Charles J. Glover

The effect of long-term oxidation on the rheological properties of polymer modified asphalts☆

Abstract The effect of long-term aging on rheological properties of polymer modified asphalt binders was studied. Modifiers included diblock poly(styrene-b-butadiene) rubber, triblock poly(styrene-b-butadiene-b-styrene), and tire rubber. Asphalt aging was carried out either at 60 °C in a controlled environmental room or at 100 °C in a pressure aging vessel [AASHTO Provisional Standards, 1993]. Both dynamic shear properties and extensional properties were investigated. Polymer modification resulted in increased asphalt complex modulus at high temperatures, decreased asphalt complex modulus at low temperatures, broadened relaxation spectra, and improved ductility. Oxidative aging decreased asphalt temperature susceptibility, damaged the polymer network in binders, further broadened the relaxation spectrum, and diminished polymer effectiveness in improving asphalt ductility.

An Investigation of Asphalt Durability: Relationships Between Ductility and Rheological Properties for Unmodified Asphalts

Abstract Literature reports indicate that the ductility of binders recovered from asphalt pavements correlate with cracking failure. However, ductility measurement is a time and material consuming process, and subject to reproducibility difficulties, as are all failure tests. The purpose of this study was to correlate ductility with DSR properties analogous to the SHRP procedure of using BBR S and m to screen for the thermal cracking. DSR measurements are much faster and consume much less material than ductility measurement. Fourteen unmodified asphalts were oxidized to different levels of aging at temperatures ranging from 60 to 200°C. Experimental data show that the extensional flow of conventional asphalt binders can be qualitatively described with a simple elongation model using a viscoelastic Maxwell element. Based on this model, a map of the dynamic shear modulus G′ vs. ε′/G′ was used to track changes in ductility with aging. Also, ductility correlated remarkably well with G′/(ε′/G′) for different binders aged at different conditions.

PHYSICAL PROPERTIES OF ASPHALT-RUBBER BINDER

ABSTRACT This study was performed to determine how the rheological properties of asphalt-rubber binders are affected by various parameters. Properties studied were asphalt composition, rubber dissolution, and the low-, intermediate-, and high-temperature rheological properties, measured with the bending beam rheometer. dynamic shear rheometer, and rotational viscometer, respectively. The rheological properties of the asphalt-rubber binder were determined to be dependent on the rubber content (weight percent), rubber particle size, and base asphalt composition. By controlling these variables, an asphalt-rubber binder with improved low-temperature cracking resistance, improved mid-temperature rutting resistance and temperature susceptibility, and a non-detrimental high-temperature compaction viscosity, all relative to the base asphalt, can be produced.

APPLICATION AND USE OF THE ATR, FT-IR METHOD TO ASPHALT AGING STUDIES

Infrared analysis is an important analytical tool in the study of asphalt chemistry. Infrared spectra indicate the existence or absence of chemical functional groups. This is valuable especially in the carbonyl region ({approx} 1,700 cm{sup {minus}1}), since this area can indicate the amount of asphalt aging. Physical properties, such as viscosity, have been related to the carbonyl absorptions. The purpose of this paper is to demonstrate the advantages, for asphalt analysis, of the single reflection attenuated total reflection (ATR) method with respect to ease of analysis and repeatability. Changes in the IR spectra of asphalt samples due to oven or hot-mix aging or due to apparent reactions in solution can be readily measured.

INVESTIGATION OF THE CURING VARIABLES OF ASPHALT-RUBBER BINDER

ABSTRACT A curing study was undertaken to determine the effect of asphalt type, rubber content, rubber mesh size, rubber source, curing time, curing temperature, and rate of mixing on the properties of asphalt-rubber binder. Properties studied were asphalt composition, rubber dissolution, molecular weight distribution, and the low, intermediate, and high-temperature rheological properties. These properties were found to be dependent on the above listed variables. Most notable were the curing variables of curing time, curing temperature, and rate of mixing. Increasing the curing time, curing temperature, and rate of mixing increased the amount of rubber dissolution into the asphalt during the curing process. Increased rubber dissolution was determined to improve the low- and intermediate-temperature rheological properties of a binder. Furthermore, after the initial increase in high-temperature viscosity with the addition of rubber, the high-temperature viscosity decreased significantly with increased rubbe...

