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.     

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.     

Influence of surface area and size of crumb rubber on high temperature properties of crumb rubber modified binders

There are many variables of crumb rubber modifier (CRM) and asphalt binder, affecting the interaction of the CRM with the binder when crumb rubber modified binder (CRM binder) is produced. In this study, the influence of the surface area of CRM blends on the high temperature properties, i.e., the complex modulus (G¹), the phase angle and high temperature grade of the CRM binders was investigated. To this end, the surface areas of CRM particles were measured using the BET (Brunauer, Emmett and Teller) tester, while weighted average particle size of CRM blends was calculated based on their graduations and then used as a size index. High temperature properties of CRM binders were measured using Dynamic Shear Rheometer (DSR) test. A total of 108 CRM binders were produced using different combinations of these variables. Results observed from this study indicated: (1) the surface area of the ambient CRM was twice as large as that of the cryogenic one, leading to a much higher G¹ and phase angle of the CRM binders; (2) the phase angle and G¹ were affected by both the surface area and average size; however, the average size is the predominating factor; and (3) ambient CRM binders were produced about 3 °C in high temperature grade higher than cryogenic CRM binders.     

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).     

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.     

Development of an empirical model for determining G*/sin δ in crumb rubber modified binders

This paper describes the development of an empirical model which may be used for predicting the G*/sin δ for neat and crumb rubber modified (CRM) binders. The model was developed using 36 unique CRM binder combinations, crumb rubber concentrations were varied at 5% intervals between 5% and 20%. The effects of crumb rubber particle size on model accuracy were also studied, ultimately a model was produced with the capability of predicting G*/sin δ values over a range of temperatures and crumb rubber concentrations. By definition, the upper limit of the performance grade is dependent on the G*/sin δ value; therefore, the relationship was also considered in terms of high end failure temperature.The rubber coefficient for G*/sin δ (R_cg) was identified as an important parameter in the estimation of G*/sin δ in addition to the CRM. This term is a quantitative representation of the increase typically witnessed in G*/sin δ values with the addition of CRM. Ambient ground CRM exhibited higher R_cg values than cryogenically ground particles. Additionally, 95% confidence intervals were generated for the predictive model, thus providing a range of accuracy for the model. The resulting confidence intervals were approximately ±1300 Pa, these confidence intervals were seen to capture 92.6% of the 462 data points used. Findings from this research suggest that the differences between cryogenic and ambient CRM binder are accurately described using the R_cg, furthermore binder properties may be predicted using an empirical equation.     

Effects of furfural activated crumb rubber on the properties of rubberized asphalt

The use of furfural (C₅H₄O₂) as an activation agent has been suggested as a method to improve the rheological properties of asphalt binders due to its compatibility with crumb rubber. This study uses five different crude sources and both ambient and cryogenic produced crumb rubber modifiers (CRM). The rheological properties for furfural activated and conventional CRM binders were evaluated using the dynamic shear rheometer (DSR) and the gel permeation chromatography (GPC). The results indicated that furfural activation has variable effects on the properties of the CRM binder. However, the most pronounced effect is shown in the storage stability improvement which will have an effect on the storage of CRM binder. Also, the activation caused a reduction in the ratio of the small molecular size distribution which is considered an improvement in the binder properties.     

Analysis of digestion time and the crumb rubber percentage in dry-process crumb rubber modified hot bituminous mixes

The use of crumb rubber modifier (CRM) in bituminous mixes made by the dry process is not as widely used as the wet process. Nonetheless, this process has advantages, such as the potential to consume larger quantities of crumb rubber, thus resulting in greater savings in energy and natural resources. This research study contributes to the further development and evolution of the dry process through the analysis of the effect of the digestion time (the contact time between the crumb rubber and the bitumen) and the quantity of crumb rubber on the mix design properties. The results of the study showed that the digestion time had no influence on the selection of the optimal binder content or on the compaction of the mixture. In contrast, the digestion time was found to have an impact on the mechanical performance of the mix. In this respect, an increase in the quantity of crumb rubber contributed to a corresponding increase in the amount of bitumen needed, and also caused the mix to become less compact. This study showed that a crumb rubber percentage of less than 1% of the total weight of the mix and a digestion time of 90 min produced the best results.     

