Search

Waste materials such as waste tire rubber (WTR), waste cooking oil (WCO), bio-oils, waste engine oil (WEO), and other waste oils have been the subject of various scientific studies in the sustainable and waste research field. The current environmental concerns have been identified to protect natural resources and reuse waste materials. Accordingly, this work reviews the use of recycled waste tire rubber mixed with waste oils (waste cooking oil, waste engine oil) and bio-oils that can be extracted from waste oils to rejuvenate asphalt in reclaimed pavements. This new solution may reduce the massive amounts of WTR and waste oils and produce a more environmentally sustainable material. Reclaimed, aged asphalt has been rejuvenated to achieve various penetration capabilities and properties by blending asphalt with one or more waste materials to evaluate the binder using standard tests. Many solutions with promising results in improving the properties of asphalt mixtures have been selected for further characterization. This review highlights that the addition of WTR and waste materials to rejuvenated asphalt binders improves stability, enhances the viscoelastic properties, provides better fatigue and crack resistance performance, and enhances the compatibility of the rejuvenated rubber oil asphalt. Moreover, the flashing point, softening point, ductility, and penetration of aged asphalt and Poly(styrene-butadiene-styrene)-rubber-rejuvenated and waste-rubber-oil-rejuvenated asphalt were enhanced after applying the rejuvenator compound. On the other hand, adding waste oil to WTR and asphalt reduces the viscosity and enhances the storage stability compared to the asphalt rubber binder.

Crumb tire rubber (CTR) is one of the most common bitumen modifiers used to improve bitumen rheological properties. However, the rubberized bitumen has shown poor storage stability and workability in the application which affect the service performance of the pavement. This work investigated the feasibility of application of waste rubber/oil (WRO) produced by light pyrolysis of CTR in waste cooking oil as a bitumen modifier. The chemical properties, thermal behaviors and reaction process of WRO were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy and TGA/DSC synchronous thermal analysis. The thermodynamic parameters of WRO were calculated by TGA/DTG data, and the thermal stability of WRO was analyzed. The storage stability, physical and rheological properties of WRO modified bitumen and rubberized bitumen were evaluated by separation test, conventional tests and rheological tests, respectively. Results show that, the chain scission and depolymerization occur in the cross-linked network structure of CTR after light pyrolysis, which result in the reduction of rubber hydrocarbon content in gel CTR and the molecular weight of CTR. Natural rubber appears in the sol of the lightly pyrolyzed CTR, and the content of the oxygen-containing functional groups in the sol increases. The thermal behaviors of WRO become complicated, and thermal stability is enhanced from the apparent active energy. Compared to rubberized bitumen, the storage stability, plasticity at low temperature and workability of WRO modified bitumen are greatly improved. However, the resistance to rutting and deformation at high temperature become worse. Further study will be conducted to enhance the high temperature performance with additional additives.

Approximate rubber/bitumen homogeneous system formed by desulfurization and degradation of crumb tire rubber in bitumen under high temperature is beneficial to enhance the storage stability of rubberized bitumen. However, the main problems during the processing of desulfurized and degraded rubberized bitumen are aging caused by volatilization of light components, and burning or explosion due to the direct utilization of low flash point bitumen. Therefore, waste cooking oil was proposed as a safer medium to desulfurize and degrade crumb rubber prior to production of rubberized bitumen. This study focused on the feasibility and effectiveness of the application of waste cooking oil in desulfurizing and degrading rubber particles through co-pyrolysis of them at mild temperature (240–280 °C). Chemical and microscopic analyses were performed to investigate the structural changes of vulcanized rubber. Results showed that solubility of rubber powder reached above 60 wt% after pyrolysis in waste cooking oil, which increased with higher temperatures and more of oil, while increased to a maximum at 2 h and then decreased with the extension of time. The rubber hydrocarbon content decreased greatly, and dramatic reduction of carbon, hydrogen and sulfur elements happened according to component and elemental analyses. The surface of pyrolysis product was even and smooth without obvious rubber particles. The grooves and cavities of rubber residues in scanning electron microscopy micrographs proved that shedding of degraded polymer molecules occurred. Fourier transform infrared spectra revealed that breakage of carbon-sulfur, carbon=carbon and sulfur=oxygen bonds took place during pyrolysis, with appearance of natural rubber characteristic peak.