Binder Oxidative Aging in Texas Pavements: Hardening Rates, Hardening Susceptibilities, and Impact of Pavement Depth

Aging of binders in pavements is much less understood than laboratory aging of neat binders because of a number of complications. Complications include suitable extraction and recovery methods; uncontrolled variables and unknowns such as mixture characteristics (e.g., air voids), maintenance treatments, traffic, and climate; sustaining of a research effort to study a given pavement during an appropriate time frame (in excess of one decade); and cost. An ongoing research effort sponsored by the Texas Department of Transportation studied binder oxidative hardening at 15 pavements across Texas. Results indicate that typically unmodified binders in pavements oxidize and harden to a degree that exceeds generally accepted pavement aging assumptions. In addition, this hardening may extend much deeper into the pavement than has been previously assumed or documented. Data suggest that pavements can oxidize at surprisingly uniform rates with depth once early oxidation occurs and that these rates continue for an extended time. As a rough measure, 1 month environmental room aging of 1-mm neat binder films at 60°C was equivalent to about 15 months in Texas Highway 21 after the early higher hardening rate period.

The effects of chemical composition on asphalt microstructure and their association to pavement performance

The primary objective of this paper was to investigate the impact of asphalt chemical composition on the microstructure and performance characteristics of asphalt binder. The methods implemented in this study include adsorption–desorption chromatography analysis and a range of atomic force microscopy (AFM) and chemical force microscopy techniques. It was revealed through the study that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. Particular microstructures that emerged via chemical doping were then discovered to have unique chemical polarity, which explicitly impact durability and performance of asphalt. In fact, a surprising correlation was found between the saturates chemical parameter and the effects of oxidative aging on asphalt behaviour. The findings from this research directly contribute to the improvement of modelling capability while also creating new prospects for enhancing the performance characteristics and durability of asphalt binder.

Production of Asphalt-Rubber Binders by High-Cure Conditions

A curing study was undertaken to determine the effect that asphalt composition, rubber content, rubber mesh size, curing time, curing temperature, and rate of mixing have on asphalt-rubber properties. Curing temperatures of 232°C or 260°C (450°F or 500°F) and a high-shear laboratory mixer were used to produce the asphalt-rubber blends. The properties studied were rubber dissolution; rubber settling; molecular weight distribution; and low-, intermediate-, and high-temperature rheological properties. Increasing the curing temperature from 232°C to 260°C (450°F to 500°F) drastically increased the rate of devulcanization and depolymerization of the rubber, whereas increasing the rate of mixing from 4,000 rpm to 8,000 rpm drastically decreased the settling rate of rubber in a binder. Lower-molecular-weight asphalts were better at devulcanizing the rubber; higher-molecular-weight asphalts were better at depolymerizing the rubber. These high-cure binders are homogeneous in appearance and slow to phase separate on standing; they have acceptable compaction viscosities at hot-mix temperatures, higher G*/sinδ at rutting temperatures, and lower stiffness at cold temperatures than does the base asphalt.

The Effects of Asphaltenes on the Chemical and Physical Characteristics of Asphalt

There are about two million miles of asphalt pavement in this country and billions of dollars are spent annually on building and repairing them. Asphalt roads are constructed with layers of graded crushed stone glued together with asphalt. There are several properties that an asphalt must possess to be a good glue. Obviously it must have good adhesion to the stone. It must set up in a reasonable time and it must be sufficiently ductile to resist cracking under stresses from traffic and temperature changes.

Oxidative Aging of Asphalt Binders in Hot-Mix Asphalt Mixtures

This study evaluated the effect of different aggregate sources along with their Corresponding change in mixture characteristics to determine the influence of both on binder oxidation rates and changes in mixture stiffness when compacted mixtures were exposed to laboratory aging conditions. The two aggregate sources, Colorado and Nevada, had different gradations and different water absorption rates, which led to differences in the calculated asphalt binder apparent film thicknesses (AFT) for each mixture. Two asphalt binders, an unmodified PG 64-22 and a styrene–butadiene–styrene–modified PG 64-28, were used. The overall findings of the study indicated that both the aggregate and mixture characteristics influenced the oxidation rates of the binder, with the two binders oxidizing by similar amounts when aged in mixtures with the same characteristics (AFT and mixture air voids). The oxidation changes in the binder had differing effects on the stiffness of the mixture as a function of age. Not only were the aggregate and mixture characteristics important to the mixture stiffness and aging relationship, but the binder characteristics themselves, in particular polymer modification, influenced the aging and stiffness relationships of mixtures with age.