Michael J Farrar

New Technique for Measuring Low-Temperature Properties of Asphalt Binders with Small Amounts of Material

A new technique, which uses 4-mm parallel plates on a dynamic shear rheometer (DSR) with machine compliance corrections, was developed to measure low-temperature properties of asphalts. Good results have been achieved at test temperatures as low as −40°C. The test method requires only about 25 mg of material instead of 15 g for the bending beam rheometer (BBR). Also, no specimen premolding is needed, and a relatively low temperature (60°C to 70°C) is required to load the samples into the measuring system. The key to the new technique is correction for errors due to machine compliance. Two types of machine compliance correction were applied to the dynamic frequency sweep data in this work. The following areas were investigated: effects of machine compliance on the measured low-temperature properties, reproducibility of data, consistency among data collected on different sizes of plates after machine compliance corrections, and comparison between the corrected data from DSR and converted BBR data. Results show that this new technique is a reliable, rapid, and simple to perform test method, allowing for analysis of low-temperature properties of asphalt binder as well as extracted samples from pavements and other materials such as cold-mix asphalt and emulsion residue that require low-temperature operations and small samples.

New Low-Temperature Performance-Grading Method: Using 4-mm Parallel Plates on a Dynamic Shear Rheometer

Mechanical measurements on asphalt binders to determine the performance grade of the low-temperature specification are typically carried out with a bending beam rheometer (BBR). The BBR test requires considerable material to fabricate a specimen (approximately 15 g per beam). The relatively large amount of asphalt binder required for the BBR limits its applications. The BBR is difficult to apply to extracted asphalt binder or to other situations in which there is a limited amount of binder, for example, residue from emulsions. This paper proposes an alternate mechanical test to the BBR to determine low-temperature PG. Only approximately 25 mg of asphalt binder are required to perform a test. The test employs 4-mm-diameter parallel plates on a dynamic shear rheometer (DSR) and includes a correction for machine compliance. This correction allows testing to −40°C. A low-temperature specification from the 4-mm rheometry is suggested by the establishment of a correlation between BBR creep stiffness data and DSR stress relaxation data. The shear stress relaxation data used in this work were interconverted from dynamic frequency sweep data. A strong linear correlation was observed between BBR and DSR data from 11 asphalt binders.

Evolution of the Crossover Modulus with Oxidative Aging: Method to Estimate Change in Viscoelastic Properties of Asphalt Binder with Time and Depth on the Road

This study is based on recovered binders from a hot-mix asphalt comparative test site constructed in Arizona in 2001 with mix collected during construction and cores collected in 2005 and 2010. The intent of the study is to evaluate the potential of using the evolution of the binder crossover modulus with time and depth in the pavement to determine the change in linear viscoelastic properties of the binder during the life of the pavement. The crossover modulus is one of three parameters in the Christensen–Anderson (CA) complex shear modulus model. The CA model is used in this study to develop complex modulus and phase angle master curves of the binder as a function of field time, depth, and temperature. The master curves generated demonstrate the change in SHRP specification parameters, such as m-value and creep stiffness, as well as in the mix dynamic modulus with time and depth on the road. In addition, although asphalt dependent, a linear relationship between oxygen uptake and the log of the crossover modulus is reported.

Evaluation of surface treatment practices in United States

The University of Wyoming and the Wyoming Department of Transportation are performing a comprehensive research study on the performance of surface treatments. A survey consisting of 16 questions about the maintenance, construction, agency policies, evaluation procedures, and testing equipment of surface treatments was distributed to all 50 state departments of transportation; 47 of these agencies responded. The responses were summarized and analyzed for trends.

RESILIENT MODULUS TESTING OF LEAN EMULSIFIED BASES

A research study conducted jointly by the Wyoming Department of Transportation and the University of Wyoming examined the effect of low emulsified base treatment on resilient modulus values. The study involved selecting two types of aggregate, treating duplicate samples with variable amounts of emulsified asphalt, and performing resilient modulus tests on the samples at various ages. Data were then analyzed to evaluate the variations in resilient modulus values due to the changes in testing time or percentage of emulsified asphalt added. The following conclusions were reached: resilient modulus testing can be used to evaluate emulsified asphalt-treated bases; aging samples before testing will cause a substantial difference in resilient modulus values; and low percentages of emulsion treatments increase resilient modulus.

Recovery and Laboratory Testing of Asphalt Emulsion Residue: Application of Simple Aging Test and 4-mm Dynamic Shear Rheometer Test

This study involves application of two new test methods to the recovery of asphalt emulsion residue, long-term oxidative aging of the residue, and mechanical testing of the unaged and aged residue to determine low- and intermediate-temperature rheological properties. The new methods are the simple aging test (SAT), which is a thin-film (300 μm) oxidative aging test, and a dynamic shear rheometry technique (commonly referred to as 4-mm DSR), which allows testing to −40°C and requires only 25 mg of material. Three polymer-modified emulsions are recovered by two methods: AASHTO PP 72-11 Method B and use of an SAT plate. Both methods use the same evaporative technique to recover the residue (6 h at 60°C in a forced draft oven). The rheological properties (m-value, G* sin d, and ductility) of the recovered emulsion residues by both methods are reported as well as the rheological properties of the aged emulsion using the SAT. The rheological properties of the unaged emulsion residues recovered are roughly equivalent. The proposed SAT recovery method and application of 4-mm DSR offer significant improvements over Method B and current DSR methodology. The recovery process is simpler with the SAT plate than with Method B, and the SAT plate has been designed so that it can be placed directly in a standard pressure aging vessel (PAV) for long-term aging, and the time required for standard PAV aging is reduced from 20 to 8 h. There is no extrapolation of intermediate-temperature DSR data to low temperature. The error from instrument compliance at low temperature is corrected in the 4-mm DSR procedure.

