National Center For Asphalt Technology Research Articles

Repeatability and Reproducibility of Pavement Density Profiling Systems

The work conducted in this study was designed to establish achievable testing tolerances for non-destructive pavement density measurements using Density Profiling Systems (DPSs). Nine and six sensors were used to determine the precision of repeatability and reproducibility in the laboratory and the field, respectively. A minimum of six sensors (considered in this study as independent laboratories) were needed to comply with the minimum number of participants required in the current ASTM standard practice (ASTM E691). The methodology included the development of laboratory precision evaluation with a total of nine sensors and two different mixtures (9.5 mm fine-graded mix, 19.0 mm coarse-graded mix) compacted at four density levels (97%, 94%, 91%, and 88% of Gmm). For the field portion of this study, pavement sections built at the National Center for Asphalt Technology (NCAT) Test Track in 2021 served as experimental variables. These sections were built with fine-graded asphalt mixtures and open-graded mixes as wearing courses. Additionally, the pavement sections included three underlying materials: new asphalt (binder layer), milled asphalt surface, and granular base, with thicknesses ranging from 3.8 to 13.9 cm. Density profile testing was conducted at two locations: within the mat (center of the lane) and along the joint. Computed precision statements regarding dielectric values within and between laboratories were about double for field results compared to laboratory results. However, when converted to density, the statements were significantly below the reported statements for Bulk Specific Gravity and Vacuum Sealing in the laboratory and Nuclear and Electromagnetic density gauges in the field.

Laboratory Characterization of Additive-Modified Asphalt Concrete Mixtures

There is a need for a more rapid system of evaluation and implementation for new and existing asphalt additives, especially because of the prohibitive cost of full-scale performance evaluations. To help to meet this need, the Additive Group (AG) experiment at the National Center for Asphalt Technology (NCAT) was developed and began in 2021. A comprehensive laboratory evaluation of six mixtures, each modified with a popular additive type selected by the AG state DOT sponsors, was conducted. Simultaneously, full-scale test sections were constructed at the NCAT test track to evaluate the field performance and structure behavior of each modified mixture. Trafficking of these test sections is currently underway, and estimated to be completed in 2024, at which point an investigation linking the laboratory and field results will be done. This paper presents the completed laboratory evaluation of each AG mixture via complex dynamic modulus (E*), direct tension cyclic fatigue, and bending beam fatigue testing. The wet-process rubber modified mixture was found to have reduced E* and initial flexural stiffness, but increased fatigue resistance, relative to the styrene-butadiene-styrene (SBS)-modified control mixture. The dry-process rubber-modified mixture displayed similar trends, though to a lesser degree. Conversely, the dry-process plastic-modified mixture was found to have increased E* and initial flexural stiffness, but reduced fatigue resistance, relative to the SBS-modified control mixture. The other AG mixtures—a dry-process fiber and a wet-process plastic-modified mixture—were found to display E*, initial flexural stiffness, and fatigue resistance similar to that of the SBS-modified control mixture.

Effect of type and aggregate gradation on the functional properties of porous asphalt (case study of Iran)

Porous asphalt mixtures are gaining popularity due to their ability to effectively drain surface water and mitigate traffic noise in regions with high rainfall. However, compared to conventional asphalt pavements, these types of pavements with high void content necessitate specific guidelines for achieving an optimal mix design. The performance characteristics of porous asphalt mixtures are notably influenced by the grading and composition of materials, especially with regards to their resistance to moisture damage. This study aimed to investigate the properties of porous asphalt mixtures using limestone and siliceous aggregates with varying gradations, while maintaining bitumen contents of 5% and 6%. In accordance with the regulations set forth by the National Center for Asphalt Technology, the findings indicate that siliceous-based aggregates exhibit improved void characteristics (increased by 3%) and permeability (increased by 11%). However, they also display reduced resistance to moisture-induced failures (decreased by 4%). On the other hand, adhering to the gradation recommendations provided by the National Asphalt Pavement Association guidelines, except for a slight decrease of 3% in moisture sensitivity, yields an overall enhancement of 25% in other performance characteristics. To analyze the data, statistical methods were employed, resulting in regression models with a minimum R2 value of 0.97. These models helped determine the optimal binder percentage for different aggregate types and gradations, providing valuable insights for practical implementation.

