Binder Bond Strength Test Research Articles

Analysis of moisture susceptibility of foamed warm mix asphalt based on cohesion, adhesion, bond strength, and morphology

Although foamed warm mix asphalt (FWMA) offers several benefits, concerns exist regarding the potential moisture damage that can be produced within it. Boiling water tests, the surface free energy (SFE), the binder bond strength (BBS), and atomic force microscopy (AFM) morphologies are all used to analyse the moisture damage of asphalt. These methods were evaluated and compared in this study. The results indicate that some residual moisture remains trapped in asphalt after foaming and that the foaming states for base asphalt and SBS modified asphalt attain stability after 6 min and 15 min, respectively. Boiling water tests are unsuitable for evaluating the adhesion of FWMA. SFE and BBS tests demonstrated that the residual foaming water undermines the bond strength of FWMA by reducing the cohesion energy. The Scanning Electron Microscope (SEM) and AFM methods were used to identify differences between morphologies by investigating the various foaming water contents. The results of SFE, BBS, and AFM morphologies were observed to be in agreement. Although cohesive failure modes were observed in the BBS experiment, foaming water aggravates the adhesion failure and causes moisture damage owing to the participation of external water. Furthermore, the results indicate that less water damage resistance is associated with substantial amounts of foaming water. These findings provide a clearer understanding of the moisture susceptibility of FWMA.

Effect of cohesive and adhesive parameters on the moisture resistance of thin friction course (TFC) with varying mix design parameters

Thin friction course (TFC), one typical pavement surface treatments (PSTs), is mixed with modified asphalt emulsion, fine aggregate, and cement. Moisture-induced damage is one of the main distresses usually occurring in TFC. To mitigate potential moisture damage, varying TFCs with different combinations of emulsion, SBR latex, and cement dosages were investigated by the wet track abrasion test (WTAT). Then, the adhesive strength and cohesive stiffness of corresponding residue emulsion-cement mastics were estimated based on the binder bond strength (BBS) test and the strain sweep test, respectively. The results indicated that the increased emulsion, SBR latex, and cement dosages are beneficial to the moisture resistance of TFC. The pull-off strength of BBS test shows poor correlation with the aggregate losses and the failure type is cohesion by observation, which means the adhesion strength of the residue mastic-aggregate bond is higher than the cohesive strength based on the limited data. Furthermore, based on the strain sweep test, it was found that the cohesive parameters, including the maximum shear stress and the complex modulus at the strain level of 7% could perfectly correlate with the average aggregate loss with a correlation coefficient of 0.8841 and 0.8678, respectively. Therefore, both SBR and cement modification could enhance the cohesive stiffness of the cement-binder mastics and then improve the moisture resistance of the TFC.

Laboratory Investigation of the Adhesion and Self-Healing Properties of High-Viscosity Modified Asphalt Binders

Water damage often occurs on porous asphalt pavement during service life because of the well-developed pore structure. Determining the adhesion and adhesion healing properties of high-viscosity modified asphalt (HVMA) under water condition is beneficial to understand the water damage process of porous asphalt. In this study, the modified binder bond strength test was first conducted to investigate the adhesion property and self-healing behavior of HVMA at different conditions. Then, the surface energy test was carried out to further characterize the differences in adhesion property of HVMA. Moreover, the gel permeation chromatography test and fluorescence microscopic test were used to investigate the influence of chemical composition and polymer morphology on the adhesion property of HVMA. Results show that the presence of water reduces the adhesion property of HVMA. The addition of polymers leads to an increasing adhesion strength and a decreasing self-healing ability of HVMA. The self-healing ability of HVMA improves with the increase of temperature, but also shows a decreased trend when the healing time is long at high-temperature water immersion. The effect of polymers on the adhesion property of asphalt has two aspects. First, the swelling of polymers leads to an increasing content of polar heavy components in HVMA, thus enhancing polarity adsorption between asphalt and aggregate. Moreover, a polymer-centered interfacial diffusion layer can be formed during the adsorption of light components, which increases the overlapping area of structural asphalt between adjacent aggregates. This can also improve the adhesion property at the asphalt–aggregate interface.

