Warm Mix Asphalt Mixes Research Articles

Effects of WMA Technologies on Asphalt Binder Blending

AbstractBecause of environmental and economical benefits, the paving industry has made attempts to incorporate recycled asphalt pavement (RAP) or recycled asphalt shingle (RAS) into warm mix asphalt (WMA). However, the low temperatures at which WMA is produced may affect the virgin-recycled binder blending in RAP/RAS mixtures. In this study, a lab testing procedure was developed to evaluate the effects of WMA technologies on binder blending. The results from the study showed that WMA additives, including sasobit, rediset, cecabase, and evotherm, slightly decreased the viscosity of the asphalt binder at 135°C. However, control binder tested at 165°C showed significantly lower viscosity than WMA binders. This may raise the concern over workability of nonfoaming WMA mix. WMA additives yielded higher blending ratio than control mix produced at 135°C, but hot mix asphalt (HMA) produced at 165°C still showed the highest blending ratio value. This indicates that a concern still exists over asphalt blending even ...

Laboratory evaluation of the effect of low-temperature application of warm-mix asphalts on interface shear strength

A potential drawback, not yet investigated, of low application temperatures of asphalt mixes could be a reduced interface shear strength. Such low temperatures could be due to improper construction as well as to the use of warm mix asphalt (WMA) technology. In this sense, this paper illustrates an experimental laboratory research aimed at characterizing interface shear properties of double-layered asphalt systems. The upper layer of the specimens (WMA or hot mix asphalt control mix) was mixed and compacted at different temperatures in order to simulate different application conditions. A plain bitumen and a polymer modified binder were used for the asphalt mixes whereas an organic (wax) additive was selected as warm modifier. Experimental data were also compared with the stress field of a typical flexible pavement calculated through a layered elastic theory (LET) model. The research study mainly showed that interface shear strength sensibly decreases for low application temperatures of the upper layer (below 140°C) regardless of bitumen type and presence of the warm additive. However, the use of polymer modified bitumen as binder for the upper layer asphalt concrete leads to noticeably higher interface shear strength at any test temperature reducing the risk of delamination.

Laboratory evaluation of stiffness, low-temperature cracking, rutting, moisture damage, and fatigue performance of WMA mixes

Despite the environmental and compaction benefits of warm mix asphalt (WMA), several researchers have expressed concerns over laboratory and field performances of WMA mixes. In this study, a wide range of laboratory tests, namely, dynamic modulus, creep compliance, fatigue, moisture damage, and rutting, was conducted to evaluate the performance of different types of WMA mixes. For this purpose, three WMA mixes, consisting of one mix produced using a zeolite-based WMA additive (containing water), one surface course mix, and one base course mix, the latter two produced with a chemical-based WMA additive with surfactant technology, were collected from different field projects in Texas. In addition, three hot mix asphalt (HMA) mixes with aggregate gradations similar to those of the collected WMA mixes were produced in the laboratory to compare the performance of WMA and HMA mixes. Overall, the WMA mixes yielded lower stiffness, reduced potential of low-temperature cracking, lower fatigue resistance, and a higher rutting potential compared with their HMA counterparts. However, a mixed trend of moisture-induced damage potential was observed for WMA and HMA mixes, when evaluated using retained tensile strength ratio (TSR) and stripping inflection point (SIP) obtained from the Hamburg wheel tracking (HWT) test. In other words, no correlation was found between TSR and SIP values, indicating that passing a TSR test does not guarantee better performance of a mix when tested using an HWT. The results from this study reveal that performance of a WMA mix widely depends on the technology and the type of other additives (e.g. anti-stripping agent) used. The findings of this study are expected to be useful to pavement professionals to better understand the performance of WMA mixes and to develop a database of input parameters for the Mechanistic-Empirical Pavement Design Guide.

Flow Number Test and Assessment of AASHTO TP 79-13 Rutting Criteria

The flow number (FN) test was recommended in NCHRP Project 9-19 as a simple performance test for rutting evaluation of asphalt mixtures. The test showed good correlation with rutting performance of mixtures from WesTrack, MnROAD, and FHWA's accelerated loading facility. Despite this fact, no standard protocol was recommended for temperature and required stress level. Subsequent NCHRP studies allowed the development of a provisional standard. AASHTO TP 79-13 includes test parameters for stress and temperature, specimen conditioning, and minimum FN criteria that were established for hot-mix asphalt (HMA) and for warm-mix asphalt (WMA) on the basis of traffic level. In NCHRP Project 9-47A, the rutting potential of WMA mixtures was compared with that of HMA mixtures by using the FN test and the rutting criteria included in the AASHTO TP 79-13 were also evaluated. The analysis included results of samples produced by using field and lab mixtures. Thirteen mixes using 10 WMA technologies and eight corresponding HMA mixes were included. The FN test results for plant-produced WMA mixes were found to be statistically lower than those for corresponding HMA mixes in more than two-thirds of the comparisons. The study also found that the FN criteria recommended for both HMA and WMA seemed appropriate for evaluating plant-produced mixes. Another finding from the study was that FN results from lab-produced WMA mixtures were consistently lower than FN values from field mixtures; this result suggests that adjustments to the specimen conditioning requirements should be considered.

