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Article

Study on Rheological Properties of Waste Cooking Oil and Organic Montmorillonite Composite Recycled Asphalt

by
Cheng Xie
1,
Qunshan Ye
2,*,
Lingyi Fan
2,
Anqi Weng
2 and
Haobin Liu
1
1
Guangxi Beitou Transportation Maintenance Technology Group Co., Ltd., Nanning 530201, China
2
School of Traffic and Transportation Engineering, Changsha University of Science and Technology, Changsha 410114, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(10), 3149; https://doi.org/10.3390/buildings14103149
Submission received: 7 September 2024 / Revised: 29 September 2024 / Accepted: 30 September 2024 / Published: 2 October 2024
(This article belongs to the Special Issue Research on Advanced Materials in Road Engineering)
Browse Figures
Versions Notes

Abstract

:
Pre-treated waste cooking oil (WCO) and organic montmorillonite (OMMT) were employed for the recycling of aged asphalt, which resulted in the improvement of the design of WCO asphalt rejuvenators and the enhancement of high-temperature performance of WCO-recycled asphalt. The effect of the rejuvenator and the properties of recycled asphalt were evaluated by viscosity, dynamic shear rheometer (DSR), bending beam rheometer (BBR) and scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) tests. The results indicated that aged asphalt could be obviously softened and restored to the level of original asphalt by adding 6% WCO. However, the high-temperature properties of recycled asphalt would be declined by adding too large a dose of WCO rejuvenator. The high-temperature performance of recycled asphalt was significantly improved by the WCO-OMMT complex rejuvenator, and the viscosity and rutting factor of recycled asphalt were increased. Light components of aged asphalt could be supplemented by WCO of the complex rejuvenator. The volatilization of small molecules could be slowed down by the peel structure formed by OMMT and small molecules of the asphalt, which resulted in the proportion of small molecular substances (SMS) being increased by 4% and improvement of the colloidal structure of aged asphalt. The high-temperature and low-temperature performance of recycled asphalt can be improved concurrently by the combination of 6% WCO and 1% OMMT, and this was evidenced by the fact that the high-temperature and low-temperature PG were all upgraded by one level.

1. Introduction

Asphalt materials have been widely used in the construction of high-performance roads due to their excellent road performance [1]. To ensure driving safety and comfort, it is necessary to regularly maintain and repair the road surface, which will generate a large amount of waste asphalt mixtures. According to statistics, over 160 million tons of waste are generated annually on main highways alone [2]. The proper disposal and reuse of road waste has become a widely concerning issue for transportation [3] and environmental protection departments, and experts and scholars [4]. The appropriate treatment of gutter oil such as animal fat, waste cooking oil (WCO), and acidified oil is a problem faced by many countries around the world. The main components of gutter oil are fatty acids and triglycerides, and a large amount of waste oil damages water quality and affects ecological balance. Besides, WCO is a huge health risk if it goes back to the table [5]. The problem of reasonable disposal and full reuse of gutter oil urgently needs to be solved [6,7]. Regarding this issue, WCO had been used to recycle waste asphalt to achieve “dual waste utilization” [8], and it can ease the pressure of fossil energy depletion faced by countries around the world [9].
The relevant research results indicated that aged asphalt could be effectively softened by the abundant aromatic light components in WCO, depolymerizing large molecular aggregates in asphalt, significantly restoring the low-temperature performance of aged asphalt [10], with better aging resistance than original asphalt [11], verifying the feasibility of WCO as an asphalt rejuvenator [12]. The asphalt mixture prepared by composite modification of WCO and SBS has better anti-rutting performance and low-temperature crack resistance [13]. The physicochemical properties of WCO also affect the performance of its regenerated asphalt. Jain et al. found that the optimal dosage of WCO rejuvenator decreased from 7.03% to 5.73% after esterification treatment, and the diffusion of WCO in asphalt was also improved [14,15]. WCO-recycled asphalt with lower acid value (0.4–0.7 KOH/g) and viscosity (140–540 mm2/s) had better high- and low-temperature rheological properties [16]. However, excessive WCO content had adverse effects on the high-temperature performance of recycled asphalt [17,18], while montmorillonite (MMT) is a commonly used modifier to improve the high-temperature performance of asphalt [19]. However, the MMT weakens the low-temperature properties of asphalt. Related research results have shown that MMT-modified asphalt had better high-temperature stability, deformation resistance, and UV aging resistance than original asphalt [20,21,22]. Due to the intercalation effect of MMT with small molecules in asphalt and the barrier effect of montmorillonite on oxygen, modified asphalt has better resistance to thermal-oxidative aging [23]. Organic montmorillonite (OMMT) performed better in adhesion to asphalt than MMT and had a better modification effect [24,25]. In addition, OMMT improved the storage stability of its modified asphalt [26,27] and increased the compatibility between the modifier and asphalt [28].
In summary, few scholars have used OMMT to modify pretreated WCO to make composite rejuvenators, and the use of WCO as a raw material for rejuvenators could reduce its harmful effects on the environment and human beings. Besides, the low-temperature performance of asphalt reduced by OMMT could be improved by WCO [29]. Therefore, WCO was modified with OMMT in this study to enhance the high-temperature performance of recycled asphalt. The rheological properties and micro-rejuvenation mechanisms of the WCO-OMMT composite recycled asphalt were investigated, providing a reference for the optimization of WCO rejuvenator designs.

