Eddie N Johnson

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.

The Effect of Recycled Asphalt Materials on Hot Mixed Asphalt Pavement Performance

Rises in construction and asphalt binder costs, as well as the growing pressures on landfills, have contributed to the increased use of Recycled Asphalt Shingles (RAS) in Hot Mixed Asphalt (HMA) Pavement Mixtures. Initial incorporation of Manufacturers Waste Scrap Shingles (MWSS) into HMA pavements yielded encouraging results and prompted waste management organizations, industry and government to investigate incorporation of Tear-Off Scrap Shingles (TOSS). As of 2009, the Minnesota Department of Transportation (Mn/DOT) standard specifications only allowed a 5% MWSS replacement for the allowable Recycled Asphalt Pavement (RAP) and TOSS was permitted, only with, “prior approval from the engineer”. This need to get approval greatly reduced the willingness of local entities to use TOSS. Furthermore, a high-profile, pre-mature, and expensive, pavement failure prompted many to re-evaluate the benefits of using RAS in HMA pavement mixtures. A multi-agency research effort between Mn/DOT and the Minnesota Pollution Control Agency (MPCA) was initiated with the goal of making a recommendation on a comprehensive RAS specification, including the option of using TOSS that would allow agencies to realize the economic and environmental benefits without compromising pavement performance or durability. The research study (1) incorporated both controlled laboratory experiments and evaluations of in service pavements. Several producers submitted their ground RAS samples to the Mn/Dot laboratory for inclusion in the study. These RAS samples were tested for gradation, and deleterious materials (DM) content; these results were later used to assist in the development of an initial specification. In addition, the RAS samples were tested for the performance grade (PG) of the asphalt binder. Laboratory-produced HMA mixtures incorporating: Tear-Off Scrap Shingles (TOSS), or Manufacturer Waste Scrap Shingles (MWSS), and/or Recycled Asphalt Pavement (RAP) were tested for both asphalt binder PG grades and mixture dynamic modulus. It was concluded that the shingle properties, especially the fineness of the grind, and shingle type and the amount of recycled materials used in the HMA mixture had an impact on pavement performance. The knowledge gained from the collaborative research effort helped decision makers make an informed decision on a 2010 comprehensive RAP/RAS specification, which now allows the use of TOSS as a substitute for the total RAP content of the mix.

Flexible Slurry-Microsurfacing System for Overlay Preparation: Construction and Seasonal Monitoring at Minnesota Road Research Project

Microsurfacing mixtures are made of high-quality aggregate and asphalt emulsion components. They are produced at the project site by a mobile microsurfacing machine that mixes and places the product. Normal micro-surface designs contain approximately 13.5% emulsion and include a performance grade (PG) 64-22 asphalt cement (AC). This study investigates the field performance of softer-AC flexible slurry surfacing mixtures used for preparation and surface courses. A PG 48-34 AC was chosen for flexible slurry–microsurfacing mixtures constructed on four test cells at the Minnesota Road Research Project low-volume road facility near Albertville, Minnesota, in September 2005. This AC was used to produce mixtures for both surface preparation and wear courses. The mixtures used a reduced emulsion percentage for rut filling and an increased emulsion percentage for normal leveling courses. A single surface course mixture with the increased emulsion level was placed over the entire project. Pre- and postconstruction evaluations of cracking, rutting, and smoothness were performed. These evaluations were repeated at 6 months, following one winter of service. At 6 months an overall 71% of transverse cracking had reflected through the microsurface. Reflected distress from longitudinal cracks and patched areas was negligible. The rutting condition at 7 months was found to be similar to that at postconstruction, in which an overall 20% decrease was attributed to microsurfacing. Smoothness was favorably affected by microsurfacing construction. International roughness index values were correlated to the amount of material placed in the surface preparation course.

Thermoplastic Inlay Pavement Markings: Field Performance and Effect on Hot-Mix Asphalt

This report documents the study of the field performance of an inlay type of thermoplastic pavement marking material along with the 2-year-old bituminous pavement to which it was applied. Evaluation included physical performance of the product and the effect on overall durability of the pavement surface. The installation was performed in May 2006 on a bituminous test cell at the Minnesota Road Research Projects Low Volume Road. A total of 524 ft2 of inlaid thermoplastic pavement marking material was installed on a 4-in. surface of Superpave® hot-mix asphalt, including one segment installed along 100 ft of the left wheel path of a lane that received standard truck load configurations, and two crosswalks that received load configurations that varied by lane. From May 16, 2006, to August 1, 2007, the installations received 6,809 and 2,003 repetitions of the standard 80K and overloaded 102K truck configurations, respectively. The installation was a decorative treatment, not a retrofit of longitudinal lines on the existing pavement.

Effect of Crack Sealant Material and Reservoir Geometry on Surface Roughness of Bituminous Overlays

Many state, county, and municipal highway agencies have experienced the formation of bumps when placing single-lift overlays or the first lift of a multiple-lift overlay. These bumps are produced at the location of a previously existing crack, and even then almost exclusively when the crack has been sealed in advance of the overlay. When such bumps are not covered with a subsequent lift, what remains is often a rough ride on a newly overlaid roadway. The effects of crack sealant material type and geometry (shape) of the routed cracks in the existing surface on the formation of bumps in bituminous overlays are described. A matrix of four sealant type treatments and six geometries was designed and implemented in a test section in Jackson County, Minnesota. The overlay on the test section was constructed in September 2007. Results of this investigation indicate that cooler pavement surface temperatures, no over-band, hot-poured crumb rubber, and hot-poured elastic sealants provide the best resistance to the formation of bumps in overlays.