Phillip B Blankenship

Evaluation of Aspects of E* Test by Using Hot-Mix Asphalt Specimens with Varying Void Contents

A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the Mechanistic–Empirical Pavement Design Guide developed in NCHRP Project 1-37A, which has drawn much attention among asphalt technologists. The objectives in this study were (a) to consider and compare different analysis techniques for construction of the master curve and (b) to measure and analyze the effect of permanent strain on samples that have been evaluated with one of the simple performance tests, dynamic modulus. It was found that differences existed in the calculated asymptote values and the shape of the master curve, depending upon which method was adopted. Recommendations are made for modifications to the testing protocol and for further work to determine the effect of permanent strain at higher test temperatures.

Wisconsin Experiences with Reflective Crack Relief Projects

Many agencies place hot-mix asphalt overlays on deteriorating jointed or cracked portland cement concrete pavements to improve the ride, protect the pavement structure, and reduce noise. Reflection cracking of the joints and preexisting cracks through the overlay is a persistent problem. In climates such as that in Wisconsin, the initial reflective cracks often appear within a year or two. The Wisconsin Department of Transportation and the City of Milwaukee tried a fine-aggregate, asphaltrich, polymer-modified asphalt mix interlayer to absorb joint movements, delay reflective cracking, and protect the existing pavement. Four Wisconsin projects are discussed. In the first project, constructed in 1996, the interlayer showed no effect on delaying reflection cracking within the first 3 years. Later projects, however, included specifications for performance-related design tests for flexural beam fatigue and Hveem stability and were overlaid with improved mixtures to complement the flexible interlayer. The late...

Comparison of Performance Properties of Terminal Blend Tire Rubber and Polymer Modified Asphalt Mixtures

Incorporation of used tires in asphalt mixtures has been a major advancement in the using recycled materials in asphalt pavements. Tires contain some of the polymeric components that have been used to modify the asphalt binders for decades, but in a solid form. This paper presents the result of a research to examine whether or not the proper application of the tire rubber in asphalt mixtures can enhance the pavement’s mechanical properties to the same degree that the traditional polymeric binder modifiers do. The performance of a terminal blend tire rubber mixture was compared to a polymer-modified mixture through mechanical testing at the Asphalt Institute laboratory. Two mixtures in this study were designed with the same gradation in accordance with the California standard specifications, one with polymer, and the other with terminal blend asphalt. Flexural beam fatigue test, Superpave shear test, and disk-shaped compact tension test were conducted to evaluate the performance of the mixtures with respect to fatigue cracking, rutting, and low temperature cracking, respectively. The results revealed that the terminal blend mixture would have a better rutting performance. Furthermore, the terminal blend mixture exhibited a slightly more ductile behavior at the low temperature of -12°C. The two mixtures showed a similar performance with respect to fatigue cracking at 20°C.

Factors Affecting Asphalt Pavement Density and the Effect on Long Term Pavement Performance

The Kentucky Transportation Center, the Asphalt Institute, and the Kentucky Transportation Center worked together in order to identify factors that affect asphalt pavement density, and to then evaluate their effect on long term pavement performance. By determining which variables are most influential to pavement performance (i.e. roller pattern, temperature when rolled, etc.), and then monitoring the attention given to those variables, Kentucky would be able to increase the service life of asphalt roadways by at least 25%, therefore saving as much as

Evaluation of the DC(T) test in discerning the variations in cracking properties of asphalt mixtures

30 million annually on a resurfacing budget of

Effect of Long-Term Ambient Storage of Compacted Asphalt Mixtures on Laboratory-Measured Dynamic Modulus and Flow Number

129.2 million (2007), while still maintaining the current roadway level of service. Ensuring that the pavement roller is able to roll the surface at the appropriate temperature can result in increases in density of up to 4%. An asphalt mix having 11% voids failed at approximately 400,000 cycles @ 350 microstrains, compared to that same mix at 7% air voids failing at 600,000 cycles @ 350 microstrains, resulting in a lab fatigue life increase of 50%. Two primary results were found from this study. First, by ensuring the compaction roller reaches the pavement before the temperature is allowed to drop substantially, up to a 4% increase in density can be achieved. Second, by increasing density 4%, lab fatigue life can be increased by as much as 50%. From these results, by practicing proper construction techniques one could conservatively expect to see increases in the service life of an asphalt surface of up to 25% in the field.

