Laboratory evaluation of the effects of short-term oven aging on asphalt binders in asphalt mixtures using HP-GPC

Both the RTFO (rolling-thin film oven) aging of asphalt binders and the STOA (short-term oven aging) of asphalt mixtures are designed to simulate aging during the construction of hot mix asphalt (HMA) pavements. Many studies have been conducted evaluating the aging effects on asphalt binders since their properties can be easily measured using many conventional tests, such as rotational viscometer, DSR (dynamic shear rheometer), and BBR (bending beam rheometer). However, studies on asphalt mixture aging have been limited to mechanical properties such as strength and fatigue characteristics because considerable effort is required to identify the aging of the asphalt binder in a mixture. This study evaluated the effects of short-term oven aging on asphalt mixtures using the GPC (gel-permeation chromatography) procedure. Nine asphalt mixtures, using three different binder sources, were prepared and five short-term aging methods were used to evaluate these mixes. For comparison, the RTFO aging was also conducted for nine asphalt binders. The aging of a binder within asphalt mixtures, including polymer-modified mixtures, could be identified under various short-term aging conditions. Statistical analysis of the GPC test results indicated that two commonly used short-term aging methods in the laboratory, a 154 °C oven aging for 2 h and a 135 °C oven aging for 4 h, are not significantly different, based on the increase in the large molecular size (LMS) ratios. The RTFO aging method was found to have less effect on binder aging than the short-term oven aging methods of asphalt mixtures.     

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.     

Influence of aging on the evolution of structure,morphology and rheology of base and SBS modified bitumen

The influence of aging on the evolution of structure, morphology and rheology of base bitumen and SBS modified binders was investigated by Fourier transform infrared (FTIR), atomic force microscopy (AFM) and dynamic shear rheometer (DSR), respectively. Two laboratory simulation aging methods, named standard rolling thin film oven (RTFO) test and pressure aging vessel (PAV) test were applied in this study. The aging temperature of PAV was selected at 60 °C, which is considered to be consistent with the real high temperature within an asphalt pavement in the field. After aging, it was found that more carbonyl and sulphoxide groups but less chain segments of butadiene were available. With the oxidation of base bitumen and the degradation of SBS segments, obvious asphaltene micelles appeared in both binders, consistent with the changes of softening point and rheology of base bitumen and SBS modified binders.     

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.     

Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity

Asphalt binder viscosity is of great importance during the production process of hot mix asphalt mixture as typically asphalt plants will store binders between 149 °C and 177 °C. SHRP guidelines state that asphalt binder viscosity must not exceed 3 Pa s. Therefore, given the documented increases in asphalt viscosity when modified with crumb rubber modifier (CRM) it is necessary to produce asphalt binder that fulfills the SHRP criteria while not exceeding plant mixing and storing requirements. This paper reports the results of an investigation of the importance of CRM properties on viscosity of CRM binder. Two binder sources were modified at four concentration levels using four different crumb rubber sources; the viscosities of the produced binders were evaluated by AASHTO T 316. Crumb rubber properties were evaluated by elemental analysis using a scanning electron microscope (SEM) and by determination of glass transition temperature (T_g) using a differential scanning calorimeter (DSC). In general, results indicate that processing procedure and tire type plays an important role in the determination of CRM binder viscosity.     

Effects of rejuvenator on performance-based properties of rejuvenated asphalt binder and mixtures

Firstly, the performance-based properties of rejuvenated aged asphalt binders, i.e., the blends of aged binders containing a rejuvenator at various percentages, were investigated under high, intermediate and low temperatures. The tests were conducted on the blends at three stages as follows: no aging, rolling thin film oven (RTFO) residuals and as well RTFO + pressure aging vessel (PAV) residuals through dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. Optimum concentrations of the rejuvenator needed for the blends to reach a target PG grade were obtained from the blending charts of the rejuvenated aged binders in terms of performance properties. The rejuvenator is a soft binder containing a low asphaltene content of 2 wt%. Secondly, selected performance-based properties were conducted on hot mix asphalt (HMA) using the rejuvenated aged binder and a virgin HMA as a control mixture. Results showed that the rejuvenator affected significantly the performance-based properties of both the rejuvenated aged binders and the mixtures containing the rejuvenated aged binders. It was possible to get optimum concentrations of the rejuvenator using the blending charts so that the rejuvenated binders reach a target PG grade. The mean value of the concentrations was proved to be more reliable through the performance-based properties of the mixtures if it is used for a design value for recycling. The properties of the asphalt paving mixtures with the rejuvenated binders were even improved or in the same level as the properties of the virgin mixtures.     

