Surface Free Energy Method Research Articles

Assessing the influence of nano graphene oxide application in mitigating the adverse effects of runoff pH on the moisture susceptibility of asphalt concretes

The specifications of runoff entered the pavement has an essential role in the severity of moisture damage of asphalt concretes. Changing the pH of runoff has a negative impact on moisture damage and intensifies this damage in asphalt concretes. Accordingly, in this study, the impact of nanographene oxide (NGO) as a contaminant adsorbent and bitumen modified to decrease the destructive impacts of acidity changes in runoff has been investigated. For this purpose, limestone and siliceous aggregates, PG 64–16 bitumen, and NGO in two different contents (0.3 % and 0.5 % of the weight of bitumen) were utilized. To asses the strength of asphalt concretes with different runoff pH conditions, hydrochloric acid and sodium oxide were used to simulate acidic and basic runoffs, respectively. The indirect tensile strength (ITS) of asphalt concretes in different environmental states was tested to compare the severity of moisture sensitivity. Moreover, the surface free energy (SFE) elements of bitumen and aggregates were calculated utilizing the Wilhelmy Plate (WP) and the Universal Sorption Device (USD), respectively. The parameters of SFE theory were used to assess the mechanisms of water damage potential. The SFE results showed that NGO decreased the debonding energy (DE) of the mixtures. Changes in DE in neutral environments were minor, but with the polarization of environmental conditions, especially in basic states, these changes intensified. The application of NGO improved the total bitumen SFE, which reduced the possibility of moisture sensitivity as a cohesive failure. The results of mechanical methods indicated that the use of NGO in specimens with limestone and siliceous aggregate increased the indirect tensile strength ratio (TSR) in moisture conditions with different degrees of acidity. The mechanical experiment results also confirmed the SFE method's results that the effect of using NGO on increasing the TSR index at pH equal to 7 was minor, and it was intensified in acidic and basic waters.

The effect of runoff acidity on fatigue cracking of hot mix asphalt using thermodynamic concepts

This study examined the fatigue performance of hot mix asphalt (HMA) under the influence of runoffs entering the pavement with different acidity degrees. Based on the fatigue test results, changing the runoff acidity and increasing the temperature decreased the number of cycles leading to HMA fracture (fatigue life) and accelerated the damage. The results of the surface free energy (SFE) method were aligned with the fatigue test results, indicating that changing the runoff acidity increased the bitumen-water adhesion SFE, aggregate-water adhesion SFE, and bitumen-aggregate debonding SFE. These changes diminished the fatigue cracking resistance of HMA. According to the Pull-Off test results, altering the runoff acidity and increasing the temperature reduced the adhesion and cohesion strength. According to the two principal factors in fatigue cracking (fracture adhesion and cohesion), the reduced fatigue life of the samples due to variations in the runoff acidity and temperature increase was acceptable according to the SFE and Pull-Off test results. The independent samples t test revealed that changing the runoff acidity led to a significant decline in the asphalt samples' performance parameters compared to neutral conditions.

Moisture damage resistance of pyro-oil modified bitumen with hydrated lime using surface free energy approach

