R. E. Link

Evaluation of High Temperature Rheological Characteristics of Asphalt Binder with Carbon Nano Particles

In recent years, nano technology, a relatively new field in science dealing with structures that are on the nano scale, have been used in numerous applications to improve properties of various materials. However, the use of this technology has not been explored in detail in the area of asphalt binder materials. The objective of this study was to investigate and evaluate the high temperature rheological properties of the binders containing various percentages of carbon nano particles. The experimental design for this study included the utilization of five binder sources, three binder grades (PG 64-22, PG 64-16, and PG 52-28), one type of nano particle, and four percentages of nano particles (0.0 %, 0.5 %, 1.0 %, and 1.5 % by weight of the virgin binder). Some of the rheological characteristics of these binders were obtained, including rotational viscometer (four testing temperatures of 120, 135, 150u2009, and 165°C) and dynamic shear rheometer. The results of the experiments indicated that the addition of nano particles was helpful in increasing the viscosity, failure temperature, phase angle, and viscous and elastic modulus values and in improving the rutting resistance of the binders. On the other hand, the binder sources and grades generally influenced their rheological properties as the nano particles were added to the asphalt binder.

Effects of Various Long-Term Aging Procedures on the Rheological Properties of Laboratory Prepared Rubberized Asphalt Binders

Rubberized asphalt has been used to improve the mechanical characteristics (e.g., rutting resistance, fatigue life, friction, and skid resistance) of hot mix asphalt mixtures. The objective of this research was to investigate the rheological characteristics of the rubberized asphalt binders after various long-term aging procedures, using the penetration index, the dynamic shear rheometer, the bending beam rheometer, and high pressure-gel permeation chromatographic testing. The experimental design included the use of three binder sources, three binder grades (PG 64-22, PG 64-22+10 %-40 ambient rubber, and PG 76-22) and three aging states, i.e., virgin, rolling thin film oven, and pressurized aged vessel [four test temperatures (65, 80, 100, and 110°C) and five aging durations (15, 20, 40, 80, and 144 h) under the pressure of 2070 kPa]. The test results show that, as expected, the use of crumb rubber can effectively improve the PG grade and aging resistance of the virgin asphalt binder. A series of rheological properties (e.g., penetration, stiffness, m-value, and percentages of large and small molecular sizes) illustrate that the PG 64-22 binder, mixed with 10 %-40 ambient rubber, yields similar or improved rheological properties in comparison with PG 76-22 using 3 % styrene-butadiene-styrene polymer after various long-term aging procedures.

Effects of Moist Aggregates on the Performance of Warm Mix Asphalt Mixtures Containing Non-Foaming Additives

The objective was to conduct a laboratory investigation of moisture susceptibility and rutting resistance of non-foaming warm mix asphalt (WMA) mixtures containing moist aggregates. Gyration number and weight loss of various samples, indirect tensile strength (ITS), tensile strength ratio (TSR), rut depths of dry and moisture conditioned specimens, as well as failed temperatures and rutting factors of recovered binders were measured for all mixtures. The experimental design included two aggregate moisture contents (0 and ∼0.5 % by weight of the dry mass of the aggregate), two lime contents (1 and 2 % lime by weight of dry aggregate) and one liquid anti-stripping agent (ASA), three non-foaming WMA additives (Cecabase®, Evotherm®, and Rediset®) with control, and two aggregate sources. A total of 34 mixtures were designed and a total of 340 specimens were tested in this study. The test results indicated that the aggregate source significantly affects the ITS and rutting resistance regardless of the WMA additive, ASA, and moisture content. In addition, the ITS and rut depth of the non-foaming WMA mixtures containing moist aggregates generally satisfied the demand of pavement without additional treatment. The mixtures with three WMA additives exhibited similar rutting resistance under dry and wet conditions. The liquid ASA, used in this study, for moisture resistance is not recommended to use in WMA mixtures containing moist aggregates as the aggregate is sensitive to moisture.

A Comparison of Warm Asphalt Binder Aging with Laboratory Aging Procedures

Warm asphalt has been gaining increasing popularity in recent years; however there are several characteristics about warm asphalt that are still unknown. While several studies have been conducted to study the performance of warm asphalt mixtures, aging characteristics of warm mix asphalt (WMA) binders are not known in great detail. This paper presents the results of a limited study to evaluate the aging characteristics of two WMA binders artificially aged in the rolling thin film oven (RTFO) and the pressure aging vessel and comparing them with binder extracted from freshly prepared and artificially aged warm asphalt mixtures. RTFO aging was performed at 163°C and a lower temperature to simulate warm asphalt aging. Tests on binders aged in the laboratory and binders extracted from freshly mixed and aged mixtures indicated that the WMA binders extracted from WMA mixtures had significantly lower viscosities and G∗/sin δ compared to binders extracted from hot mix asphalt (HMA) and binders aged in the RTFO at 163°C (325°F). This indicates that the lower mixing and compaction temperatures reduce the aging of the warm asphalt binders. Also, binders extracted from WMA had significantly lower creep stiffness values and significantly higher m-values compared to warm asphalt binders aged in the RTFO at 163°C (325°F) and binders extracted from HMA. Binders containing WMA additives did not have higher G∗ sin δ values, indicating that the warm asphalt additives do not negatively affect the fatigue properties of the binders. Gel permeation chromatography analysis indicated that the addition of the warm asphalt additives did not have any significant effect on the %LMS of the binders used in this study.