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.     

Laboratory investigation of the properties of asphalt concrete mixtures modified with TOP–SBS

Benefits of adding Tall oil pitch (TOP), Styrene-butadiene-styrene (SBS) and TOP + SBS to AC-10 in variant quantities to AC-10 were investigated. Initial research was done to determine the physical properties of asphalt cement and modifiers.Seven asphalt binder formulations were prepared with 8% of TOP; 8 + 3, 8 + 6 and 8 + 9% of TOP + SBS, respectively; 3, 6 and 9% of SBS by total weight of binder. After that, Marshall samples were prepared by using the modified and unmodified asphalt binders.Additionally, compression strength test were done in different conditions to determine water, heat and frost resistance of all Marshall samples.Fatigue life and plastic deformation tests for Marshall samples (for different asphalt mixtures: modified and unmodified) were carried out using PC controlled repeated load indirect tensile test equipment developed at Suleyman Demirel University by Tigdemir (SDU-Asphalt Tester).The results of investigation indicate that asphalt mixture modified by 8% TOP + 6% SBS gives the best results in the tests that were carried out in this study, so that, this modification increases physical and mechanical properties of asphalt binder.     

Relation of mechanical properties of recycled aged CRM mixtures with binder molecular size distribution

This paper presents an experimental analysis of the relationship between molecular sizes of mixed rubberized binders (aged rubberized binders + virgin rubberized binders) and the engineering properties of recycled aged rubberized mixtures. Gel permeation chromatography (GPC) was utilized to characterize the molecular size change of rubberized binders depending on three aging levels and four long-term aged (LTA) binder percentages. Rubberized mixtures were artificially long-term aged in the laboratory, and the aged rubberized mixtures were recycled at 0%, 15%, 25%, and 35% (by weight of total mixture) using typical recycling guildelines. Samples of laboratory-prepared recycled aged rubberized mixtures were tested for indirect tensile strength (ITS) in dry and wet states, rutting resistance, resilient modulus, and ITS after long-term aging in the laboratory. In general, the results indicated that the compositional changes of mixed rubberized binders have good correlations with the engineering properties of recycled aged rubberized mixtures, except for the resilient modulus.     

Effect of crumb rubber modifiers on high temperature susceptibility of wearing course mixtures

This paper investigates the effects of different sizes of crumb rubber modifier (CRM) on the high temperature susceptibility of three gradations (AC-10, AC-20 and PA) of wearing course mixtures. A wet process and 10% CRM by total weight of binders were used in these studies and the control variables for these studies included three CRMs of sizes 0.15 mm, 0.30 mm and 0.60 mm. The evaluations were twofold. Firstly, a comparison of the properties of those modified and unmodified binders at a wide range of testing temperatures and ageing conditions was conducted. Secondary, a comparison of the rutting resistance of the CRM and conventional mixtures was made. The results show that all the CRMs have overall contributed to better performance of both binders and mixtures at high temperatures. In addition, among these three CRM sizes, mixtures modified with 0.15 mm CRM exhibited the best effect on the dense-graded mixture (AC-10 and AC-20) whereas mixtures modified with 0.60 mm CRM exhibited the best effect on the open-graded mixture of porous asphalt (PA).     

Interaction effects of crumb rubber modified asphalt binders

The application of crumb rubber in asphalt mixtures is intended to improve the binder properties by reducing the binder’s inherent temperature susceptibility. This research investigated the interaction effects of CRM binders as a function of various blending treatments in the laboratory. For this study, CRM binders were produced using seven blending times (5, 30, 60, 90, 120, 240, and 480 min), three blending temperatures (177, 200, and 223 °C), and four rubber contents (5%, 10%, 15%, and 20% by weight of asphalt binder). The results from this study showed that (1) The interaction time and interaction temperature for CRM binders were observed to have significant effect on the binder properties; (2) The longer time and higher temperature for interaction of CRM binders resulted in an increase in the high failure temperature and the viscosity. This is thought to be due to the increase in the rubber mass through binder absorption. However, this study found that the control binder of PG 64-22 had little change of the binder properties as a function of interaction conditions; (3) The CRM percentage influence is statistically significant on the viscosity and G^*/sin δ values. Also, the asphalt binder with higher CRM percentage showed a higher large molecular size (LMS) value, and the increase in CRM percentage is considered to result in the additional loss of the low molecular weight in the asphalt binder to the CRM.     

