Effect of Biorejuvenator on Postconsumer Recycled Plastic Modified Asphalt Mixes: Laboratory Investigation and Environmental Impact Analysis

In recent years, use of postconsumer recycled (PCR) plastics in asphalt mixes has been gaining popularity owing to increased environmental awareness, and the need to promote sustainability and conserve natural resources. When using the dry process, incorporation of PCR plastic in asphalt mixes poses several challenges, including mixing, sample preparation, and testing. Use of balanced mix design (BMD) for asphalt mixes containing PCR plastic poses additional challenges that have not been adequately covered in previous studies. To this end, changes in the volumetric properties and performance of PCR plastic-modified asphalt mixes were investigated in this study. For this purpose, an asphalt mix having a nominal maximum aggregate size (NMAS) of 9.5 mm and PG 64-22 binder was designed using the BMD approach. Three different percentages (0.25%, 0.5%, and 1% by weight of aggregate) and two different PCR plastics, namely low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) were incorporated in the mix using the dry process. Volumetric properties, namely maximum theoretical specific gravity, bulk specific gravity, voids in mineral aggregate, voids filled with asphalt, air void contents, and densities were determined for both control- (0% plastic) and modified mixes. Also, indirect tensile strength, indirect tensile asphalt cracking test, and Hamburg Wheel Tracking tests were performed to assess the performance of these mixes. A comparison of performance for both plastic type and amount and issues related to the incorporation of PCR plastic using the dry process are discussed in this paper.

Among different recycled materials, use of post-consumer recycled (PCR) plastics in asphalt mixes provides several benefits, including economic, environmental, and improvement in performance. Resistance to fatigue cracking of asphalt mixes is used in the design and performance assessment of asphalt pavements. The purpose of this study was to evaluate the effect of PCR plastics on the stiffness and resistance to fatigue cracking of asphalt mixes. Specifically, this study addressed the changes in the dynamic modulus, cracking tolerance index (CTIndex) and percent loss (%Loss) from Cantabro abrasion test with the addition of PCR plastic in different amounts. For this purpose, a surface mix (NMAS of 9.5-mm) with PG 64-22 binder was modified using three different percentages (0.25%, 0.5%, and 1% of aggregate) of PCR plastic. Two different PCR plastics, namely low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), were incorporated in the asphalt mix using the dry process. Dynamic modulus test, indirect asphalt cracking test (IDEAL-CT), and Cantabro test were performed on both control and plastic-modified mixes. The stiffness, resistance to fatigue cracking, and %Loss of plastic-modified mixes were compared with those of the control mix as well as between mixes with two different types and amounts of PCR plastics. In addition, laboratory performance of the plastic-modified mixes was compared with performance of a typical pavement under traffic loading analyzed using the AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software. The findings of this study are presented in this paper.

This study aims to evaluate the performance of high-performance asphalt concrete modified with 12 % of asphaltenes and 0.15 % of polyethylene terephthalate (PET) fibers using a balanced mix design (BMD) approach. The addition of asphaltenes changes the performance grade (PG) of the base binder with a continuous PG 70.2–25.9 to a continuous PG 82.9–21.8. The research focuses on assessing the cracking resistance of the modified mixes using the indirect tensile asphalt cracking test (IDEAL-CT) while ensuring sufficient rutting resistance examined with the Hamburg wheel-track (HWT) test. The HWT test results demonstrate considerable improvements in the modified fiber mixes tested at 60°C, with a rut depth of 5.5 mm at 20,000 passes. This indicates excellent rutting resistance with a rutting resistance index that is almost 5 times compared with that of the control mix, which shows signs of moisture damage. The IDEAL-CT test results show a strong impact of fiber addition in that the CTIndex at 37°C of the fiber-modified mixes (a value of 87) is higher than the threshold for a Super Mix (a value of 70), and it is also very similar to that of the softer unmodified mixes tested at a standard temperature of 25°C (a value of 91). The higher test temperature for IDEAL-CT is based on the modified binder PG and is selected because at 25°C the tensile strength of the modified mixtures is very high, which masks the influence of fibers. Based on the BMD analysis and using a performance space diagram, the incorporation of asphaltenes and waste PET fibers yields a Super Mix that warrants field verification. The BMD approach proves valuable in understanding the effects of different modifications on asphalt mixes, providing a thorough understanding of their performance characteristics.

