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During the past decades, to minimize Greenhouse Gas (GHG) emissions and asphalt fumes during the asphalt mix production and construction process, various warm mix asphalt (WMA) additives have been developed and successfully applied. Currently, as production of WMA reaches close to that of Hot Mix Asphalt (HMA) in the US, the varied definition of WMA is questioned in this paper. Not only are the temperature reduction ranges from HMA defined by various studies too wide, but also the minimum threshold to be classified as WMA is often too small. In this paper, a new category of "Cool Mix Asphalt (CMA)" is proposed to distinguish it from the newly defined WMA based not on the reduction amount from HMA temperature but its actual production temperature. It is proposed that HMA should be defined as asphalt mixtures produced at temperatures between 140 and 160 °C (between 284 and 320 °F), WMA as production temperatures between 120 and 140 °C (between 248 and 284 °F), and CMA as production temperatures between 100 and 120 °C (212 to 248 °F). By defining their actual production temperatures rather than reduction temperatures from HMA, WMA and CMA will be clearly defined. This paper then presents a new Polymer Cool Mix Asphalt (PCMA) additive called "Zero-M", which was developed to lower the mixing temperature to around 110 °C (203 °F). Recently, test sections using Zero-M were successfully constructed in Korea, Italy and Vietnam, and their laboratory test results of field cores and production and construction experiences are described in this paper. The chemistry and compositions of Zero-M are discussed along with its mechanism to significantly lower the production temperature of PCMA. All test sections constructed in three countries met the in-place compaction density requirements of their respective countries, which were close to or higher than those of the control HMA test sections. [ABSTRACT FROM AUTHOR]

Low temperature cracking potential is a primary concern for asphalt mixtures with high RAP contents. To minimize the thermal cracking, various rejuvenators have been utilized in the past. In this study, Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the level of oxidation of asphalt. To evaluate the low-temperature cracking potential of aged asphalt with and without rejuvenators, the fracture surface images were captured using Cryo-Scanning Electron Microscopy (Cryo-SEM). The Cryo-SEM images were then analyzed using the image processing technique. The rejuvenated asphalt specimens exhibited less fractured surface than the aged asphalt. Finally, the Fracture Index was computed to rank each asphalt sample in terms of low-temperature cracking potential. Based on the test results, it can be concluded that the use of the Cryo-SEM technology combined with the image processing technique is a promising method to visually observe the fracture surface of asphalt and compute the Fracture Index to estimate the low-temperature cracking susceptibility. [ABSTRACT FROM AUTHOR]

• Based on the SCB-IFIT test results, for both 34% and 45% RAP mixtures, rejuvenators were effective in lowering cracking potential. • Based on a condition survey, rejuvenators were effective in delaying an initiation of cracking. • High RAP mixtures with 34% and 45% RAP materials were successfully constructed in Iowa while exceeding Iowa DOT's field density requirement of 93%. • Continuous PG grading rejuvenated asphalt binders were performed where Tufftrek was more effective in lowering both critical high and low temperatures than Invigorate. • Based on HWT test results, both rejuvenators more effective in lowering the moisture susceptibility than a softer binder and Tufftrek was more effective in lowering a rut depth than Invigorate. Although thirty-one US states utilize 20% recycled asphalt pavement (RAP) or greater in asphalt pavements, Iowa limits the usage of RAP to 20%, and 30% with a softer binder in the surface layer. Because high RAP mixtures can cause asphalt mixtures to stiffen due to the hardening effect of the aged binder, rejuvenators should be used to improve the cracking resistance of high RAP mixtures. Due to increasing demand for sustainable, and environmentally materials, two bio-based rejuvenators, Invigorate and Tufftreck, were considered for this study. To evaluate effect of rejuvenators on high RAP mixtures, field test sections were constructed in Cerro Gordo County, Iowa, 2020. The field test consists of six different sections with two rejuvenators and three different RAP contents of 22%, 34% and 45%. Performance grading (PG) of asphalt with rejuvenators adopted for the field test sections lowered both high and low temperatures of the virgin asphalt. Based on the eight cores for each test section, all six test sections with or without rejuvenators exhibited field densities between 93.6% and 95.2%, exceeding the minimum requirement of 93%. First, loose field samples were compacted at the laboratory for Hamburg wheel tracking test, semi-circular bending test, and disc-shaped compact tension test. Second, the laboratory test results were analyzed to determine if rejuvenators were effective in mitigating rutting, moisture damage and cracking. Based on the analysis of limited laboratory test results, Tufftrek was effective in lowering rutting and moisture damage whereas, for minimizing cracking, using a soft binder was most effective. Third, a condition survey on test sections was performed in one year after construction. Based on a condition survey of six test sections, no rutting was observed from all test sections, but some low-severity cracks were observed in sections without rejuvenators. Based on the limited condition survey results, it can be concluded that rejuvenators were effective in delaying the initiation of cracking. [ABSTRACT FROM AUTHOR]

