Warm Mix Asphalt Technology Research Articles

Development of Calculation Tool for Assessing the Energy Demand of Warm Mix Asphalt

Warm Mix Asphalt (WMA) technologies allow significant lowering of the production and pavement temperature of conventional Hot Mix Asphalt (HMA) thus reducing the energy demand and greenhouse gas emission in the atmosphere. In order to provide the necessary information on environmental and economical potential of WMA in each specific case these benefits have to be acknowledged in quantitative analysis with a Life Cycle Assessment (LCA) tool. The calculation model, presented in the paper, was developed according to EN ISO 14040 as inventory of energy flow for asphalt production, which is the first phase in developing LCA tool. The calculation involves all the main areas that can be influenced by choosing WMA instead of HMA, including production, paving and compaction of asphalt, mining and/or manufacturing of all component materials and transportation. The amount of used energy and the energy sources were defined for each of the processes allowing to express the results in terms of total energy demand distribution by the energy source or by unit process, which is significant in further calculation of carbon footprint. The case study results present the comparison of asphalt energy consumption for seven different modules. Transportation distances and the construction design were defined as typical for a paving site in Latvia. The results showed 7% to 18% energy gain for the WMA in comparison with the reference HMA and indicated that the asphalt production and paving process depend almost entirely on non-renewable energy sources and changes between different modules in this case mostly affect the use of natural gas.

Performance Evaluation of Warm- and Hot-Mix Asphalt Mixtures Based on Laboratory and Accelerated Pavement Tests

A number of warm-mix asphalt (WMA) technologies are used to reduce the temperature at which the asphalt mixtures are produced and compacted, apparently without compromising the performance of the pavement. The main objective of this study is to determine whether the use of an innovative wax-based LEADCAP WMA additive influences the performance of the asphalt mixture, which is produced and compacted at significantly low temperatures. The WMA pavement using LEADCAP additive (WMA-LEADCAP) along with a control HMA pavement was evaluated with respect to their performances of rutting resistance, crack resistance, and viscoelastic property based on the laboratory dynamic modulus test, indirect tensile strength test, and in-door accelerated pavement test (APT) results. With the limited data carried out, the LEADCAP additive is effective in producing and paving asphalt mixture at approximately 30°C lower temperature than a control HMA mixture, and the performances of WMA-LEADCAP pavement are comparable to a control HMA pavement.

Characterization of Fracture Properties of Asphalt Mixtures as Measured by Semicircular Bend Test and Indirect Tension Test

The objective of this study was to investigate the intermediate temperature fracture resistance of various asphalt mixtures, as measured by the semicircular bending (SCB) and indirect tension (IDT) test methods, and to correlate these fracture properties to the cracking performance of Louisiana asphalt pavements. Effects of design and process-based factors such as mixture-producing technologies (e.g., hot mix versus warm mix), asphalt binder grades, aging of test specimens, and reclaimed asphalt pavement (RAP) content on the fracture properties were investigated. Results indicated that the SCB-measured critical strain energy release rate (Jc) values showed good correlation with the IDT-measured toughness index values, especially when laboratory-produced mixtures were compared. In addition, the asphalt binder grade and aging condition of specimens influenced the fracture properties of asphalt mixtures. Asphalt mixtures with polymer-modified asphalt binders exhibited greater fracture resistance than did those with unmodified asphalt binders. The aging of specimens decreased the fracture energy of asphalt mixtures while increasing their strengths. Warm-mix asphalt (WMA) technologies used to produce asphalt mixtures at reduced mixing and compaction temperatures did not negatively affect the fracture resistance of the produced mixtures. Further, incorporating high RAP contents of up to 30% in the WMA production did not seem to reduce the fracture resistance of the produced mixtures. The SCB-measured Jc values demonstrated a good correlation with field cracking performance data. These results demonstrate the suitability of the SCB test method for predicting the cracking performance of asphalt pavements at intermediate service temperatures.

