This study evaluated the short-term performance properties and predicted cracking performance of asphalt mixtures containing polymer-modified asphalt (PMA) binders and recycled polyethylene (RPE). To that end, binder rheological testing, mixture performance testing, and FlexPAVE simulations were conducted. Furthermore, three PMA mixtures were selected for field evaluation on the National Center for Asphalt Technology Test Track and rapid performance testing during production. The PMA binders modified with styrene-butadiene-styrene (SBS), reactive elastomeric terpolymer (RET), and RET-compatibilized RPE had significantly improved elasticity and rutting resistance compared with the unmodified binder. The PMA binders also exhibited good storage stability with minimal separation tendency. Both polymer modification of the asphalt binder and adding RPE via the dry process improved the rutting resistance of the mixture. Although the unmodified and PMA mixtures exhibited notably different load-versus-displacement curves from the Indirect Tensile Asphalt Cracking Test (IDEAL-CT), they had similar cracking tolerance index (CTindex) results. The G(f)-versus-l(75)/m(75) interaction diagram allowed a more robust understanding of the IDEAL-CT results by considering mixture toughness and brittleness, and their interactions with CTindex. In all cases, polymer modification increased the stiffness and fatigue damage resistance of asphalt mixtures, while adding RPE via the dry process embrittled the mixtures, making them more susceptible to fatigue damage. The PMA mixtures had significantly better predicted cracking performance in FlexPAVE simulations than the unmodified mixture. This improvement was mainly caused by polymer modification of the asphalt binder. Finally, adding dry RPE pellets improved the rutting resistance but reduced the intermediate-temperature cracking resistance of the plant-produced PMA mixture containing an SBS-modified binder.

This study aimed to evaluate the repeatability of locked-wheel skid trailer (LWST) and sideway-force coefficient routine investigation machine (SCRIM) measurements and investigate the influences of test speed and test temperature on the friction measurements. This study selected 14 test sections from the NCAT Test Track with different surface texture and friction characteristics. The LWST and SCRIM tests were conducted at different test speeds and test times (or temperatures) on the two consecutive days. The repeatability analysis indicates that both LWST skid number (SN) and SCRIM reading (SR) measurements were most repeatable at a test speed of 50 mph and tangent section. The SN measured in the late afternoon and SR measured at noon were more repeatable than those measured at other times. This study recommended an acceptable precision of friction measurement be within 2.5 SN or 3 SR units. In addition, this study concluded that the SN and SR had a good linear correlation. The statistical regression analysis demonstrates that test speed, air temperature, pavement mean profile depth, and pavement type were significant variables affecting asphalt pavement friction. The developed regression models for SN and SR were helpful to correct the friction measurements to a reference speed or temperature.

This study aimed to evaluate the feasibility of using more dolomite aggregates in asphalt surface mixtures that are typically used by West Virginia Division of Highways (WVDOH). The laboratory test results indicated that increasing dolomite content in asphalt surface mixtures resulted in a faster deterioration rate at the early polishing stage. In addition, asphalt surface mixtures containing more than 50% dolomite coarse aggregates would significantly reduce roadway safety. The field test results validated that dolomite shall not exceed 50% of coarse aggregate in asphalt surface mixture if the projected traffic volume is greater than 3.0 million equivalent single axle loads (ESALs).

The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. This study selected six pavement sections with low skid resistance from the National Center for Asphalt Technology Test Track for shotblasting abrasion. These sections included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four coarse aggregate types (limestone, granite, dolomite and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure the surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking and surface roughness were periodically monitored. The test results indicated that shotblasting treatment was effective in improving the friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and coarse aggregate type.

