Warm Mix Asphalt Sections Research Articles

Laboratory and Field Performance Evaluation of Warm Mix Asphalt Incorporating RAP and RAS

Pavement sustainability draws attention from different stakeholders in recent years. Warm mix asphalt (WMA) incorporating reclaimed asphalt pavement (RAP) or reclaimed asphalt shingles (RAS) has been widely recognized as a sustainable combo for pavement construction by conserving natural resources and reducing greenhouse gas emission. However, as their usage surges, little research has been conducted to date through a comprehensive laboratory and field evaluation to verify the performance of WMA incorporating RAP and RAS compared to traditional hot mix asphalt (HMA). In this research, five WMA sections with different WMA techniques and one control HMA section constructed in Oklahoma were continuously monitored for four years. The aggregate consensus, source, and gradation properties were tested in the laboratory. Mixture characteristics for lab-compacted samples including cracking resistance, rutting performance, moisture susceptibility, and water permeability were measured to compare WMA to HMA incorporating RAP and RAS. In addition, pavement surface conditions in terms of pavement cracking, rutting, roughness, texture, and friction were collected from the field site ten times in four years by using several state-of-the-art high-speed devices without traffic control. The laboratory and four-years field monitoring results demonstrate that WMA incorporating RAP and RAS accomplishes desired performance while providing sustainable benefits.

Field implementation of WMA mixtures containing recycled asphalt shingles (RAS)

Combining Warm Mix Asphalt (WMA) technology with another green technology (asphalt recycling) can lead to a double saving in total cost of asphalt paving production. In this study, field implementation of Hot Mix Asphalt (HMA) with Recycled Asphalt Shingles (RAS) and WMA mixture containing RAS was performed and both mixtures were tested at asphalt laboratory for performance evaluation. To analyze binders and mixtures performance, Fourier-Transform Infrared (FTIR) Spectroscopy test, block cracking test, rutting and moisture resistance (Hamburg Wheel Tracking) test, thermal cracking potential (Disc-Shaped Compacted Tension) test were conducted. A short and medium-term field evaluations were also carried out. Binder extracted from mixtures constructed with and without WMA additive showed the same Performance Grade (PG); however, the extracted binder from WMA mixture was a little softer than the binder extracted from HMA but not enough to bump down the PG grade. Based on sulfur and carbonyl indexes calculated from FTIR test results, WMA mixture found to be more aged. No block cracking was observed in HMA and WMA mixtures by determining G-R values and developing block cracking black space chart. HWT results showed that using WMA technology in asphalt mixtures containing RAS resulted in a relatively better moisture and rutting resistance. The DCT results indicated almost the same fracture energy for both mixtures. The short-term field evaluation after one year of construction showed that the overall condition of both HMA and WMA sections are satisfactory. However, medium-term evaluation (after 39 months) showed more traverse cracks and stripping in WMA mixture.

Field Monitoring of the Long Term Pavement Performance (LTPP) Warm-Mix Asphalt (WMA) Site in Oklahoma

As Warm-Mix Asphalt (WMA) moves into mainstream use, the lower WMA production temperature and injection of water in some WMA technologies have raised concerns on how it may affect short- and long-term field performance over the design life. Under the Long Term Pavement Performance (LTPP) Specific Pavement Study 10 (SPS-10) experiment initiative, the Oklahoma Department of Transportation (ODOT) constructed six testing sections with five different WMA methodologies and one HMA control section. This paper presents the application of several art-of-the-state high speed instruments to collect comprehensive array of pavement performance data for long term performance monitoring of this site. The newly developed 3D laser imaging technology is used to collect 1mm 3D surface data for the evaluation of pavement surface distress and transverse profiling for rutting. Longitudinal profiling for roughness and macro-texture for safety are acquired via a high speed inertial profiler, while pavement friction is continuously collected using a Grip Tester. Four data collection events have been performed since the construction of the site. Data collected on the WMA sections and the control HMA section are compared and evaluated for surface performance deterioration. It is demonstrated that the WMA sites using various technologies exhibit better or comparable performance relative to the conventional HMA, in terms of pavement cracking, rutting, and roughness. Aggregate properties and mixture design significantly impact the pavement macro-texture and skid resistance properties.