Moisture damage (MD) in bituminous mixtures occurs due to the loss of cohesion in the bitumen or adhesion between the binder and aggregates. The existence of moisture may influence the bonding between aggregates and bitumen, which may affect the moisture susceptibility of the bituminous mix. Therefore, there is a need to understand the bonding-debonding properties and the moisture susceptibility of binders and mixes, at the material selection stage. Surface free energy (SFE) method is one of the proven techniques to quantify the moisture susceptibility of bituminous mixtures, by using contact angle (CA) determination of the component materials of the mix. This study aimed to evaluate the effect of hydrated lime (HL) on the moisture susceptibility of bituminous mixtures, with control (VG30) bitumen and pyro-oil modified bitumen (POMB) having different percentages of pyro oil, using the SFE approach. Also, the study compared the SFE characteristics of VG30 and POMB with and without the optimum content of HL. POMB binders were prepared by the addition of high-density polyethylene (HDPE) pyro oil in percentages of 1, 3, and 5% in a control bitumen. HL was added as 20%, 25%, and 30% by weight of bitumen in VG30 and POMB bitumen. The aggregates used in the study were limestone, basalt, gravel, and their SFE components were directly considered from the literature. The sessile drop method was used to measure the CA of bitumen and, in turn, determine the various SFE parameters using Van Oss–Chaudhury–Good theory. The moisture susceptibility of mixtures with and without HL was evaluated and compared. From the results, the MD resistance of the bituminous mixtures with modified and unmodified bitumen was found to be increased after the optimum of HL, depending upon the type of aggregates used. Basalt has a 27.41%, 23.38%, and 10.48% greater energy ratio (ER) with POMB1/25, POMB3/25, and POMB5/30, respectively, than VG30/30, the highest ER in modified base bitumen. This indicates that HDPE pyro-oil treatment improves MD resistance for basalt. Whereas for limestone and gravel, VG30/30 gives a maximum value of ER as compared to any other combination of HL modified POMB. The ER values would assist highway agencies in selecting the most compatible binder–aggregate combinations.

Analysis of performance parameters based on surface free energy to evaluate moisture susceptibility of asphalt mixtures modified with calcined marl dust

ABSTRACT This study investigates the impact of calcined marl dust (CMD) on moisture susceptibility in asphalt mixtures with limestone and granite aggregates. The surface free energy (SFE) method and Hamburg wheel tracking test were used to assess this influence. Bitumen was mixed with various CMD percentages (0%, 10%, 25%, 40%) to analyze adhesion work, debonding work, and wettability. Results were utilized for energy ratios (ER1 and ER2) to gauge moisture susceptibility, while rut depth ratio (RDR) analysis was also conducted for these mixtures. The study found that higher aggregate total SFE correlated with decreased ER1 and ER2 values, showing strong correlation (R2 of 0.7974 for ER1 and 0.6572 for ER2) with RDR. At the optimal CMD content of 25%, the modified asphalt mix with limestone aggregate showed a 35% improvement in ER1 and a 21.6% enhancement in ER2, signifying improved moisture resistance.

Interfacial adhesion between recycled aggregate and asphalt mastic filled with recycled concrete powder

Recycled aggregate (RA) and recycled concrete powder (RCP) hold significant potential as environmentally sustainable raw materials for asphalt mixtures. In this study, a comprehensive investigation was conducted on the bonding properties between RA and RCP-filled asphalt mastic (RCPAM). This investigation utilized an image processing-assisted modified water boiling test, binder bond strength (BBS) tests, and the surface free energy (SFE) method. The results indicate that the boiling water test method, even with the assistance of 2D image processing analysis, cannot adequately evaluate the adhesive characteristics of the RA-RCPAM interface. This limitation could be attributed to the relatively small number of samples tested and the significant variation in surface properties of RA. Increasing both the filler-to-asphalt (F/A) ratio and RCP replacement ratio adversely affected the interfacial bond strength of the RA-RCPAM interface. On the other hand, an increase in RA surface roughness contributed to a higher bond strength. Based on the experimental results, a best-fit multivariate mixed model was proposed to predict the interfacial bond strength between RCP-filled asphalt mastic and recycled aggregate within a given range of RCP replacement ratio, surface roughness, and filler-to-asphalt (F/A) ratios. The analysis of SFE suggested that moisture damage to RCPAM was caused by both cohesive and adhesive failure. Additionally, the minimal impact of adhesion work in wet condition with increasing RCP content suggested that adhesion failure energy was only marginally affected by the inclusion of RCP, even in the presence of moisture. These findings are expected to enhance the understanding of interfacial adhesion characteristics and moisture susceptibility of the RA-RCPAM interface.