Evaluation of Low-Temperature Cracking Performance of Warm-Mix Asphalt Mixtures

In the field of asphalt concrete, the use of warm-mix asphalt (WMA) has become one of the most popular methods of meeting sustainability demands. Researchers have determined that WMA use can lead to reductions in fuel consumption and emissions. Early literature hypothesized that an additional benefit, regardless of the WMA additive or process used, was decreased susceptibility to thermal cracking. The current study examined this hypothesis through laboratory testing of four WMA mixtures produced at a reduced production temperature and a reference hot-mix asphalt (HMA) mixture. The disk-shaped compact tension, indirect tension, and acoustic emission tests were used to characterize the low-temperature properties of the mixture. The fracture energy results of the disk-shaped compact tension test showed that the chemical additives improved fracture energy in comparison with HMA and that the organic and foaming additives reduced fracture energy. The indirect tension creep compliance test produced similar results, in which the two chemical additive–modified WMA systems increased mixture creep compliance, while the other two systems did not significantly alter creep compliance as compared with the control HMA mixture. Acoustic emission testing provided further information regarding the low-temperature behavior of WMA mixtures. The foaming additive displayed an embrittlement temperature similar to that of HMA, whereas the organic additive increased the embrittlement temperature. The two chemical additive–modified mixtures produced differing embrittlement temperatures. It was concluded that resistance to thermal cracking was not ensured by producing WMA mixtures at lower temperatures. Therefore, performance testing is critical to evaluating WMA technologies in locations susceptible to low temperatures.

Low Temperature Performance of Sasobit-Modified Warm-Mix Asphalt

In the summer of 2008, a field trial project using Sasobit-modified warm-mix asphalt (WMA) was established in Alaska, which was Alaska’s first experience with a WMA technology. Previous studies conducted by writers identified a number of engineering benefits of Sasobit-modified WMAs over conventional hot-mix asphalt (HMA). This paper presents a further assessment focusing on low temperature performance of both Sasobit-modified WMA binders and mixes. A series of binder tests including bending beam rheometer (BBR), direct tension test (DTT), and asphalt binder cracking device (ABCD) tests were conducted. Indirect tension tests (IDT) of mixtures along with a thermal cracking analysis were performed to obtain a more definitive answer regarding the WMA application for cold-weather conditions. Results showed a decrease of tensile strength for both WMA binders and mixtures at low temperatures, and the cracking temperatures of both WMA binders and mixtures increased with the increase of Sasobit content. However, the increase in cracking temperature was very slight, which indicated that Sasobit addition had an insignificant effect on resistance to low temperature cracking. Therefore, Sasobit-modified WMA should be suitable for the Northern Region of the Alaska Department of Transportation and Public Facilities (AKDOT&PF) without compromising the resistance to low temperature cracking.

아스팔트 피막두께 변화에 따른 중온 아스팔트의 접착성질에 관한 연구

Warm-Mix Asphalt(WMA) technologies have been developed since 15 years ago, which are internationally and domestically concerned with energy-saving and environmental-friendly technologies in public and private sectors of highway engineering. The performance of asphalt mass is traditionally evaluated by the penetration, viscosity, or Superpave tests. This research, however, is focused more on the properties depending on asphalt film thicknesses instead of evaluating asphalt mass behaviors by those tests. For this approach, a new testing protocol and analysis method are described by the bonding properties on each film thickness. This testing method and analysis tool are borrowed from those of DSR Moisture Damage test and applied by using ARES. The analysis results indicate that there is a limit film thickness between and , which causes significant changes of the properties. In addition, the results show that the property changes of Hot-Mix Asphalt(HMA) and WMA on the limit film thickness are also different. Therefore, it is suggested that the properties on thin film thicknesses between and should be considered in order to evaluate WMA properly.