Laboratory evaluation of foaming-based and chemical-based warm mix asphalt

A recent joint study by Arizona State University and the Arizona Department of Transportation (ADOT) was conducted to evaluate certain warm mix asphalt (WMA) properties in the laboratory. WMA material was taken from an actual ADOT project that involved two WMA sections. The first section used a foamed-based WMA admixture, and the second section used a chemical-based WMA admixture. The rest of the project included control hot asphalt mixture. The experimental plan included three main objectives. The first objective was to explore the concept of re-heating WMA by conducting the dynamic modulus |E*| at 21.1 °C (70 °F) and compare plant to laboratory prepared mixtures using specimens from the foaming-based mixture. The second objective was to evaluate the effect of WMA on the compaction energy. The third objective was to assess the moisture damage using the Hamburg wheel-track test and AASHTO T-283 tensile strength ratio (TSR) test. The |E*| results tested at 21.1 °C for both laboratory prepared and plant foaming-based mixtures showed similar |E*| values. The statistical analysis indicated that there is no statistical significance of the dynamic moduli between the two mixtures at two compaction temperatures 132 °C (270 °F) and 154 °C (310 °F). This indicated that there is no effect of re-heating on the plant produced WMA mixture. The compaction energy results supported the conclusion from the re-heating study. The moisture sensitivity evaluation based on the TSR results indicated low resistance to moisture damage; while the Hamburg testing results indicated very good performance.

Non-destructive evaluation of sustainable pavement technologies using artificial neural networks

Evaluation and characterization of pavements that incorporate sustainable technologies and materials such as warm mix asphalt (WMA) and Reclaimed Asphalt Pavements (RAP) becomes especially important for their future applicability. Artificial neural networks (ANN) have been recently used to forward-calculate pavement layer moduli from falling weight deflectometer (FWD) test results. A full bond layer interface condition is commonly assumed to perform pavement layer moduli calculations; however, this condition is not guaranteed to happen in the field. The objective of this study was to develop ANN models capable of predicting pavement layer moduli rapidly and reliably for full bond and full slip layer interface conditions. ANN models were used to estimate the moduli of the National Center for Asphalt Technology (NCAT) Test Track structural sustainable sections for the full bond (FB) condition and the full slip (FS) condition. The results indicated that WMA sections had lower moduli at all tested temperatures compared to a control section (7–10% lower), likely due to the reduced binder aging experienced by these sections. RAP sections had higher moduli (16–43% higher) and were less susceptible to changes in temperature due to the presence of stiffer aged binder. Overall, backcalculated layer moduli using the conventional iterative approach had the highest error, followed by a significant decrease in error by ANN predicted moduli under full bond condition. However, the consideration of the ANN with full slip condition yielded the best results (lowest error).

Evaluation of Field Performance of Warm-mix Asphalt Pavements in India

The United States and European countries are increasingly using “warm-mix” technologies that allow a significant reduction in the production and placement temperatures of asphalt mixes. Such mixes are also gaining popularity in other parts of the world in countries like China, Brazil and India. Though warm-mix asphalt (WMA) is a relatively new technology, contractors and Government agencies in the West have been quick to recognize the environmental and performance benefits of warm- mixes due to extensive research. This research has also allowed several Government agencies, such as the Federal Highway Administration (FHWA), to promote WMA as an important technological innovation for the industry. Many agencies have developed specifications for the use of WMA, which allows more contractors to use WMA. In India, Central Road Research Institute (CRRI) has carried out initial research on the effects of WMA on Indian mixes. Certain warm-mix technologies have since been used to pave major national and state highways as well. However, lack of awareness and skepticism of field performance is shying more contractors and agencies from using WMA extensively as in the West.This paper attempts to evaluate the field performance of two pavements constructed using an IRC accredited surfactant based chemical warm-mix technology. The two pavements evaluated in this study were produced and placed at a significantly lower temperature relative to the control hot-mix sections. Both the pavements were evaluated after considerable exposure to weather elements and traffic. Methods like Benkelman beam deflection, bump integrator value, and Marshall stability, resilient modulus and static creep test on field cores were used to evaluate the performance of the WMA sections in comparison to the control hot-mix sections. The results of the study indicate that in spite of the several monsoons and heavy traffic both pavements were exposed to, the performance of the warm-mix sections was equal or better compared to the control hot-mix sections. Due to the improved densities achieved at the site, and due to the reduced oxidation of the bitumen as a result of the lower production and placement temperatures, the performance of the warm-mix seemed to be improved in terms of permanent deformation and resilient modulus.

