Christopher Ericson

Effect of Silo Storage Time on the Characteristics of Virgin and Reclaimed Asphalt Pavement Mixtures

Many hot-mix asphalt plants store material in heated silos before it is ready to be transported to construction sites. The time that material is stored in the silo is not controlled and varies widely, depending on several factors. As the material is exposed to elevated temperatures, short-term aging of the binder may occur. Another important consideration is the interaction between reclaimed asphalt pavement (RAP) and virgin binders, as blending or diffusion could occur between the binders. In this study, a virgin and 25% RAP mixture were sampled at incremental silo storage times up to 10 h. Characterization testing included performance grading, rheological indexes, Glover–Rowe parameter evaluation, rolling thin film oven aging on the binders, complex modulus, a simplified viscoelastic continuum damage model (S-VECD) for fatigue, and thermal stress restrained specimen testing of the mixtures. Simulations that used layered viscoelastic critical distresses pavement analysis to predict fatigue behavior from the S-VECD model were used to show the potential effects of silo storage time on pavement life. Results from all tests indicated that mixtures aged with an increase in silo storage time. RAP materials experienced a greater effect; this effect may be a function of the air void content or indication of blending–diffusion in the silo. Rolling thin film oven aging showed that current laboratory conditioning methods do not necessarily simulate asphalt plant production. Production parameters, such as silo storage time, have a significant impact on mixture performance.

Coarse Aggregate Angularity and Its Relationship to Permanent Deformation of Gravel-Aggregate Hot-Mix Asphalt in New York State

This study evaluated the asphalt mixture performance of various gravel and crushed stone sources with different levels of crushed face counts as determined by ASTM D5821. Coarse aggregate angularity and texture were also evaluated with AASHTO T326 and aggregate imaging system testing. Each of the asphalt mixtures designed and tested used three asphalt binders: (a) neat PG 64-22, (b) polymer-modified PG 64-22 meeting New York State Department of Transportation (New York State DOT) elastic recovery specifications, and (c) polymer-modified PG 76-22. The permanent deformation properties of the different asphalt mixtures were measured with the asphalt pavement analyzer (AASHTO TP63) and the asphalt mixture performance tester (AASHTO TP79) with confining pressure applied to the specimens. Aggregate testing showed that ASTM D5821 correlated poorly with both AASHTO T326 and the aggregate imaging system. Situations also occurred in which aggregates had identical crushed counts but different levels of uncompacted void contents. The asphalt mixture performance tester that used confining pressure correlated well with the uncompacted voids content results of AASHTO T326. However, stresses applied in the asphalt pavement analyzer did not sufficiently mobilize the asphalt mixtures to allow differences in aggregate angularity to be clearly noted. Both asphalt tests were sensitive to asphalt binder high-temperature stiffness as determined by AASHTO TP70. Statistical analysis of the data resulted in a table that allows the New York State DOT to use aggregate angularity (as determined by AASHTO T326) and nonrecoverable creep compliance (as determined by AASHTO TP70) interchangeably to ensure that hot-mix asphalt (HMA) blends containing gravel aggregate perform as well as HMA blends containing crushed-stone aggregate.

Fatigue Performance of Re-Refined Engine Oil Bottom-Modified Asphalt: Laboratory Study

Re-refined engine oil bottom (REOB), one of several products obtained from refining recovered engine oil, has been used in the asphalt industry since the 1980s. Generally, REOBs are used to help soften the base asphalt binder and are commonly used from 3% to 10% by weight to achieve desired low temperature asphalt binder properties. Recently, blame for poor cracking performance in a number of Canadian and northern U.S. pavement sections has been laid on the use of REOBs. This issue has prompted state agencies in the northeast United States to ban its use, without necessarily understanding how REOB affects asphalt binder and mixture performance. A research effort was conducted to evaluate the laboratory performance of asphalt binders and mixtures modified with REOB. Performance grading, master stiffness curves, the double-edge notch tension test (DENT), and black space analysis were conducted on the asphalt binders at different levels of laboratory aging. The research study showed that while being able to achieve softer asphalt binder grades in accordance with AASHTO R29, the addition of REOB accelerated the age-hardening effects in the asphalt binder, with higher levels of age hardening occurring at higher REOB dosage rates. The study also indicated that while the stiffness properties at low temperatures were not affected by REOB, the relaxation properties were highly affected. The black space analysis, using the Glover–Rowe approach, and the DENT test showed promise in identifying the age-hardening effects and correlated well with mixture fatigue cracking.

Moving Toward Asphalt Binder and Mixture Protocols to Minimize Fatigue Cracking on Asphalt Airfields

The Port Authority of New York and New Jersey (PANYNJ) owns and operates two of the most heavily used airports in the United States. Newark Liberty International Airport (Newark) in New Jersey and John F. Kennedy International Airport (JFK) in New York handle approximately 1 million arrivals and departures each year. Although their runways witness an extreme amount of loading, the primary distress observed on them is top-down fatigue cracking with little to no rutting. Recently, the PANYNJ observed premature top-down fatigue cracking at two runways at Newark. After an evaluation of several runways at JFK and Newark, it was discovered that asphalt mixtures of similar design were resulting in varying levels of fatigue cracking performance. For a better understanding of the fatigue cracking performance of asphalt mixtures placed on airport runways in the New York and New Jersey area, a forensic study was conducted on field cores recovered from five runways maintained by PANYNJ. Asphalt binder was recovered and tested from the field cores at different depths from the pavement surface. The test results of the study showed that the ΔTcr parameter, measured with the critical low-temperature results from a bending beam rheometer, could be used within a purchase specification to help mitigate the potential receipt of asphalt binders prone to accelerated aging and cracking. Meanwhile, the overlay tester and the semicircular bending flexibility index were found to be capable of potential implementation as quality control tests to ensure that asphalt mixtures produced for asphalt airfields in the New York and New Jersey area were not susceptible to top-down fatigue cracking.