The Balanced Mix Design (BMD) approach has gained significant momentum in the current era due to concerns about the performance of asphalt pavements designed by the volumetric mix design method. The BMD incorporates laboratory performance tests as a crucial part of the asphalt mix design acceptance process. However, establishing the performance thresholds is essential to reach the asphalt mixes intended performance and avoid premature failures. The present study aims to develop the performance thresholds through a comprehensive statistical analysis by performing the Indirect Tensile Cracking Test (IDT-CT) and Hamburg Wheel Tracking Test (HWTT). Data points from 28 different projects were used to perform the statistical analysis. Following the development of BMD thresholds, the laboratory investigation of four different projects was conducted, and the binder content ranges for four mixes corresponding to the BMD thresholds were determined. Based on probabilistic analysis, this study proposed three alternative criteria for benchmarking, ranging from least conservative to most conservative. Moreover, it was determined that establishing performance thresholds based on the traffic and design levels of the roadway was more effective. Also, different performance thresholds were assigned for the PG76-22ER polymer-modified binder used for Level 4 projects used in warmer regions to account for the climate effect.

Influence of gradation on asphalt mix rutting resistance measured by Hamburg Wheel Tracking test

Plastic pollution has become one of the major concerns in the world. Plastic waste is not biodegradable, which makes it difficult to manage waste plastic pollution. Recycling and reusing waste plastic is an effective way to manage plastic pollution. Because of the huge quantity of waste plastic released into the world, industries requiring a large amount of material, like the pavement industry, can reuse some of this mammoth volume of waste plastics. Similarly, the use of reclaimed asphalt pavement (RAP) has also become common practice to ensure sustainability. The use of recycled waste plastics and RAP in HMA mix can save material costs and conserve many pavement industries’ resources. To successfully modify HMA with RAP and waste plastic, the modified HMA should exhibit similar or better performance compared to conventional HMA. In this study, recycled waste plastic, linear low-density polyethylene (LLDPE), and RAP were added to conventional HMA, separately and together. The mechanical properties of conventional and modified HMA were examined and compared. The fatigue cracking resistance was measured with the IDEAL Cracking (IDEAL CT) test, and the Hamburg Wheel Tracking (HWT) test was conducted to investigate the rutting resistance of compacted HMA samples. The IDEAL CT test results showed that the cracking resistance was similar across plastic modified HMA and conventional HMA containing virgin aggregates. However, when 20% RAP aggregates were used in the HMA mix, the fatigue cracking resistance was found to be significantly lower in plastic modified HMA compared to conventional HMA. The rutting resistance from the HWT test at 20,000 passes was found to be similar in all conventional and modified HMA.

Field performance validation of the Louisiana balanced asphalt mix design framework

This study aims to analyse the behaviour of asphalt concrete produced from recycled plastic-modified bitumen. This particular production process is known as the wet method, which involves the blending of low melting point recycled plastics, mostly polyolefins, in hot bitumen before mixing with preheated aggregate. Based on a comprehensive research study that investigated several recycled plastics for the wet method, two common low melting point plastics from two different collection streams were evaluated: a low-density polyethylene from post-industrial recycling operations and a source of commingled plastic (polyethylene and polypropylene) from the collection of post-consumer plastics. Plastic-modified bitumen was produced with different recycled plastic contents ranging from 0.5 to 6% of the bitumen weight. First, the storage stability of the plastic-modified bitumen was evaluated. Then, asphalt mixes were produced using the plastic-modified bitumen. The testing scheme included measurements of the compactability and densification behaviour of the mixes, moisture resistance, viscoelastic behaviour via the flexural stiffness test, IDEAL-CT test to evaluate cracking tolerance, fatigue resistance through the four-point bending beam test, and rutting resistance via Hamburg wheel tracking. The study found that adding a high plastic content significantly reduced the storage stability of the plastic-modified bitumen. Adding plastic was found to have a minor impact on the compactability, while it reduced the moisture resistance with increasing plastic addition and modified the viscoelastic behaviour of the asphalt mixtures. Finally, the study found that plastic provided benefits to the cracking and rutting resistance of asphalt mixtures to different extents depending on the plastic type and plastic content.