Mechanical, thermodynamical, and microstructural characterization of adhesion evolution in asphalt binder-aggregate interface subjected to calcium chloride deicer

Frigid weather and freezing road conditions in cold regions result in reduced pavement surface friction, compromised vehicle maneuverability, leading to deteriorated transportation safety. Given their effectiveness and low cost, using chloride-based deicing agents such as CaCl2 has become a standard winter maintenance strategy for many highway agencies. However, coupled with freeze–thaw (F-T) cycles, CaCl2 can adversely affect the durability of asphalt pavements and cause complex distresses such as moisture-induced damage, among others. Despite this fact, the mechanisms and the extent of the damage made to the asphalt binder-aggregate interface due to use of chloride salts are not well-understood. This study was undertaken to characterize the mechanisms by which different eutectic concentrations of aqueous CaCl2 solutions and F-T cycles affect the adhesion between asphalt binder and different aggregates through a multi-scale characterization and testing program. Given the rise in use of polymer-modified asphalt binder a PG 64–34 asphalt binder and aggregates of granite, quartzite, and limestone mineralogies were evaluated. More specifically, pull-off strength of the aggregate-binder systems subjected to different aqueous concentrations of CaCl2 and F-T cycles were determined. In addition, surface free energy method as a thermodynamic-based approach was employed to determine the effect of salt concentration on the adhesion and debonding energies, and the moisture-induced damage potential of the binder-aggregate interfaces. Furthermore, atomic force microscopy was employed to evaluate the effect of salt concentration and F-T cycles on surface morphology, nanostructure, and adhesion of the asphalt binder. The applied multi-scale characterization provided invaluable information about the physio-chemical phenomena responsible for the accelerated damage in asphalt binder-aggregate interface when subjected to different aqueous concentrations of CaCl2. Gaining an accurate understanding of the damage mechanism is necessary for developing new materials and methods for combatting salt-accelerated moisture-induced damage in cold regions as a result of winter maintenance operations.

The investigation of surface free energy components and moisture sensitivity damage of asphalt mixes modified with carbon black using the sessile drop method

Asphalt pavement is vulnerable to moisture damage when water infiltrates the asphalt-aggregate interface and weakens their bond. To prevent this problem, researchers have explored the use of additives to increase resistance against moisture damage. The moisture sensitivity of asphalt mixtures can be assessed by measuring their basic properties related to the mechanism of moisture damage. One effective approach to this is using the surface free energy method, which calculates bond energies between different materials’ surfaces and identifies the most appropriate combination of asphalt and aggregate. High cohesion or adhesion bonding is crucial for the proper performance of asphalt mixtures, such as moisture damage resistance. This study aimed to investigate the effect of carbon black additive on moisture damage resistance using surface free energy methods, comparing results with the Tensile Strength Ratio (TSR) test. Modified asphalts containing 4, 8, 12, and 16% carbon black were tested, with natural base asphalt as a control sample. The study used surface free energy theory to determine moisture sensitivity parameters of asphalt mixtures by obtaining surface free energy components of the raw materials and testing the ratio of tensile strength. Results showed that adding 8% carbon black to the asphalt mixture improved moisture sensitivity, and increasing additive content up to 16% reduced it but still provided better results than samples made with pure asphalt. The study concluded that the surface free energy method can determine the suitable combination of asphalt and aggregate materials for resistance against moisture damage.

Assessing the effect of short and long-term aging on moisture damage of hot mix asphalt using two different methods

ABSTRACT The effects of short-term aging (STA) and long-term aging (LTA) on moisture damage mechanisms were investigated using mechanical and thermodynamic methods. PG58-22 and PG64-16 asphalt binders modified with Dodecylamine (DA) and Wetfix (WT) additives and limestone and granite aggregates were used. The moisture sensitivity was assessed using the indirect tensile strength (ITS) test via the modified Lottman test and the surface free energy (SFE) method. As asphalt binder becomes harder due to aging, ITS values increase in dry conditions. However, ITS values decrease due to the texture and mineralogical properties of aggregates, the reduction of mastic cohesion and asphalt binder-aggregate adhesion because of water infiltration and weakening of the mixture in wet conditions. The tensile strength ratio (TSR) test revealed that TSR values decrease due to aging. The cohesion free energy of the PG64-16 asphalt binder increased by 8.9% in the STA state and by 29.8% in the LTA state compared to the unaged state. This rise in PG58-22 was about the same as that in PG64-16. Asphalt binder aging in all the samples reduced the adhesion energy. These variations indicated that aging reduces the probability of cohesion failure and increases the probability of adhesion failure.