Properties of Portland cement-modified asphalt binder using Superpave tests

This study investigates the effect of cement additive on some properties of asphalt binder using Superpave testing methods. Six cement-to-asphalt (C/A) ratios were considered in the study: 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 by volume of asphalt binder. The experimental tests that were conducted in the study included the Superpave rotational viscosity (RV) test and the dynamic shear rheometer (DSR) test. The RV test was conducted at the Superpave-specified high temperature of 135 °C that represents the average mixing and laydown temperature, and at seven different rotational speeds of 5, 10, 20, 30, 50, 60, and 100 rpm. On the other hand, the DSR test was conducted at four test temperatures of 58, 64, 70, and 76 °C; one lower and two higher than the Superpave high performance grade (PG) temperature of the asphalt binder used in the study (PG 64). The loading frequency used in the DSR test was 10 rad/s (1.59 Hz) as specified by the Superpave system. Results of the study showed that the addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135 °C and different rotational speeds. The C/A ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and the value of the DSR G^*/sin δ rutting parameter of asphalt binders. The C/A ratio had insignificant effects on the Newtonian behavior, the phase angle (δ), and the elastic behavior of asphalt binders. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G^*) value. The increase in the C/A ratio improved the rutting parameter, G^*/sin δ value, at all temperatures. The increase in C/A ratio improved the Superpave high PG temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G^*/sin δ value). It was also shown that the best function that described the relationship between each of RV, G^*, and G^*/sin δ and the C/A ratio was the exponential function with high coefficient of determination (R²).     

Study on properties of recycled tire rubber modified asphalt mixtures using dry process

To minimize waste tires pollution and improve properties of asphalt mixtures, properties of recycled tire rubber modified asphalt mixtures using dry process are studied in laboratory. Tests of three types asphalt mixtures containing different rubber content (1%, 2% and 3% by weight of total mix) and a control mixture without rubber were conducted. Based on results of rutting tests (60 °C), indirect tensile tests (−10 °C) and variance analysis, the addition of recycled tire rubber in asphalt mixtures using dry process could improve engineering properties of asphalt mixtures, and the rubber content has a significant effect on the performance of resistance to permanent deformation at high temperature and cracking at low temperature.     

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.     

Effect of organo-montmorillonite on aging properties of asphalt

Effects of organo-montmorillonite (OMMT) on thermo-oxidative and ultraviolet (UV) aging properties of asphalt were investigated. The results show that the viscosity aging index (VAI) and softening point increment (ΔS) of OMMT modified asphalt decrease significantly due to introduction of OMMT, and the ductility retention rate of the modified asphalt is also evidently higher than that of the pristine asphalt after thin-film oven test (TFOT) and pressure aging vessel (PAV) aging. In the meantime, both VAI and ΔS of the modified asphalt are obviously lower than that of the pristine asphalt after UV aging. Furthermore, compared with the pristine asphalt, the results of dynamic shear rheometer (DSR) testing exhibit smaller changes in rut factor (G*/sin δ) after TFOT and lower fatigue factor (G*sin δ) after PAV for the modified asphalt, which suggests that the effect of thermo-oxidative aging on dynamic rheological behaviors of the modified asphalt is restrained due to introduction of OMMT.     

Shear bond strength between asphalt layers for laboratory prepared samples and field cores

This paper describes the laboratory measurement of shear interface properties between asphalt layers using the Leutner test. Results are presented and compared for both laboratory prepared specimens and field cores. The standard Leutner test was modified by the introduction of a 5 mm gap into the shear plane to reduce edge damage caused by misalignment of the specimen and specimens that incorporate a thin surfacing material were extended using a 30 mm thick grooved metal cylinder to eliminate dependence of the shear strength on surfacing thickness. The laboratory produced surfacing/binder course combinations incorporating the 20 mm Dense Bitumen Macadam (20 DBM) binder course showed the highest average shear strengths when nothing was applied at the interface and the lowest average shear strengths when the tack coat was applied at the interface. The average shear strength from field cores was found to increase as the class of the road increases for both surfacing/binder course interfaces and binder course/base interfaces.     