Rutting characterization of warm mix asphalt and high RAP mixtures

The objectives of this study were to perform a rutting characterization of warm mix asphalt (WMA) mixtures and mixtures containing high reclaimed asphalt pavement (RAP) and to determine the effects of production temperature and material type on permanent deformation. This study was based on data from the National Center for Asphalt Technology (NCAT) Test Track Phase IV research cycle and included a control section, two WMA sections and two sections with 50% RAP. Field measurements indicated that high RAP mixes had higher moduli and experienced lower vertical pressures than virgin mixes. The use of WMA technologies tended to increase permanent deformation while the addition of high RAP contents resulted in less rutting. Laboratory tests on recovered binders showed increased binder stiffness for high RAP mixes and no significant effect for virgin WMA mixes. Mixture tests of laboratory compacted samples did not reflect the observed field performance accurately.

Performance Evaluation of Field-Produced Warm-Mix Asphalt Mixtures in Manitoba, Canada

This study evaluated the resistance of field-produced warm-mix asphalt (WMA) mixtures obtained from field sections in Manitoba, Canada, to moisture damage, reflective cracking, and permanent deformation. The project, constructed in the summer of 2010, included a side-by-side hot-mix asphalt (HMA) control section and three WMA sections in which the Advera, Evotherm 3G, and Sasobit technologies were used. The mixtures' susceptibility to moisture damage was evaluated by their unconditioned and moisture-conditioned indirect tensile strength (ITS) and dynamic modulus (|E*|) at multiple freeze–thaw cycles. All mixtures met the minimum unconditioned ITS criterion of 65 psi at 77°F and the minimum indirect tensile strength ratio of 80% after one freeze–thaw cycle. Although comparable tensile strength and |E*| ratios were observed for the mixtures after one freeze–thaw cycle, the WMA–Sasobit mixture exhibited lower resistance to moisture damage when assessed after three freeze–thaw cycles. Except for the WMA–Sasobit mixture, the WMA mixtures showed similar or higher resistance to reflective cracking when measured by means of the Texas A&M Transportation Institute overlay tester. All WMA mixtures exhibited similar resistance to permanent deformation in the flow number test at the LTPPBind 50% reliability temperature (118°F) as compared with the HMA control section. However, none of the mixtures (including the HMA) met the proposed flow number criterion for WMA. When the mixtures were tested in the flow number test at the effective pavement temperature (92°F), a different ranking for their resistance to rutting was detected. Continuous field monitoring for performance of the various sections will help in assessing any proposed criterion as well as the effectiveness of WMA mixtures in cold weather areas such as Manitoba.

Warm-Mix Asphalt Pilot Project in Connecticut

This paper presents the details on the first official state warm-mix asphalt (WMA) pavement project in Connecticut. The construction took place between July 20 and July 22, 2010, and it involved three experimental sections: a control section with a conventional hot-mix asphalt (HMA) and two WMA sections that used wax and foamed asphalt. All three sections are located on Route 70 in central Connecticut. Each section is approximately 1 km long and includes lanes in both directions. The construction was done as a 50-mm overlay with 12.5-mm Superpave® mix. Each mix was sampled over a 3-day construction period for further evaluation in the laboratory. The materials were collected in loose form and reheated and compacted under laboratory conditions (laboratory-fabricated specimens). This paper discusses the effect of mixture type as shown by the results from several tests conducted in the laboratory, including the semicircular bending test, the Hamburg wheel tracking test, the indirect tensile test, and the disk-shaped compact tension test. The results from the WMA specimens were also compared with conventional HMA specimens. Finally, the paper presents the performance data from all three test sections after the first winter season and correlates these observations with the laboratory results.

Evaluation of Warm Mix Asphalt Mixtures Containing RAP Using Accelerated Loading Tests

Abstract This paper presents the results of a study that was conducted to evaluate the performance and constructability of warm mix asphalt (WMA) mixtures containing reclaimed asphalt pavement (RAP). Four sections were constructed at the indoor Accelerated Pavement Loading Facility at Ohio University. Aspha-min, Sasobit, and Evotherm WMA mixtures were used in the wearing course layer of the first three sections. In addition, the fourth section had a conventional hot mix asphalt (HMA) mixture, which was used as a control. Temperature was monitored during the production, placement, and compaction of WMA and HMA mixtures. Furthermore, emission tests were conducted at the asphalt plants during the production of each of the evaluated mixtures. Falling weight deflectometer (FWD) and rolling wheel tests were conducted at different temperatures on all evaluated sections. The results of this study showed that emissions were reduced during the production of the Aspha-min and Sasobit WMA mixtures by at least 50 % for volatile organic compounds, 60 % for carbon monoxide, 20 % for nitrogen oxides, and 83 % for sulfur dioxide, when compared to the control HMA mixture. In addition, although WMA mixtures were produced and compacted at much lower temperatures, they achieved better field densities than the control HMA mixture. The FWD test results showed that at 40°F (4°C) test temperature, the control HMA mixture had significantly lower stiffness than that of the WMA mixtures. However, the FWD stiffness measurement of the HMA and the WMA mixtures were statistically indistinguishable at the intermediate and high test temperatures of 70°F (21.1°C) and 104°F (40°C), respectively. Finally, the rolling wheel test results indicated that the three WMA sections, especially the Evotherm section, exhibited more rutting than the control HMA section during the post primary compaction stage. However, the rutting rate of the HMA section was higher than those of the WMA sections in the secondary stage, which suggests that the rutting difference may slowly be mitigated.