Use of chip seal treatments to mitigate pavement roughness progression in cold regions

ABSTRACT Chip Seals are a type of pavement preservation treatment characterised by its ability to reduce pavement deterioration and restore surface condition. Chip seal performance, like other pavement preservation treatments, depends on several factors such as environmental conditions, traffic level and the condition of the existing pavement structure prior to treatment application. In cold regions, the presence of freeze and thaw cycles promotes the generation of thermal cracks and possible tenting distresses, consequently, pavement roughness has been a prominent parameter to assess treatment performance. The objective of this study was to evaluate the roughness progression on several chip seal configurations in a cold climate region, utilising a set of field performance data from the Pavement Preservation Group Study, a broader research study conducted by the National Center for Asphalt Technology and the Minnesota Department of Transportation’s Road Research Facility. The main findings indicate that chip seals provide a negligible effect on immediate roughness improvement; however, on a long-term basis, they provide a reduction in IRI progression over time. The magnitude of the IRI benefit is dependent on the type of chip seal implemented and the traffic level experienced.

Structural Performance of an Asphalt Pavement Containing Cold Central Plant Recycling and Full-Depth Reclamation

Pavement recycling techniques are often perceived as only applicable to lower traffic volume roadways. However, recent studies have shown their potential for long service lives in higher traffic volume applications. This study documented the response of an asphalt pavement section, constructed using full-depth reclamation (FDR) and cold central plant recycling (CCPR), on a portion of I-64 in Virginia reconstructed between 2016 and 2019. The pavement section was instrumented and the response was compared with a similarly instrumented pavement section (Section S12) placed at the National Center for Asphalt Technology (NCAT) Test Track in 2012. Previous studies have shown that Section S12 is a long-life pavement and it carried 30 million equivalent single axle loads (ESALs) while showing no evidence of deterioration at the pavement surface or from installed instrumentation. The results from the I-64 Segment II project showed that it had much lower horizontal strain values at the bottom of the asphalt layers but slightly higher vertical pressure values on top of the subgrade when compared with NCAT Section S12. Despite the slightly higher values (about 1 pounds per square inch [psi] difference), the vertical pressure on top of the subgrade was very low for both pavement sections. The study confirmed that a recycled pavement section could be constructed and result in low strain and pressure values and is expected to have a long service life in a high traffic volume environment.

Effect of Mill and Thin Overlays on Roughness for Pavements in Cold Climate Locations

Mill and thin asphalt overlays are a popular preservation treatment for asphalt and composite pavements owing to their ability to address a variety of distresses. Their effectiveness depends on different factors such as traffic, climate, and condition of the pavement at the time of treatment, with typical treatment lives ranging from 5 to 12 years. In cold regions, performance in relation to roughness is of particular interest, as factors like frost action and thermal cracking tend to accelerate roughness progression. The objective of this study was to evaluate the effect of thin asphalt overlays on pavement roughness in cold climate locations using a set of field performance data from the Pavement Preservation Group Study, a broader research study conducted by the National Center for Asphalt Technology and the Minnesota Department of Transportation’s Road Research Facility. The findings indicated that treatment application resulted in both short- and long-term benefits. Following construction, a performance jump was obtained, which was greater for pavement sections with higher International Roughness Index (IRI) IRIpre values. This can be interpreted as rougher sections benefiting more in the short term than smoother sections, where the IRI is already low. Conversely, pavements with lower roughness at the time of treatment obtained greater life-extending benefits. This is interpreted as smoother pavements obtaining a greater benefit over time, and reinforces the concept of preserving pavements while in good condition to maximize pavement life. The magnitude of the benefits was also dependent on the type of milling machine used.