Evaluation of warm mix asphalt containing recycled asphalt shingles

Advances in asphalt materials have led to the incorporation of higher amounts of recycled asphalt materials in mixtures that can be produced at reduced temperatures. Two demonstration projects were constructed to assess the performance of mixtures that use warm mix asphalt (WMA) and recycled asphalt shingles (RAS) at reduced temperatures. WMA mixes were produced at 120°C. Eighteen pavement sections were monitored each year after construction. Performance tests were conducted on all mixes to measure material properties at a range of temperatures. Additional tests were conducted for one of the field projects to show the influence of increasing RAS on moisture susceptibility. Results indicate that WMA can successfully be used with a RAS mixture. Benefits of adding additional RAS include improvement in rutting, stripping inflection point (SIP), and higher or similar dynamic modulus values at increased test temperatures.

Moisture susceptibility of warm mix asphalt: A statistical analysis of the laboratory testing results

Warm Mix Asphalt (WMA), an alternative to Hot Mix Asphalt, has gained popularity in the recent years. In this research, the effects of aggregate gradation, hydrated lime and Sasobit has been investigated in WMA mixes. Indirect Tensile Testing was performed on dry and saturated samples. Response Surface Methodology was applied to analyze the data. The results indicated that in the case of Indirect Tensile Strength at saturation condition (ITSsat) all the first and second order terms of the aggregate grading, hydrated lime and Sasobit contents, as well as their interactive terms, were statistically significant at 90% confidence level. In the case of Tensile Strength Ratio (TSR) and Indirect Tensile Strength at dry condition (ITSdry) parameters, the interactions between grading and Sasobit contents were rather poor.

Evaluation of Warm Mix Asphalt Mixtures Containing Reclaimed Asphalt Pavement through Mechanical Performance Tests and an Acoustic Emission Approach

Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) have become the primary methods for enhancing sustainability in the asphalt industry in recent years. To further enhance sustainability benefits, asphalt producers have begun using RAP and WMA in combination. Research to date has focused on evaluating WMA-RAP mixtures in terms of moisture sensitivity and permanent deformation characteristics as measured in laboratory performance tests. In the present paper, the authors investigate a set of WMA mixtures that encompass a variety of variables, including four WMA additives (Evotherm 3G, Rediset LQ, Sasobit, and Advera) and three RAP contents (0, 15, and 45%). A common belief among practitioners is that the reduced aging in the asphalt binder associated with lower production temperatures in WMA mixtures leaves additional headroom for the incorporation of higher amounts of RAP, which is generally a stiffer, more brittle material. To fully characterize the performance of WMA-RAP mixtures, the authors evaluated the low-temperature, cracking behavior of these mixtures in conjunction with moisture and rutting resistance characterization. They achieved the low temperature testing of WMA-RAP mixtures through the disk-shaped compact tension [DC(T)], indirect tension (IDT) creep compliance, and acoustic emission (AE) tests. Test results showed that chemical additives improved moisture susceptibility according to the AASHTO T 283 standard test and fracture and bulk stress relaxation characteristics using the DC(T) and IDT tests, respectively. The organic Fischer-Tropsch wax-modified WMA mixtures performed the best among the WMA mixtures in terms of rutting resistance. The introduction of RAP led to the increased resistance to permanent deformation and moisture damage. Conversely, RAP reduced thermal cracking resistance according to the low-temperature performance tests in both HMA and WMA. The authors observed the same trend in AE test results as WMA-RAP mixtures exhibited warmer embrittlement temperatures as compared with control mixtures and are therefore expected to be more prone to thermal cracking. On the basis of these findings, thermal cracking resistance remains an issue to be considered in WMA mixtures containing RAP. Additionally, performance testing has shown to be a valuable tool for the evaluation of RAP and WMA mix designs to avoid performance issues in the field.

Laboratory evaluation of moisture damage and rutting potential of WMA foam mixes

This study was conducted to evaluate the rutting and moisture damage distresses which are the two major concerns in warm mix asphalt (WMA) performance. Two different methods were used to produce WMA mixes using foam bitumen technology. In the first method, the samples were prepared by transforming total bitumen of the mix into foam bitumen, whereas in the second method, two bitumens (soft and hard), the latter in foaming state, were added to the mix resulting in the same bitumen penetration in the final cured samples. The results of testing indicated that lowering the mixing and compaction temperatures resulted in increased moisture susceptibility and rutting potential of both WMA foam mixes. The Marshall quotient values and wheel tracking test results showed that the rutting potential of the WMA foam mixes were significantly greater than the control hot mix asphalt. The addition of hydrated lime powder was found to be effective in decreasing rutting and moisture susceptibility of the WMA foam mixes.

