Moisture-induced Damage Potential Research Articles

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.

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.

Laboratory Characterization of Moisture-Induced Damage Potential of Asphalt Mixes Using Conventional and Unconventional Performance-Based Tests

Laboratory Characterization of Moisture-Induced Damage Potential of Asphalt Mixes Using Conventional and Unconventional Performance-Based Tests

Rutting and moisture-induced damage potential of foamed warm mix asphalt (WMA) containing RAP

Despite significant economic and environmental benefits, performance of warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP) remains a matter of concern. Among the current WMA technologies, the plant foaming technique (called “foamed WMA” in this study) has gained the most attention, since it eliminates the need for chemical additives. In the present study, the laboratory performance, namely rutting and moisture-induced damage potential of foamed WMA containing RAP were evaluated and compared with those of similar hot mix asphalt (HMA) containing identical amount of RAP. Dynamic modulus, Hamburg wheel tracking (HWT) and flow number tests were performed to assess the rutting resistance of the mixes. Also, stripping inflection point from HWT tests and tensile strength ratio after AASHTO T 283 and moisture induced sensitivity test (MIST) conditioning were used to evaluate the moisture-induced damage of asphalt mixes. It was found that MIST conditioning effectively simulates the moisture-induced damage and can capture the propensity of asphalt mixes to moisture damage more distinctly compared to AASHTO T 283 method due to application of cyclic loadings. The foamed WMA was found to exhibit higher rutting and moisture-induced damage potential due to lower mixing and compaction temperatures compared to HMA. However, the increase in RAP content was found to reduce rutting and moisture-induced damage potential for WMA. Therefore, the lower stiffness of foamed WMA may be compensated with the addition of stiffer binder from RAP.

Influence of Bio-oil Modification on Moisture-Induced Damage Potential of Asphalt Binder and Mix

Abstract Bio-oil (BO) derived from waste wood has the potential to be the modifier for asphalt binders. This study attempts to evaluate the effect of BO on the moisture damage potential of asphalt binder and mix by blending BO at two dosages (2 % and 4 %, by weight) in AC30. BO was obtained by fast pyrolysis of waste wood. To achieve this objective, surface free energy (SFE), bitumen bond strength, and indirect tensile strength tests were conducted for evaluating the cohesive and adhesive bond strength, the work of debonding, energy ratios (ERs), pull off tensile strength (POTS), and tensile strength ratio (TSR). The test results indicated that the addition of BO improves the cohesive and adhesive bond strength. Also, an increase in the work of debonding was observed by conducting the SFE test. Thereafter, ERs indicated that BO has compromised the moisture damage resistivity of AC30. A reduction in POTS was also observed on inclusion of BO. TSR of mixes reduced consistently on BO addition, thereby indicating that BO has compromised the moisture-induced damage resistivity of mixes. However, all mixes resulted in more than 80% TSR value, which is the minimum requirement to counter the moisture-induced damage. A “good” correlation was observed between ERs and TSR. This study concludes that although the inclusion of BO is a promising prospect, BO has the propensity to compromise the moisture-induced damage resistivity of the asphalt mix.

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

In recent years, major initiatives have been taken to replace non-renewable materials with environmentally friendly and sustainable ones. The present study was undertaken to apply a scalable process for laboratory production of Cellulose Nanofibers (CNF) and to evaluate feasibility of using the produced CNF as a sustainable plant-based asphalt additive to improve the mechanical properties and durability of asphalt pavements. To achieve this goal, CNF was produced in the laboratory by applying electrospinning technique. Structure, morphology, and the size distribution of the produced CNF were evaluated using Scan Electron Microscopy. Also, tensile strength tests in two perpendicular directions were conducted on lab-produced CNF. The effect of incorporating different amounts of CNF in three types of asphalt binders, namely PG 58-28, PG 64-34, and PG 70-28 on fracture energy and dynamic viscosity of binder blends were evaluated by conducting Izod impact and rotational viscometer tests, respectively. Additionally, effect of CNF dosage in binder on its adhesion and moisture-induced debonding potential with aggregates of three different mineralogy was evaluated by conducting binder bond strength test. Furthermore, effect of incorporating CNF in asphalt mixes on their cracking, rutting, and moisture-induced damage potential was evaluated by conducting semicircular bend, Hamburg wheel tracking, and tensile strength ratio tests, respectively. From the tests conducted on asphalt binders and mixes, it was concluded that, incorporation of CNF resulted in an overall improvement in binder-aggregates adhesion, an asphalt binder with a higher fracture energy and dynamic viscosity, and an asphalt mix with a higher resistance to rutting, cracking, and moisture-induced damage.