Preparation of Wax-Based Warm Mixture Additives from Waste Polypropylene (PP) Plastic and Their Effects on the Properties of Modified Asphalt

The production of high-performance, low-cost warm mix additives (WMa) for matrix asphalt remains a challenge. The pyrolysis method was employed to prepare wax-based WMa using waste polypropylene plastic (WPP) as the raw material in this study. Penetration, softening point, ductility, rotational viscosity, and dynamic shear rheological tests were performed to determine the physical and rheological properties of the modified asphalt. The adhesion properties were characterized using the surface free energy (SFE) method. We proved that the pyrolysis temperature and pressure play a synergistic role in the production of wax-based WMa from WPPs. The product prepared at 380 °C and 1.0 MPa (380-1.0) can improve the penetration of matrix asphalt by 61% and reduce the viscosity (135 °C) of matrix asphalt by 48.6%. Furthermore, the modified asphalt shows favorable elasticity, rutting resistance, and adhesion properties; thus, it serves as a promising WMa for asphalt binders.

Presentation of thermodynamic and dynamic modules methods to investigate the effect of nano hydrated lime on moisture damage of stone matrix asphalt

ABSTRACT Stone matrix asphalt (SMA) mixtures are the most resistant type of asphalt mixtures today in which the aggregate skeleton bears the bulk load. In this study, the effect of nano hydrated lime (NHL) on the moisture sensitivity of SMA mixtures was investigated. To examine the effect of NHL, the surface free energy (SFE) method and the dynamic modulus (DM) test were applied under wet and dry conditions on mixtures constructed with limestone and granite aggregates. The SFE results indicated that the granite aggregates had a greater polar component and limestone aggregates had a higher non-polar component which shows their higher moisture resistance. The adhesion free energy (AFE) results showed that the adhesion of base bitumen and limestone aggregate was higher, and using NHL improved the AFE values. The results of DM tests indicated that as the load cycles raised, the wet to dry DM ratio reduced and using NHL increased this ratio. The reduction slope of the DM ratio in samples constructed with granite aggregates showed a faster trend compared to limestone aggregates, and using NHL improved the resistance of SMA mixtures constructed with granite aggregates to moisture more than limestone aggregates.

Influence of novel long-chain active composite rejuvenators on interfacial adhesion between aged SBS modified asphalt and aggregate

In this study, the novel long-chain active composite rejuvenators (NLCACRs) were composed of long-chain active rejuvenators (LCARs) and aromatic hydrocarbon oil (ArO). Surface free energy method (SFE method), boiling water test method (BWT method) and related parameters were used to evaluate the effect of NLCACRs on interfacial adhesion between aged SBS modified asphalt (ASBS-MA) and granite, and preliminarily predict the moisture sensitivity of asphalt-aggregate system. The results indicated that NLCACRs could increase the surface free energy of ASBS-MA, and the increased range varied with the composition and structure of NLCACRs. The NLCACRs could not only supplement the light components lost by asphalt during aging, but also reconstruct the damaged structure of aged SBS, so they were more effective for the recovery of cohesion work of ASBS-MA. NLCACRs could significantly increase the interfacial adhesion between ASBS-MA and acid granite, and decrease the moisture sensitivity of rejuvenated SBS modified asphalt (RSBS-MA)-granite system. And the results of the BWT method indicated that long-term aging decreased the adhesion grade between SBS modified asphalt and granite from G4 to G2. NLCACRs could restore the adhesion grade of ASBS-MA and granite to the level of original SBS modified asphalt. The comprehensive analysis of the influence of NLCACRs on the interfacial adhesion between ASBS-MA and aggregate showed that the theoretical law (SFE method) was consistent with that of the actual (BWT method). This study could help to explore the influence of NLCACRs on the moisture stability of aged SBS modified asphalt mixture and provide the theoretical basis for its application in practical engineering.

