Benjamin F. Bowers

Characterizing Rheological Properties of Binder and Blending Efficiency of Asphalt Paving Mixtures Containing RAS through GPC

AbstractUse of recycled asphalt shingles (RAS) into asphalt mixture has become more popular in asphalt paving industry due to dwindling natural resources and potential economic benefits. However, one critical question arises as to how much of aged asphalt binder in RAS can be effectively blended with virgin binder during mixing and construction. This paper presents a laboratory study in which gel permeation chromatography (GPC) was used to determine the blending efficiency of RAS. A correlation was first established between percentages of large molecules (LMS) obtained from GPC and rheological properties of RAS binders. Then the relationship was used to estimate the blending efficiency of RAS binders. The effects of aggregate size, RAS content, and mixing time on blending efficiency were evaluated. The test results show that the percentage of LMS was highly correlated with the complex shear modulus (G*) of asphalt binder. Increasing mixing time led to a better blending of RAS mixture. Aggregate size did n...

Investigation of Sequential Dissolution of Asphalt Binder in Common Solvents by FTIR and Binder Fractionation

AbstractAn investigation into the potential for sequential dissolution of asphalt fractions in a staged extraction scenario was conducted for common asphalt solvents. Asphalt cement subjected to six sequential washes in trichloroethylene (TCE), tetrahydrofuran (THF), toluene, or decahydronaphthalene (decalin) were evaluated using Fourier-transform infrared spectroscopy (FTIR) and fractionated for asphaltene content. The results from the FTIR were evaluated statistically using a one-way ANOVA test and the solvents induced no difference in mean carbonyl index. However, the fractionation of the asphalt cement after staged extraction showed that decalin and THF sequentially dissolved the asphalt cement while toluene remained suspect. Trichloroethylene does not appear to sequentially dissolve the asphalt cement fractions. The findings are in agreement with solubility calculations based on Hansen solubility parameters.

Dynamic Modulus of Recycled Pavement Mixtures

Pavement recycling techniques have been shown to be effective for rehabilitating pavements by reducing environmental impacts, construction costs, and time. For various reasons, many highway agencies have not widely embraced these processes despite the demonstrated advantages. One such reason is that the mechanical properties of these materials have not been widely studied, resulting in a lack of consensus on proper design values, which causes concern for highway agencies. This study sought to determine the dynamic modulus of field-produced and field-cured recycled pavement materials from 24 projects constructed in the United States and Canada. The dynamic modulus is one of the primary material parameters for mechanistic–empirical pavement design and performance prediction. On the basis of a statistical test and observation of the constructed master curves, this study found that the three pavement recycling processes studied (cold central-plant recycling, cold in-place recycling, and full-depth reclamation) had a similar range of dynamic modulus values. In addition, cold central-plant recycling and cold in-place recycling showed greater stiffness temperature dependency than that of full-depth reclamation, suggesting that the binder from the existing reclaimed asphalt pavement may play a role in their stiffness properties. The master curves also showed that the use of chemical additives generally increased the stiffness and reduced the temperature dependency of the recycled materials. The master curves showed that dynamic modulus values were similar when emulsified asphalt and foamed asphalt were used as the stabilizing and recycling agents.

Investigation of Tack Coat Failure in Orthotropic Steel Bridge Deck Overlay

The failure of tack coat on orthotropic steel bridge decks is of concern because the loss of bonding ability between layers jeopardizes the deck overlay. This study investigated tack coat failure on an orthotropic steel bridge deck overlay. A field survey on overlay distress was first conducted on a regular double-layered epoxy asphalt concrete overlay to identify the major distresses. A follow-up survey was conducted by using infrared spectroscopy to detect the changes in chemical functional groups that may respond to distress. Contact analysis in a finite element platform was used to analyze the influence of the tack coat on the mechanistic characteristics of the deck overlay. Finally, shear clamps were used to evaluate the shear resistance performance of the tack coat. Comparisons of tack coat materials were made to support maintenance strategies for deck overlays.

Laboratory Evaluation of a Plant-Produced High Polymer–Content Asphalt Mixture

Reflective cracking in asphalt overlays placed over jointed concrete pavements is of major concern in Virginia, as well as nationally, and has generated interest in various reflective crack mitigation techniques that are easy to implement. One technique is the use of binder modifiers, such as asphalt rubber, polymer-modified asphalt binders, or high polymer–content (HP) modified binders. In the summer of 2014, the Virginia Department of Transportation placed an HP asphalt mixture produced by using an asphalt binder that contained approximately 7.5% styrene-butadiene-styrene polymer in a trial section within a subdivision as a low-risk means to assess constructability and laboratory performance. The HP mixture was evaluated in comparison with a typical surface asphalt mixture with a 9.5-mm nominal maximum aggregate size, as a control. Testing was performed on specimens fabricated from reheated control and HP mixture samples, as well as on specimens fabricated from site-compacted samples and road cores of the HP mixture. In addition, binder grading was performed on the control binder and modified binder. The HP binder was significantly more elastic than the control binder. Comparable dynamic moduli were found for reheated mixture specimens, although site-compacted and road core specimens from the HP mixture had lower stiffness than the control mixture. The HP mixture performed better in rutting and in fatigue. The Texas overlay test indicated similar crack resistance between the two mixtures; however, measured loads of the HP specimens were nearly half those of the control specimens. The results of laboratory testing indicated that the mixture incorporating the HP binder should have a far greater fatigue life and rut resistance than the control mixture.

