Daniel Swiertz

Estimating the Effect of Recycled Asphalt Pavements and Asphalt Shingles on Fresh Binder, Low-Temperature Properties Without Extraction and Recovery

The use of recycled asphalt pavements (RAP) and recycled asphalt shingles (RAS) as components of new asphalt mixes is expected to reduce construction costs, protect the environment, and conserve dwindling natural resources. However, the use of high percentages of RAP and RAS requires mix adjustments to accommodate the stiffer binder, which in turn requires quantification of the effect of the RAP and RAS binder on the fresh binder used in the mixture. Current methods for such estimates are performed on the basis of either chemical extraction and recovery of the binder or backcalculation from gyratory compacted samples. The former is not desirable because of the unknown effects of the chemical solvents on the binder, and the latter requires extensive laboratory work and resources. This paper modifies the analysis procedure for estimating the low-temperature properties of RAP binder by means of testing mortars and binders in the recently developed bending beam rheometer. The modified testing procedure was verified by testing artificial RAP materials, and found capable of estimating low-temperature grade of aged binder within 1°C of the known grade. Furthermore, the application of the procedure to RAS allowed for the introduction of the basis for the development of RAP and RAS blending charts to estimate the final grade of blended binder in mixtures. The feasibility of extending the procedure to study the effect of RAP and RAS on binder fracture properties is also presented in this paper.

Measuring the Influence of Aggregate Coating on the Workability and Moisture Susceptibility of Cold-Mix Asphalt

The purportedly higher moisture susceptibility of emulsified asphalt mixtures relative to traditional hot-mix asphalt is a primary concern limiting their more widespread use. Of the factors contributing to moisture susceptibility in cold-mix asphalt (CMA) that can be controlled by mix designers, aggregate coating is one of the most obvious physical means to reduce this distress. More complete aggregate coating is expected to help limit the moisture susceptibility of CMA by reducing the amount of water that can be absorbed into exposed aggregate. This paper refines a recently developed method to quantify aggregate coating in CMA by using digital imaging analysis and applies the procedure to several aggregate–emulsion systems to isolate factors most directly affecting aggregate coating. After the most significant factors were identified, a regression analysis of the coating matrix was used to develop quantitative models to predict coating of aggregates in CMA as a function of mix design parameters. Models were used to predict several representative levels of aggregate coating, and laboratory-compacted candidate mixtures were assessed for workability and moisture susceptibility by using a compactability parameter and modified tensile strength ratio test, respectively. Results show that the workability and moisture susceptibility of CMA are highly dependent on the level of aggregate coating predicted by the quantitative models; this finding suggests that the imaging procedure can be used not only to reliably predict aggregate coating in CMA but also to develop practical, performance-based limits on plant-produced CMA mixtures in terms of aggregate coating.

Characterization of Asphalt Pavement Surface Texture

This paper presents improved analysis methods for characterizing asphalt pavement surface texture and focuses on the use of laser profiling techniques to estimate friction characteristics. Derived from signal processing theories, texture spectral analysis methods show promise for improving characterization of the tire–pavement interface. Texture parameters measured with spectral analysis techniques represent a means for quantifying surface properties. Current methods to analyze frictional properties rely on the mean profile depth (MPD) and mean texture depth (MTD) texture parameters. Although these parameters are used widely, they do not capture the range and distribution of surface asperities on the pavement surface. Knowing the distribution of surface asperities is critical for assessing friction characteristics. Thus, texture spectral analysis methods are anticipated to improve on the MPD and MTD parameters by capturing relevant texture-level distributions. This study investigates the applicability of laser profiling systems for measuring pavement surface texture and subsequent relationships to friction. Models accounting for aggregate and mixture properties are developed and related to texture parameters through analysis of constructed field sections and corresponding laboratory samples. Results indicate that stationary laser profiling systems can capture the microtexture and macrotexture spectrum and suggest that a comprehensive friction characterization of asphalt mixtures can be obtained in a laboratory setting. With this analysis system, it is believed that asphalt mixture designers will have an improved tool by which to estimate pavement surface texture and frictional properties.