Interfacial bond strength and moisture induced damage characteristics of asphalt mastic-aggregate system composed of Nano hydrated lime filler

The present study was undertaken to investigate the impact of a unique combination of fillers on interfacial bond strength and moisture-induced damage potential of asphalt mastic. One asphalt binder (AC-30), three fillers including Basalt (B), Hydrated Lime (HL), and Nano-Hydrated lime (NHL) were selected to prepare asphalt mastics for a wide range of filler-binder (f/b) ratio (0.6 to 1.2). The dosages of HL and NHL were considered 0%, 5%, 10%, 15%, and 20% by weight of asphalt binder, and the dosage of B filler was adjusted to meet the respective f/b ratio. The interfacial bond strength and moisture-induced damage potential of asphalt mastic specimens were determined using the Bitumen Bond Strength (BBS) test. The BBS test parameters inferred that both B-HL and B-NHL filler combinations can enhance the bond strength and moisture damage resistance of asphalt mastic. Besides, asphalt mastic composed of B-NHL filler can be less susceptible to bond failure and moisture damage with improved adhesion and cohesion properties than B-HL filler. Additionally, asphalt mastic composed of a lower percentage (10%–15%) of NHL filler showed better bond strength and moisture damage resistance over mastic composed of a higher percentage (15%–20%) of HL filler. Asphalt mastic prepared with an f/b ratio less than 1.0 was found to be suitable to achieve better performance considering the moisture-induced damage properties. Grey relational analysis (GRA) method was used to analyze the correlation degree between filler properties and moisture damage properties of asphalt mastics. Based on the GRA results, Rigden voids and specific surface area are suggested to be the two most influential properties on the moisture-induced damage potential of asphalt mastic.

Comparative evaluation of moisture susceptibility of modified/foamed asphalt binders combined with different types of aggregates using surface free energy approach

Moisture damage in asphalt pavement is a major concern for the state and federal highway agencies for many years. The surface free energy (SFE) is demonstrated to be a reliable mechanistic approach for evaluating the moisture-induced damage potential of asphalt mixes. The objective of this study was to use SFE approach to evaluate the effects of foamed/modified asphalt binders and aggregate type on the moisture susceptibility of asphalt mixes. The SFE components (polar and dispersion) of PG 64-22 asphalt binders, modified with 2–4% SBS, 2–4% nanoclay, 2–4% fly ash, 3.5% devulcanized rubber (DVR), or foamed by injecting water, were estimated from contact angle measurement. Also, the SFE components of five types of aggregates, namely limestone, gravel, basalt, granite, and sandstone were obtained from the literature. The energy ratio parameters calculated from the work of cohesion and adhesion were used to estimate the moisture-induced damage potential of various asphalt mixtures. The results showed that the total SFE and work of cohesion of PG 64-22 increased with the addition of SBS, nanoclay, and fly ash while decreased with the use of DVR and foaming process in asphalt binder. Based on the energy ratio parameters, the combination of asphalt binder with different types of aggregates has been recommended with the resistance to moisture-induced damage potential. The results presented herein are expected to assist in selecting appropriate asphalt binder and aggregates with desirable moisture resistance.