High friction surface treatment (HFST) is commonly used to improve surface friction of asphalt pavements at high crash rate locations, and the objective of this study is to assess the feasibility of using alternative friction aggregates in HFST. Three-wheel polishing device (TWPD) was used to simulate the actual traffic polishing in the laboratory. Firstly, the texture and friction properties of HFSTs with 12 friction aggregates were characterized using circular track meter (CTM) and dynamic friction tester (DFT) after various TWPD polishing cycles (0 k, 70 k, and 140 k). The laboratory results showed that both DFT60 and mean profile depth (MPD) decreased with TWPD polishing cycles, and the DFT60 and MPD results after 70 k TWPD polishing cycles had no significant difference with those values after 140 k TWPD polishing cycles. In addition, a good linear correlation was observed between DFT60 and MPD. Based on the DFT60 results, two bauxite HFSTs showed the best friction performance, and taconite was found to be a suitable alternative aggregate source for HFST. This study also found that slag, silica, and quartz were not good candidates for HSFT application due to the poor texture and friction properties of the corresponding HFSTs. Based on the laboratory evaluation results, eight friction aggregates were selected to pave the HFST sections at the National Center for Asphalt Technology (NCAT) Test Track, which was subjected to 2.6 million equivalent single axle loads (ESALs) in six months. The CTM, DFT, and lock-wheel skid trailer (LWST) were used to characterize the texture and friction properties of field HFST sections, and both DFT and LWST results showed that the bauxite HFST exhibited better friction performance than the granite and flint HFSTs. In addition, there were good linear correlations existing between laboratory DFT60 and MPD results with the corresponding field measurements. Lastly, the influences of aggregate properties (i.e., particle size, durability, angularity, and shape index) on the texture and friction properties of HFST were investigated. The statistical analysis indicated that particle size had significant effects on the MPD and DFT60 of HFST. Meanwhile, only angularity showed a linear relationship with the MPD results of HFST.

The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. The National Center for Asphalt Technology (NCAT) Test Track is a 1.7-mile oval where the accelerated loading research is conducted on experimental asphalt pavements. In this study, six pavement sections with low skid resistance were selected for shotblasting abrasion, which included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four aggregate types (limestone, granite, dolomite, and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking, and surface roughness was periodically monitored. The test results indicated that shotblasting treatment was effective in improving the long-term friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting, and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and aggregate type.

Micro surfacing is a treatment capable of addressing minor surface defects, protecting the pavement structure from moisture, and overall extending pavement life when applied to structurally sound pavements. This treatment is suitable for use on high traffic volume roads, providing a cost-effective alternative for state highway agencies. To better evaluate field performance of micro surfacing, a full-scale test section was placed on the National Center for Asphalt Technology (NCAT) Test Track during its fifth research cycle in 2014. An existing pavement section constructed in 2009 was identified as a suitable candidate for pavement preservation. The pavement consisted of 7 in. of asphalt concrete over 4.8 in. of aggregate base and had started to show signs of deterioration after receiving over 17.5 million equivalent single axle loads (ESALs), but was in overall good condition. The section was split into two subsections, leaving one untreated and placing a type II micro surface on the other. Both subsections have been monitored periodically, measuring performance indicators such as cracking, rutting, IRI and friction. Since treatment, an additional 17 million ESALs have been applied to the pavement over the course of five years. The observed results show that micro surfacing has been effective in slowing down pavement deterioration compared to the control section. Findings are similar to those observed on other NCAT full-scale test sections located on open roadways, which are not subjected to accelerated testing.