The use of waste cooking oil (WCO) in crumb tire rubber (CTR) pyrolysis not only improves the safety and controllability of the preparation process, but also recycles these two waste resources effectively. In this study, WCO was used as the solvent to pyrolyse CTR at high temperature to prepare waste rubber oil (WRO). The changes of CTR in molecular structure and rheological properties during thermal energy accumulation were explored through thermogravimetric analysis, Fourier transform infrared spectrometer, gel permeation chromatography and dynamic shear rheometer. The compatibility of CTR with virgin asphalt before and after pyrolysis was described by segregation test. Results show that, with the rise of temperature, depolymerized and broken rubber macromolecule in CTR continue to crack into molecules with less molecular weight, while more of natural rubber and carbon black are released. The rheological properties of WRO have changed greatly, i.e. the decreased zero shear viscosity, the improved flowability and the better plasticity. Complex chemical reactions occur during the pyrolysis of CTR, but no new functional group is generated except for the released natural rubber. The segregation test shows that, the compatibility of CTR with virgin asphalt can be improved by adopting WCO for pyrolysis.

Resource recovery from waste has emerged as one of the grand challenges for civil engineers in the 21st century. Waste cooking oil (WCO) and crumb rubber (CR) are both promising renewable resources and more and more attention has been paid to them. This study explores the effect of the process variables - mass ratio of WCO to binary mixture, reaction temperature and reaction time - on the chemical characteristics of CR desulfurized by WCO. Chemical component, molecular weight distribution and morphology were characterized through thermogravimetric analysis, gel permeation chromatography, scanning electron microscopy. Based on the results, the desulfurization mechanism of crumb rubber was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Results showed that with the increasing temperature and the dosage of WCO, more rubber hydrocarbon with smaller molecules was generated, while cross-linked structure was destroyed and complex structural changes occurred. An increased dosage of WCO has significant influence on the morphologies of vulcanized rubber, manifesting a decreased roughness and a clearer “groove” structures. Reaction temperature has little effect of that due to enough high desulfurization degree. Before 2 h of the desulfurization, the effect of reaction time is similar to that of dosage of WCO, but the desulfurization degree decreases due to chain growth after 2 h. In order to ensure effective desulfurization and avoid energy consumption, the time of less than 2 h, at least the temperature of 260 °C and 0.4 to 0.5 mass ratio of WCO are recommended.

With the rapid increase in the production of reclaimed asphalt pavement (RAP), asphalt pavement rejuvenation technology has attracted significant research attention. To improve the performance of recycled asphalt pavement mixtures, the rejuvenators are usually needed. A waste rubber/oil (WRO) rejuvenator was self-developed by mixing crumb rubber (CR) with waste cooking oil (WCO) at high temperature. However, the chemical dynamic interaction process between WCO and CR, and the effect of reaction time on the rejuvenation properties of the WRO rejuvenators still remained unclear. Therefore, in this study, the functional group and molecular weight of WRO rejuvenators with different reaction times and various WRO rejuvenated asphalts were studied by Fourier transform infrared spectroscopy and gel permeation chromatography, respectively. The rheological properties of various WRO rejuvenated asphalts were also tested using dynamic shear rheometer and bending beam rheometer. The result indicated the occurrence of complex depolymerization and recombination reactions of the polymers released from CR. WRO with higher rubber content exhibited higher polymer concentration. The WRO rejuvenator with a longer reaction time provided more viscous supplement and less elastic retention to the aged asphalt. As the reaction time of the WRO rejuvenator increased, the WRO rejuvenated asphalt showed less resistance to ageing, and the concentration of large molecules and sulfoxide function group in WRO rejuvenated asphalt was reduced. Based on the results, the recommended reaction time of WRO is 0.5 h.

Waste cooking oil (WCO) is proved to be effective in desulfurization of crumb tire rubber (CTR), which can be considered as a sustainable desulfurization technology and an alternative way to solve the poor storage stability of asphalt rubber. However, WCO pre-desulfurized CTR (ODR) modified asphalt displays a compromised high-temperature performance, leading to a limited application of ODR in asphalt modification. In this study, ODR/styrene–butadiene-styrene (SBS) composite modified asphalt was developed to make up the loss of high-temperature performance. The reaction mechanism of ODR/SBS composite modified asphalts with and without sulfur was investigated via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatograph (GPC) and fluorescence microscope (FM). Rheological tests were conducted to clarify the effects of ODR, SBS and sulfur on the rheological behavior of the modified asphalt. FTIR, GPC and FM results proved that crosslinking reaction occurred during the composite modification of ODR, SBS copolymer and base asphalt in the presence of sulfur with moderate content, forming a continuous and homogeneous microstructure with a significantly increased large molecular weight, which is less prone to produce phase segregation. The ODR composite modified asphalt with 3 wt% SBS and 0.4 wt% sulfur presents the best rutting resistance due to the increase of the elastic network structure and cracking resistance due to the presence of WCO and the released rubber chain. The above composite modified asphalt meets the standard traffic level at 76 °C and the specification at −34 according to the multiple stress creep recovery and bending beam rheometer tests.