Warm mix asphalt: an overview

One of the causes of pollution associated with the construction of transportation infrastructures is the emission of greenhouse gases into the atmosphere. Even though the use of Warm Mix Asphalt technology has many advantages that are not related to the reduction of gas emissions, WMA technology is also good for the environment because it produces asphalt at temperatures 20–40° lower in comparison to Hot Mix Asphalt. The temperature reduction achieved by WMA comes from the use of various technologies that have been developed in recent years, and which can be classified in the following three groups: organic additives, chemical additives, and water-based or water-containing foaming processes. Although all of them pursue the same goal, the manufacturing process differs. Thus, their aim is mainly to reduce bitumen viscosity, which in turn improves mix workability, produces fewer emissions, and generally creates better working conditions. This paper is an overview of the different technologies used in the manufacturing of WMA. It analyzes the materials, additives, mix design and performance of the asphalt made by this technology. It also describes its benefits and drawbacks, and underlines the need for further research in this area.

Investigation of Moisture Dissipation in Foam-Based Warm Mix Asphalt Using Synchrotron-Based X-Ray Microtomography

Foam-based Warm Mix Asphalt (WMA) technologies decrease the viscosity of the asphalt so that it is workable during construction. However, after construction, viscosity increases rapidly as the foam disappears and temperature drops. During the process of dissipation of foam, depending on the environmental conditions, the moisture may not escape and may be trapped inside the mixture. This trapped moisture can cause detrimental failures by breaking the adhesive bonds between the aggregates and the asphalt binder (because of diffusion and freeze/thaw cycles). It is crucial to know how the moisture escapes from the asphalt mixture as the specimen cools down and foam disappears. In this research, dissipation of the moisture from foamed asphalt binders was directly measured and quantified by using a high-resolution synchrotron-based X-Ray Microtomography (XRM) system. Different foamed asphalt binders were instantly frozen by using liquid nitrogen at different times after the initial foaming. The 3D internal structure images of these specimens were acquired by using XRM available at the Argonne National Laboratory (ANL). These images were analyzed and the moisture dissipation processes in different types of asphalt binders were directly quantified. It was observed that the rate of moisture dissipation in high performance grade (PG) (stiff) binders was slower than that of low PG grade (soft) binders. It was also observed that the size distribution of moisture bubbles in the binders varied in different binders.

Structural and rheological characterization of wax modified bitumens

The research focuses on the use of waxes as asphalt modifiers. Bitumen/wax blends were produced by addition of controlled quantities of different type of wax to a 70/110 unmodified bitumen. Five different waxes were used, including synthetic hydrocarbons Fischer–Tropsch wax, Montan waxes and amidic-modified waxes. Blends were subjected to different rheometric and thermal testing to relate their characteristics with those of the wax in temperature ranges of technical interest. It was found that bitumen/wax blends have a peculiar and quite complex mechanical response, connected with the melting/crystallizing properties of the wax and the degree of residual crystallinity into the blend. The effects of wax on the binder rheology were found to be mainly controlled by the compositional characteristics of the wax. The experimental program carried out provides different indications for the development of the warm mix asphalt technology and for the general evaluation of wax modification of asphalt binders.

Laboratory Evaluation of Sasobit-Modified Warm-Mix Asphalt for Alaskan Conditions

A number of completed or ongoing studies on different aspects of warm-mix asphalt (WMA) have being conducted in the United States, indicating pavement professionals’ strong interest in exploring the application of this innovative technology. In the summer of 2008, a field trial project using Sasobit-modified WMA was established in the southeastern region of Alaska, which was Alaska’s first experience with a WMA technology. In line with this field experimental feature project, this paper presents a systematic laboratory study of both Sasobit-modified WMA binders and mixes. Engineering properties of Sasobit-modified WMA binders and mixes were experimentally evaluated, and the effects of Sasobit addition on the WMA’s performance in terms of low temperature behavior, rutting resistance, and moisture susceptibility were investigated. Research results identified a number of engineering benefits of Sasobit-modified WMAs over conventional HMA. Sasobit-modified WMAs reduced mixing and compaction temperatures, improved workability and rutting resistance, and had insignificant effect on moisture susceptibility. These effects indicated the suitability of this WMA technology for central and southeastern regions of the Alaska Department of Transportation and Public Facilities (AKDOT&PF). The indirect tension test results showed a decrease of WMAs tensile strength at low temperatures. Additional tests at lower temperatures, along with a more complete thermal cracking analysis need to be performed to obtain a more definitive answer regarding the low temperature performance of these mixes for the northern region of AKDOT&PF.