Rejuvenation effect of waste cooking oil on the adhesion characteristics of aged asphalt to aggregates

There are many studies on the rejuvenation of waste cooking oil (WCO) on reclaimed asphalt pavement (RAP), focusing mostly on mechanical properties of asphalt mixture while rarely on the adhesion of asphalt to aggregates. In this study, the surface free energy (SFE) method and molecular dynamics (MD) simulation were used to study the effect of WCO on the adhesion of asphalt and aggregate from the macroscopic and nanoscopic levels, respectively. Four types of aggregates (basalt, limestone, granite, and sandstone) and minerals (SiO2, MgO, CaCO3, and CaO) representing aggregates were selected. The SFE of asphalt and aggregate was obtained, then the adhesion work, debonding work, and the energy ratio (ER) were calculated to evaluate moisture susceptibility. Then the asphalt-mineral interface model was built and the adhesion work under dry and wet conditions and interaction energy were analyzed. The results show that from the SFE perspective, WCO can improve the SFE parameters of aged asphalt and its adhesion work with aggregates, whereas the rejuvenation effect decreases with the increase of WCO content. The aging process will increase the debonding work of the interface, resulting in aged asphalt easier stripping from the aggregate. The resistance to moisture damage ranks as basalt > limestone > granite > sandstone. From the SFE perspective, the van der Waals interaction contributes the main component of adhesion work of asphalt with SiO2, MgO, and CaO, while the electrostatic interaction is the main component with CaCO3. Under the wet condition, the adhesion work of the asphalt-SiO2 interface is affected to the smallest extent due to the minimal interaction between SiO2 and water molecules. Combining with the results of the SFE method and MD simulation, WCO plays a rejuvenation effect, improving the resistance to moisture damage. This study can guide the selection of aggregates to make WCO recycled asphalt mixture with sound moisture resistance.

Evaluation of the adhesion property and moisture stability of rubber modified asphalt mixture incorporating waste steel slag

The present study was conducted to recycle waste tire rubber and steel slag (SS) in asphalt pavement and investigates the moisture stability of asphalt mixtures incorporating these solid wastes. To this end, two types of aggregates (SS and diabase), three kinds of SS content and multiple freeze–thaw cycles were considered and three kinds of adhesion assessment methods: pull-out test and surface free energy (SFE) method, and freeze–thaw splitting test were performed. Three corresponding adhesion evaluation indicators like adhesion strength, SFE characteristics, and tensile strength ratio were obtained and six energy parameters were introduced to characterize moisture susceptibility of asphalt mixture. To explore the relations between the SFE parameters and the adhesion evaluation indicators, a grey correlation analysis method was adopted. Asphalt mixtures with high consumption of SS obtained a better moisture resistance because SS has a superior adhesion strength and higher SFE components than diabase aggregate. Stripping energy increase was found to be the main failure mode of the asphalt rubber-SS aggregate system. SFE method provides a comprehensive and accurate evaluation of adhesion property of loose asphalt rubber–SS aggregate system and moisture stability of compacted asphalt mixtures.

Moisture-induced damage potential of asphalt mixes containing polyphosphoric acid and antistripping agent

This study examines the effects of PPA and ASA on interfacial energies and moisture-induced damage potential of mixes using a Surface Free Energy (SFE) method. The SFE components of binder blends containing different amounts of PPA and ASA and aggregates were determined using Dynamic Wilhelmy Plate and Universal Sorption Device-based tests, respectively. Based on the measured SFE components and interfacial energy, it was found that using PPA with or without ASA does not affect cohesive bond of binder. However, depending on aggregate type, PPA may improve adhesive bond. Also, using an amine-based ASA does not improve the resistance to moisture-induced damage of binders or mixes containing PPA. Therefore, using an amine-based ASA with PPA-modified asphalt binder is not recommended. Among different PPA amounts considered, using 1.5% PPA with and without ASA was found to be the most effective concentration in improving the adhesive bond and wettability of binders with aggregates.