2. Materials and Methods

2.1. Raw Materials

2.1.1. Original Asphalt

The original asphalt (OA) used in this study was the 70# petroleum asphalt from Hunan Baoli Asphalt Co., Ltd. (JiangYin City, China), with its technical specifications presented in Table 1.

2.1.2. Waste Cooking Oil

The WCO provided by a recycling and recycled-catering waste oil enterprise in Shandong mainly contains alkanes, carboxylic acids, triglycerides, and fatty acids, with an average molecular weight of 890. Its moisture and impurity content was less than 1%; the performance indexes are shown in Table 2, and the physical morphology is shown in Figure 1. To improve the high- and low-temperature performance of recycled asphalt [14,15], a pretreatment of WCO was performed through an esterification reaction to reduce its acid in this study [37]. The pretreatment was carried out at a reaction temperature of 240 °C, a reaction time of 3 h, a molar ratio of glycerol to fatty acids of 1:1.1, and a stirring rate of 500 revolutions per minute. The acid value of the treated WCO was measured to be 2.52 mg KOH/g.

2.1.3. Organic Montmorillonite

The OMMT used in this paper was derived from Rongshui Ronglong Mining Co., Ltd. (Liuzhou, China), which was aggregated in the form of soil blocks or spherical particles, and its color was between white and light gray and showed the luster and smoothness of the soil. The OMMT performance index is shown in Table 3, and the physical morphology is shown in Figure 2.

2.1.4. Composite Rejuvenator

Following a review of pertinent literature, it was discovered that modified asphalt with a WCO to OMMT ratio of 1:1 produces the best results [42]. The proportion of WCO in recycled asphalt ranges from 2% to 10% [43]. Considering that this paper focuses on the rejuvenation of RA, the significantly increased polar macromolecules after OA aging. Therefore, the amount of OMMT is reduced and set to 0, 1%, and 2%.
Pre-treated WCOs with relative asphalt masses of 2%, 4%, 6%, and 8% were mixed by a shear apparatus and compounded with 0%, 1%, and 2% OMMT at 100 °C, 500 r/min, and 10 min. Twelve groups of WCO-OMMT composite asphalt rejuvenators were prepared, the naming of the regenerators is shown in Table 4. In this table, 6% W + 1% O refers to 6% WCO compound with 1% OMMT, while 6% W was the 6% WCO added by itself.

2.2. Test Methods

2.2.1. Preparation of Asphalt Samples

Following ASTM D2872 [44], an indoor asphalt simulation aging test was performed. The short-term aging asphalt was prepared using the rotary film oven test (RTFOT) method at a temperature of 163 °C for 85 min. It was then subjected to the pressure-aging vessel (PAV) at a temperature of 100 °C, a pressure of 2.1 MPa, and for 20 h to produce long-term aging asphalt (RA). Following being heated to a molten condition, the long-term aged asphalt was mixed with varying amounts of WCO-OMMT composite recycling agent. Then, the recycled asphalt was finished by shearing with a high-speed shear for 30 min at 135 ± 5 °C and 2000 r/min, and named according to Table 4.

2.2.2. Measurement of Brookfield Rotational Viscosity

The asphalt rotational viscosity test was conducted using a Brookfield rotational viscometer from the United States, with rotor number 27 and a test temperature of 135 °C.

