Timothy R Clyne

Effect of Reclaimed Asphalt Pavement (Proportion and Type) and Binder Grade on Asphalt Mixtures

Reclaimed asphalt pavement (RAP) has been used in the United States for more than 25 years because of the benefits in costs and environmental stewardship. The recent substantial increases in asphalt prices have led asphalt technologists to examine the increase in RAP use. The evaluation of the performance of the asphalt mixture containing RAP is therefore a priority for the asphalt materials community. This paper investigates the effect of RAP percentage and sources on the properties of asphalt mixtures. Ten asphalt mixtures, including two different RAP sources, three RAP content percentages (0%, 20%, 40%), and two different asphalt binders (PG 58-28 and PG 58-34) were investigated in this study. The complex dynamic modulus was performed on all mixtures at different temperatures and frequencies, and semicircular bend (SCB) fracture testing was performed for all mixtures at three low temperatures. Experimental results indicate that asphalt mixtures containing RAP have higher dynamic modulus values than the control mixtures containing no RAP. The stiffer asphalt binder was found to result in higher dynamic modulus values for both the control and the RAP-modified mixtures. Experimental data also show that the RAP source is not a significant factor for the dynamic modulus at low temperatures, although it significantly affects dynamic modulus values at high temperatures. In addition to test temperature, the RAP percentage was found to significantly affect the SCB fracture resistance of mixtures. However, for the dynamic modulus, values for the softer binder were higher than for the stiffer one at low temperatures. No significant statistical relationship between dynamic modulus and fracture energy was found.

High-Temperature Rheological Properties of Asphalt Binders

Previous research efforts have shown that the rutting parameter used in the performance grade asphalt binder specifications, |G*|/ sin δ, does not reasonably predict the rutting potential of asphalt mixtures, especially when modified binders are used. A number of other parameters, such as the zero shear rate viscosity and the permanent strain accumulated under repeated creep and recovery, were investigated; however, no consensus was achieved. This paper investigates the use of zero shear rate viscosity and of repeated creep permanent strain as potential specification parameters and discusses the importance of temperature susceptibility and of strain tolerance to the rut resistance of asphalt binders.

Evaluation of field aging effects on asphalt binder properties

ABSTRACT The oxidative aging that takes place in the asphalt binders used in the construction of asphalt pavements significantly affects the performance of the pavements during their service life. In this paper two issues that still generate a lot of debate in the research community are investigated: how far aging penetrates inside the asphalt layer and how reasonable laboratory aging tests simulate the aging occurring in the field. Cores were obtained from three cells at MnROAD facility and the binders were extracted and recovered from 25 mm slices cut along the depth of the cores. The properties of the recovered binders as well as the properties of the original binders aged in laboratory conditions were investigated, using standard testing procedures part of the current specifications as well as additional test methods. The results indicated differences in aging effects with location inside the asphalt layer and significant differences between the recovered and the laboratory aged binders.

Low Temperature Fracture Properties of Polyphosphoric Acid Modified Asphalt Mixtures

AbstractThe low temperature fracture properties of polyphosphoric acid (PPA) modified mixtures are evaluated and compared with those of polymer modified mixtures. The main objective is to determine whether PPA can partially or completely substitute traditional polymer modifiers, without adversely affecting the mixture’s resistance to thermal cracking. Laboratory compacted and field cored test samples from the Minnesota Road Research Project (MnROAD) were tested using traditional methods as well as newly developed fracture testing protocols: indirect tensile test (IDT), semicircular bending test (SCB), and disk-shaped compact tension test (DCT). The effects of temperature, air-void content, comma and long-term aging on low temperature fracture properties were analyzed; and field performance observations of the test cells from MnROAD were discussed. On the basis of the analysis, the fracture resistance of the PPA modified mixture is less than that of the SBS modified mixture. However, when PPA is used to su...

Laboratory Evaluation of Asphalt Binders and Mixtures Containing Polyphosphoric Acid

Four modified asphalt binders were investigated for performance grade, multiple stress creep and recovery (MSCR), mixture dynamic modulus, and mixture fatigue resistance: polyphosphoric acid (PPA) only, PPA plus Elvaloy, styrene–butadiene–styrene (SBS) only, and SBS plus PPA. MSCR data indicated that the binder modified with PPA only had the highest nonrecoverable compliance and lowest percentage of recovery, whereas the binders modified with PPA plus Elvaloy and with SBS plus PPA were best, with the lowest nonrecoverable compliance and highest percentage of recovery, depending on whether the extracted or laboratory binder was evaluated. The dynamic modulus test results illustrated a smaller difference between mixtures, except where the binder modified with PPA plus Elvaloy had a more desirable variation in stiffness (e.g., softer at high frequencies and low temperatures, and slightly stiffer at low frequencies and high temperatures). The fatigue life ranking was different before the data were normalized for controlled strain conditions with the use of viscoelastic continuum damage principles. Without normalization, data from the two SBS-modified mixtures (with and without PPA) had the highest average fatigue life; however, with normalization, the data for mixtures modified with PPA plus Elvaloy exhibited the highest average fatigue life. Implications of the results are that PPA modification strategies can provide adequate resistance to rutting and moisture damage and that modification with PPA only is not the same as (and is statistically less resistant to fatigue cracking than) modification with polymer or with polymer plus PPA. Also, comparable fatigue cracking resistance can be achieved with the use of SBS alone or SBS plus PPA, which uses less polymer in conjunction with PPA.