Moisture Susceptibility of Polymerized Stone Matrix Asphalt Mixtures using Warm Mix Asphalt Technologies using Moist Aggregates

Abstract The present study is focused on evaluating the moisture susceptibility of polymerized stone matrix asphalt (SMA) mixtures using moist aggregates and three different warm mix asphalt (WMA) additives. Indirect tensile strength (ITS), tensile strength ratio (TSR), deformation, and toughness were performed to determine the moisture sensitivity of these mixtures. The experimental design included two aggregate moisture contents (0% and ∼0.5% by weight of dry mass of the aggregate), three sources of aggregates (A, B, and C) and three WMA additives (Asphamin, Sasobit, and Evotherm) along with control mixture, and four different types of binders (i.e., PG 64-22 + 10% crumb rubber (−40 mesh CR), PG 64-22 + 15% CR, PG 64-22 + 20% CR, and PG 76-22 with fibers) were used in this study. In total, 384 samples were utilized for the ITS testing in this study. Test results indicated that even though by using 2% hydrated lime as an anti-stripping agent, 32% of the mixtures failed to meet the TSR requirement of 85% as per SCDOT specifications. Mixtures with PG 76-22 + fibers showed improved wet ITS values compared to rubberized SMA mixtures as using moist aggregates. No significant differences in the wet deformation values were observed for mixtures using WMA additives using moist aggregates. Mixtures with 15% CR content showed improved resistance to the percent toughness loss under a warm water bath treatment. Test results indicated that recycled rubberized asphalt binder can be effectively used to improve resistance to moisture-induced damage of SMA mixtures as using WMA technology.

Building Sustainable Pavements with Wax-Based Compound Using a Warm-Mix Asphalt Technology in Korea

Building Sustainable Pavements with Wax-Based Compound Using a Warm-Mix Asphalt Technology in Korea

소형 포장 가속시험기를 이용한 중온 아스팔트 혼합물의 소성변형저항성 및 수분민감도 평가

Warm-mix asphalt(WMA) technology has been developed to allow asphalt mixtures to be produced and compacted at a significantly lower temperature. The WMA technology was identified as one of means to lower emissions for and has been spread so quickly in the world. Recently, two innovative WMA additives has been developed to reduce mixing and paving temperatures applied in asphalt paving process in Korea. Since the first public demonstration project in 2008, many WMA projects have successfully been constructed in national highways. In 2010, the WMA field trial was conducted on new national highway construction under Dae-Jeon Regional Construction Management Administration. The two different WMA loose mixtures(WMA and WMA-P) and a HMA mixture were collected at the asphalt plant to evaluate their mechanical performance in the laboratory. The Third-scale Model Mobile Loading Simulator(MMLS3) was adopted to evaluate rutting resistance and moisture damage under different traffic and environmental conditions. In this study, plant-produced WMA mixtures using two WMA additives along with the conventional hot mix asphalt(HMA) mixtures were evaluated with respect to their rutting resistance and moisture susceptibility using MMLS3. Based on the limited laboratory test results, plant-produced WMA mixtures are superior to HMA mixtures in rutting resistance and the moisture susceptibility. The WMA additive was effective for producing and compacting the mixture at lower than the temperature for the HMA mixture.