2.2.3. Rheological Properties

Using a dynamic shear rheometer (DSR) according to regulations, the following tests were conducted on different recycled asphalts to evaluate their high-temperature performance: Temperature Sweep (TS) (rotor: 25 mm; gap: 1 mm; temperature: 4–82 °C; angular frequency: 10 rad/s; strain level: 6%), Frequency Sweep (FS) (rotor: 8 mm; gap: 2 mm; temperature: 5, 10, 15, 28, 40 and 52 °C; frequency: 0.016–16 Hz), and multiple stress creep recovery (MSCR) tests (rotor: 25 mm; gap: 1 mm; 1. Stresses: 0.1 kPa, cyclicality: 20; 2. Stresses:3.2 kPa, cyclicality:10). The low-temperature rheological properties of different asphalts at −12 °C and −18 °C were evaluated using a bending beam rheometer (BBR).

2.2.4. Microscopic Characterization

The Fourier Transform Infrared Spectrometer (Nicolet iS50) form Thermo Fisher Scientific Inc., Carlsbad, CA, USA was used to conduct infrared spectroscopy tests on matrix asphalt and WCO-OMMT recycled asphalt with different degrees of aging, with a wavelength range of 500–4000 cm−1.
The scanning electron microscopy was used to obtain the surface morphology of matrix asphalt, long-term aged asphalt, and WCO-OMMT recycled asphalt, with magnifications of 500× and 2000×.
Using Gel Permeation Chromatography (PL-GPC50) form Agilent Technologies, Inc., Santa Clara, CA, USA, tetrahydrofuran (THF) form TSE Industries (Shanghai) Co., Ltd., Shanghai, China with a concentration of 2 mg/mL was selected as the organic solvent to analyze the molecular weight and distribution characteristics of matrix asphalt and WCO-OMMT regenerated asphalt samples with different degrees of aging.

3. Results

3.1. Study on the Rheological Properties of Composite Reclaimed Asphalt

3.1.1. Viscosity

The viscosity of recycled asphalt can be effectively reduced by increasing WCO content, which is shown in Figure 3. This result was related to the fact that the light component in WCO significantly reduced the molecular interaction force and frictional resistance in RA [45]. Notably, the viscosity of the recycled asphalt with 6% WCO was closest to that of OA. Therefore, 6% could be considered as the optimal amount of WCO. The viscosity of the composite recycled asphalt increased with the addition of OMMT when WCO was combined with OMMT. This phenomenon might be related to the stable intercalated or exfoliated structure formed by OMMT [46]. Specifically, the viscosity of the composite recycled asphalt containing 6% WCO and 1% OMMT was most similar to that of OA. Thus, 6% W + 1% O could be regarded as the optimal amount of WCO-OMMT.
Viscous activation energy refers to the amount of energy required for a viscoelastic material to overcome internal viscous resistance during flow or deformation. This energy level indicates the degree of molecular activation when the material is heated [47]. A larger viscous activation energy indicates a greater temperature sensitivity of the material’s viscosity level [48]. The calculation procedure is illustrated in Equations (1) and (2). And the viscous activation energies of several asphalt are shown in Figure 4.
η ( T ) = K e E η R T
l g η ( T ) = l g K + E η 2.303 R T
In the equation, Eη represents the viscous activation energy, with units of J·mol−1; η(T) denotes the viscosity at temperature T, with units of Pa·s; K is a material constant; and R is the gas constant, with a value of 8.314 J·mol−1·K−1.
The viscous activation energy (Eη) in Figure 4 shows the same regularity as in Figure 3. This indicates a good correlation between viscosity and viscous flow activation energy in the WCO-OMMT recycled asphalt system. The Eη of recycled asphalt decreased with an increase in WCO content and rose with increasing OMMT content. This phenomenon could be associated with the dilution effect of WCO on polar macromolecules in RA reducing the intermolecular interaction forces and thus decreasing the energy required for the flow units to overcome the site barriers [49]. However, the adsorbability of OMMT towards small molecules in the asphalt and WCO led to an increase in macromolecules of recycled asphalt [50], which was the reason for the decrease in Eη of the composite recycled asphalt. Remarkably, the Eη of recycled asphalt for 6% W and 6% W + 1% O were closest to OA, which were considered as the optimum dosage of WCO and OMMT, respectively, in this paper.
The 6% W and 6% W + 1% O exhibited the best performance recovery for RA after combining the results of viscosity and viscous activation energy, and so the properties of the three groups of composite recycled asphalt at 6%W would be investigated primarily in the following sections.