Relationship among cohesion, adhesion, and bond strength: From multi-scale investigation of asphalt-based composites subjected to laboratory-simulated aging

Identifying the properties of the bond strength between aggregates and asphalt binders is critical to understand the strength and fracture behavior of asphalt mixture. Some efforts have been made on the effect of aging on the bonding property of the asphalt binder. However, there is no consensus result and the mechanism that drives the change of bonding property remains unclear. The objective of this study is to investigate the influence of aging on the bonding property, and to explain the reason lies behind. To achieve this goal, four neat asphalt binders were treated with short-term aging and long-term aging. The bond strength and the adhesion force were measured by binder bond strength test on a macro scale and atomic force microscope on a micro scale, respectively. Based on the result obtained in this study and previous publications along with the adhesion theories, it is found that a moderate aging contributes to the bond strength while a sever aging does not necessarily improve the bond strength. The change of bond strength under an aging condition can be explained by the cohesion force in asphalt binders and the adhesion force between asphalt binders and aggregates. Based on the results, it can be concluded that the cohesion force increases with aging time as a result of asphaltenes association. The adhesion force increases initially and then decreases, and the wettability is thought to be responsible for the reduction of adhesion force. The adhesion reduction can be observed on the three phases (catana phase, peri phase, para phase) of the asphalt binders, which leads to the adhesion reduction on the whole asphalt binders. These findings help to provide a better understanding of the change of bonding property of asphalt binders during an aging process, which contributes to the improvement of bond strength by enhancing the wettability of each phase in asphalt binders appropriately. The results have practical significance and can help to optimize the materials production process.

Shear adhesion evaluation of various modified asphalt binders by an innovative testing method

During the last decades, the number of vehicles, as well as the traffic load, has dramatically increased, which has strongly shortened the life of pavements and increased maintenance cost. Most asphalt pavement diseases are resulted from adhesion failure which occurred between asphalt and aggregates. The adhesion properties are crucial factors that influence the capability of asphalt to resist stripping from aggregates. In this paper, shear adhesion test, an innovative test method based on energy theory by using Dynamic Shear Rheometer was introduced and performed to evaluate the effects of various modifiers and additives of different amounts on asphalt shear adhesion property. Meanwhile, binder bond strength (BBS) test was also applied to test the adhesion tension strength of the modified asphalt, and the results from two tests were compared with each other. Furthermore, correlation analysis between findings obtained from shear adhesion test and Hamburg wheel-tracking device (HWTD) test under wet condition was conducted.Shear adhesion test results indicated that SBS, crumb rubber, terminal blend (TB) rubber powder and compound modifier TB rubber powder + SBS improved the shear adhesion property, while polyphosphoric acid (PPA) and ethylene bis-stearamide wax (EBS) had an adverse effect on it. The results acquired from BBS test were roughly consistent with shear adhesion test results when evaluating the variation tendency of adhesion properties of some asphalt which is modified with different amounts of modifiers. The results of the shear adhesion test were in good correlation with the stripping inflection point (SIP) in HWTD test when evaluating the certain kind of asphalt which was modified with different amounts of modifiers, except for some modifiers that would change the asphalt stiffness modulus significantly.

Influence of Recycled Asphalt Pavement on Interfacial Energy and Bond Strength of Asphalt Binder for Different Types of Aggregates

The bond between aggregate and asphalt binder depends on many factors, such as chemistry of materials, nature of aggregates, and quality of asphalt binder. The present study evaluates the effects of recycled asphalt pavement (RAP) on the bonding behavior of asphalt binder for acidic (granite and quartzite) and basic (basalt and limestone) aggregates. AC30 binder was blended with different proportions of RAP binder (15%, 25%, and 40%). The interfacial energy and bond strength of 16 combinations (four asphalt binders × four aggregates) of aggregate-asphalt binder system were evaluated based on a surface free energy (SFE) approach and binder bond strength (BBS) test, respectively. One of the strong motivations of the present study was to evaluate how interfacial energy parameters calculated based on the SFE of an aggregate-asphalt binder system may correlate with the outcome obtained from a BBS test. The results showed that AC30 binder modified with RAP binder had a good performance for basic aggregates compared with acidic aggregates. Basic aggregates (limestone and basalt) showed cohesive failure before and after conditioning, indicating minimal effects of water on interfacial bond strength. However, acidic aggregates (granite and quartzite) showed cohesive failure in dry conditions and adhesive failure after wet conditioning, implying detrimental effects of water on interfacial bond strength for these aggregates. The failure pattern of aggregates in cohesion was supported by a reduction in cohesion energy of asphalt binder after the addition of RAP binder. Correlation between interfacial energy parameters (obtained from SFE) and BBS strength depends on aggregate types and failure patterns.