Ground tire rubbers were lightly pyrolyzed in a twin-screw extruder and applied as potential alternative for asphalt. The composition of lightly pyrolyzed rubber prepared at different pyrolysis temperatures was characterized by gel permeation chromatography, thermogravimetric analysis and extraction analysis. The rheological properties of LPRs and their mixture with asphalt were evaluated by dynamic rheological analysis. LPR with high sol content had typical properties similar to base asphalt, like low viscosity and balanced rheological properties. LPR could be used over 50% by weight as asphalt alternative, which endowed the asphalt with outstanding lower temperature property.

Terminal blend (TB) rubberized asphalt binder can be produced through the dissolution of crumb rubber modifier (CRM) in asphalt, meanwhile other modifiers, like styrene–butadienestyrene (SBS) polymer and crosslinking agent sulphur are supplemented to enhance the properties of modified asphalt. The effect of sulphur on asphalt oxidation and polymer degradation is not well documented for TB rubberized asphalt binder. This paper investigates anti-aging potential of sulphur in TB rubberized asphalt binder from chemical and mechanical perspective. Carbonyl index and butadiene/styrene ratio, which are derived from fourier transform infrared (FTIR) spectrums, are applied to analyse carbonyl growth and butadiene reduction. Gel permeation chromatography (GPC) based polymer retention index is used to detect the change of polymer molecular weight. The complex modulus |G*| is used to calculate hardening index and phase angle master curve is used to analyse the elastic contribution of sulphur. Crosslinking agent sulphur does not have definite positive or negative effect on the carbonyl growth of TB rubberized asphalt binders in this laboratory aging study. However, sulphur does help to alleviate the age hardening behavior. For miscible TB rubberized asphalt binders, 0.3% or 0.4% sulphur can improve the resistance to polymer degradation. In addition, sulphur can improve elastic response of TB rubberized asphalt binder even for pressurized aging vessel (PAV) aged asphalt.

In order to improve the performance of recycled mixture containing reclaimed asphalt pavement (RAP), it is usually necessary to add the rejuvenators. Waste cooking oil (WCO) has been used to rejuvenate recycled binder materials, and some studies have proposed adding virgin polymers to improve fatigue performance of recycled mixture. The output of crumb tire rubber (CTR) is large and the price of it is cheap. However, the compatibility between CTR and the aged binder is poor. In this paper, the CTR was mixed with WCO for pre-desulfurization to prepare the waste rubber/oil (WRO) rejuvenator. The high and low temperature rheological properties before or after aging of the rejuvenated binders were tested by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), and the functional groups of rejuvenated binders was detected by fourier transform infrared spectrometer (FTIR). Multiple stress creep and recovery (MSCR) test was conducted to measure rutting resistance. A WCO-based rejuvenator and an aromatic oil were chosen as control groups. It was found that WRO had the potential to be used as an asphalt rejuvenator. The 70 min reaction time of the WRO rejuvenator was determined by viscosity curve and infrared spectrograms. WRO rejuvenator significantly improved the low temperature properties of aged binder, and partially retaining the high temperature properties of aged binder. With 10% WRO rejuvenator, the performance grade of the artificial aged binder was recovered from 82–16 to 70–28. After aging, the high and low temperature continuous grading of the WRO rejuvenated binder did not change much.

The purpose of this study was to investigate the properties of hot-mix asphalt (HMA) prepared with devulcanized crumb rubber–modified asphalt (DCRMA), which was processed by using pre-devulcanized crumb rubber at a lower temperature (165°C). HMA with different DCRMA content in weight were investigated, and it was found that the optimal binder content was 6.1% by weight. The packing grading mixture design method was applied in the design of DCRMA HMA. A series of laboratory tests including the submerged Marshall Stability, wheel tracking test, dynamic modulus test, small beam bending test, and four-point flexural fatigue test, were carried out to characterize the properties of DCRMA HMA. From the experimental results, it could be concluded that the pre-devulcanized crumb rubber can be used as one kind of good modifier for asphalt rubber to improve hot storage stability. DCRMA could also act as a cost-effective, modified binder in dense-graded asphalt mixture, and benefit the low temperature property and pr...