3.1.2. Rutting Factor

Rutting is one of the main diseases of asphalt roads; driving safety and comfort are seriously affected by it, and the possibility of other pavement diseases also increases. A road with a higher rutting factor is more durable, capable of supporting heavier loads, and resistant to deformation [51]. The rutting factor curves for recycled asphalt with varying WCO and OMMT levels are displayed in Figure 5.
Figure 5 indicates that the rutting factors of different recycled asphalt decreased with the WCO percentage increasing, and increased with the OMMT content increasing. The rutting factor was closest to the OA level when the WCO component was 6%. However, RA would be extremely softened by 8% WCO, causing the rutting factor to be lower than OA. This could be attributed to an excessive amount of light components contributed from 8% WCO to RA, which caused an excess of viscous components in the recycled asphalt and weakened its ability to run at high temperatures. Therefore, 6% WCO was found to be the optimal dosage to restore the rutting factors of RA to OA levels. Figure 5b demonstrated that the resistance to rutting of recycled asphalt could be effectively improved by using OMMT, which was the function of intercalation structure [52] formed by OMMT and small molecules of asphalt and WCO.

3.1.3. High-Temperature Creep Recovery Rate

The percentage of form recovery that an asphalt sample can attain following stress removal is indicated by the creep recovery rate (R). A higher R-value denotes a material’s ability to withstand permanent deformation caused by repeated loads, hence indicating a stronger capacity for recovery. The creep recovery rates of various asphalts under varying stress and temperature conditions are shown in Figure 6.
Figure 6a demonstrates the negative correlation between the WCO content and temperature and the R of the rejuvenated asphalt. The R of the recycled asphalt was higher than the OA at the same temperature and stress level. The recycled asphalt almost completely lost its elastic properties when the WCO content was 8% under 3.2 kPa stress and 64 °C temperature. This indicated that the recovered asphalt’s elastic proportion was reduced under these circumstances, leading to permanent deformation under external loading. As a result, the structural stability and durability of the roadway can be seriously weakened by this permanent deformation. The R of composite recycled asphalt increased with the dosage of OMMT when WCO was combined with it, as shown in Figure 6b. Remarkably, the R of composite recycled asphalt with different dosages of OMMT and 6% WCO was higher than that of OA. This indicated that the elastic deformation ratio of aged asphalt was improved by OMMT efficiently. This enhancement can be attributed to the strong adhesive force that exists between OMMT and the molecules of asphalt [53], which caused the macromolecule content of composite recycled asphalt to increase so that the mobility in a variety of stress and temperature conditions of recycled asphalt decreased by it. Additionally, the recovered asphalt was shielded from creep damage to the elastic and load-resistant properties of the nano intercalation structure formed by OMMT [54]. As a result, the possibility of cracks in composite recycled asphalt was reduced and the actual service life was increased.

3.1.4. Performance Grade

(1)
High-temperature Performance Grade (PG)
The high-temperature PG of recycled asphalt exhibits a declining tendency when WCO content rises, as demonstrated in Table 5. Remarkably, the high-temperature PG of aged asphalt returned to the OA level when the WCO content hit 6%. However, the high-temperature PG of recycled asphalt for 8% W was weakened to below OA. This proved once again that the high-temperature performance of recycled asphalt could be adversely affected by 8%W. The addition of OMMT resulted in an increase in the high-temperature PG of the recovered asphalt after combining WCO and OMMT. According to this result, the high-temperature performance of recycled asphalt was effectively improved by OMMT. Additionally, the high-temperature grade of the recycled asphalt was shown to be elevated by one level at both 1% and 2% concentrations of OMMT in comparison to OA.
(2)
Low-temperature Performance Grade (PG)
The creep stiffness (S) and creep rate (m) of recycled asphalt with varying WCO and OMMT dosages are displayed in Figure 7 and were derived from the BBR test.
Figure 7 illustrates that further addition of OMMT increased the S and decreased the m of the rejuvenated asphalt, and the trends within WCO and OMMT regarding m and S were opposed. Table 6 displays the low-temperature PG of RA and various recycled asphalts, by the ASTM D7643-22 [55].
Table 6 indicates a positive correlation between the WCO content and the low-temperature PG of the recovered asphalt, demonstrating the enhancement of the resistance to low-temperature cracks and improvement of the stress relaxation property of the aged asphalt by adding WCO. The low-temperature PG reduced as the OMMT component grew in the composite recovered asphalt. Notably, the low-temperature PG started to decline when the OMMT dosage hit 2%. The composite recovered asphalt showed an adhesive and plasticizing effect from the sheet-like structure produced by OMMT. This resulted in a decrease in low-temperature crack resistance and an increase in the cohesion energy density of composite recovered asphalt. Consequently, the high- and low-temperature PG grades of the composite reclaimed asphalt would be raised one level by adding 6% W + 1% O, and the 6% W +1% O could be regarded as the most effective dose to recover the performance of RA. In particular, the low-temperature PG was the most critical factor in determining the optimal dosage of the WCO-OMMT composite rejuvenator.