Investigation of Superpave Fine Aggregate Angularity Criterion for Asphalt Concrete

Fine aggregate angularity (FAA) requirement is one of the aggregate consensus properties recommended by SHRP. Many state highway departments include FAA as part of their Superpave® mixture design specifications. Recent concerns about pavement performance and aggregate shape have caused these agencies to reinvestigate whether standard FAA testing provides information indicative of performance. This paper presents the results from standard FAA tests and digital imaging to investigate the validity of FAA requirements. Testing was performed on four asphalt mixtures representing a range of FAA values. Dynamic modulus testing was performed at three temperatures and five frequencies, and master curves were obtained using nonlinear regression. Asphalt pavement analyzer data obtained at one temperature were analyzed with respect to the rutting curve and rate of rutting. The experimental results for aggregates and mixtures were analyzed together by using statistical methods to develop correlation coefficients and linear trends. It was found that dynamic modulus and rut resistance values were strongly related to aggregate blend FAA. Some additional parameters from digital imaging also predicted modulus and rut resistance very well and should be included in future research.

Low temperature cracking performance at MnROAD

The Minnesota Road Research Project (MnROAD) was constructed in 19901993 as a full-scale pavement testing facility. Several different cells were built with various materials, mix designs, and structural designs. Two different asphalt binders were used during the original construction: PG 58-28 and PG 64-22. The sections have all shown various degrees of low temperature cracking. In general the cells with stiffer binder (PG 64-22) experienced a higher number and greater severity of thermal cracks than those with the softer binder. The ride quality of the pavements has been adversely affected by the deterioration of the low temperature cracks. In 1999 three cells were reconstructed on the Low Volume Road as a study specifically examining low temperature cracking. These sections were designed using the exact same Superpave mix design except for the asphalt binder type, which differed at the low temperature performance grade. The performance grades for Cells 33, 34, and 35 were PG 58-28, 58-34, and 58-40 respectively. After several years in service these sections have begun to show marked differences in performance. Cell 35 has shown the most cracking, even though it has the softest grade at -40. The cracks on Cell 35 do not look like typical thermal cracks, while Cell 33 exhibits the expected typical thermal cracks. Cell 34 had virtually no distress after six years.

Low-Volume-Road Lessons Learned: Minnesota Road Research Project

The Minnesota Department of Transportation built the Minnesota Road Research Project (MnROAD) and its low-volume road (LVR) between 1990 and 1993. The 2.5-mi LVR consists of a two-lane roadway that originally contained gravel, hot-mix asphalt, and concrete test sections designed for low-volume road research. Each of these test sections is trafficked by a controlled five-axle tractor-semitrailer to simulate conditions of rural roads in two load configurations, resulting in the same equivalent axle loads. Over the years, a number of activities and studies have taken place that have used information from MnROADs LVR. The first 10 years of findings related to the LVR in the areas of facility, hot-mix asphalt, portland cement concrete, aggregate surfacing, seasonal load limits, and non-pavement-related lessons learned are summarized.

Minnesota Road Research Data for Evaluation and Local Calibration of the Mechanistic–Empirical Pavement Design Guide's Enhanced Integrated Climatic Model:

This paper describes research to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate-modeling package used in the Mechanistic–Empirical Pavement Design Guide (MEPDG). First, the study uses temperature data collected at the Minnesota Road Research Project (MnROAD) facility from portland cement concrete (PCC) and asphalt concrete (AC)–PCC pavements to investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG-user inputs for thermal conductivity of PCC. Overall, the paper examines measured data from MnROAD for AC-PCC pavements and their single-layer PCC counterparts and attempts to explain how similar pavement systems and their thermal characteristics are taken into account in the MEPDG. The paper concludes that evaluation of the material thermal inputs should be part of a process of local calibration and adaptation of the MEPDG.

Low-Volume Road Performance Related to Traffic Loadings at Minnesota Road Research Project

The Minnesota Department of Transportation built the Minnesota Road Research Project (MnROAD) between 1990 and 1993. The low-volume road consists of a two-lane roadway that originally contained hot-mix asphalt (HMA) and portland cement concrete (PCC) test sections. Each of these test sections is trafficked by a controlled five-axle tractor-semitrailer. The trucks have two different load configurations, resulting in the same equivalent single-axle loads (ESALs) over time. The first configuration consists of a legally loaded 80,000-lb (80-kip) truck that runs on the inside lane 4 days per week, and the second configuration consists of an overloaded 102,000-lb (102-kip) truck that runs on the outside lane 1 day per week. The field performances of the different MnROAD test sections over time resulting from the different loading applications are compared. As expected, the thermal cracking performance of HMA was not affected by the traffic loadings, because it is a distress caused by the environment. Similarly, the ride quality of both HMA and PCC pavements was not noticeably different between the two lanes. However, rutting and fatigue cracking of asphalt pavements and faulting of PCC pavements were more severe in the lane with the 80-kip truck than they were in the lane with the 102-kip truck. The higher number of repetitions at a lower load level in the 80-kip lane produced more distress than did the lower number of repetitions at a higher load level in the 102-kip lane. The data presented show that the concept of ESALs may not be appropriate for mechanistic–empirical design procedures.