Influences of alternative friction aggregates on texture and friction characteristics of high friction surface treatment

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.

Use of a Hot-Mix Asphalt Plant to Produce a Cold Central Plant Recycled Mix: Production Method and Performance

Cold central plant recycling (CCPR) of asphalt mixtures continues to grow in interest among agencies and asphalt mixture suppliers. However, one implementation challenge has been the need to invest in new equipment to produce the mixture. In 2015, the National Center for Asphalt Technology (NCAT) worked with a local contractor to produce a CCPR mixture through a standard hot-mix asphalt (HMA) plant. The mix was then placed in a test section on the NCAT Pavement Test Track with a highly modified dense graded HMA overlay. The process used to produce the mixture in the HMA plant is outlined along with the performance of the mixture after heavy truck loading in comparison with a control section with a highly modified dense graded hot-mix asphalt in lieu of CCPR. After 17 million equivalent single axle loads the test section containing the CCPR mixture is performing as well as the control section. This shows that CCPR can be successfully produced using an HMA plant, which may encourage mix suppliers and agencies to conduct trial projects with CCPR, implement CCPR into standard practice, and further justify new CCPR equipment investments.

High Friction Surface Treatment Deterioration Analysis and Characteristics Study

High friction surface treatment (HFST) is used to improve friction on curved roadways, especially on curves that have a history of wet pavement crashes. Observations on the long-term performance monitoring of HFST sections at the National Center for Asphalt Technology (NCAT) Test Track showed friction (skid number, SN) dropped significantly at the end of service life of HFST, creating unsafe driving conditions. There is no clear, observed friction deterioration trend to predict the friction drop when using friction performance measures like SN. Therefore, there is an urgent need to explore and develop supplementary HFST safety performance measures (such as aggregate loss) that can correlate to friction deterioration and provide predictable, cost-effective, and easily measurable results. The objectives of this paper are to (i) analyze the correlation between HFST aggregate loss percentage area and friction value using a dynamic friction tester (DFT), and (ii) study the characteristics of HFST deterioration associated with aggregate loss, at the NCAT Test Track and at selected HFST curve sites in Georgia (using 2D imaging and high-resolution 3D laser scanning). Results show a strong correlation between HFST aggregate loss percentage area and DFT friction coefficient. Where friction measurement is used as the primary safety performance measure, it is recommended that HFST aggregate loss be used as a supplementary performance measure for monitoring the HFST safety performance deterioration. Aggregate loss can be easily identified by characteristics such as color and texture change. Preliminary texture analyses of 3D HFST surface profiles show lower mean profile depth (MPD) and ridge-to-valley depth (RVD) texture indicators can also identify loss of aggregate spots on HFST surface.

Utilization of Cold Central Plant Recycled Asphalt in Long-Life Flexible Pavements

Long-life flexible pavements are well documented and used widely across the U.S. Found in every climate zone and traffic classification, long-life pavements do not experience deep structural distresses such as bottom-up fatigue cracking or substructure rutting. Full-scale test sections, built in 2003 at the National Center for Asphalt Technology (NCAT) Test Track, provided the basis for an optimized design approach that utilizes strain distributions for long-life thickness design. These sections, containing only virgin materials, were subjected to 30 million standard axle loadings with excellent performance in terms of rutting, cracking, and roughness. In 2012, three new sections were built at the Test Track using cold central plant recycled asphalt materials as the base layer. These layers, made from nearly 100% reclaimed asphalt pavement (RAP), supported hot mix asphalt layers that also included RAP with one section featuring in-place stabilization of the existing aggregate base. This paper provides a direct comparison between the sets of sections to compare and contrast their performance histories and structural characterization, and consider their economic and environmental impacts. None of the recycled sections are exhibiting any surface deterioration, despite heavy trafficking, and the section with a stabilized base is exhibiting lower strains than established long-life pavement thresholds. The economic analysis suggested that the recycled sections can deliver similar performance at a lower average structure normalized section cost than the non-recycled sections. Furthermore, the section with the stabilized base and 76% recycled material is likely a long-life pavement and can potentially outperform the sections with no recycled content.