Effect of additives and aging on moisture-induced damage potential of asphalt mixes using surface free energy and laboratory-based performance tests

ABSTRACT Lack of mechanistic foundation and poor correlations with field performance of conventional laboratory-based tests has accelerated the search for a mechanistic-based approach for screening of asphalt mixes for moisture-induced damages. According to recent studies, surface free energy (SFE) method can be used to mechanistically quantify bond strength and debonding of binder-aggregate system in presence of water. This study was undertaken to evaluate the effects of different additives, namely warm mix asphalt (WMA) additive (amine-derived), amine-based anti-stripping agent (ASA), polyphosphoric acid (PPA) and reclaimed asphalt pavement (RAP) on the moisture-induced damage performance of asphalt mixes through the use of laboratory-based performance tests and SFE method. For this purpose, different energy parameters were determined from SFE components of binder blends and aggregate. Asphalt mixes with different additives were produced to evaluate moisture-induced damage using indirect tensile strength (ITS) and Illinois semi-circular bend (IL-SCB) tests. A new parameter, known as fracture energy ratio (Gf ratio) obtained from IL-SCB test, was used to correlate fracture energy with moisture-induced damage potential of mixes. Also, the effect of short-term and long-term aging on the moisture-induced performance of asphalt mixes were evaluated. Furthermore, correlations between moisture-induced damage parameters from laboratory-based performance tests and SFE method were investigated.

Laboratory Characterization of Asphalt Binders Containing a Chemical-Based Warm Mix Asphalt Additive

Abstract Different technologies, namely foamed asphalt, synthetic waxes, zeolites, and chemical additives, are used to produce warm mix asphalt (WMA). This study was undertaken to evaluate the effect of using different amounts of an amine-based chemical WMA additive on the rheology, performance grade (PG), and moisture-induced damage potential of an asphalt binder (PG 58-28). Superpave specifications were used to evaluate the rheological properties and PG of the asphalt binder. Also, a mechanistic approach-based on the surface free energy (SFE) method was used to evaluate the moisture-induced damage potential of the asphalt binder combined with commonly used aggregates in an asphalt mix. It was found that the dynamic viscosity of the asphalt binder was not significantly affected after blending it with the WMA additive. It was also observed that the Superpave high-temperature PG and the rutting factor did not reduce by an increase in the WMA additive content. However, the continuous low-temperature PG of the asphalt binder decreased with an increase in the amount of WMA additive. Furthermore, it was found that the fatigue resistance increased after blending the binder with the WMA additive. The SFE results of the asphalt binder revealed that the WMA additive used in this study reduced the moisture-induced damage potential of the asphalt mixes. However, the extent of this improvement was found to largely depend on the aggregate type. The outcomes of this study are expected to help better understand the influence of amine-based chemical WMA additives on rheological and long-term performance of asphalt mix.

Effect of WMA additive on properties of PPA-modified asphalt binders containing anti-stripping agent

ABSTRACT The current study was undertaken to evaluate the effect of Polyphosphoic Acid (PPA) on rheological properties of different grades of asphalt binders containing a chemical Warm-Mix Asphalt (WMA) additive in presence and absence of a liquid Anti-Stripping Agent (ASA). Also, the effect of chemical WMA additive, PPA and ASA on rutting and moisture-induced damage potential of asphalt mixes was evaluated. Polymer-modified and non-modified asphalt binders were blended with different amounts of PPA, WMA additive, and ASA and tested in a Dynamic Shear Rheometer and a Bending Beam Rheometer. The results indicated that blending WMA additive and PPA with all tested binders increased their rutting and fatigue resistance. However, blending PPA with asphalt binders in presence of the WMA additive and ASA was found to reduce their resistance to fatigue cracking. Also, the use of WMA additive, ASA and PPA was found to reduce the effectiveness of the PPA in bumping the high-temperature Performance Grade (PG) of asphalt binder with an insignificant effect on low-temperature PG. Furthermore, conducting Hamburg wheel tracking and indirect tensile strength ratio tests on asphalt mixes containing WMA additive, PPA and ASA showed a low susceptibility to rutting with no significant indication of moisture-induced damage.