Laboratory Investigation of Fatigue Characteristics of Rubberized Asphalt Mixtures Containing Warm Asphalt Additives at a Low Temperature

The fatigue life of an asphalt pavement is directly related to various factors of a typical warm mix asphalt (WMA) mixture. Improving the understanding of the fatigue behavior of the rubberized WMA mixtures is helpful in recycling the scrap tires and saving energy. This study explores the utilization of the conventional fatigue analysis approach in investigating the cumulative dissipated energy, stiffness, and fatigue life of rubberized asphalt concrete mixtures containing WMA additives. The fatigue beams were made with one rubber type (−40 mesh ambient crumb rubber), two aggregate sources, two WMA additives (Asphamin and Sasobit), and tested at 5°C. The test results indicated that the addition of crumb rubber and WMA additive not only reduced the mixing and compaction temperatures of rubberized asphalt mixtures offset by crumb rubber but also slightly extended the long-term performance of pavement when compared with conventional asphalt mixtures.

A New Static Strength Test for Characterization of Rutting of Dense-Graded Asphalt Mixtures

A new static-test protocol was developed for measuring the deformation resistance of asphalt mixtures at high temperature, 60°C. A round edge loading head was used for estimating rut-related performance by statically pressing a specimen at the flat top center. The value measured by this test is considered as a strength against deformation or deformation strength and designated as “SD.” The SD has shown a high correlation with the rut depths of wheel tracking (WT) and the asphalt pavement analyzer (APA) tests. In this study, the feasibility of utilizing this test method to predict the rutting potential of asphalt mixtures is shown. Stiffness (G∗/sinu2009δ) test data for asphalt binders, two rutting tests’ (WT and APA) data, and SD data for various laboratory mixtures were used in this evaluation. More than 50 field mixtures were also used for APA and SD tests. Correlation analyses showed that the SD had very high correlation with the stiffness of the binder (R2=0.9), with rut depth of WT (R2>0.90) and somewhat less with rut depth of APA (R2=0.77). It was concluded that the newly developed test is comparable to WT and APA and that the SD is a property providing a reasonable estimation of rut potential of asphalt mixtures at high temperatures, even though it is a static-test property.

Effects of Binders on Resilient Modulus of Rubberized Mixtures Containing RAP Using Artificial Neural Network Approach

The prediction of the resilient modulus values of rubberized mixtures containing reclaimed asphalt pavement (RAP) materials involves a number of interacting factors or engineering parameters (variables) and is a very complex issue. Artificial neural networks (ANN) are useful tools in place of conventional physical models for analyzing complex relationships involving multiple variables and have been successfully used in many civil engineering applications. The objective of this study was to develop a series of ANN models to simulate the resilient modulus of rubberized mixtures (ambient and cryogenic rubbers) at 5, 25, and 40°C using seven input variables including material components such as rubber and RAP percentages as well as the rheological properties of modified binders (i.e., viscosity, G*sin δ, stiffness, and m-values). The sensitivity analysis and important index of each variable were performed in this study. The results indicated that ANN-based models are more effective than the regression models and can easily be implemented in a spreadsheet, thus making it easy to apply. In addition, the validation analysis of the models showed that ANN-based models might be used for other types of mixtures. Moreover, the results of the sensitivity analysis and important index of input variables in ANN models also indicated that the rheological properties of asphalt binders can be employed to predict the resilient modulus values effectively at various testing temperatures. The validation of the model also illustrates that the developed ANN can be used to predict the resilient modulus values from other research projects.

Simplified Presentation of the Stress-Energy Method for General Commercial Use

To help the dynamic stress versus energy method for constructing cushion curves gain more commercial acceptance, this paper presents two improvements to previous work. First is the reporting of stress-energy equations ( A and B values) for several more commercially available cushion materials. Second is a simplified method for manipulating and displaying the stress-energy equation using a common spreadsheet program. This simplified method makes cushion curves dynamic and accessible without the need for a programming language, and presents the results in industry-standard format. Combining these two components help make the stress-energy method more accessible for packaging engineers working in industry.

Prediction of Cushion Performance Less Than One Inch Thick

An important tool packaging engineers use when designing cushions to protect products from shock is the cushion curve. Cushion curves show deceleration values along the vertical axis versus the static loading (weight divided by bearing area) along the horizontal axis for a given thickness of cushion material and given drop height. Commercially available cushion curves display a thickness of one inch and greater. However, many times packaging engineers design packages with cushions less than one inch thick. This leaves the packaging engineer to either guess deceleration levels below one inch thick by trial and error, or to extrapolate from existing cushion curve data. The purpose of this study was to determine if using existing cushion curve information would accurately predict deceleration values below one inch thick. To do this, a procedure was developed comparing information collected from expanded polystyrene cushion samples greater than one inch thick (correlating to existing cushion curves) compared to information collected from samples less than one inch thick. The comparison looked for difference between the datasets. It was found that in fact there was a statistical difference, meaning existing cushion curves should not be used to predict deceleration values for cushion thicknesses below one inch.

Evaluation of Statistical Validity of Some Asphalt Binder Grade Systems

The performance grade (PG) and the penetration (pen) grade systems were examined for their statistical validity. It is found from this limited study that the pass/fail high-temperature of the PG binder follows a normal distribution. Since PG system has no gap between each grade, the binder falling out of limit trespasses into another binder grade. The Korean pen grading system has the same problem. Therefore, many products can have similar property levels with an adjacent-grade even though the mean value is within the specification limit. The PG binder will have a high chance of passing the rheological requirements at above the upper limit but the least chance of falling below the lower limit because the means were above median and variations were higher than they should be. Since PG is characterized without gap between each grade, the producer must maintain the coefficient of variation below the current level to satisfy the quality control limit of the product. Similarly, in other grading systems such as the Korean pen specifications, due to its lack of a gap between grades, higher percentage of products will be duplicated even if the mean is at the median of the specification limits due to material’s quality uncertainty. Especially if the mean moves toward the upper limit, one-half of the binder grade will be overlapped with the higher binder grade. Therefore, these specifications should be statistically examined for further modification.