Comparison and relationship between indices for the characterization of the moisture resistance of asphalt–aggregate systems

The complex and diversified asphalt modification makes it harder for the assessment of testing methods capable of characterizing the performance of different modified asphalt in the presence of water. In this study, three representative test methods addressing the moisture performance of asphalt were evaluated and compared: surface free energy (SFE) test, binder bond strength (BBS) test and Hamburg wheel tracking device (HWTD) test. Results indicate that the HWTD test can be a benchmark test while the BBS test is a screening test in characterizing the moisture performance of various modified asphalt. In addition, the surface energy component obtained from the receding procedure in the Wilhelmy Plate Method correlated better with the adhesion property of asphalt than those based on the advancing procedure did. The various indices obtained from the three tests were classified as suitable or unsuitable indices on the basis of the analysis of specific additives. Furthermore, based on the degree of their improvement in the moisture performance, additives were classified into three grades: (1) the first grade including linear styrene–butadiene–styrene (SBS), branched SBS and gilsonite; (2) the second grade including high-density polyethylene, and polyphosphoric acid; (3) the third grade including asphalt rubber and terminal blend asphalt. Finally, it was found that base binders with shorter-chain structures and lower aromatics contents showed better moisture resistance in the HWTD test. High mobility of base asphalt binder negatively influenced the corresponding mixture’s moisture sensitivity.

Testing the bond strength between cold bitumen emulsion composites and aggregate substrate

Bitumen emulsion mixtures derive their mechanical properties from the cohesion provided by the bituminous mastic formed by bitumen and filler, and from its adhesion to the aggregate particles. In cold bitumen emulsion mixtures, the mastic film is produced upon emulsion breaking and the bond strength between mastic and aggregate must be evaluated considering the evolutive nature of the material, and thus the curing process. In this study, the binder bond strength (BBS) test was used to evaluate the bond strength between a bitumen emulsion, a cold mastic prepared using limestone filler and two aggregate substrates (limestone and basalt). A 2 k factorial experiment was conducted also considering the influence of substrate moisture (dry and wet), curing time (24 and 72 h), curing temperature (25 and 40 °C) and moisture damage on the bond strength. The results demonstrated that, although both emulsion and mastic showed good affinity with the aggregate substrates, the adhesion bond between emulsion and basalt substrate was the most durable and that the use of a limestone filler penalised the moisture sensitivity of the systems. The BBS test was also able to show the positive effect of curing time and temperature on the bond strength.

Investigation of Critical Factors Determining the Accuracy of Binder Bond Strength Test to Evaluate Adhesion Properties of Asphalt Binders

Abstract The bond strength between asphalt and aggregates is a crucial parameter in evaluating the ability of asphalt mixture resistance to moisture-induced damage. Factors affecting the bond strength were investigated based on the binder bond strength (BBS) test. The effects of asphalt film thickness and loading rate on the results of the BBS test and the relationship between these two factors were further studied. Then, specimens were subjected to four moisture conditions to study the impact of water on the bond strength. Furthermore, the impact of the complex modulus on the bond strength was studied using the dynamic shear rheometer (DSR) test. Finally, the pull-off test results were compared with the findings obtained from the Hamburg wheel-tracking device (HWTD) test regarding the moisture sensitivity of mixtures under dry and wet conditions. Results indicate that the pull-off tensile strength (POTS) increased with an increase of the loading rate, whereas POTS decreased with the increase of the film thickness. It was proved that an equivalent relationship between these two factors existed in the BBS test. It is interesting that the measured POTS values were basically equal when the loading curves of the same asphalt overlap under different combinations of film thickness and loading rate. Water had a significant impact on the bond strength, and the moisture condition in the early state was important in determining the moisture sensitivity of the mixtures. Furthermore, POTS increased with the complex modulus of asphalt binder, whereas the phase angle of asphalt determined the extent to which the film thickness will affect the BBS test results. The comparison of the BBS and HWTD tests confirmed that the BBS test could address the mixture resistance to water damage.

Laboratory evaluation of self-healing properties of various modified asphalt

The self-healing capability of asphalt materials has been known for many years. Related studies have focused mostly on the healing mechanism or self-healing behavior during load repetitions. Limited work has been accomplished to fully understand the healing performance of different modified asphalt. In this paper, the effects of various contents of different modifiers on the healing capability of binders were investigated by a simple self-healing test procedure to give suggestions to ensure better choice of asphalt materials with good healing properties. Results from the Binder Bond Strength (BBS) test indicate that the modifier significantly affected the healing potential of asphalt binder depending on both the type and content of modifier that was used. Interestingly, increased modifier content deteriorated the healing capability of the base binder regardless of the type of additive employed, thereby suggesting that soft binders are more desirable for healing. Furthermore, methylene plus methyl hydrogen to carbon (MMHC) ratio was verified to be useful for predicting the healing potential of base asphalt binder but was found to be unsuitable for characterizing the healing potential of modified asphalt. By contrast, rotational viscosity @135°C can predict the healing property in the case of base and modified asphalt. Finally, the Four-Point Beam Fatigue (4PB) test further confirmed that the BBS test can help to determine the healing potential of asphalt binders in an efficient and simple manner.