The use of Warm Mix Asphalt (WMA) for the construction of roads around the world is growing rapidly. This paper presents a new organic WMA product that has been recently introduced to the US market, which is Polyethylene (PE) Wax-based WMA additive with crystal controller to increase the low temperature cracking resistance and anti-stripping agent to enhance moisture susceptibility. To determine the optimum dosage rate, the viscosities of the binder with varying amounts of additive were measured. Based on the Asphalt Binder Cracking Device (ABCD) test, it was found that the low-temperature cracking temperature of asphalt binder would not be affected by the amounts of the additive up to 3.0%. The new Polyethylene (PE) Wax-based WMA mixtures with Reclaimed Asphalt Pavement (RAP) materials were also tested using the Hamburg wheel tracking device and the wheel passes were significantly higher with WMA mixtures PG 64-28 binder, Minnesota aggregates and 25% RAP than the ones with 64-22 binder, Iowa aggregates and 10% RAP. The Hamburg test results seemed to be influenced by more on the characteristics of aggregates and RAP materials than the WMA additive. Two in-service roads in Iowa and Minnesota were successfully rehabilitated using the PE Wax-based WMA mixtures. The average void of 3.8-cm (1.5-inch) WMA overlay (9.0%) was higher than that of HMA overlay (7.0%) placed on an urban street in Iowa City. It was partly due to asphalt temperature that was lowered to match the lower aggregate temperature. However, it is interesting to note that the average air void of the cores obtained from the rehabilitation section of the same street using the same WMA was significantly lower (6.0%). In Minnesota's state highway, the average air voids of four WMA and HMA cores for quality control were 5.85% and 5.29%, respectively and those of four other WMA and HMA cores for quality assurance were 6.05% and 6.01%, respectively. The WMA pavements were easier to reach 94% density with fewer passes of a compactor than the HMA. [ABSTRACT FROM AUTHOR]

As part of the validation effort to evaluate the consistency of a new cold in-place recycling using foamed asphalt (CIR–foam) mix design process for the Iowa Department of Transportation, the dynamic modulus and repeated load tests were conducted to evaluate the performance characteristics of CIR–foam mixtures over a wide range of loading and temperature conditions. The main objective of this research is to study the impacts of the foamed asphalt contents and reclaimed asphalt pavement (RAP) material characteristics on dynamic modulus and flow number. Dynamic modulus and repeated load tests were conducted on CIR–foam mixtures with RAP materials collected from seven different CIR project sites located throughout Iowa. Dynamic modulus values of the RAP materials varied depending on the sources and foamed asphalt contents. Coarse RAP materials with a small amount of residual asphalt content exhibited a higher modulus value at 4.4°C but exhibited a lower dynamic modulus value at 37.8°C than fine RAP materials with a large amount of residual asphalt content. Flow numbers were varied significantly depending on their RAP sources and foamed asphalt contents. Fine RAP materials with a hard residual asphalt binder exhibited a higher flow number than coarse RAP materials with a soft residual binder. The relative rankings of RAP materials in terms of the flow number did not change when the foamed asphalt was increased from 1.0 to 3.0%, which supports the repeated load test being consistent in evaluating a rutting potential of RAP materials. [ABSTRACT FROM AUTHOR]

The main objective of this study is to validate a new mix design procedure for cold in-place recycling using foamed asphalt (CIR-foam) developed for the Iowa Department of Transportation. First, reclaimed asphalt pavement (RAP) materials were collected from seven different CIR construction sites located across the state of Iowa. To determine the consistency of a new CIR-foam mix design procedure, the mix design was performed seven times using these RAP materials. The test specimens were prepared using gyratory compactor rather than Marshall hammer because it produced more consistent mixtures for various foamed asphalt contents and curing conditions. The indirect tensile strength test was performed on the vacuum-saturated specimens prepared using each of seven RAP material sources for five different foamed asphalt contents (1.0, 1.5, 2.0, 2.5, and 3.0%), given a fixed moisture content of 4.0%. As the foamed asphalt content increased from 1.0 to 3.0% at 0.5% increments, air voids in the CIR-foam mixtures decreased gradually. The indirect tensile strength of CIR-foam specimens cured for two days at 60°C was significantly higher than that of CIR-foam specimens cured for three days at 40°C. Based on the new mix design procedure, the optimum foamed asphalt contents were consistently found at values between 1.5 and 2.5% for all seven different RAP materials. The stiffer residual asphalt required more foamed asphalt, whereas the higher residual asphalt content did not require a smaller amount of foamed asphalt. The raveling test result was very sensitive to the curing time and the foamed asphalt content, such that RAP materials with a large amount of stiff residual asphalt would exhibit more potential for raveling. [ABSTRACT FROM AUTHOR]

The main objective of this study is to determine mix design parameters for cold in-place recycling with foamed asphalt. First, the foaming process of laboratory foaming equipment was validated by varying the water and asphalt content. 1.3% water content was adopted to create the optimum foaming characteristics in terms of the expansion ratio and the half-life at 170°C under air pressure of 400 kPa and water pressure of 500 kPa. The mix design was then performed using both the indirect tensile test and the Marshall test for 13 combinations of foamed asphalt content and water content for three different gradations. The water content did not appear to affect the test results significantly. Maximum stability (both wet and dry samples), maximum bulk density, and indirect tensile strength (both wet and dry samples) were all obtained around 2.5% foamed asphalt content. Overall, the highest Marshall stability and indirect tensile strength were obtained in the order of fine, field, and coarse reclaimed asphalt pavement gradations. It is recommended that the indirect tensile strength based on wet samples be adopted for determining the optimum foamed asphalt content. [ABSTRACT FROM AUTHOR]

Highlights: [•] Evaluate available test methods for longitudinal joint quality control. [•] Develop specifications to ensure the longitudinal joint with proper performance. [•] Evaluate the effect of segregation on longitudinal joint density performance. [Copyright &y& Elsevier]

• WMA and HMA showed similar level of aging based on FTIR and Block Cracking tests. • According to short-term field evaluation, both WMA and HMA performed similarly. • Medium-term field evaluation indicated that it takes some time for WMA test section to start to deteriorate. • HMA and WMA did not show significant difference in rutting, moisture sensitivity and thermal cracking. 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. [ABSTRACT FROM AUTHOR]