An Advanced Low Temperature Rheological and Fracture Test Method for Bitumen Purchase Specifications and Pavement Performance Prediction: 4-mm DSR/ABCD

This paper proposes an advanced low temperature rheological test method which could be used to supplement and improve current purchase specifications for grading bitumens, and at the same time provide pavement low temperature thermal crack prediction for the Mechanistic Empirical Pavement Design Guide (MEPDG). The method is referred to as 4-mm DSR/ABCD i.e. 4-mm diameter parallel plate dynamic shear rheometry combined with the Asphalt Binder Cracking Device (ABCD) test. In addition to traditional low temperature binder purchase specifications such as m-value, creep stiffness and binder cracking temperature, the 4-mm DSR/ABCD method allows calculation of the thermal cracking temperature in the asphalt mix from a cooling event. The application of 4-mm DSR is an alternative to the mix indirect tensile (IDT) creep test. The fracture stress of the binder from the ABCD is an alternative to the mix IDT strength test. Mix IDT creep compliance and strength are the two primary inputs to the low-temperature, thermal cracking module in the MEPDG.

Quantification of Water in Asphalt by Karl Fischer Titration and Its Application to Emulsion Recovery

In this study, the Karl Fischer (KF) titration method for quantification of water was successfully applied to asphalt binder. Previously, observed side reactions between the titration solvent and certain functional groups present in asphalt prevented accurate KF-type titration. However, recent advances in KF solvent formulation have allowed for rapid titration of water in asphalt with minimal interference reactions. Repeatable results were obtained with moisture-sensitive techniques such as drying glassware, using only anhydrous solvents, and performing all sample preparation in a dry atmosphere. The developed KF titration method was implemented in the evaluation of three competing laboratory asphalt emulsion residue recovery procedures. All three methods showed sufficient removal of water for rheologic testing of the eight recovered residues. Measuring the water content in recovered residues by the mass lost at 135°C was not suitable for some emulsion residues because of the evaporation of nonwater solvent or distillate at the elevated temperature.

Comparative Field Performance of Asphalts from Multiple Crude Oil Sources

A comparative pavement performance site was built in 2001 in central Arizona with four unmodified PG 76-16 asphalts. The four asphalts from different crude oil sources and blends were used to build sections of pavement about three-quarters of a mile long. All other variables (e.g., aggregate source and gradation, geometric and structural design, traffic, climate, and compaction) were held as constant as possible. In a typical project, a construction contractor could have purchased any of the four asphalts because all met the project specifications. Before construction of this site, a search was conducted for existing projects for which the asphalt source was varied and location documentation and original construction materials were available. No such projects were found. The mission was to acquire real-world, long-term pavement performance data for asphalts from different crude oil sources so that the validity of existing and new long-term performance predictive test methods could be examined. The focus was on performance variations related to asphalt crude oil source and thus asphalt compositional features. Several chemical and rheological tests were performed on the asphalts to gain information to relate to field performance. The four asphalt sources showed remarkable differences in performance. Similar comparative pavement performance sites were located in Wyoming, Nevada, Arizona, Kansas, Minnesota, and the Yellowstone National Park east entrance. All sites are monitored annually.

New bitumen performance indicators - A feasibility study

Since the 1999 Eurobitume Workshop, the search and validation of performance related bituminous binder properties continues to be a key issue for the paving industry in Europe, as well as in the rest of the world (especially for binders with complex rheological behavior). Important progress has been made and concepts such as the complex modulus measured with Dynamic Shear Rheometers (DSR) and low temperature stiffness and relaxation behavior measured with the Bending Beam Rheometer (BBR) have become familiar, along the lines of the Superpave system implementation in the US. Measurements in the linear domain of viscoelasticity have however also shown their limits and a new generation of binder tests, which try to directly address failure behavior, is now developing. Along with “conventional” rheology, three such test methods have been contemplated in this paper. In the low temperature domain, the ABCD (Asphalt Binder Cracking Device) test mimics the TSRST (Tensile Strength Restrained Specimen Test) performed on bituminous mixes. The LAS (Linear Amplitude Sweep) test is expected to be related to fatigue whereas the MSCRT (Multiple Stress Creep & Recovery Test) addresses high temperature performance. To evaluate the ability of each test method to differentiate between binders, the investigations have been based on three bitumen of the same penetration grade (70/100) but very different in chemical structure, varying from a “gel” to a “sol” structure (colloidal index of 0.24 to 0.09). Full rheology (DSR, BBR), MSCRT, ABCD and LAS tests have been conducted on all three bitumen, as well as on the corresponding RTFOT hardened and RTFOT+PAV aged binders. Further developments on the LAS test and its relation to fatigue performance are discussed in a separate paper by WRI.