Analysis of High-Friction Surface Texture with Respect to Friction and Wear

High Friction Surfaces (HFS) are applied to increase friction capacity on critical roadway sections, such as horizontal curves. HFS friction deterioration on these sections is a safety concern. This study deals with characterization of the aggregate loss, one of the main failure mechanisms of HFS, using texture parameters to study its relationship with friction. Tests are conducted on selected HFS spots with different aggregate loss severity levels at the National Center for Asphalt Technology (NCAT) Test Track. Friction tests are performed using a Dynamic Friction Tester (DFT). The surface texture is measured by means of a high-resolution 3D pavement scanning system (0.025 mm vertical resolution). Texture data are processed and analyzed by means of the MountainsMap software. The correlations between the DFT friction coefficient and the texture parameters confirm the impact of change in aggregates’ characteristics (including height, shape, and material volume) on friction. A novel approach to detect the HFS friction coefficient transition based on aggregate loss, inspired by previous works on the tribology of coatings, is proposed. Using the proposed approach, preliminary outcomes show it is possible to observe the rapid friction coefficient transition, similar to observations at NCAT. Perspectives for future research are presented and discussed.

3D-finite element pavement structural model for using with traffic speed deflectometers

ABSTRACT The traditional practice for pavement structural capacity evaluation is mostly dependent on the falling weight deflectometer (FWD) measurements. However, this practice has several challenges due to its stationary nature. Recently, a Rolling Weight Deflectometer (RWD), capable of measuring the pavement deflections at regular traffic speeds, has been introduced into the market. This research aims to develop a finite element (FE) model simulating pavement structural response under the moving RWD loads. This model could be further utilised for accurately estimating pavement layers mechanical characteristics. The model was successfully validated utilising the RAPTOR (a commercially available RWD) data collected on the National Center for Asphalt Technology (NCAT) test track. A good correlation between the simulated and the measured values was found – yielding an average root mean square percentage error (RMSPE) of approximately 2.40% between the RAPTOR and the FE deflections.

Life-Extending Benefit of Chip Sealing for Pavement Preservation

Chip seals are effective pavement preservation treatments that are usually applied to address non-fatigue cracking, weathering, and raveling, to seal the surface, to delay oxidation, and, finally, to improve skid resistance. This study used field performance data of test sections from the Pavement Preservation Group Study being conducted by the National Center for Asphalt Technology and the Minnesota DOT’s Road Research Facility. Data from test sections located in a low-traffic-volume road with a hot, wet, no-freeze climate collected over a period of 7 years were used to evaluate the effect of several chip seal treatments. Treatments range from single layer to multilayer systems, and include different construction techniques such as rejuvenating scrub seal and fiber membrane. Also, a section was crack sealed before the application of a single layer chip seal to assess the benefits. A semi-parametric survival analysis was performed to determine the differences in median time to failure (MTTF) for different chip seal sections versus a controlled section—representing a “do-nothing” scenario. The results showed that the MTTF for a single layer chip seal ranges from 6.8 to 9.1 years depending on the pretreatment condition. Crack sealing before chip seal could extend the MTTF by an additional 1–3 years, depending on initial conditions. Double and triple layer chip seals extend the MTTF beyond 10 years. Finally, the scrub seal provided the highest benefits, with survival rates close to 100% after 10 years of performance.