The effect of crumb rubber modifier (CRM) on the performance properties of rubberized binders in HMA pavements

The application of crumb rubber modifier (CRM) in asphalt mixtures is intended to improve the properties of binder by reducing the binder’s inherent temperature susceptibility. During the interaction with asphalt binder, the CRM particles absorb a portion of the oils in asphalt binder and the particles swell; therefore increasing the viscosity and stiffness of the CRM binder. Still, the performance properties of CRM binders in hot mix asphalt (HMA) pavement are considered to be unclear due to the various interaction effects of CRM with asphalt binders, depending on the CRM percentage, source and size. In this study, a laboratory investigation was conducted on the properties of CRM binders as a function of CRM processing method and percentages. A total of twenty-four CRM binders (3 binder sources * 2 CRM processing methods * 4 CRM percentages) were produced and artificially aged through an accelerated aging process. Evaluation of the CRM binders included the following testing procedures: Viscosity at high temperature, performance properties at high and intermediate temperatures, and cracking properties at low temperature. The results from this study indicated that the higher CRM percentages for CRM binders seemed to lead to a higher viscosity, a better rutting resistance and a less chance for low temperature cracking. In general, the ambient CRM was found to be more effective on producing the CRM binders that are more viscous and less susceptible to rutting and cracking.     

Determination of the optimum conditions for tire rubber in asphalt concrete

The Taguchi method was used to determine optimum conditions for tire rubber in asphalt concrete with Marshall Test. The tire rubber in asphalt concrete was explored under different experimental parameters including tire rubber gradation (sieve #10–40), mixing temperature (155–175 °C), aggregate gradation (grad. 1–3), tire rubber ratio (0–10% by weight of asphalt), binder ratio (4–7% by weight of asphalt), compaction temperature (110–135 °C), and mixing time (5–30 min). The optimum conditions were obtained for tire rubber gradation (sieve #40), mixing temperature (155 °C), aggregate gradation (grad. 1), tire rubber ratio (10%), binder ratio (5.5%), compaction temperature (135 °C), mixing time (15 min).     

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.     

Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt

In order to sort some important factors affecting the performances of CRM asphalt and evaluate the performances of different CRM asphalt, this study encompassed one kind of base asphalt binder, four kinds of crumb rubber, tread rubber (TR), heavy truck (HT), small truck (ST) and agriculture tire (AT) crumb rubber, two kinds of particle size, 60 mesh and 80 mesh, and three contents. Softening point, low temperature ductility, and penetration index are selected as basic evaluation indicators in analysis. Variance analysis shows that the crumb rubber content is the primary affecting factor in general, followed by the crumb rubber type, and particle size comes last. The greater the crumb rubber content is, the higher the softening point and the penetration index are, and the smaller the low temperature ductility is. Modified effects between 60 mesh and 80 mesh don’t manifest significant difference. The modified effects of TR-crumb rubber and HT-crumb rubber are better while the low temperature ductility of AT-CRM asphalt is the worst. Also according to the results of DSR and BBR test, TR-CRM asphalt has a better and comprehensive performance at the crumb rubber content of 20% by weight of base asphalt binder, and, if the price is also considered, selecting HT-CRM asphalt with the crumb rubber content of 15% is ideal. The study also finds an interesting phenomenon that the rutting factors of CRM asphalt may be remarkably different, although the softening points of them are the same.     

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).     

A laboratory study on stone matrix asphalt using ground tire rubber

This research investigated the feasibility using asphalt rubber (AR), produced by blending ground tire rubber (GTR) with an asphalt, as a binder for stone matrix asphalt (SMA). Two different sizes of GTR produced in Taiwan were used. The potential performance of AR–SMA mixtures was also evaluated. The results of this study showed that it was not feasible to produce a suitable SMA mixture using an asphalt rubber made by blending an AC-20 with 30% coarse GTR with a maximum size of 0.85 mm. However, SMA mixtures meeting typical volumetric requirements for SMA could be produced using an asphalt rubber containing 20% of a fine GTR with a maximum size of 0.6 mm. No fiber was needed to prevent drain-down when this asphalt rubber was used. The AR–SMA mixtures were not significantly different from the conventional SMA mixtures in terms of moisture susceptibility from the results of AASHTO T283 tests. The results of the wheel tracking tests at 60 °C show that rutting resistance of AR–SMA mixtures was better than that of the conventional SMA mixtures.     

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.     

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.     

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.     

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.     

废胶粉改性沥青改性机理及其性能研究

从沥青和废胶粉的化学成分和分子结构入手,介绍了沥青及废胶粉的种类、胶粉多种粉碎工艺以及废胶粉沥青改性的生产方法,分析了废胶粉改性沥青的改性机理,并参考国内外专家的研究结果给出了影响废胶粉改性沥青性能的各种可能因素,最后论述了废胶粉改性沥青的路用性能。