This study investigates the performance of asphalt concrete containing recycled plastics as synthetic aggregates in the dry mixing process. Two types of recycled plastics were used, namely, acrylonitrile butadiene styrene (RABS) and Polyethylene Terephthalate (RPET), based on the high-temperature properties of the plastics that make them suitable to be treated as synthetic aggregates (i.e. do not melt during the asphalt mixing phase). The proportions of recycled plastics were chosen at 0.5%, 1%, 2% and 4% of the mix mass. The laboratory testing programme includes the evaluation of compactability properties, moisture resistance, cracking resistance via IDEAL-CT test, fatigue resistance via four-point bending beam test and rutting resistance via Hamburg wheel tracking (wet) test. It was found that the inclusion of recycled plastics did affect the compactability of the mixes depending on their relative size and shape. On the other hand, the inclusion of recycled plastics did not significantly vary the moisture resistance of asphalt mixes. The cracking and rutting behaviour of asphalt mixes that incorporated recycled plastics were also modified and some benefits were observed depending on the plastic content and size.

Incorporating waste plastic into asphalt pavement is an evolving recycling strategy based on a circular economy approach. Dow has cooperated with MU to use optimal recycle plastic to target better pavement performance with less plastic leaking pollution. The goal is to find the optimal method to cooperate waste plastic with asphalt mixture, that is, an economical and environment-friendly way to target better mixture performance. Linear low-density polyethylene (LLDPE) and waste Polyethylene Terephthalate (PET) is the main plastic used in this project. Other additives (GTR, ElvaloyTM, and PPA) are also added to the mixture by dry process or wet process with the goal to improve the compatibility of plastic in the asphalt mixture. Various binder tests were conducted to evaluate the effect of LLDPE and PET modified binder by a wet process. AASHTO Superpave binder performance grading (PG) tests (Viscosity, DSR, BBR) test was utilized to characterize the workability, high-temperature (rutting) performance, and low temperature (cracking) performance. AASHTO Superpave method was performed to explore the LLDPE modified mixture performance with MoDOT criteria. Rutting resistance, cracking resistance at different temperatures were studied with a suite of laboratory tests, such as the Hamburg Wheel Tracking test (HWT), DC(T) test, IDEAL-CT test. Water samples from the rutting test and the permeability test were also further tested for microplastic detection. In terms of performance grade (PG) of chemically treated waste PET modification by wet process, this study is analogous to Leng's study (2018). Waste PET modification, up to 15 percent by weight of the binder, slightly increases the workability, high temperature, and low-temperature performance. Appreciate range for the amount of waste plastic was determined to be 2-3 percent by weight of the bitumen regard to PG performance. Elvaloy (PPA)-only or LLDPE pellet-only modified binder increases binder viscosity, which indicates a harder binder at the same temperature. Thus, the fail temperature from the DSR test at high temperature and intermediate temperature also improve. The increase in viscosity from the additives has a negative effect on the m value and stiffness of BBR test results. The combination of both LLDPE pellets and Elvaloy (PPA) made the binder even stiffer with viscosity increasing from 0.421 pa*s to 1.319 pa*s, which is more than three times. The addition of plastic by dry process affected specimens in mixture volumetric properties and performance test results. Melted plastic remains very viscous and dense and was not coated on the dense-graded aggregates used in this study. Plastic modified asphalt mixtures decreased the theoretical maximum gravity of the mixture for the volumetric property. Performance tests results show that plastic modified mixture greatly improve rutting resistance with rut depth from 17.1mm to 0.9 mm, which satisfied the MODOT criteria of 12.5 mm rut depth and enhance low- temperature cracking resistance to some degree. Even the CT index of LLDPE modified mixtures fails to meet the recommended threshold of MODOT, the CT index improves with the increase of LLDPE amount and the decrease of LLDPE size. It's also worth mentioning that the smaller size of LLDPE also helps to disperse itself in asphalt mixture, which produces a more stable and reliable asphalt mixture in the long term. Even stiffer with viscosity increasing from 0.421 pa*s to 1.319 pa*s, which is more than three times. The addition of plastic by dry process affected specimens in mixture volumetric properties and performance test results. Melted plastic remains very viscous and dense and was not coated on the dense-graded aggregates used in this study. Plastic modified asphalt mixtures decreased the theoretical maximum gravity of the mixture for the volumetric property. Performance tests results show that plastic modified mixture greatly improve rutting resistance with rut depth from 17.1mm to 0.9 mm, which satisfied the MODOT criteria of 12.5 mm rut depth and enhance low- temperature cracking resistance to some degree. Even the CT index of LLDPE modified mixtures fails to meet the recommended threshold of MODOT, the CT index improves with the increase of LLDPE amount and the decrease of LLDPE size. It's also worth mentioning that the smaller size of LLDPE also helps to disperse itself in asphalt mixture, which produces a more stable and reliable asphalt mixture in the long term.