3.2. Study on Micro-Rejuvenation Mechanism of Composite Recycled Asphalt

The samples used in this section of the micro-tests were original asphalt (OA), short-term aging original asphalt (OA-R), long-term aging original asphalt (RA), 6% W + 1% O composite recycled asphalt (WOA), and the corresponding short-term aging composite recycled asphalt (WOA-R) and long-term aging composite recycled asphalt (WOA-P).

3.2.1. Analysis of Fourier-Transform Infrared Spectroscopy Tests

Figure 8 illustrates the FTIR spectra of various asphalts and WCO-OMMT composite rejuvenator. Absorption peaks were observed at 2923 cm−1 and 2854 cm−1 for -CH3, at 1375 cm−1 and 1455 cm−1 for -CH2, and at 1600 cm−1 for the stretching vibrations of benzene ring-conjugated olefinic double bonds in RA, WOA, and WCO-OMMT from Figure 8a, as well as similar groups present in OA [56]. This indicated that the lighter components lost during the aging process of the asphalt could be supplied by the WCO in the composite rejuvenator. WOA showed a new SiO2 absorption peak at 1200 cm−1, and a comparison of the spectra of WCO-OMMT revealed that this peak came from the OMMT in the composite rejuvenator. Notably, the peak height of C=O of WCO-OMMT was higher than that of WOA. This could be related to the fact that the WCO-OMMT composite rejuvenator was fully dispersed into the RA and the concentration of C=O was reduced, resulting in a lower peak height of C=O in WOA. No additional absorption peaks were found in WOA when the functional group absorption peaks of RA, WCO-OMMT, and WOA were compared. This indicated that the addition of the WCO-OMMT rejuvenator to RA mostly produced a recovery effect through the physical mixing and the supply of lightweight components, instead of via a chemical reaction or the creation of new substances between the composite rejuvenator and RA. In both WOA-R and WOA-P, new C=O absorption peaks were detected at 1700 cm−1, and there was a substantial boost in the height of the S=O absorption peaks at 1030 cm−1 from Figure 8b. According to this, molecules with S and C oxidation reactions occurred in WOA as it aged [57]. Early in the aging process during which C=O and S=O creation was most concentrated, and as aging went on, the rate at which these two groups formed decreased [58]. The asphalt became more brittle and tough during this reaction process, performing better at high temperatures and performing worse at low ones.

3.2.2. Analysis of Scanning Electron Microscopy Tests

Figure 9 illustrates the SEM images of OA, RA, and WOA, with surface smoothness decreasing in the following order: OA, WOA, RA. There were almost no holes or fold structures on the surface of OA, but the RA had a wavy, folding appearance. The above phenomenon was due to poorer flow characteristics caused by a reduction in the number of light components and a decline in component compatibility following OA aging. Since no obvious folding or other structures were observed on the WOA surface at 500× magnification, the magnification was adjusted to 2000×. There were still some fold textures and surface depressions brought on by macromolecular aggregation on the surface of WOA in Figure 9c [59]. This indicated that RA could not be completely restored to OA levels by the composite rejuvenator. However, the surface smoothness of WOA was much better than that of RA, showing that the composite rejuvenator had a positive rejuvenation impact and the flow characteristics of RA could be significantly improved by it.

