换红外光谱(FTIR)技术可实现SBS改性沥青中SBS含量的准确、快速测试.     

不同试验方法的老化沥青疲劳性能研究

通过旋转薄膜烘箱试验(RTFOT)和压力老化试验(PAV),对70~#基质沥青、苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)改性沥青、高黏沥青(HV)和基于化学改性原理的SBS/橡胶复合改性沥青(SRC)进行短期老化和长期老化,采用温度扫描试验、时间扫描试验、多重应力蠕变恢复(MSCR)试验和线性振幅扫描(LAS)试验对4种沥青的疲劳性能进行了研究.结果表明:SRC沥青的疲劳性能和抗老化能力最佳;温度扫描试验不能很好地区分不同沥青的疲劳性能差异;时间扫描试验可有效表征4种沥青的疲劳性能,但其耗时较长;MSCR试验中出现了平均弹性恢复率(R_(0.1)和R_(3.2))在长期老化之后大于短期老化之后的情况,其指标规律性和适用的沥青范围尚不明确;LAS试验可以表征沥青在重复荷载作用下的累积损伤发展过程,得到的损伤特征曲线和疲劳方程可有效评价各种沥青的疲劳性能.     

Preparation and rheological characterization of asphalt binders reinforced with layered silicate nanoparticles

Bentonite clay (BT) and organically modified bentonite (OBT) were used to reinforce and modify a bituminous paving asphalt binder. The modified asphalt binders were produced by melt processing under sonication and shearing stresses. The interlayer spacing of silicate layers in bentonite, organically modified bentonite and the modified asphalt binders were analyzed by wide angle X-ray diffraction (WAXD). The softening point, viscosity and ductility of the modified asphalts were tested as a function of clay content and clay type. The dynamic shear rheological tests showed that the modified asphalts have higher rutting resistance. Bending beam rheometer (BBR) test results for aged specimens (through rolling thin film oven (RTFO) and pressure aging vessel (PAV)) indicated that adding BT and OBT can significantly improve low temperature rheological properties and cracking of asphalt.     

Rheological evaluation of ethylene vinyl acetate polymer modified bitumens

The morphological, thermal and fundamental rheological characteristics of ethylene vinyl acetate (EVA) copolymer modified bitumens are studied in this paper. Nine plastomeric EVA polymer modified bitumens (PMBs) have been produced by laboratory mixing bitumen from three sources with an EVA copolymer at three polymer contents. The morphology, thermal properties and rheological characteristics of the EVA PMBs have been analysed using fluorescent microscopy, differential scanning calorometry and dynamic mechanical analysis using a dynamic shear rheometer, respectively. The results of the investigation indicate that EVA polymer modification increases binder stiffness and elasticity at high service temperatures and low loading frequencies with the degree of modification being a function of bitumen source, bitumen–polymer compatibility and polymer concentration. Filler type modification is evident at low temperatures, temperatures above the melting temperature of the semi-crystalline EVA copolymer and for those modified binders that do not exhibit a dominant polymer network.     

Characterization of warm mix asphalt binders containing artificially long-term aged binders

Reclaimed asphalt pavement (RAP) comprises one of the largest recycled materials, and warm mix asphalt (WMA) technologies become more commonly used due to their promising advantages in the United States and Europe. This paper addresses the laboratory investigation of performance properties of WMA binders containing aged binders. The recycled binders with the additives were produced using two (i.e., zeolite Aspha-min^® and wax Sasobit^®) of the available warm asphalt processes. The recycled WMA binders were artificially short-term and then long-term aged through the rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were carried out on the binders through the rotational viscometer, the dynamic shear rheometer (DSR), and the bending beam rheometer (BBR). In general, the results of this study indicated that (1) the additives and aged binders played an important role in determination of the binder properties; (2) the use of lower PG grade as a virgin binder (PG 58-28 in this study) was critical on offsetting the increase of binder stiffness caused by the addition of WMA additives and aged binders; and (3) even at the low recycling percentage of 15%, the lower PG grade was needed to get the results meeting current Superpave binder requirements.