Rheological characterization of wax-modified asphalt binders at high service temperatures

The research reported herein focuses on the rheological characterization of wax-modified asphalt binders used in warm mix asphalt (WMA) technology. Wax-modified asphalt binders were produced by adding controlled quantities of different types of wax to a 50/70 unmodified bitumen. Five different kinds of wax were used, including synthetic hydrocarbons Fischer–Tropsch wax, Montan waxes and amidic-modified waxes. All the blends were subjected to different rheometric tests to assess their mechanical response at high service temperatures. The viscous deformation mechanism was analyzed with reference to static and repetitive creep loading; it was found that the viscous deformation is strongly affected by the presence of both hydrocarbons and amidic-modified waxes. Wax-modified binders exhibited an effective improvement in intrinsic resistance to non-reversible deformation, even in high applied stress and cyclic loading conditions. It was observed that the chemical composition and the consequent physical characteristics of the wax are the most important factors regulating the final behavior of wax-modified asphalt binders at high service temperatures. The final contribution of the experience performed is related to the technical evaluation of wax-modified asphalt binders and to the general development of WMA technologies for pavement applications.

Influence of organic wax on bitumen characteristics

Statement problem: The study investigated effect of organic wax Sasob it wax (S) on the characteristics of bitumen 80/100-penetrati on grade. The consistency of bitumen is measure of its susceptibility to temperature change and resistance to flow which affects ability and resistance to deformation of the mixture. Approach: This study reviewed the bitumen modification process in relation to Warm Mix Asphalt (WMA) technology, using S as a modifier. The study investigated the penetration, s oftening point and viscosity measurements of modified bitumen 80/100-penetration grade (binder), using the Brookfield viscometer. The binders mixed with various percentage of the wax S 1-5% were investigated. Results: Results from the study showed an increase in softening poin t, decrease in penetration with an increase in S. The viscosity of binder also decreases at hi gher temperatures while at midrange temperatures the viscosity increases with an increa se in additive. Conclusion: This study has provided a valuable data on the effect of additive S on increasing the kinematic viscosity of binder at low temperature and decreasing the dynamic viscosity at high temperature, been attributed to the presence of S wax with high hydr ocarbons molecular content in the binder. Also increasing the additive decreases penetration and increases softening points, The study recommends the use of 2% S for modification of PEN 80/100. Key wards: Sasobit wax, softening point, Warm Mix Asphalt (WMA)

Performance Characteristics of Thin-Lift Overlay Mixtures

This study designed and evaluated the performance of thin-lift mixtures that incorporated a high reclaimed asphalt pavement (RAP) content, recycled asphalt shingles (RAS), and a warm-mix asphalt (WMA) technology, both individually and collectively. A Superpave® 9.5-mm mixture was designed with new materials and designated as the control mixture. The same control mixture was developed with 40% RAP, with 5% RAS, and with 35% RAP and 5% RAS. Each of the mixture designs was then repeated at a lower mixing and compaction temperature according to a wax-based WMA technology. The effect of the RAP, RAS, or both on the stiffness of each mixture was measured by using the dynamic modulus. The performance of each mixture was determined by measuring (a) its reflective cracking resistance with an overlay tester, (b) its low-temperature cracking resistance with an asphalt concrete cracking device, and (c) its moisture susceptibility with a Hamburg wheel tracking device. In addition, binder was extracted from each mixture and the performance grade determined. The mixtures that incorporated high RAP content, RAS, or both exhibited higher stiffness, which was confirmed with the extracted binder grading results. The use of RAP, RAS, or both reduced the reflective cracking resistance but did not have a negative impact on the low-temperature cracking resistance of the mixtures. Moisture susceptibility test results indicated that the addition of RAP, RAS, or both improved the mixtures' resistance to moisture failure. The addition of WMA technology to the mixtures provided similar or improved performance in most of the mixture tests.

