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Liquid rubber (LR) has been proven to be a valuable asphalt modifier capable of addressing the existing deficiencies associated with crumb rubber–modified asphalt (CRMA), including poor workability and storage stability. Therefore, an accessible preparation method based on olefin metathesis was explored to produce optimal LR from crumb rubber (CR) in the laboratory. This research established the optimal laboratory preparation conditions for LR and investigated the performance of liquid rubber–modified asphalt (LRMA) mixture when used in pavement. A total of 32 LR samples were generated by olefin metathesis and physical swelling under various catalytic and swelling conditions. The physical properties, viscosity, and storage ability of LRMA were evaluated to select the optimal preparation parameters for LR. A comprehensive analysis was performed to compare the physicochemical characteristics of LR and the original CR through microscopic examinations with scanning electron microscopy (SEM), Fourier-transform infrared spectrometry (FTIR), and gel permeation chromatography (GPC). An in-depth evaluation assessed the stability at high temperatures, the properties at low temperatures, and the moisture stability of LRMA and CRMA mixtures. Experimental results showed that the optimal laboratory preparation conditions for LR were a catalyst dosage between 3‰ and 5‰, a catalytic duration of 48 h, a swelling temperature of 160°C, and a swelling time of 8 h. Moreover, LR possessed a smooth surface without rubber particles. The molecular weight and distribution of LR were considerably reduced compared with those of CR after olefin metathesis and physical swelling. The introduction of LR significantly enhanced the cracking resistance of the base asphalt mixture. However, the enhancement effect of LR on the base asphalt mixture to resist high-temperature rutting and moisture damage was inferior to that of CR. [ABSTRACT FROM AUTHOR]

Crumb rubber (CR) from grinding waste tires has served as an asphalt modifier in asphalt pavement construction for decades. Incorporating CR in asphalt mixtures by the dry method is becoming popular with the emphasis on low carbon emissions, greenness, and sustainability. However, the poor compatibility and mechanical performance of dry-mixed asphalt rubber limit its application. This work presents the effect of practical activation treatments on the microstructure of CR and mechanical properties of the resulting asphalt binder and mixtures, aiming to modify CR surface features and improve the performance of asphalt mixtures. According to previous work, the activation treatment methods of high-temperature, preswelling, the two combinations, and microwave irradiation for CR were compared. Meanwhile, the surface morphology, chemical features, and dispersion degree of various activated CR as well as rutting resistance, low-temperature performance, and moisture stability of the resulting asphalt and asphalt mixtures were evaluated. The results indicated that selected activation methods significantly change the surface morphology and chemical features of CR, and the activated CR shows a flocculent structure with porous surface and reactivity. Preswelling with high-temperature and microwave activation for CR endows the modified asphalt with significantly improved viscoelastic properties. Preswelling with high-temperature activated CR asphalt shows better low-temperature cracking resistance. Asphalt modified with activated CR presents homogeneous and compatible states in microscopy compared with ordinary asphalt rubber. Incorporating activated CR in asphalt mixtures by the dry method is a promising technique in view of improved low-temperature cracking resistance and moisture stability. [ABSTRACT FROM AUTHOR]

Waste ethylene-propylene-diene monomer (EPDM) rubber and tire pyrolytic oil (TPO) derived from waste tire pyrolysis have shown promising results for their use in asphalt binder modification. However, their incorporation has shown improvements mainly either on rutting or fatigue behavior of the resultant asphalt binders. Composite modification may be a viable option to achieve improved performance with these two materials. The aim of this study was to evaluate the rheological, morphological, and chemical properties of asphalt binders produced through both individual and composite modifications using waste EPDM rubber and TPO. For composite modification, two different blending schemes were used: (1) sequential addition of TPO and EPDM rubber to the heated base asphalt binder; and (2) premixing of TPO and EPDM rubber prior to addition to the heated base asphalt. In the latter case, before being added to the base asphalt, TPO premixed EPDM rubber was conditioned at two temperatures (25°C and 90°C) to see the effect of different conditioning temperatures in composite modification. Firstly, the conventional properties of all the binders in the unaged state were assessed, followed by the evaluation of short-term-aged binders for Superpave and Shenoy rutting parameters, frequency sweep, zero shear viscosity, multiple stress creep and recovery, and Burger's modeling. The long-term-aged binders were evaluated through the Superpave fatigue parameter, Glover-Rowe parameter, and linear amplitude sweep. Fourier transform infrared (FTIR) spectroscopy and optical microscopy were used for chemical and morphological analyses. The premixing of EPDM and TPO accompanied with conditioning at 90°C imparted a synergistic effect with improvements in both rutting and fatigue performance of binder. The improvement in performance attributes was ascribed to the preswelling of EPDM rubber with TPO, which was evident from the morphological analysis. FTIR provided evidence of chemical interaction between EPDM rubber and TPO during the conditioning and blending processes. [ABSTRACT FROM AUTHOR]