Effects of Reheating Procedure and Oven Type on Performance Testing Results of Asphalt Mixtures

Reheating and oven-aging procedures of plant-produced asphalt mixtures in laboratories are important topics to consider as performance testing of mixtures becomes more popular among agencies. Differences between laboratory equipment and procedure could significantly affect performance properties. The objective of this study is to investigate the influence of sample size, oven type, and variation in reheating/aging temperatures on the results of two performance tests on plant-produced mixtures. A selected mixture was tested for volumetric properties and performance using Hamburg wheel-tracking (HWT) and semi-circular bending (SCB-IFIT) tests. Results show that reheating mixtures uncovered and in smaller containers could significantly reduce the time to achieve aging temperature, and could make the process more efficient and consistent. In addition, aging using three different oven types showed that temperature within ovens can vary significantly depending on the location of the sample inside the oven, which affects the time required to reach the target temperature, and thus may also influence the aging of the sample. The mixture volumetric properties show that the effect of various heating conditions is marginal. Using the developed reheating/aging procedure of this study, the results of the HWT and SCB-IFIT tests showed no substantial effect of oven type on rutting and cracking resistance. The overall results indicate that there is a need to standardize the conditions of reheating, sample geometry, and to verify uniformity of temperature in ovens. Such standardization can further reduce variability and thus should be part of the AASHTO/ASTM standard procedures for quality control, or of laboratory equipment calibration procedures.

Use of the Hamburg Wheel-Tracking Test to Characterize Asphalt Mixtures in Cool Weather Regions

The Hamburg wheel-tracking test (HWTT) has shown promise to predict permanent deformation resistance and moisture damage potential of asphalt mixtures. Several state agencies have implemented the test as a mixture evaluation and design tool. One aspect of the test that remains a topic of research is the testing temperature. Many studies and specifications use 50°C for all testing, but some use a test temperature that depends on the base asphalt used in the mixture. Concern exists about the use of 50°C as the sole test temperature in cooler weather regions, such as Wisconsin, because the asphalts used in such regions tend to be relatively soft (high temperature grades of PG 58 and below). This paper presents findings in support of an effort to apply the HWTT to mixtures in cold climates with the use of three test temperatures and several mixture design variables. The paper presents the effects of the mixture design traffic level, the PG of the binder, and the binder modification level on the deformation resistance, creep slope, stripping slope, and stripping inflection point (SIP). The HWTT was found to be sensitive to the factors evaluated in this study. On the basis of statistical analysis of the test data, logical trends were observed. The testing temperature was found to affect not only the response variables but also the level of significance of controlled factors. The effectiveness of the SIP to characterize the moisture sensitivity of mixtures requires more research to validate the effect of moisture damage on HWTT results.

Mix Design Factors to Reduce Noise in Hot-Mix Asphalt

Noise generated from high-trafficked roadways is a significant source of noise pollution in urban environments. As population centers continue to expand, so too does the demand for quiet, serviceable pavements. Traffic noise is derived from two basic sources: standard vehicle engine operation and tire–road interaction. Reduction of the former has been a goal of automobile manufacturers since the introduction of automobiles nearly a century ago, but little focused research has been applied to the latter, especially in the United States. Research to determine the mix design factors that significantly influence noise generation in asphalt pavements is almost nonexistent. This study investigates the mix design and construction factors that influence noise generation in dense-graded hot-mix asphalt by means of noise prediction models. Laser profiling systems are used to measure pavement surface texture parameters. Models that predict noise generation as a function of these surface texture parameters are used to demonstrate the sensitivity of noise generation to commonly encountered mix design and construction variables for hot-mix asphalt. After various mixtures produced in the laboratory were characterized and various field sections were profiled, statistical analysis was conducted to determine the effect of mix variables on texture and estimated noise. Results indicate that reduction in noise at the tire–pavement interface can be achieved by considering specific mix design parameters, including gradation, asphalt content, and nominal maximum aggregate size. The percentage of air voids in the mixture (compaction effort) was also found to significantly influence tire–road noise emission.