Over time, new pavements deteriorate due to the effect of traffic loads and the environment. If appropriate treatments are applied during the early stages of deterioration, it is possible to improve pavement conditions and extend pavement life without increasing expenditures. The National Center for Asphalt Technology (NCAT) has partnered with the Minnesota DOT’s Road Research Facility (MnROAD) to conduct a pavement preservation study that evaluates the life-extending benefit of a variety of preservation treatments, ranging from crack sealing to thin overlays. The objective of this research partnership is to develop performance curves for the treated pavements under different conditions (climate, traffic and initial condition of the pavement). In this study, full-scale test sections were treated first in a southern location (Alabama) on roadways subjected to both low and high traffic levels, starting in the summer of 2012. The experiment was extended in 2016 to include test sections in a northern location (Minnesota) to evaluate the effect of cold climate, also for low and high traffic levels. Throughout this time, cracking, roughness, rutting and macrotexture data were collected biweekly to evaluate pavement performance. The observed trends in the first years of the experiment indicate that there is not a significant variation in roughness or rutting over time, and that performance is mainly affected by the amount of cracking. Furthermore, the condition of the pavement at the time of treatment significantly affects the performance of the treated pavements, as pavements that are treated while still in good condition tend to remain in that category for a longer time. The results also demonstrate the effectiveness of applying pavement preservation treatments versus the “do nothing” scenario. After 4.8 years, the amount of cracking observed is less than the amount expected if the sections were left untreated, even for sections treated with applications that are not designed to address cracking. The results shown in this paper should be considered preliminary and used with caution. Data collection efforts continue in both southern and northern locations with the objective of determining the life-extending benefits of pavement preservation treatments as a function of initial condition, climate and traffic.

This paper reports on the final surface characterization and full forensic analysis of a highly modified asphalt pavement versus conventional Hot Mix Asphalt (HMA) at the National Center for Asphalt Technology (NCAT). The highly modified asphalt pavement is 20% thinner than a series of companion sections. The sections were subjected to 20 million Equivalent Single Axle Loads (ESALs) over a period of 5 years. At the end of two full track cycles, the thinner highly modified section has outperformed the others in permanent deformation and bottom up fatigue cracking. Modeling results give quite reasonable agreement with observed performance. The performance results validate pavement modeling reported at the International Conference on Perpetual Pavements (ICPP) in October and demonstrate that substantial thickness reduction is possible while retaining and even improving long term performance. Equally important, material properties of highly modified mixes may be used to adjust the damage model calibration factors in the AASHTOWare/r/ Pavement ME Design software so that appropriate pavement thickness can be determined through rational design. This methodology has been put into practice and so far the performance results on commercial projects have validated the design predictions.

The National Center for Asphalt Technology (NCAT) has ongoing Preservation Group study that is trying to ascertain how much cure agency can get for of pavement preservation (as the saying goes, an ounce of prevention is worth a pound of cure). Details of this study, that is documenting the condition of 25 100-foot pavement sections prior to treatment, then recording deterioration over time after treatment, are presented here. The aim is to establish life-extending benefit curves for various preservation treatments as a pre-treatment condition, in addition to as a function of time and traffic.

Compared with a conventional hot-mix asphalt mixture, an open-graded friction course (OGFC) is more prone to pavement distresses, such as cracking and raveling, which result in a shorter service life. One way to potentially improve the performance of OGFC is to enhance the interface bond between the OGFC and the underlying layer by applying a heavier tack coat. This study evaluated the effectiveness of using a heavier tack coat on the field performance of OGFC by comparing the field performance of the same OGFC mixture with different tack coats placed on Sections N1 and N2 of the National Center for Asphalt Technology pavement test track in Opelika, Alabama. In Section N1, a heavier polymer-modified tack coat was applied with a spray paver immediately before the OGFC layer was placed. In Section N2, a distributor truck applied a trackless tack at a regular application rate. The sections were trafficked to 10 million equivalent single-axle loads by a fleet of heavy trucks for 2 years. The field performance of these two sections was monitored weekly. Field performance characteristics measured included pavement stiffness, pavement structural response, surface functional characteristics, and pavement distresses. The results showed that the OGFC layer in Section N1, in which a heavier tack coat was applied, performed better than that in Section N2, in which a conventional tack coat was used. It is recommended that a heavier tack coat be used to improve the performance of OGFC surfaces.

This report describes the National Center for Asphalt Technology (NCAT) Pavement Test Track and presents an overview of the experiments conducted there from 2009 to 2011 (fourth cycle). Information for experiments includes: background, objectives, methodology, test track performance, analysis, and conclusions. Chapters include: Surface layer performance experiments, Structural experiments, and Additional analyses. Synopses of major findings from previous cycles are included as well as the benefit/cost of test track studies.