This study evaluated tire pyrolytic oil (TPO) derived from waste tire pyrolysis as a rejuvenating agent for three types of aged asphalt binders (unmodified, polymer-modified, and crumb rubber–modified). Gas chromatography–mass spectrometry (GC–MS) was performed to identify chemical compounds present in TPO. The rheological characteristics of all binders were examined through the complex viscosity–frequency profile, zero-shear viscosity, failure temperature, Black space diagrams, Cole–Cole plots, Superpave fatigue parameter, Glover–Rowe parameter, and linear amplitude sweep (LAS) tests. Mass loss was also determined for the rejuvenated binders. All binders were subjected to Fourier transform infrared (FTIR) analysis, and sulfoxide and carbonyl indices were computed. Atomic force microscopy (AFM) was conducted to study the effect of TPO on the micromorphology of the binders. The normalized Euclidean distance approach was used to rank the rejuvenated binders with respect to the proximity of their rheological and FTIR characteristics to that of the unaged binder. The use of TPO as a rejuvenating agent enabled the aged binders to achieve properties comparable to those of the unaged asphalt binder. The AFM-based rejuvenation index (RI) indicated a good potential of TPO as a rejuvenator. The results of the binder rheological parameters and the FTIR indicators investigated in the study indicated that a 9% dosage of TPO as a rejuvenating agent was the most effective. [ABSTRACT FROM AUTHOR]

The asphalt modifier formed by the miscibility of waste cooking oil and rubber is referred to as WRO. WRO modifiers prepared from waste tire crumb rubber (WTCR) and waste cooking oil (WCO) have the potential for solving the problems of segregation of rubber asphalt and the low recycling rate of waste cooking oil. The results of the Cole-Cole curve show that the WRO modifier can remarkably enhance the miscibility of WTCR and base asphalt. The Fourier transform infrared spectrometer (FTIR) tests proved that WTCR, WCO, and base asphalt were mainly physically miscible during the preparation of the WRO modifier and modified asphalt. In the process of preparing the WRO modifier and modified asphalt, the rubber undergoes devulcanization, conjugated double bond reduction, and oxidation reactions. The WRO modified asphalt presents great workability, storage stability, high-temperature elastic recovery, low-temperature crack resistance, and deformation recovery ability. In addition, the results of the multiple stress creep and recovery (MSCR) tests present that the WRO modified asphalt has desirable antirutting properties. The optimal preparation process of the WRO modifier preferred by orthogonal design is stirring 0.5 h at 260°C, and the mass ratio of WTCR and WCO is 6∶4. [ABSTRACT FROM AUTHOR]

Pyrolysis technology is receiving growing attention for managing postconsumer tire and plastic waste streams. Pyrolytic char is generated as a byproduct in the pyrolysis process and faces challenges regarding its stable and reliable reuse. The use of tire pyrolytic char (TPC) and plastic pyrolytic char (PPC) has recently gained interest in asphalt binder modification, which can be a feasible and attractive alternative for their utilization. The present study focused on a multifaceted investigation at three levels: (1) characterization of the pyrolytic chars (TPC and PPC), (2) characterization of asphalt binders modified with different dosages (0%, 5%, 10%, 15%, and 20%) of TPC and PPC focusing on conventional, rheological, microscopic, and thermochemical tests, and (3) mechanical characterization of asphalt mixtures fabricated with TPC- and PPC-modified binders in terms of rutting, moisture damage, and fatigue performance. Leachate toxicity was also evaluated to ensure that the use of TPC and PPC in asphalt mixtures is safe for the environment. Results showed that both TPC- and PPC-modified binders and mixtures showed better rutting resistance than the control binder and mixture up to 20% dosage. Fourier transform infrared (FTIR) spectroscopy showed that TPC and PPC interacted chemically with the base binder during modification. Leaching tests indicated that TPC and PPC could be safely used in asphalt mixtures for pavement construction. Comparing the fatigue and moisture damage results, it was found that the optimum performance was achieved at a 10% dosage of both TPC and PPC. This observation was consistent with fatigue tests on binders and asphalt mixtures. [ABSTRACT FROM AUTHOR]