Friction and Texture Retention of Concrete Pavements

In the late 1980s and early 1990s, the Alabama Department of Transportation (ALDOT), U.S., noticed a decline in skid trailer numbers on concrete pavements shortly after grinding operations. The engineers at the time suspected that the coarse aggregate caused the decline in these numbers and the resulting conclusion led to a ban of carbonate aggregates in mainline concrete pavement in Alabama that is still in place. This detailed laboratory study re-examines the fundamental friction issues that led to this policy. A total of 48 aggregate, grinding, and grooving combinations were tested as part of this study. Three aggregate sources were examined: a siliceous source, a “hard” limestone source, and a “soft” limestone source. Two blade spacings were examined for grinding operations: 52 blades/ft and 60 blades/ft. Some ground specimens were also grooved. Finally, a set of specimens had the Next Generation Concrete Surface (NGCS) applied to them. The specimens were polished with the National Center for Asphalt Technology (NCAT) three-wheel polishing device (TWPD). The dynamic friction tester was used to evaluate friction values at various points through the polishing process. After the polishing, the macrotexture was characterized using the circular track meter. Across the board, the highest performing texture was that with no grooves and 52 blades/ft. Very generally, the loss of friction decreased with increasing siliceous content. However, some of the trends were extremely minor and, in a few cases, siliceous aggregates caused higher friction loss. There were numerous instances when blended carbonate/siliceous concrete pavement surfaces performed better than sole siliceous concrete pavement surfaces.

Limiting Strain Distribution Criteria for Perpetual Pavement Design Using AASHTOWare Pavement ME Design

Perpetual asphalt pavement designs have been based on controlling horizontal strains at the bottom of the asphalt layer and vertical strains on top of the subgrade to prevent bottom-up fatigue cracking and subgrade rutting, respectively. Traditionally, single strain thresholds had been used as limits where damage accumulation begins and propagates. The concept of strain distributions was introduced at the National Center for Asphalt Technology (NCAT), and it was found to better represent the wide response spectrum in asphalt pavements caused by the different loading and environmental conditions. This concept was developed based on information and data collected from the NCAT Pavement Test Track, and from this a limiting strain distribution was created to assist with perpetual pavement design. Several studies analyzed the criteria using pavement responses calculated from PerRoad predicted strains in Test Track sections and existing perpetual pavements. A limitation of the AASHTOWare Pavement ME Design software is its inability to output the pavement responses necessary for perpetual pavement design. The objective of this study was to analyze pavement response data predicted from an integration of the AASHTOWare Pavement ME Design software outputs and a JULEA based program developed at NCAT to create a limiting strain distribution for perpetual pavement design using the AASHTOWare Pavement ME Design software. Strains were calculated for Test Track sections using these tools and based on the results a limiting strain distribution was developed. This limiting strain distribution was then further evaluated using eight sections that won Perpetual Pavement Awards. Results showed that the horizontal strain distributions obtained from Test Track sections could differentiate the sections with cracking and the sections that did not crack. In the further evaluation, the horizontal strain distributions from the perpetual pavements did not exceed the limiting strain distribution developed from the Test Track sections, except for a section which surpassed it by a small margin at the 80th and higher percentiles. Vertical strains were also determined for these pavements and the current 200 microstrains at 50th percentile design criteria was met by all the sections.

Developing Life-Extending Benefit Curves for Asphalt Pavements with Preservation Treatments

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.

Nondestructive Full Coverage Asphalt Stripping Detection Using 3D Radar

Since subsurface stripping extent is important for maintaining the road network, Minnesota Department of Transportation (MnDOT) uses forensic measures such as coring. The destructive nature and lack of coverage provided by this accepted method makes finding nondestructive methods for detecting stripping of in situ asphalt pavements an important need for MnDOT and many other agencies. Stripping between hot mix asphalt layers can cause premature failure of pavements. Knowledge of the lateral location, depth and extent of stripping can affect the timing and type of pavement preservation, maintenance, or rehabilitation. This paper reports on use of a DX1821 antenna to collect data at a frequency step of 20 MHz ranging from 50 MHz to 3050 MHz with a dwell time of 7.52 μs using a GeoScope Mk IV control unit on a full-scale asphalt pavement constructed at the National Center for Asphalt Technology (NCAT) test track with built-in stripping. Signals from the known stripped and non-stripped locations were used to evaluate statistical and energy based approaches. It is shown that a maximum energy ratio method, an approach that has been successfully applied to acoustic emission applications in the past, can improve signal clarity for stripping detection using ground penetrating radar (GPR). These results are confirmed using highway speed measurements at the Minnesota Road Research Facility with core validation.