Fatigue Evaluation of Warm-Mix Asphalt Mixtures

Warm-mix asphalt (WMA) is the generic term used to refer to a group of technologies that are used to produce asphalt pavement mixtures at temperatures lower than those of traditional hot-mix asphalt (HMA). One of the potential benefits of WMA is that it provides better fatigue cracking characteristics than does HMA. The lower temperatures should reduce the aging of asphalt binders that occur during production. The reduced aging of asphalt binders should lead to improved fatigue characteristics of asphalt mixtures. The research reported here addressed two main objectives. The first was to study the impacts of three WMA technologies on the fatigue cracking resistance of HMA by using one asphalt binder and two aggregate sources. The fatigue characteristics were measured by using a uniaxial, cyclic, direct tension compression test. The second objective was to analyze the data produced by the test by using the simplified viscoelastic continuum damage approach proposed in the NCHRP 9–43 Phase I report. Three WMA technologies were used: Advera, Evotherm 3G, and Sasobit. All mixtures were produced by using a PG 64-22 virgin binder. Data showed no significant difference between HMA mixtures and WMA mixtures for each mix except for the Advera.

Evaluating the Effect of Warm-Mix Asphalt Technologies on Moisture Characteristics of Asphalt Binders and Mixtures

The effect of warm-mix asphalt (WMA) technologies on the moisture susceptibility of a mixture and the adhesion characteristics of the asphalt binder used in it was evaluated. A 9.5-mm Superpave® mixture designed with performance-grade asphalt PG 64-22 was used as the control mixture. Four types of WMA technologies were evaluated: Advera, Evotherm, Sasobit, and SonneWarmix. The Hamburg wheel-tracking device (HWTD) was used to evaluate the effect of each WMA technology on the moisture susceptibility of the mixture at three aging times and three aging temperatures. A liquid antistrip and hydrated lime were added to any mixture that failed the HWTD to determine if they could correct the failure. Because the moisture susceptibility of a mixture is related to failure in the adhesive bond between the binder and the aggregate, a pulloff test, the bitumen bond strength (BBS) test, was used to evaluate the impact of the WMA technologies on the adhesion characteristics of the asphalt binder. The HWTD test results indicated that the moisture resistances of all mixtures improved significantly with an increase in aging time or temperature. Mixtures aged at longer times and at higher aging temperatures exhibited the best performance. The addition of the antistrip agents improved the HWTD results. The BBS test showed that only Sasobit had a significant effect on the pull-off tensile strength of the binder, although only under dry conditions. Overall, no correlation between the BBS and the HWTD was found.

Late-Season Paving of a Low-Volume Road with Warm-Mix Asphalt

This paper documents late-season paving of a gravel, low-volume roadway on Mitkof Island in the Tongass National Forest in southeast Alaska. The project was Alaska's first experience with warm-mix asphalt (WMA) technology. In 2008, Sasobit (1.5% by weight of asphalt) was added to a PG 58-28 polymer-modified asphalt at the producer's plant, barge-shipped 800 mi to the project site, and used for paving the two-lane, 24-ft-wide roadway located 20 mi south of Petersburg, Alaska. About 23,000 tons of WMA were placed with no major problems. Compaction of the WMA was achieved at about 50°F lower than the conventional hot-mix asphalt (HMA) used in an adjacent project. Reduced fumes were observed compared with the HMA. The contractor reported fuel savings and ease of WMA compaction. One roller was used to compact the WMA and achieve mix density. Postconstruction smoothness and rut depth measurements revealed trends similar to those at the adjacent conventional HMA project. The project will be monitored for 3 years to assess near-term performance. Loose-mix samples collected from the WMA project and the adjacent HMA project were used to produce laboratory-compacted specimens for performance testing. Modulus and rutting test results showed that WMA was stiffer and more rutting-resistant than the conventional mix. No adverse low-temperature cracking issues were detected. WMA's moisture susceptibility was similar to that of the conventional mix. With this successful WMA experience, it is expected that WMA will be used in future Alaskan paving projects, especially for late-season paving and for remote, low-volume roadways.

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.