Investigation of moisture susceptibility of SBS modified asphalt containing Alumina Trihydrate by static contact angle measurements

Although several studies have been carried to discover the asphalt mixture performance when Alumina Trihydrate (ATH) as a flame retardant was added into, the moisture susceptibility of asphalt mixture containing ATH is still not fully clear. In this study, the moisture susceptibility of binders containing ATH were assessed through the surface free energy (SFE) obtained by the sessile drop method. A commonly used SBS modified asphalt with different dosages (0%, 6%, 8%, 10%, 12%, and 14%) of ATH were prepared to determine the physical properties, flame retardancy and SFE parameters. Experimental results indicated that the addition of ATH increased the viscosity, softening point, G*/sinδ and limiting oxygen index, but decreased the penetration and ductility. What's more, increases in total SFE, cohesive energy and work of adhesion were observed with the addition of ATH. Conversely, the work of debonding, wettability and energy ratio decrease due to the addition of ATH. It is concluded that the ATH has a significant negative effect on the moisture-induced damage potential of asphalt mixture from the view of micromechanisms. The recommended percentage of ATH was 6-8% in consideration of physical properties, flame retardation and moisture susceptibility

Micro-Structural Analysis of Moisture-Induced Damage Potential of Asphalt Mixes Containing RAP

Abstract This study was undertaken to evaluate the effects of reclaimed asphalt pavement (RAP) on moisture-induced damage potential of asphalt mixes using two different approaches: (i) micro-structural analysis of aggregate–asphalt bonding based on the surface free energy (SFE), and (ii) mechanical testing of asphalt mixes using retained indirect tensile strength ratio (TSR) and Hamburg wheel tracking (HWT). This study involved two phases. In the first phase, the SFE (non-polar, acidic and basic) components of a virgin PG 64-22 binder mixed with 0, 25, and 40 % of simulated RAP binder and aggregates (limestone, rhyolite, RAP extracted aggregate) were measured using a dynamic contact angle (DCA) device and a universal sorption device (USD), respectively. Thereafter, composite work of adhesion and composite work of debonding, and composite energy ratios for each combination of asphalt binder and aggregates were determined to assess the moisture-induced damage potential of the mixes containing different percentages of RAP (0, 25, and 40 %). In the second phase, the TSR and HWT tests were conducted on asphalt mixes containing different percentages of RAP (0, 25, and 40 %) to evaluate their moisture-induced damage potential. Both the methods showed that the moisture-induced damage potential decreased with increasing amount of RAP in asphalt mixes. A strong correlation was found to exist between the moisture-induced damage potential predicted using the micro-structural method and laboratory performance tests. It was found that the micro-structural energy approach, as a mechanistic framework, can be successfully used as an indicator of moisture-induced damage potential of the asphalt mixes. It is expected that the present study would be helpful in understanding the moisture-induced damage potential of flexible pavements containing RAP.

Laboratory characterisation of asphalt mixes containing RAP and RAS

Due to its economic and environmental benefits, using reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in new hot-mix asphalt (HMA) has become an integral part of today's asphalt industry. The advantages of using RAP and RAS in HMA are not limited to economic and environmental benefits, and may result in improving a number of mix performance characteristics including rutting and resistance to moisture-induced damage. Despite aforementioned benefits, concerns over premature pavement distresses resulting from using RAP and RAS limit their usage in HMA. Furthermore, because of the lack of mechanistic performance data, use of new mixes containing RAP and RAS remains limited. Therefore, the present study was undertaken to investigate the effects of using different amounts of RAP and RAS on laboratory performance of HMA, and to generate valuable input design parameters for implementation of the mechanistic-empirical pavement design guide (M-EPDG), using local materials. Four types of base course mixes containing 0% RAP, 25% RAP, 40% RAP and 20% RAP+5% RAS, and three types of surface course mixes containing 0% RAP, 25% RAP and 20% RAP+5% RAS were tested. Laboratory tests were conducted to evaluate stiffness, low-temperature cracking, fatigue life, rut and moisture-induced damage potential of the mixes. It was found that dynamic modulus and creep compliance of the asphalt mixes increase and decrease, respectively, with an increase in the amount of RAP and/or RAS used in the mix. Fatigue life was found to increase with increasing RAP content up to 25%, and to decrease when the RAP and/or RAS content exceeded 25%, or when RAS was used in the mix. It should be noted that this conclusion was drawn based on a 15% increment in RAP content. Hamburg wheel tracking (HWT) test results showed increased resistance to rutting and moisture-induced damage, with an increase in the amount of RAP and/or RAS. However, the tensile strength ratio test results were not confirmed by HWT. The findings of this study are expected to be helpful in understanding the effects of using different amounts of RAP and RAS on the performance of asphalt mixes produced using local materials. Furthermore, valuable design input parameters, developed in this study for new mixes containing RAP and RAS, may be used for calibration of the M-EPDG input parameters, with local materials.