Effect of Laboratory Mixing and Compaction Temperatures on Asphalt Mixture Volumetrics and Dynamic Modulus

As the temperature of an asphalt pavement drops to below freezing point, the asphalt material starts to lose its ductility, and consequently, the asphalt mixture becomes more susceptible to cracking. The disk-shaped compact tension [DC(T)] fracture test has been used to quantify the fracture properties of asphalt concrete at subzero temperatures for more than a decade. The Asphalt Institute laboratory has successfully utilised the DC(T) test in several research studies. As a result of these studies, a valuable database is gathered which represents the sensitivity of the DC(T) test, and exhibits how the test is capable of capturing the effect of various factors on the performance of asphalt mixtures at low temperatures. This paper briefly presents the findings from some of these studies. The paper presents the response of the DC(T) test to the variations in several factors relative to asphalt pavements including the crude source of the asphalt binder, ageing of the asphalt mixture, deficiency in the in-place density, pavement temperature, using a warm-mix agent, using RAP and RAS materials, and chip sealing as a preservation method. The test showed to be well capable of capturing the variations in these factors; therefore, it can be utilised by the pavement managers to assess the changes in the specimens from the asphalt pavements over time to help determine if any maintenance or rehabilitation action is required. Furthermore, the test can be used to evaluate the laboratory-made mixtures and ascertain if they would perform satisfactorily in their designated environmental conditions.

Development of the indirect ring tension fracture test for hot-mix asphalt

The asphalt mixture performance tester (AMPT) requires an exhaustive examination of the factors that influence the dynamic modulus and flow number test results. Interlaboratory research conducted in NCHRP Project 9–29, Phase 4, showed that dynamic modulus test results were highly dependent on the testing laboratory and the preparation of the AMPT specimens. Factors could include the oxidative aging and the steric hardening of asphalt in the mixture specimens during storage in a laboratory. The Asphalt Institute, Lexington, Kentucky, performed an experiment in cooperation with FHWA to evaluate the effect of ambient laboratory sample storage on the mechanical properties of asphalt mixture specimens. A half-factorial test matrix with triplicate specimens was developed to evaluate the effect of the following factors on the dynamic modulus and flow number of a laboratory standard mixture: storage duration (1 to 84 days), binder type (PG 64–22 and modified PG 76–22), storage of the specimen in a bag, and the cutting and coring of the specimen after compaction or immediately before it was tested. The results showed that storage duration could affect significantly the properties of the mixture with neat binder. The bagging of specimens did not seem to prevent their stiffening. However, storage of specimens uncut and uncored seemed to delay the stiffening phenomenon.

Laboratory Investigation of Asphalt Pavements with Low Density and Recommendations to Prevent Density Deficiency

Employment of conventional asphalt testing protocols for characterization of polymer-modified asphalts remains a challenge. NCHRP launched Project 9–39 to identify an approach to determine the mixing and compaction temperatures applicable to unmodified and modified asphalt binders. The Asphalt Institute, Lexington, Kentucky, in cooperation with FHWA, embarked on the research reported here to evaluate how mixture performance is affected by laboratory mixing and compaction temperatures. Samples were mixed and conditioned at various temperatures and conditioning durations with modified and unmodified binders. Volumetric analysis confirmed that slight changes in the mixing temperature did not change the results of volumetric testing. Compacted samples were tested to determine the dynamic modulus as an indication of pavement performance. A comprehensive statistical analysis was performed, and the overall results showed that the impact of the conditioning temperature and duration on the dynamic modulus was more significant than the influence of the mixing temperature. Further, for modified binders the significance of the impact of the mixing temperature seemed to be a function of the crude source of the binders.

The FHWA’s Demonstration Project for Enhanced Durability of Asphalt Pavements through Increased In-Place Pavement Density

Almost all of the current hot-mix asphalt (HMA) fracture tests are considered to be research tools. This paper describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be used at the Department of Transportation level. Numerical modelling was utilised to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. An experimental plan was developed to optimise the test parameters for HMA specimens. The experiment results revealed that the test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Moreover, the data from laboratory tests were utilised to estimate the maximum allowable crack lengths for the pavements based on a viscoelastic model.