Addressing Raveling Resistance in Chip Seal Specifications

Chip seals are applied to existing roadways to slow deterioration and improve pavement surface conditions without increasing the pavement’s structural capacity. The raveling of chip seals can cause damage to vehicles and thus is a safety concern. Raveling resistance is related to both material application rates and material properties. The current chip seal specifications fail to adequately address the material-related aspects of raveling resistance. This study seeks to develop recommendations to address raveling resistance in future chip seal specifications. Strain sweep binder tests, binder bond strength (BBS) tests, and Vialit chip seal mixture tests were conducted to assess early raveling, late raveling, and wet raveling at two intermediate temperatures. The results demonstrate that the bond that develops between the residual binder and the aggregate is highly dependent on the interaction between the emulsion and the aggregate during curing. The importance of emulsion–aggregate compatibility in raveling resistance indicates that raveling resistance cannot be addressed in binder specifications alone. Rather, it is recommended that intermediate temperature raveling resistance should be addressed during chip seal mixture design. Vialit and BBS tests, in which emulsion is cured on rock, can both be used to effectively quantify the aggregate loss potential of a chip seal. These two tests are able to capture the benefits of polymer modification and produce results that correlate. However, the Vialit tests are easier to implement than the BBS tests and require no expensive equipment. Therefore, Vialit tests are recommended to address early, late, and wet raveling resistance in future chip seal specifications.

Evaluation of Adhesion Properties of Modified Asphalt Binders with Use of Binder Bond Strength Test

Moisture damage is a prominent problem of asphalt pavements. The bond strength between asphalt and aggregates is a crucial factor that influences the capability of asphalt to resist moisture-induced damage. In this study, a binder bond strength (BBS) test was conducted to evaluate the effects of various modifiers and additives of different amounts on bond strength between asphalt and aggregates. Furthermore, the influence of styrene–butadiene–styrene (SBS) on adhesion behavior of asphalt binder was investigated through a gel permeation chromatography (GPC) test. Finally, the results of the BBS test were compared with the findings obtained from a Hamburg wheel-tracking device (HWTD) test, which reflected the moisture sensitivity of mixtures under wet conditions. Results indicated that gilsonite, high-density polyethylene, and polyphosphoric acid improved the bond strength of the base asphalt; SBS had no positive effects on asphalt adhesion properties; and SBS at a low amount reduced the bond strength. Ethylene bis-stearamide wax, crumb rubber, terminal blend (TB) rubber powder, and compound modifier TB rubber powder plus SBS decreased the bond strength. The GPC test results showed that SBS possibly did not actively contribute to the formation of bond strength between asphalt and aggregates. Test data for BBS and HWTD tests under wet conditions confirmed that there was no discernible correlation between these two tests when adhesion properties of modified asphalts were evaluated. However, the results of the BBS test were in accordance with those of the HWTD test when the adhesion of asphalt with different amounts of the same modifier and the mixture resistance to water damage were evaluated.

On the investigation of self-healing behavior of bitumen and its influencing factors

Bitumen, which combines individual aggregate particles, is crucial in the self-healing of asphalt materials. However, the underlying mechanism and influencing factors of self-healing remain ambiguous. In this study, the effects of different factors were investigated using a multi-failure-healing cycle test based on the Binder Bond Strength (BBS) test. Then, Computed Tomography scan (CT-scan) test was performed to visually confirm the results of the BBS test. Results indicate that bond strength recovery displays various patterns over time under different conditions. What is unexpected is that the water exerts multiple effects on the healing potential of bitumen, although it negatively influences the healing capability of this material over time. In addition, the healing capability of bitumen continuously increases with healing temperature. The result of CT-scan test further confirms this phenomenon and indicates that healing temperature is more important than healing time. As for the aging process, it elicits different effects on the base bitumen and modified binder. Both the BBS test and CT-scan test show the negative effect of Styrene–Butadiene–Styrene (SBS) modifier on the healing potential of the base bitumen. Moreover, CT-scanned images reveal that three healing stages can be suggested to interpret the healing behavior: gathering, moving, and rounding.