This experimental study evaluated the performance of modified asphalt mixtures prepared by incorporating 2%, 4%, and 6% linear low-density polyethylene (LLDPE) by weight of asphalt binder through a series of tests. The microstructural analyses using scanning electron microscopy (SEM) were conducted on asphalt samples to assess the engineering properties of the asphalt mixes. Finally, ANOVA statistical analysis has been employed to determine the statistical significance of the differences in all tests’ means. Based on laboratory findings, the Marshall stability test result showed that the modified asphalt mixes up to 4% LLDPE had enhanced performance by 12.7% compared to the control mix. A significant decrease (up to 31.3%) in binder penetration was demonstrated due to the incorporation of LLDPE into the asphalt mix. The softening point of the LLDPE–asphalt mixes was increased by up to 17.6%. It was also demonstrated that the incorporation of such LLDPE dosages maintains the flow limits within the specified range; however, the flow of the asphalt mix with 4% LLDPE was 3.17 mm which is the nearest to the average value of the upper and lower acceptable limits. The air voids of mixes with LLDPE content more than 4% by was decreased to less than 4% which is not recommended in high-temperature climates to control mixture bleeding. Microscopic analysis revealed an improvement in the densification of asphalt microstructures, attributed to the LLDPE particles significantly changing the rheology and viscosity of the base mixture and making the hot asphalt mixture more homogeneous. Based on the physical and rheological properties investigated in this study, it could be concluded that 4% LLDPE produces the best performance in asphalt mixtures. Overall, the ANOVA analysis demonstrated that the incorporation of LLDPE into asphalt mixes has a significant impact on all of their properties.

The global desire to improve the performance of road pavements and move towards a sustainable transportation system has immensely encouraged the usage of fibers in asphalt paving materials. In this study, glass fibers trademarked as ESGFIBER produced by the ESG Industry company Limited from Daejeon, Korea were added in dense-graded asphalt mix. The purpose of this study was to evaluate effects that fibers have on volumetric properties, mechanical properties, and long-term performance of asphalt concrete mixes. ESGFIBER were mixed together with aggregates and asphalt binder in asphalt mix and five different asphalt mixes with different dosage of fibers were evaluated in this study. The Marshall mix design method was used for designing all asphalt mixes, and laboratory tests indirect tensile strength test, deformation strength test and Hamburg wheel tracking test were conducted to evaluate moisture susceptibility, fatigue cracking behavior and rutting resistance of asphalt concrete mixes. The results showed that when ESGFIBER were added in asphalt mix moisture susceptibility, fatigue cracking and rutting resistance were both improved. The usage of ESGFIBER in asphalt concrete mixes can be very beneficial since the mechanical and long-term performance were improved upon the addition of fibers.

Assessment of microplastics production from waste plastics-modified asphalt pavement

Effect of laboratory-produced cellulose nanofiber as an additive on performance of asphalt binders and mixes

Using recycled plastics in asphalt could be challenging because of possible composition variations and contaminants. Post-consumer recycled (PCR) and post-industrial recycled (PIR) plastics can differ in composition, consistency over time, amount of contaminates, and degradation potential. Additionally, PCR and PIR plastics may contain chemical additives from their manufacturing process and residues of other materials after recycling. Thus, significant health and safety uncertainties surround the occupational exposure of asphalt workers to hazardous air pollutants (HAPs) emitted during the production and construction of recycled-plastic-modified (RPM) asphalt mixtures. When subjected to elevated temperatures, certain recycled plastics may release HAPs, including polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). This study examined fumes emitted during four laboratory methods of adding PCR plastics in asphalt mixtures via the dry process that simulated the production of these RPM mixtures at asphalt plants. The fume analysis followed the US National Institute for Occupational Safety and Health (NIOSH), the US Environmental Protection Agency (EPA), and the International Organization for Standardization (ISO) methods for collecting, characterizing, and quantifying PAHs. The chemical characterization of the utilized PCR plastics was performed using gas chromatography/mass spectrometry (GC/MS) analysis. Results indicated that the evaluated PCR plastics did not introduce new compounds to the fumes but may have changed the observed concentration of the compounds in the fumes. Nonetheless, the concentrations of the detected HAP VOCs were significantly below the US Occupational Safety and Health Administration (OSHA) threshold values.