In a jointly executed program Delft University of Technology in The Netherlands and Kraton Polymers have developed a new generation of SBS modified asphalt binders that allow construction of thinner and more durable pavements. To validate the findings from these studies, Kraton Polymers committed to a field trial in 2009 at the National Center for Asphalt Technology (NCAT) in Auburn, Alabama, United States. A highly modified asphalt base course at reduced thickness is compared to a standard base course under heavy truck loading. As a result of the good performance of the first section, the opportunity arose to pave another section at NCAT in August 2010. An adjacent section needed urgent repair as high deformations in the subgrade lead to severe cracking of the asphalt. A highly modified, fatigue resistant overlay mix was paved over the cracked base. In this paper the latest results are given of the two full scale test sections for highly modified asphalt pavements at NCAT.

As asphalt prices have continued to escalate over the past few years, a great deal of interest has been focused on using more Reclaimed Asphalt Pavement (RAP) or finding a material that can replace a portion of the asphalt binder in asphalt concrete (AC) mixtures. Hot liquid sulfur was used as an extender of asphalt binder in hot-mix asphalt (HMA) in the 1970s and the early 1980s. However, a sharp increase in the sulfur price, significant generation of fumes and odors, and the problematic transportation and introduction of hot liquid sulfur into the HMA brought its utilization in road paving to an end by the late 1980s. To overcome these obstacles a solid sulfur pellet technology, known as Shell Thiopave(5), was developed. The sulfur pellet is an asphalt mixture modifier that also extends the asphalt binder. The technology also contains other additives beyond elemental sulfur designed to lower the mixing temperature as a warm-mix asphalt (WMA) mixture and to reduce odors and fumes during production. This paper details a comprehensive laboratory evaluation of a control mix and sulfur-modified asphalt mixtures with varying binder replacement levels. Laboratory performance tests were conducted to measure the resistance of these mixes to moisture damage, permanent deformation, fatigue cracking, and low-temperature cracking. The results of the study showed that the sulfur-modification resulted in a tangible increase in stiffness over the control mixture when tested for dynamic modulus. This increase in stiffness afforded these mixes superior rut resistance versus the control mix in the Asphalt Pavement Analyzer, Hamburg Wheel-Track Device, and Asphalt Mix Performance Tester (AMPT). However, moisture susceptibility testing, both by the determination of a tensile strength ratio (TSR) and Hamburg testing, showed increased moisture susceptibility for these sulfur-modified mixes. The addition of the sulfur modifier also influenced the estimated endurance fatigue limit (EFL) of those mixtures. Compared to the control mix, one sulfur modified mix exhibited a higher estimated EFL, one mix showed an equivalent EFL, and two mixes had lower EFL. Finally, the low-temperature cracking resistance of the asphalt mix was not significantly affected by the presence of sulfur modification.

The occurrence of higher air and surface temperatures in urban areas is known as the urban heat island (UHI) effect. Reducing the UHI effect may decrease summer energy use and improve human and ecological health. The Leadership in Energy and Environmental Design certification system has awarded up to three points for construction projects that provide any combination of the following cool pavement strategies for up to 75% of the site landscape: ( a) shading hard surfaces on the site with landscape features, ( b) using high-reflectance materials with a minimum solar reflectance index (SRI) of 29, and ( c) utilizing an open-graded pavement or porous pavement system. Although a guide to the design and construction of porous asphalt pavements has existed for some time, such a guide is not readily available for high-reflective asphalt pavements. The objective of this study is to identify and validate high-reflectance asphalt materials and pavement surface treatments that are suitable for use in parking lots and other large paved surfaces, have a minimum SRI of 29, and are economical. In this study, six technologies exhibited SRI values of 29 or greater: E-Krete microsurfacing, Street-Bond coating, synthetic binder, Densiphalt, and chip and sand seals using light-colored aggregates. Another technology, surface gritting using light-colored aggregate, most likely would have exhibited SRI values of at least 29 if the aggregate had adhered properly to the asphalt mat.