Life-Extending Benefit of Crack Sealing for Pavement Preservation

Crack sealing and filling is used as a pavement preservation treatment to prevent water infiltration and loss of load-carrying capacity, hence extending the life of the pavement. This study used field performance data of test sections from the Pavement Preservation Group (PG) Study being conducted in part by the National Center for Asphalt Technology (NCAT). Data from test sections located in a low traffic volume road with a hot, wet, no-freeze climate collected over a period of more than 6 years were used to evaluate the effect of crack sealing and filling, either as a stand-alone treatment or in combination with other surface treatments. A semi-parametric survival analysis was performed to determine the difference in median time to failure (MTTF) for sections with and without crack sealing. The results showed that when used as a stand-alone treatment on a pavement in “good” condition, the life-extending benefit from crack sealing/filling could not be calculated for the selected analysis period because the MTTF would not be reached within 10 years. The estimated benefit for pavements in “fair” and “poor” condition ranged from 1.1 to 7.3 years, depending on pretreatment condition and travel lane. If used in combination with a chip seal, the additional life-extending benefit for a pavement in “good” condition is approximately 2 years, and is slightly decreased to approximately 1.5 years if the pavement is in “fair” to “poor” category. Test sections continue to be monitored as part of a broader long-term study.

Role of Preventive Treatments in Low-Volume Road Maintenance Program: Full-Scale Case Study

The lack of information on reliable life-extending benefit for pavement preservation treatments led the National Center for Asphalt Technology (NCAT) to conduct a preservation study applying preservation treatments on a low-volume county road in Auburn, Alabama, which began in 2012. The primary objective of the study is to develop performance models for preservation treatments to be used in pavement management systems. Performance measures including rutting, cracking, and roughness are collected on a regular basis to the present date. Among all the collected measures, only cracking shows an upward trend and therefore was used in this study as the performance index for the analysis. The present study aims to implement a semi-parametric survival analysis technique to assess the effectiveness of treatments used, and to investigate associated risk factors. The study confirms that preservation strategies significantly decrease the risk of failure when compared with a “do-nothing” scenario. It was found that initial condition, treatment family, recycled material usage, and crack sealing application have a significant impact on future deterioration. It is also concluded that survival analysis techniques are useful tools in aiding decision makers in the selection of proper treatment choices.

Performance of Chip Seal Treatments in Two Different Climatic Regions

Over time, new pavements deteriorate because of the effect of traffic loads and the environment. Pavement preservation treatments, such as chip seals, are a cost-effective alternative for extending the service life of the pavement without incurring in costly rehabilitation or reconstruction activities. Chip seals are preservation treatments that can help protect the pavement structure, reduce the rate of pavement deterioration, improve skid resistance, and address minor surface problems. As part of the National Center for Asphalt Technology and Minnesota Road Research Facility Pavement Preservation Study, chip seal test sections were placed on low-traffic-volume roads in Alabama and Minnesota. The two locations were selected to represent different climate conditions. Lee County Road 159 in Auburn, Alabama, is subjected to warm, wet, no-freeze climate, while County State Aid Highway (CSAH 8) is located in a cold, wet, freeze area in Pease, Minnesota. Treatments have been in service for approximately 6 years in the southern sections, and 2 years in the northern sections. During this time, cracking, roughness, rutting, and macrotexture data were collected periodically to evaluate pavement performance. The results determined that cracking is a predominant form of distress for these treatments. While the treatments are not expected to address rutting or roughness, the results indicated little variation in the case of the southern treatments, and an increasing trend in international roughness index in the northern sections, likely related to the appearance of thermal cracking. Macrotexture data may be used to assess the functional life of the treatments.