Correlation between bond strength and surface free energy parameters of asphalt binder-aggregate system

The bonding potential is one of the imperative parameters of the asphalt binder-aggregate compositions and significantly affects the resistance of the asphalt mixtures against moisture damages. The properties of asphalt binder and aggregate have considerable effects on the moisture sensitivity and bond strength of the asphalt binder-aggregate composition. In the present study, the effects of the aging and stiffness of the asphalt binder, aggregate type, and their interactions on the bond strength and moisture susceptibility of the asphalt binder-aggregate systems were evaluated. The binder bond strength (BBS) test with a new approach of analyzing the failure pattern and the surface free energy (SFE) method were carried out to characterize the bond strength and bond energy parameters. The relationship between the bond strength, failure pattern in the BBS test, and SFE properties were presented. The results indicated strong and meaningful correlations between the SFE properties, failure patterns, and bond strength under dry and wet conditions. The meaningful and good correlations between the failure patterns and bond energies under dry and wet conditions demonstrate that the changes in the adhesive and cohesive failures in the asphalt binder-aggregate compositions highly depend on the SFE properties. Besides, according to SFE results and the failure patterns under dry and wet conditions, new energy parameters were introduced to evaluate the bond strength and moisture sensitivity.

Establishing threshold value of surface free energy and binder bond strength parameters for basaltic asphalt mixes

The present work was undertaken to establish the possible threshold values for Surface Free Energy (SFE) and Binder Bond Strength (BBS) methods for screening asphalt-aggregate systems to ensure excellent moisture damage resistance. A total of sixteen combinations of asphalt-aggregate systems consisted of warm mix additives (WMA) and recycled asphalt pavement (RAP) and WMA-RAP combinations. In addition, the study evaluates the effects of RAP, WMA, and WMA-RAP on compatibility ratio (CR), bitumen bond strength ratio (BSR), and indirect tensile strength ratio (TSR) for different combinations of aggregate-asphalt system. The results showed that compatibility and bond strength between asphalt binders and aggregates deteriorated with the addition of RAP and WMA additives. Threshold criteria for CR and BSR values were identified as 4.80 and 0.90, respectively, with reasonably good accuracy of 90% for the SFE method and 75% for the BBS method. The threshold values, along with the practical framework established in the present study, would help the highway agencies select the most compatible asphalt-aggregate combinations.

Using surface free energy method to evaluate the isothermic adsorption of free fatty acid on low-grade coal

Surface free energy analysis on low-grade coal has been conducted. This research shows the interaction between oil and coal which improve the quality of low-grade coal by coating process. Sample coal has a total surface free energy of 22.3 mJ/m2 with 17.51 % polar ratio. The interfacial energy between coal and free fatty acid (FFA) is 9.1 mJ/m2 with adhesive energy by 53.4 mJ/m2 which is able the oil to coated on the coal surface under Van der Waals force effect.

Estimating Moisture Resistance of asphalt mixture containing epoxy resin using Surface Free Energy Method and Modified Lottman test

ABSTRACT Using modified bitumen has been one of the few reliable methods adopted for improving asphalt performance against moisture sensitivity. This research offers an approach in which both mechanical methods and micro-mechanism investigations have been employed to study the effect of bitumen modified with epoxy resin on the moisture sensitivity of asphalt mixtures. Six bitumen samples: base bitumen and bitumen modified with 1% to 5% epoxy resins, and two types of aggregates (limestone and siliceous) were selected for this study. Surface Free Energy method and Modified Lottman test were used to investigate the moisture sensitivity of asphalt mixtures containing each bitumen-aggregates combination. In the first method, surface free energy values of bitumen and aggregates were estimated and then used in predicting energy parameters related to the moisture sensitivity parameters, using which the changes in adhesion and wetting properties of each bitumen-aggregates mixture were analyzed. In the second method, the indirect tensile strength test was performed on dry and wet asphalt samples, and the tensile strength ratios were obtained for each asphalt mixture, through which the moisture resistance of samples were investigated. Based on the values obtained for the three parameters, it was concluded that epoxy resin addition decreased the moisture sensitivity of asphalt mixtures containing siliceous aggregates by increasing the bitumen and aggregates adhesion as well as increasing the wetting of the aggregates surface with bitumen. Also, in asphalt mixtures containing limestone aggregates, epoxy resin improved moisture sensitivity, but this improvement was only due to increased adhesion between bitumen and aggregates, while the impact of bitumen coating on aggregates surface did not change significantly with the addition of epoxy resin. Among the asphalt mixtures studied, the highest moisture resistance was observed in asphalt mixture containing 4% epoxy resin, at which the Tensile Strength Ratio parameter showed an increase of 11.3% and 21.5% for limestone and siliceous mixtures, respectively, compared to the base asphalt mixture.