Modeling viscosity behavior of crumb rubber modified binders

Accurately predicting the viscous properties of crumb rubber modified (CRM) binders has proven difficult, especially as these properties tend to vary with changing crumb rubber concentrations and temperatures. This study explores the utilization of the statistical regression and neural network (NN) approaches in predicting the viscosity values of CRM binder at various temperatures (135 °C and greater). A total of 53 CRM binder combinations were prepared from two different rubber types (ambient and cryogenic), three different binder sources, four rubber concentrations (0%, 5%, 10%, and 15%), and five crumb rubber gradations (ADOT, SCDOT, 0.18 mm, 0.425 mm, and 0.85 mm). The results indicated that the regression model is easy to use and can be used for viscosity prediction, similarly NN-based models also provided accurate for predictions for the viscosity values of CRM binders regardless of rubber type and can easily be implemented in a spreadsheet. In addition, the developed NN model can be used to predict viscosity values of other types of CRM binders efficiently. Furthermore, the sensitivity analysis of input variables indicated that the changes of viscosity are significant as the changes of asphalt binder grade, test temperature, and rubber content. The results also show that these three independent variables are the most important factors in the developed NN models in comparison with other variables.     

Effect of pre-heating duration and temperature conditioning on the rheological properties of bitumen

It is well known that overheating asphalt bitumen can lead to oxidation and stiffening. While heating bitumen is an essential protocol in sample preparation, it is important to identify the oven setting time and temperature for lab testing. Current AASHTO standards do not specify exact oven settings for bitumen sample preparation prior to laboratory testing. This study is evaluating the effect of oven heating duration and pouring temperature during sample preparation in the rheological properties of neat and polymer-modified bitumen (PMB). Rheological properties are measured using Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer at grade-specific testing temperatures. A neat bitumen PG64-22 and two PMB PG70-22 and 76-22 in un-aged (original) and aged conditions were tested at two temperatures: 143 °C and 185 °C for 1/2, 2 and 4 h. The effect of short-term aging by rolling thin film oven was also investigated. To investigate the rheological properties over a wide range of temperatures, temperature sweep testing was conducted from 35 °C to 110 °C at a 10 rad/s frequency. The results suggest that there was no significant difference in the viscosity, complex modulus and creep stiffness for the tested bitumen. The RTFO aging index, absolute drop of complex viscosity and temperature aging indices were used to evaluate the bitumen preparation settings. The study recommends using the 143 °C and 2-h heating for proper preparation prior to standard lab testing. The study also investigated the aging influence in rheological properties for neat and PMB using the black diagram, DSR function map, and critical-stiffness temperature.     

Prediction of bituminous mixture fatigue life based on accumulated strain

This research was aimed to predict the number of cycles that cause fracture of hot-mix asphalt (HMA) based on the number of cycles at which the slope of accumulated strain switched from decreasing to increasing mode. In addition, the effect of aggregate gradation and temperature on fatigue behaviors of HMA were evaluated.HMA specimens were prepared at optimum asphalt content using the Marshall mix design procedure. The specimens were prepared using crushed limestone aggregate, 60/70 penetration asphalt, and three different aggregate gradations with maximum nominal aggregate size of 12.5, 19.0, and 25.0 mm. Five magnitudes of load (1.5, 2.0, 2.5, 3.0, and 3.5 kN) were evaluated for their effect on fatigue behavior.Constant stress fatigue tests were performed using the Universal Testing Machine (UTM) at 25 °C. Other temperatures (10, 45, and 60 °C) were evaluated at a load of 3.5 kN.The tests results indicated that the slope of accumulated strain continued to decrease until the number of loading cycles approached 44% of the number of cycles that caused fracture of the HMA. Also, the initial stiffness of asphalt mixtures was found to increase as the magnitude of the load applied increased and as the aggregate gradation maximum nominal size decreased.     

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.