Laboratory evaluation of stiffness, low-temperature cracking, rutting, moisture damage, and fatigue performance of WMA mixes

Despite the environmental and compaction benefits of warm mix asphalt (WMA), several researchers have expressed concerns over laboratory and field performances of WMA mixes. In this study, a wide range of laboratory tests, namely, dynamic modulus, creep compliance, fatigue, moisture damage, and rutting, was conducted to evaluate the performance of different types of WMA mixes. For this purpose, three WMA mixes, consisting of one mix produced using a zeolite-based WMA additive (containing water), one surface course mix, and one base course mix, the latter two produced with a chemical-based WMA additive with surfactant technology, were collected from different field projects in Texas. In addition, three hot mix asphalt (HMA) mixes with aggregate gradations similar to those of the collected WMA mixes were produced in the laboratory to compare the performance of WMA and HMA mixes. Overall, the WMA mixes yielded lower stiffness, reduced potential of low-temperature cracking, lower fatigue resistance, and a higher rutting potential compared with their HMA counterparts. However, a mixed trend of moisture-induced damage potential was observed for WMA and HMA mixes, when evaluated using retained tensile strength ratio (TSR) and stripping inflection point (SIP) obtained from the Hamburg wheel tracking (HWT) test. In other words, no correlation was found between TSR and SIP values, indicating that passing a TSR test does not guarantee better performance of a mix when tested using an HWT. The results from this study reveal that performance of a WMA mix widely depends on the technology and the type of other additives (e.g. anti-stripping agent) used. The findings of this study are expected to be useful to pavement professionals to better understand the performance of WMA mixes and to develop a database of input parameters for the Mechanistic-Empirical Pavement Design Guide.

Evaluation of moisture susceptibility of asphalt mixes containing RAP and different types of aggregates and asphalt binders using the surface free energy method

The surface free energy (SFE) measurement of asphalt binder and aggregate is considered a reliable mechanistic framework for evaluating the moisture-induced damage potential of asphalt mixes. In the present study, the SFE method was used to evaluate the effects of asphalt binder type, Reclaimed Asphalt Pavement (RAP) and its amount, and aggregate type on the moisture-induced damage potential of asphalt mixes. The SFE components (non-polar, acid and base) of a PG 64-22 and a PG 76-28 (polymer-modified) asphalt binders, blended with different amounts of RAP binder (0%, 10%, 25% and 40%) were measured in the laboratory using a Dynamic Contact Angle (DCA) analyzer. Also, the SFE components of six types of aggregates, namely limestone, rhyolite, sandstone, granite, gravel, and basalt were used in this study. The SFE components of limestone and rhyolite aggregates were measured using a Universal Sorption Device (USD), while those of the sandstone, granite, gravel, and basalt aggregates were obtained from the literature. The energy ratio parameters estimated based on the spreading coefficient, the work of adhesion, and the work of debonding were used to assess the moisture-induced damage potential of different combinations of asphalt binders and different RAP binder contents and aggregates. The SFE test results indicated that the acid SFE component of PG 64-22 and PG 76-28 asphalt binders increase with the addition of RAP binder, while the base SFE component remains almost unchanged. Also, the wettability and the work of adhesion of both PG 64-22 and PG 76-28 asphalt binders over different types of aggregates increased with an increase in RAP content (by 25% and more). Based on the energy ratio parameters, it was found that the resistance to moisture-induced damage increased with an increase in RAP content for both PG 64-22 and PG 76-28 asphalt binders and all types of aggregates, specifically when higher RAP contents were used. Moreover, it was found that the higher the total SFE of the aggregates, the lower the energy ratio parameter values. Therefore, a high total SFE component of aggregate may result in a high moisture-induced damage potential of the mix. The results presented herein are expected to be helpful in mechanistically assessing the moisture-induced damage potential of asphalt mixes, produced with polymer-modified and non-polymer-modified asphalt binders, containing RAP.