3.2.3. Analysis of Gel Permeation Chromatography Tests

Figure 10 illustrates the molecular weight distribution of different asphalts. The addition of the composite rejuvenator resulted in an effective dilution by its WCO, rich in lightweight components, and reduced the macromolecular aggregation phenomenon of RA [60]. Furthermore, the viscosity and rutting factor decreased, the small molecular substances (SMS) increased by 4%, and the comparison of the molecular weight distribution of OA and WOA revealed that the large molecular substances (LMS) in WOA was 4.1% higher than in OA, indicating that the high-temperature performance of WOA was improved over OA. The proportion of SMS of WOA was reduced by 5.8%, while the proportions of LMS and medium molecular substances (MMS) were increased by 1.5% and 4.3%, respectively, after RTFO and PAV. Additionally, there was lower SMS content and higher LMS content in WOA-P compared to RA, indicating that the high-temperature performance of WOA was further improved after aging, but the low-temperature performance was further degraded. The reduction in SMS content in WOA was attributed to the volatilization of light components of asphalt and WCO at high temperatures and the absorption of small molecules in OA and WCO by the lamellar structure formed by OMMT. To quantitatively analyze the magnitude of changes in the molecular weights of different asphalts after aging, the data in Figure 10 were processed and the magnitude of changes in the molecular weights were summarized in Table 7.
The variation of SMS in OA and WOA mainly occurs in RTFO, shown in Table 7, which was the function of the higher test temperature of the RTFO compared to PAV, during which SMS was more easily lost. Both the reducing range in SMS ratio and the increasing range in LMS ratio of WOA were reduced by 0.4% and 1.1% after supplementing with the composite rejuvenator, respectively, and the percentage of MMS increased by 1.5%, compared to OA. This was due to the delaminated structure composed of OMMT and small molecular substances [61], which obstructed the escape of small molecules from the asphalt, slowed the rate of external oxygen ingress into the asphalt, and enhanced the aging resistance of WOA. Additionally, most of the free fatty acids and small molecules with poor thermal stability were removed from the rejuvenator after pretreatment, resulting in a more stable and effective complement of light components to RA and the enhancement of the aging resistance of WOA.
For further quantitative analysis of the trends in molecular weight changes in different asphalts, Figure 11 presents the number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (PDI) of asphalts at various aging levels, and the process of calculating PDI is shown in Equation (3). A higher content of macromolecules in the asphalt results in greater Mn and Mw values [62], while an increased PDI indicates a more dispersed molecular distribution within the asphalt.
P D I = M w M n
In the equation, Mw represents the weight-average molecular weight, with units of g/mol; Mn denotes the number for average molecular weight, with units of g/mol; PDI represents the polydispersity index of asphalt.
Figure 11 displays the Mn, Mw, and PDI of several asphalts. There was a growth of Mn, Mw, and PDI of OA and WOA during aging, demonstrating that the molecular dispersion and macromolecule content of asphalts were increased, and implying that the low-temperature performance of asphalt was worsened with aging. The Mn and Mw values of WOA were revealed to be greater than those of OA at all stages, indicating that the content of macromolecular substances in WOA was higher than in OA, leading to better high-temperature performance. This corresponds with the conclusion of the asphalt rheological tests discussed earlier. Taking the growth rate in Mn and Mw from Figure 11a as variables, the superior short-term aging resistance of WOA over OA was explained by the intercalation structure formed by OMMT, which slowed down the escape of small molecules, and this result was further supported by Figure 11b. The molecular weight dispersion of WOA in the unaged to RTFO segment changed by a much smaller magnitude, suggesting that WOA was more stable in thermo-oxidative aging environments. A positive correlation between the high-temperature performance of asphalt and the PDI was demonstrated by related research. The PDI of the composite recycled asphalt was larger than that of the OA at each stage in Figure 11b, indicating that the high-temperature performance of recycled asphalt could be effectively improved by the WCO-OMMT rejuvenator.

