Thomas F. Turner

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.

N.m.r. characterization of coal pyrolysis products

Abstract Isothermal pyrolysis studies were conducted on an Illinois No. 6 and a Wyodak coal at 375 °C, 400 °C and 425 °C, using a fluidized sandbath reactor system. The amount of coal converted to tar, gas and residue was determined for different reaction durations at each temperature. Solid- and liquid-state 13 C n.m.r. techniques were used to characterize the residue coal and tars produced during varying stages of pyrolysis. Solid-state 13 C n.m.r. measurements showed that the residue coal reached its limiting aromaticity value fairly early during decomposition, and on a mass basis, the aromatic carbon in the residue remained relatively constant during pyrolysis. The aliphatic carbon mass loss was similar to the total carbon mass loss. The mass of aromatic carbon in the products was found to increase by 13% and 16% over that in the starting material for the Wyodak and Illinois No. 6 coal, respectively. The amount of aliphatic carbon that aromatized to produce the increase in aromatic carbon was 37% and 35% for the Wyodak and Illinois No. 6 coal.

Long-Term Aging Characteristics of Polyphosphoric Acid-Modified Asphalts

An experiment involving three neat asphalts and their mixtures with 1.5 wt % of polyphosphoric acid (105%) was conducted to investigate the effect of polyphosphoric acid (PPA) on the long-term aging characteristics of asphalt binders. Analytical techniques including dynamic shear rheometry, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance (NMR) spectroscopy were performed on unaged and aged PPA-modified asphalts. Rheological properties of unaged and aged modified asphalts were measured with a dynamic shear rheometer at various temperatures. The concentration of carbonyl-containing compounds present in the various unmodified and PPA-modified binders was determined by FTIR spectrometry. The thermal properties of the unmodified and PPA-modified binder were obtained by using differential scanning calorimetry. The results indicate that PPA-modified asphalts reduce rutting potential by increasing initial stiffness and reduce fatigue or low temperature cracking, or both by improving the low-temperature flow properties. The correlation between rheological properties and chemical properties of unmodified and PPA-modified asphalts is also presented. The results show a linear relationship between physical properties and chemical properties of asphalt binders with respect to oxidative aging. However, addition of PPA to asphalt alters the linear relationship. NMR results showed no new chemical species formed in the asphalt-PPA mixture.

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.

The Bitumen Intermediate in Isothermal and Nonisothermal Decomposition of Oil Shales

A common feature of oil shale decomposition models is the bitumen intermediate, which is defined to be a soluble, nonvolatile primary product of kerogen decomposition. Despite the large number of studies that have been conducted on oil shale thermal decomposition, there is a scarcity of data on the bitumen intermediate. The problem with the bitumen intermediate is that, while it is often used in oil shale decomposition, it is seldom measured experimentally. The lack of experimental data can lead to deficiencies in understanding the mechanism and kinetics of oil generation. In this chapter some comments on the role of the bitumen intermediate during oil shale decomposition are examined, with emphasis on its temperature dependence under isothermal and nonisothermal conditions. Data are presented to illustrate that significantly greater conversions of kerogen to soluble products can be accomplished by paying attention to the kinetic behavior of the bitumen intermediate, particularly for oil shales that have a large aliphatic carbon component.

Low-Temperature Oxidation Kinetics of Asphalt Binders

A simple dual-mechanism model successfully fits the oxidation of 12 unmodified asphalt binders originating from a wide variety of sources. The kinetic formulation includes fast and slow reaction paths in parallel with free radical interactions between the two reaction pathways. The same Arrhenius parameters are used for all 12 binders studied. The differences in asphalt binder oxidation rates can be explained with the use of only one adjustable parameter, the amount of reactive material available for the fast reaction. This result suggests that unmodified asphalt binders oxidize with essentially the same chemical mechanisms. Because the Arrhenius parameters apply universally, a simple test may be performed to characterize the oxidation kinetics for unmodified binders without expensive, long-term oxidation experiments at multiple temperatures. A rheological study of the materials generated in the aging of the 12 binders using dynamic shear rheometry was also performed to investigate the relationship of rheological changes with chemical changes as binders oxidize. The rheometry consisted of the generation of a series of isothermal frequency sweeps, followed by fitting the resulting master curve with the Christensen–Anderson model. Simple shifting cannot account for the master curve changes, but changes in the model parameters follow a log-linear relationship for oxidation chemical changes. These fits appear to be source dependent, suggesting that a method with two aging time conditions would be required to characterize the rheological property changes in an unmodified asphalt binder as it ages. Such a method would produce a complete master curve–shift function set at any extent of aging, suitable for input into rational performance models.

RESIDUA UPGRADING EFFICIENCY IMPROVEMENT MODELS: WRI COKING INDEXES

Pyrolysis experiments were conducted with three residua at 400 C (752 F) at various residence times. The wt % coke and gaseous products were measured for the product oils. The Western Research Institute (WRI) Coking Indexes were determined for the product oils. Measurements were made using techniques that might correlate with the Coking Indexes. These included spin-echo proton nuclear magnetic resonance spectroscopy, heat capacity measurements at 280 C (536 F), and ultrasonic attenuation. The two immiscible liquid phases that form once coke formation begins were isolated and characterized for a Boscan residuum pyrolyzed at 400 C (752 F) for 55 minutes. These materials were analyzed for elemental composition (CHNS), porphyrins, and metals (Ni,V) content.

CHARACTERISTICS OF PYROBITUMEN AND OIL OBTAINED FROM GREEN RIVER OIL SHALE PYROLYSIS

Pyrobitumens and oils generated from the isothermal pyrolysis of Green River oil shale at 400/sup 0/, 425/sup 0/, and 440/sup 0/C for different times were characterized. Elemental contents, average molecular weights, and hydrocarbon contents were determined for the pyrobitumens and oils. The pyrobitumens, a major initial pyrolysis product, had an average molecular weight exceeding 1200 and contained about 85% polars. The atomic hydrogen-to-carbon ratio, nitrogen content, and average molecular weight of the pyrobitumens changed with pyrolysis temperatures and times. The variable composition of the pyrobitumens suggests that pyrobitumen should not be considered as a single intermediate for kerogen decomposition. In contrast, oils contained 60% hydrocarbons and had a constant atomic hydrogen-to-carbon ratio and average molecular weight of about 250. However, the nitrogen content of the oils increased with increasing reaction time. The ratios of normal heptadecane/pristane and normal octadecane/phytane, and odd-even predominance of oils were sensitive to pyrolysis temperatures and times. The rate constants, frequency factors, and activation energies of the formations of the total hydrocarbons, aliphatic hydrocarbons, and aromatic hydrocarbons of the oils were calculated.