Application of Asphalt-aggregates Interfacial Energies to Evaluate Moisture-induced Damage of Warm Mix Asphalt

With increasing environmental awareness and high oil prices, use of warm mix asphalt (WMA) is gaining popularity in the asphalt industry. Different WMA technologies including use of additives to reduce the mixing and compaction temperatures are being applied. The present study uses the surface free energy (SFE) method as a mechanistic framework to evaluate the moisture susceptibility of warm mix asphalt (WMA) with Evotherm® WMA-additive. The SFE components of a modified PG64-22 asphalt binder with different percentages of Evotherm® and selected aggregates were measured in the laboratory. The work of adhesion, the work of debonding, and energy ratios were estimated to assess the moisture-induced damage potential of combinations of neat and Evotherm®-modified asphalt binders and different aggregates. The results indicated that use of Evotherm® resulted in increase in total SFE and work of adhesion and a reduction in the work of debonding, indicating a better possible aggregate-asphalt binder bond and lower moisture susceptibility potential. It is expected that the present study would be helpful in understanding the moisture-damage potential of flexible pavements constructed with WMA technologies.

Mechanistic Evaluation of the Effect of WMA Additives on Wettability and Moisture Susceptibility Properties of Asphalt Mixes

Abstract This study used a mechanistic framework (i.e., surface free energy) to evaluate the moisture susceptibility of warm mix asphalt (WMA) with three different WMA additives, namely, Sasobit, Advera, and Evotherm. The surface free energy (SFE) components of modified PG64-22 asphalt binder with different percentages of WMA additives and selected aggregates were measured in the laboratory. The wettability, the work of adhesion, the work of debonding, and energy ratios were estimated in order to assess the moisture-induced damage potential of combinations of modified asphalt binders and different aggregates. The results indicate that Sasobit and Advera are able to reduce the moisture susceptibility potential of the mixes, but their use is not recommended with highly acidic aggregates such as granite. Evotherm resulted in the highest increases in wettability, total surface free energy, and increased work of adhesion and a reduction in the work of debonding, resulting in a better possible aggregate coating with asphalt binder and lower moisture susceptibility with all types of tested aggregates relative to those of other WMA additives. Furthermore, tensile strength ratio (TSR) tests were conducted on Advera and Evotherm-modified and neat (unmodified) asphalt mixes, and the results were compared with those from the SFE test. It was found that the SFE approach is a better indicator of moisture susceptibility than the traditional TSR test. The findings of the present study would help the highway engineers and agencies to better understand the moisture damage potential of flexible pavements constructed with WMA technologies.

Effect of Antistrip Additives on Surface Free Energy Characteristics of Asphalt Binders for Moisture-Induced Damage Potential

Abstract In this study, the effect of antistrip additives on asphalt binders was evaluated by both laboratory tests and a proposed chemical model of asphalt binder based on the surface free energy characteristics. Two performance graded asphalt binders, namely, PG 64-22 and PG 70-28 and two amine-based liquid antistrip additives, namely, AD-Here HP Plus and Redicote E-6 were evaluated at different percentages (0.25 %, 0.75 %, and 1.5 %). It was found that 1.5 %AD-Here HP Plus and 1.5 % Redicote E-6 increased the total SFE of PG 64-22 by 67 % and 208 %, respectively. Also, the acid components of PG 64-22 and PG 70-28 are 2.9 dyne/cm and 2.5 dyne/cm, respectively, whereas, the corresponding base components are 0.4 dyne/cm for both. With the addition of 1.5 %. Redicote E-6 in PG 64-22, the acid component of the binder reduced by 92 % and the base component of the binder increased by 1141 %.