4. Conclusions

(1)
Aged asphalt can be effectively softened by WCO. The enhancement of low-temperature properties and decrease in high-temperature properties occur on recycled asphalt as the WCO level rises. However, the high-temperature grade of recycled asphalt will fall below the level of the OA by 8% WCO.
(2)
The high-temperature performance of recycled asphalt could be improved by the addition of OMMT, but the low-temperature property of recycled asphalt would be reduced by 2% OMMT content. The best recovery effect was achieved when the WCO-OMMT content was 6% + 1%. Composite recycled asphalt had higher high-temperature and low-temperature PG grades than OA and performed with better short-term aging resistance than OA after adding OMMT.
(3)
The colloidal structure of aged asphalt was improved by the supplementing function of the light component and the physical dilution of the WCO-OMMT rejuvenator; in the process of rejuvenation of the asphalt surface, fold structures were reduced and the relative content of small molecules increased, and there was no production of new substances.
(4)
According to the results of this paper, the WCO-OMMT rejuvenator developed in this study may be applied to the environment with higher mixing temperature when rejuvenating aged asphalt in actual construction, and the prepared rejuvenated asphalt can be used in the roadway with heavier traffic loads.

5. Future Research Interests

This paper discusses the rheological property evolution law and regeneration mechanism of WCO-OMMT composite recycled asphalt under different WCO and OMMT dosages. Based on the findings of this paper, there are aspects of this work that need to be improved. This paper did not investigate the effect of mixing WCO with different acid values and OMMT on the regeneration of aged asphalt, and future research in this area should be improved. The performance of WCO-OMMT recycled asphalt mixtures was not investigated in this paper, and future research will be conducted on the performance of WCO-OMMT recycled asphalt mixtures in terms of high-temperature stability, resistance to water damage, etc.

Author Contributions

Conceptualization, Q.Y.; Methodology, C.X. and Q.Y.; Software, L.F.; Validation, C.X. and L.F.; Formal analysis, L.F.; Investigation, A.W.; Resources, Q.Y. and H.L.; Data curation, H.L.; Writing—original draft, C.X. and A.W.; Writing—review and editing, C.X. and A.W.; Visualization, H.L.; Supervision, Q.Y.; Project administration, Q.Y.; Funding acquisition, Q.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (No. 52378437) and Ministry of Transport of People’s Republic of China (No. 2020-MS1-005).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