Effects of WMA Technologies on Asphalt Binder Blending

AbstractBecause of environmental and economical benefits, the paving industry has made attempts to incorporate recycled asphalt pavement (RAP) or recycled asphalt shingle (RAS) into warm mix asphalt (WMA). However, the low temperatures at which WMA is produced may affect the virgin-recycled binder blending in RAP/RAS mixtures. In this study, a lab testing procedure was developed to evaluate the effects of WMA technologies on binder blending. The results from the study showed that WMA additives, including sasobit, rediset, cecabase, and evotherm, slightly decreased the viscosity of the asphalt binder at 135°C. However, control binder tested at 165°C showed significantly lower viscosity than WMA binders. This may raise the concern over workability of nonfoaming WMA mix. WMA additives yielded higher blending ratio than control mix produced at 135°C, but hot mix asphalt (HMA) produced at 165°C still showed the highest blending ratio value. This indicates that a concern still exists over asphalt blending even ...

Initial Performance of Virginia’s Interstate 81 In-Place Pavement Recycling Project

Rehabilitating or reconstructing existing asphalt pavements by applying in-place pavement recycling techniques has been shown to be more cost-effective and more environmentally friendly than with traditional techniques. However, the scanty information in the literature documenting the structural and functional performance of these processes for high-volume roadways, leads to a perception by pavement engineers that the techniques are suitable only for lower-volume roads. This paper presents performance data for the 3.66-mi section of Interstate 81 in Virginia that was rehabilitated through the use of full-depth reclamation, cold central-plant recycling, and cold in-place recycling during the 2011 construction season. The performance data used to document the pavement condition included the structural capacity obtained by a falling-weight deflectometer and rut depth and ride quality measurements collected by an inertial profiler. The structural layer coefficients for the recycled materials were at the upper range of values reported in the literature. The pavement sections continued to perform well in regard to their functional and structural condition after the application of approximately 6 million equivalent single-axle loads and nearly 3 years of service. Two sections with different overlay thicknesses in the right lane also performed well after nearly 3 years of service.

Nondestructive In Situ Characterization of Elastic Moduli of Full-Depth Reclamation Base Mixtures

State highway agencies are searching for more cost-effective methods for rehabilitating roads. One sustainable solution is full-depth reclamation (FDR), which is a pavement rehabilitation technique that involves pulverizing and reusing materials from existing distressed pavements in place. However, there is little information on the long-term properties of these recycled materials. An important property, the elastic modulus, indicates the structural capacity of pavement materials and is highly recommended for design purposes by the Mechanistic–Empirical Pavement Design Guide. The elastic modulus directly affects selection of the overall pavement thickness; therefore, an accurate estimation of the modulus is key to a cost-effective pavement design. This research investigated the elastic modulus trends of three in-service pavements rehabilitated with the FDR technique during the 2008 Virginia Department of Transportation construction season. Foamed asphalt (2.7% with 1% cement), asphalt emulsion (3.5%), and portland cement (5%) were used as stabilizing agents for the FDR layers. The results of the moduli measured for the recycled base materials varied significantly over time. These changes were attributed to curing after construction, seasonal effects, and subgrade moisture. The structural capacity of the pavements improved irrespective of the stabilizing agent used.

ADDITIVES FOR SOIL-CEMENT STABILIZATION

Soil-cement stabilization is commonly used in road construction applications when temperatures exceed 10 o C. At lower temperatures, cementitious reactions proceed more slowly and strength development remains incomplete. As a component of a larger research effort, this paper reports on the use of sodium chloride (NaCl) and calcium chloride (CaCl2) for enhancing strength gain at curing temperatures of 2 o C and 10 o C. The results are mixed depending on the soil, with both increased and decreased unconfined compressive (UC) strength at both temperatures for curing durations of 3 and 7 days. For example, one local soil (Johnston County, NC) mixed with 6% Portland cement and 1.5% sodium chloride (by volume in molding moisture content) resulted in an increase in UC strength from 1748 to 2303 kPa when cured at 10 o C for 7 days. Another local soil (Buncombe County, NC) responded negatively to NaCl addition. Clay content and overall composition are postulated as controls on additive efficacy.

Air-Soil Relationships for Lime and Cement Stabilized Sub-Grades

Temporal and spatial relationships between air and soil temperature are relevant to many applications in geotechnical and geo-environmental engineering. However, such data are not often available for a given site-specific project, so it remains attractive to develop practical models that do not require extensive and esoteric parameters. The impetus for the work presented herein is the common use of lime and cement to stabilize soils in road construction. While these additives have been used successfully to increase shear strength and reduce moisture susceptibility, their performance is temperature dependent. This manuscript presents soil temperature data for lime and cement-stabilized sub-grades from four sites. In general, each site was instrumented for air temperature, sub-grade temperature and moisture content. For the soils tested, estimated thermal diffusivity values range between 5.7 x 10–7 and 7.8 x 10–7 m2/s. These results are incorporated into a sinusoidal approximation of diurnal temperature fluctuations for purposes of preliminary modeling. Limitations in this approach are discussed, along with recommendations for model refinement. This work is part of a larger effort to predict subsurface temperatures and the corresponding strength of lime or cement stabilized sub-grades with little more than a standard weather forecast.