The Effect of Aggregate-Forming Minerals on Thermodynamic Parameters Using Surface Free Energy Concept and Its Relationship with the Moisture Susceptibility of Asphalt Mixtures

Moisture damage is known to be a key factor influencing the durability of asphalt pavements. This phenomenon will reduce the mechanical properties of asphalt mixtures due to its destructive effects on the adhesion of the bitumen-aggregate system and the cohesion of the bitumen membrane. The mineral properties of the aggregates of asphalt mixtures are one of the factors affecting moisture susceptibility. Therefore, the surface free energy (SFE) method, as one of the thermodynamic methods, and indirect tensile strength test (ITST) have been used to determine the failure mechanism and the rate of change of adhesion properties of asphalt mixtures under the influence of mineralogical characteristics. Prior to the above tests, an X-ray fluorescence spectrometry (XRF) test was performed to identify aggregate-forming minerals in eight different types of aggregates with various minerals from eight mines, and also the apparent bitumen film thickness was measured. XRF test results showed that most parts of the aggregates in mines 1– 6 were composed of SiO2, which had strong acidic properties, according to the SFE results. ITST results showed that samples constructed with aggregates of mine 7 and 8 (with high CaO mineral content) experienced a higher TSR than other mixtures in all freeze-thaw (F-T) cycles. Results of the SFE method showed that aggregates with more calcareous properties had a smaller acidic component and a larger basic component. In mines 7 and 8, where the nonpolar component of their aggregates was larger, the tendency of the aggregates to adherence and wettability by water decreased. The adhesion free energy (AFE) between bitumen and aggregates with higher CaO and less SiO2 amounts was more than AFE between bitumen and aggregates with lower CaO and higher SiO2 amounts, in dry conditions. The presence of higher amounts of CaO in aggregates increased AFE of bitumen-aggregate in presence of water from a negative value to zero. In linear regression analysis, due to the positive regression coefficient of the CaO mineral, this mineral had a positive impact on TSR; on the other hand, due to the negative regression coefficient of the SiO2 mineral, this mineral had a negative impact on the TSR of asphalt mixtures.

Laboratory evaluation of the effect of rejuvenators on the interface performance of rejuvenated SBS modified bitumen mixture by surface free energy method

The surface free energy and related parameters of asphalt binder affect the wettability of asphalt binder to aggregate and its moisture sensitivity. In this research, the surface free energy and related parameters of SBS modified bitumen (SMB) after aging/rejuvenating were tested and analyzed. And then based on this data, the effect of common rejuvenator cashew shell oil and active isocyanate rejuvenators on the water damage resistance and moisture sensitivity were evaluated and predicted. The results indicated that the surface free energy of SMB decreased after aging, while rejuvenators all can enhance the surface free energy. The cohesion work of aged SMB increased after rejuvenating, and the adhesion work between aged SMB and granite were enhanced by 12.4% at least with the addition of rejuvenators, namely, rejuvenators can improve its cracking resistance and interface stability, and active rejuvenator hexamethylene diisocyanate showed the best performance. Water boiling test showed that the adhesion grade of SBS modified bitumen on granite decreased from adhesion grade 5 to adhesion grade 3 after aging, while active rejuvenators can bring the adhesion grade of aged SMB on granite to the original level. This paper would be helpful to understand the moisture resistance mechanism of rejuvenated SBS modified asphalt mixture with active regeneration technology.