Full-Scale Structural Evaluation of Fatigue Characteristics in High Reclaimed Asphalt Pavement and Warm-Mix Asphalt

Warm-mix asphalt (WMA) and the inclusion of higher percentages of reclaimed asphalt pavement (RAP) are two strategies for developing environmentally friendly pavement structures that can also reduce pavement cost. Although demonstration projects have evaluated the constructability and short-term performance of these technologies in the field, questions remain about the structural characterization and longer-term field performance. As part of the 2009 National Center for Asphalt Technology test track, four sections were constructed; they included both WMA and high-RAP contents (50% RAP). A control section did not include either technology. Every section featured embedded instrumentation that facilitated strain versus temperature characterization under truck loading. Statistical comparisons of measured strain response were conducted at three reference temperatures. At the lowest temperature (50°F), the measured strain in the control section was not statistically different from the strains of the experimental sections. At the intermediate temperature (68°F), strains in the RAP with WMA section were statistically lower than the control, but the other sections were not distinguished from the control. At the highest temperature (110°F), the strain in the control section was statistically higher than all other sections. The WMA sections were next highest, and the RAP sections were the lowest. The base mixtures of each section underwent beam fatigue testing from which fatigue transfer functions were developed. Strains entered into their section-specific transfer functions showed that the RAP–WMA section would perform the best. Continued testing and monitoring of the sections are necessary to validate this finding.

Direct Measurements of Volatile and Semivolatile Organic Compounds from Hot- and Warm-Mix Asphalt

Emissions from the production and paving of hot-mix asphalt are increasingly being scrutinized. The introduction of warm-mix asphalt (WMA) technologies could potentially lead to a reduction in these emissions. However, the measurement of these emissions is both complex and expensive. To overcome these obstacles, the University of California Pavement Research Center has developed a simplified protocol that can be used in addition to conventional methods and that allows direct comparison of emissions from different mixes measured at the pavement surface during construction. A portable flux chamber is used to capture and directly measure emissions before, immediately after, and 2 h after compaction. Emissions are collected in activated charcoal sorbent tubes and analyzed by using gas chromatography–mass spectrometry in the laboratory to identify individual compounds. The protocol was evaluated during the construction of a test track that will be used in an accelerated pavement test to compare the performance of three rubberized hot-mix asphalt controls against seven rubberized WMA sections. The measured reactive organic gases included selected volatile and semivolatile organic compounds. The results demonstrated that WMA technology type, temperature, and level of compaction greatly influence emissions characteristics. On the basis of the success of the pilot study, the project is being extended to measure other types of emissions, including polycyclic aromatic hydrocarbons, and to assess real-time analysis methods.

Field Performance of Warm-Mix Asphalt at National Center for Asphalt Technology Test Track

Warm-mix asphalt (WMA) mixes produced by an emulsion process were evaluated under accelerated loading in three total sections of the National Center for Asphalt Technology Test Track and used as the surface mix for two of the sections. Evotherm was incorporated into the same mixes used previously on the track. In-place densities of the WMA surface layers were equal to or better than the hot-mix asphalt (HMA) surface layers, even when compaction temperatures were reduced by 8°C to 42°C (15°F to 75°F). Laboratory rutting-susceptibility tests conducted in the asphalt pavement analyzer indicated similar performance for the WMA and HMA surface mixes with the PG 67-22 base asphalt. However, laboratory tests indicated an increased potential for moisture damage with the WMA mixes. The two WMA sections and the HMA section showed excellent rutting performance in the field after the application of 515,333 equivalent single-axle loads in a 43-day period. One of the WMA sections was also evaluated for quick turnover to traffic and showed good performance.