Laboratory Evaluation of Warm Mix Asphalt Influence on Theoretical Maximum Specific Gravity

Abstract Warm mix asphalt (WMA) technology provides sufficient workability for asphalt mixtures at reduced mixing and compaction temperatures. Depending on the WMA technology, the typical temperature reduction range is 20 °C to 55 °C below hot mix asphalt (HMA) production temperatures. WMA involves chemical and wax additives that are added to an asphalt binder or incorporated through the use of foaming technology. The main advantages of WMA are reduced emissions and a reduction in combustible fuel consumption. Ongoing WMA research projects have documented some differences between HMA and WMA mixes, prompting numerous research projects that are investigating these concerns. The purpose of this research is to evaluate the volumetric properties by directly comparing laboratory produced WMA and HMA mixes. This study investigates the impact of WMA additives on the volumetric properties, specifically, the theoretical maximum specific gravity (Gmm). The Gmm testing followed the procedure of ASTM D2041. Two mix designs with HMA binder were produced, one without recycled asphalt pavement (RAP) and the other with 30 % RAP. After the mix designs were completed, no additional changes were made to account for the addition of the WMA technology. The mixes included the WMA technologies Sasobit and Advera, as well as an HMA control, for a total of six different laboratory produced mixes. Each mix was produced at 120 °C, 135 °C, and 150 °C, and each mix was oven cured for 1, 2, and 4 h. The test results were analyzed using statistical principles to determine whether differences in the Gmm values were statistically significant. The results show that temperature has little impact on Gmm. Gmm was not affected by curing times of 1 and 2 h, but the longer curing time of 4 h resulted in a statistically significant increase in Gmm. Further analysis revealed that the mix sensitivity to curing time depends on the amount of RAP in the mix. For the mix designs studied, the Advera Gmm values were similar to the HMA values, but the Sasobit Gmm values were statistically lower than the Advera values.

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.

Estimation of Optimum Compaction Temperature for PMA and WMA Mixtures by Volumetric Property Evaluation

Abstract The optimum compaction temperature (OCT) is defined as the temperature at which asphalt provides proper viscosity in an asphalt mixture. For normal asphalt, the proper viscosity level has been suggested as 280 ± 30 mm2/s by the American Association of State Highway and Transportation Officials (AASHTO). This suggestion has been effectively utilized in selecting the OCT of normal hot-mix asphalt (HMA). However, because polymer-modified asphalt (PMA) and warm-mix asphalt (WMA) have been used recently, it is difficult to apply this method in general. This study evaluates important volumetric properties (air void ratio and void filled with asphalt) of HMA and WMA mixes. The three binders evaluated included 64-22 and 76-22 for HMA and 70-22 for WMA for dense-graded asphalt mixtures compacted using a Superpave gyratory compactor. The OCT at which the optimum asphalt content could be obtained was determined for the three binders. The OCTs obtained via volumetric property evaluation were 20 °C and 38 °C lower than the values determined via the AASHTO method for PMA and WMA. In mechanical performance comparisons, the mixture compacted at the lower OCT was not inferior to the mixture compacted at a higher OCT. It is therefore concluded that the OCT should be determined based on the volumetric property of mixtures, because compaction is not solely a function of viscosity, especially for PMA and WMA mixtures.

Evaluation of Foamed Warm-Mix Asphalt Incorporating Recycled Asphalt Pavement for Volumetric and Mechanical Properties

This study evaluated mixes obtained from a warm-mix asphalt (WMA) pilot project in Reno, Nevada, in the United States, in which the Ultrafoam® technology was used to produce the WMA. The evaluated mixtures included 15% recycled asphalt pavement (RAP). The study addressed the impact of curing time on volumetric properties of foamed WMA in addition to including a sample reheating study. Additionally, the field-produced WMA mixes were evaluated for moisture damage, permanent deformation and thermal cracking resistance. It was recommended that production testing for volumetric properties should be conducted within four hours of manufacturing foamed WMA at the plant. The mix should be cured in a sealed container at the expected lay-down/compaction temperature. Overall in the laboratory, the WMA mix showed no significant additional reduction in moisture damage resistance although the reverse was true for permanent deformation resistance. The WMA exhibited better thermal cracking resistance than the hot mix asphalt (HMA). A distress survey conducted after thirteen months of service showed no distresses in the WMA pavement despite its relatively lower rutting resistance observed in the laboratory.