Authors Cheng Xie and Haobin Liu were employed by the company Guangxi Beitou Transportation Maintenance Technology Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Buildings 14 03149 g001
Figure 1. WCO.
Figure 1. WCO.
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Figure 2. OMMT.
Figure 2. OMMT.
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Figure 3. Different Asphalts’ Brookfield Viscosities at 135 °C.
Figure 3. Different Asphalts’ Brookfield Viscosities at 135 °C.
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Figure 4. Different Asphalts’ viscous activation energy.
Figure 4. Different Asphalts’ viscous activation energy.
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Figure 5. (a) Rutting factor of WCO-recycled asphalt; (b) rutting factor of composite recycled asphalt.
Figure 5. (a) Rutting factor of WCO-recycled asphalt; (b) rutting factor of composite recycled asphalt.
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Figure 6. (a) The R-value of WCO-recycled asphalt; (b) the R-value of composite recycled asphalt.
Figure 6. (a) The R-value of WCO-recycled asphalt; (b) the R-value of composite recycled asphalt.
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Figure 7. (a) The S-value of WCO-recycled asphalt; (b) the m-value of WCO-recycled asphalt; (c) the S-value of composite recycled asphalt; (d) the m-value of composite recycled asphalt.
Figure 7. (a) The S-value of WCO-recycled asphalt; (b) the m-value of WCO-recycled asphalt; (c) the S-value of composite recycled asphalt; (d) the m-value of composite recycled asphalt.
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Figure 8. (a) FTIR spectra of different functional groups; (b) FTIR spectra of WOA with varying degrees of aging.
Figure 8. (a) FTIR spectra of different functional groups; (b) FTIR spectra of WOA with varying degrees of aging.
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Figure 9. (a) The SEM image of OA; (b) The SEM image of RA; (c) The SEM image of WOA.
Figure 9. (a) The SEM image of OA; (b) The SEM image of RA; (c) The SEM image of WOA.
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Figure 10. The molecular weight distribution of different asphalt.
Figure 10. The molecular weight distribution of different asphalt.
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Figure 11. (a) Average molecular weight of different asphalts with diverse degrees of aging; (b) PDIs of different asphalt with diverse degrees of aging.
Figure 11. (a) Average molecular weight of different asphalts with diverse degrees of aging; (b) PDIs of different asphalt with diverse degrees of aging.
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Table 1. Technical indexes of 70 # matrix Asphalt.
Table 1. Technical indexes of 70 # matrix Asphalt.
Technical IndexesRequirementsTest ResultsTest Specifications
Penetration at 25 °C (0.1 mm)60–7065ASTM D5 [30]
Softening point (°C)≥4650.0ASTM D36 [31]
Ductility at 15 °C (cm)≥25>100ASTM D113 [32]
Viscosity at 135 °C (Pa·s)-611.9ASTM D4402 [33]
Flash point (°C)≥260290ASTM D92 [34]
Solubility (%)≥99.599.90ASTM D2042-22 [35]
Density (g/cm3)-1.036ASTM D70 [36]
Table 2. Technical indexes of WCO.
Table 2. Technical indexes of WCO.
Technical IndexesTest ResultsTest Specifications
Density at 15 °C (g/cm3)0.91ASTM D1298 [38]
Viscosity at 60 °C (mPa·s)19ASTM D445 [39]
Acid (mgKOH/g)65.28ASTM D974 [40]
Iodine value (g/100 g)131.13ASTM D5558 [41]
ColorBlackish brown-
Table 3. Technical indexes of OMMT.
Table 3. Technical indexes of OMMT.
Technical IndexesTechnical Indicators
AppearanceOff-white powder
Diameter/thickness ratio200
Stack thickness nm≤25
Montmorillonite content96–98%
Dry powder particle size200 mesh
Moisture content %≤3
Apparent density, g/cm30.45
Table 4. Names of compound rejuvenators.
Table 4. Names of compound rejuvenators.
Name of Rejuvenator SampleDosage of WCODosage of OMMT
2%W2%0
4%W4%0
6%W6%0
8%W8%0
2%W + 1%O2%1%
4%W + 1%O4%1%
6%W + 1%O6%1%
8%W + 1%O8%1%
2%W + 2%O2%2%
4%W + 2%O4%2%
6%W + 2%O6%2%
8%W + 2%O8%2%
Table 5. The high-temperature PG of different asphalt.
Table 5. The high-temperature PG of different asphalt.
Type of Asphalt|G*|/sinδ = 1.0 kPa
Temperature (°C)		|G*|/sinδ = 2.2 kPa
Temperature (°C)		PG Temperature (°C)PG
OA70.1864.1164.11PG64
2%W80.9079.0579.05PG76
4%W76.7375.3175.31PG70
6%W70.5066.2566.25PG64
8%W65.2163.2163.21PG58
6%W + 1%O72.1470.3670.36PG70
6%W + 2%O74.5873.5973.59PG70
Table 6. The Low-temperature PG of different asphalts.
Table 6. The Low-temperature PG of different asphalts.
Type of AsphaltPG
RAP-22
2%WP-22
4%WP-28
6%WP-28
8%WP-28
6%W + 1%OP-28
6%W + 2%OP-22
Table 7. The magnitude of change in molecular weight of different asphalt after aging.
Table 7. The magnitude of change in molecular weight of different asphalt after aging.
Type of AsphaltDegree of AgingSMS (%)MMS (%)LMS (%)
OARTFO−5.5−1.0+4.4
PAV−0.7−0.3+1.0
Total−6.2−1.3+5.4
WOARTFO−4.3+0.7+3.6
PAV−1.5+0.8+0.7
Total−5.8+1.5+4.3
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Xie, C.; Ye, Q.; Fan, L.; Weng, A.; Liu, H. Study on Rheological Properties of Waste Cooking Oil and Organic Montmorillonite Composite Recycled Asphalt. Buildings 2024, 14, 3149. https://doi.org/10.3390/buildings14103149

AMA Style

Xie C, Ye Q, Fan L, Weng A, Liu H. Study on Rheological Properties of Waste Cooking Oil and Organic Montmorillonite Composite Recycled Asphalt. Buildings. 2024; 14(10):3149. https://doi.org/10.3390/buildings14103149

Chicago/Turabian Style

Xie, Cheng, Qunshan Ye, Lingyi Fan, Anqi Weng, and Haobin Liu. 2024. "Study on Rheological Properties of Waste Cooking Oil and Organic Montmorillonite Composite Recycled Asphalt" Buildings 14, no. 10: 3149. https://doi.org/10.3390/buildings14103149

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