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.

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.

Quantification of Damage in the Dynamic Complex Modulus and Flow Number Tests Using X-Ray Computed Tomography

The dynamic modulus test is conducted based on the assumption that no damage is induced during the testing process and that measurements are conducted within the linear viscoelastic region. In addition, the level of damage that occurs in the flow number test has not been quantified. The objectives of this study are to quantify the levels of damage in the dynamic complex modulus and flow number tests by using X-ray computed tomography (CT) and to characterize the microstructural properties of asphalt mixtures under loading. Four Superpave mixtures, including one conventional hot-mix asphalt (HMA) and three warm-mix asphalt (WMA) mixes, were evaluated. Two WMA processes (i.e., water foaming and Rediset additive) were used in the preparation of the WMA mixes. In addition, reclaimed asphalt pavement (RAP) was used in the preparation of the mixes at a content ranging from 15–30%. Results of the experimental program indicated that the damage incurred in the dynamic modulus test is minimal and homogeneous, but the damage incurred in the flow number test is significant and heterogeneous. In addition, specimen preparation may significantly influence the three-dimensional air voids distribution in HMA.

Rheological Evaluation of Warm Mix and Anti-Stripping Additives Modified Performance Grade Binders

ABSTRACT This study evaluated the effects of a warm mix asphalt (WMA) additive, Sasobit®, and a liquid anti-stripping agent, AD-here® HP Plus, onthe rheological properties of a selected performance grade binder (PG 64-22) as per Superpave® specifications. The optimum dosage (mass) of Sasobit®was found to be 1.5%, which was expected to reduce the mixing and the high PG temperatures by 9oC and 4.5oC, respectively. Sasobit® was also found to decrease the fatigue resistance and low temperature resistance of the base binder to some extent. Furthermore, a reduced rolling thin film oven (RTFO) temperature was expected to exhibit significant reduction in the rut resistance of the WMA. While anti-stripping agent was expected to reduce the rutting resistance, it was anticipated to increase low temperature resistance of the WMA. The findings of this study are expected to enhance rheological database and help in implementing WMA mixes in Oklahoma and elsewhere.

Evaluation of Warm-Mix Asphalt Produced with the Double Barrel Green Process

During the past 3 years, warm-mix asphalt (WMA) technologies from European countries have entered the North American market. European experiences with WMA technologies have indicated that a significant reduction in mixture temperature, mixture viscosity, energy consumption, and environmental emissions during asphalt mix production and placement can be achieved in comparison with traditional hot-mix asphalt (HMA). On the basis of North American experiences with these technologies to date, transportation agencies and HMA producers are unlikely to adopt WMA technologies solely for the reduction in manufacturing energy costs and environmental emissions, because these benefits do not cover the associated increase in investment and additive costs of WMA over HMA, even in the most expensive North American energy markets. This paper presents an evaluation of the economic, environmental, and mixture performance factors to assess the sustainability of WMA in North America. The paper examines the benefits, risks, investment and material costs, and sustainability associated with the different WMA technologies and specifically the Double Barrel Green process. Included is a mixture performance evaluation of WMA mixes containing reclaimed asphalt pavement and Manufactured Shingle Modifier produced with the Double Barrel Green System during field trials in Vancouver, British Columbia, Canada.

Using Warm-Mix Asphalt Technology to Incorporate High Percentage of Reclaimed Asphalt Pavement Material in Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) helps save natural resources and money. The percentage of RAP that can be utilized successfully in hot-mix recycling is primarily dictated by practical considerations. To avoid deterioration of the aged binder, RAP should not be exposed to relatively high temperatures. This study investigated the feasibility of using a warm-mix asphalt (WMA) additive, Sasobit H8, in successfully recycling hot-mix asphalt (HMA) with 75% RAP at a lower temperature. A control HMA was prepared with extracted aggregates and PG (performance grade) 64-28 binder at 150°C. Another HMA was produced with PG 52-28 binder at 135°C. Two WMA mixes were prepared with Sasobit H8 at 125°C, one with PG 52-28 and the other with PG 42-42 binder. Samples with design asphalt content were compacted by using 75 gyrations of the Superpave gyratory compactor. Their voids, tensile strength at −10°C, rutting potential at 60°C, and moduli at 0°C, 25°C, and 40°C (at different times) were determined and compared. The moduli samples were subjected to 60°C in between the tests. The results show that it is possible to produce mixes with 75% RAP with similar air voids as virgin mixes at lower than conventional temperatures using 1.5% Sasobit. The addition of a significantly lower grade of binder, PG 42-42, at a rate of 1.5% by weight of mix produced a mix that is most comparable with a virgin mix.

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.