Study on bond properties between RAP aggregates and virgin asphalt using Binder Bond Strength test and Fourier Transform Infrared spectroscopy

Since the aged asphalt film coating Reclaimed Asphalt Pavement (RAP) aggregates has prevented virgin asphalt from directly attaching to the aggregates, the mechanism behavior developed between RAP aggregates and virgin asphalt should be considered differently. In order to directly measure bond strength between RAP aggregate and virgin binder, the Binder Bond Strength (BBS) test was performed, and artificial coated RAP substrates were prepared employing an innovative coating treatment. The aged asphalt film thickness and the aging level of RAP substrate, combined with dry and wet curing conditions were assessed regarding to their impact on bond strength. Fourier Transform Infrared (FTIR) spectroscopy was also utilized to investigate the effect of film thickness and aggregate type on aging properties.According to BBS test results, existence of aged asphalt film had positive effects on bond properties under dry conditions. Moisture weakened this enhancement and induced more debond at the diffusion zone where the aged film and virgin asphalt blend. A proper aging level may exist at which RAP can provide optimum bond properties. Moreover, through FTIR spectroscopy, a good correlation between oxidation and film thickness was observed.

Investigation of using binder bond strength test to evaluate adhesion and self-healing properties of modified asphalt binders

The bond strength between asphalt and aggregates is a crucial parameter in evaluating the capability of a binder to resist moisture-induced damage. A novel binder bond strength (BBS) test was studied in this paper, and factors affecting the bond strength including pulling rate and asphalt film thickness were investigated to propose a reasonable test procedure. The results showed that there is an equivalent relation between the pulling rate and the asphalt film thickness. Besides, the influences of different additives on the adhesion and self-healing property of two types of asphalt (neat asphalt and SBS modified asphalt) were investigated using this modified pull-off test.Results indicate that different additives including styrene–butadiene–styrene (SBS), polyethylene (PE), polyphosphoric acid (PPA), Gilsonite, bis-stearamide wax (EBS) and rubber processing oil had significant impacts on the adhesion and self-healing properties of neat asphalt and SBS-modified asphalt. The comparison between BBS and DSR tests revealed that the complex modulus of asphalt had a dual effect on the BBS test results while the comparison of the BBS and Hamburg Wheel Tracking Device (HWTD) tests confirmed that the BBS test could address the mixture resistance to water damage.

Measuring moisture susceptibility of Cold Mix Asphalt with a modified boiling test based on digital imaging

Cold Mix Asphalt (CMA) is a promising alternative material for a wide range of paving applications from preventive maintenance and repair, to new pavement construction. However, the reported higher moisture susceptibility of CMA relative to traditional Hot Mix Asphalt (HMA) presents a challenge that limits the more widespread usage of CMA in the field up to date. To identify the potential of moisture susceptibility for CMA, a simple and effective test procedure based on modifications to the Boiling Test specified in ASTM D3625 is proposed in this paper. The modified boiling test can provide a quick measurement of moisture susceptibility for CMA in the material selection stage of the mix design. Digital imaging is used to quantify the coating of CMA mixture samples before and after the boiling test instead of subjective visual assessment. The “Coating Ratio” parameter is proposed as an index to evaluate the coating quality of CMA, and as a means to ensure adequate bonding between asphalt and aggregate. The results from the modified boiling test were verified by AASHTO TP-91 Binder Bond Strength (BBS) test and the AASHTO T-283 Tensile Strength Ratio (TSR) test of the compacted mixture. It is found that the results from modified boiling test correlated very well with those from BBS test and TSR test, indicating that the modified boiling test can be used as an effective tool to evaluate the moisture damage potential of CMA.

Evaluating Moisture Susceptibility of Cold-Mix Asphalt

Moisture damage–related distress is a primary concern limiting the application of cold-mix asphalt (CMA) as an alternative to hot-mix asphalt in the field. Thus, a simple and effective method is needed in the materials selection process to identify moisture susceptible materials. This study presents a modification to the boiling test procedure specified in ASTM D3625 based on the concept that a mix designer can limit moisture damage by controlling coating quality. The test was modified to present CMA-specific sample preparation guidelines and to remove subjectivity from the test by quantifying coating according to image analysis. Coating quality was evaluated with the coating loss ratio, defined as an index to compare coating before and after the boiling of cured loose mixtures. The relationship between coating quality and moisture resistance was verified with two separate tests: the AASHTO TP-91 binder bond strength test and the AASHTO T-283 tensile strength ratio test. The binder bond strength test provided a direct measure of the bond between binder and aggregate and how it was influenced by moisture. The effect of coating quality on bulk mixture performance was evaluated through comparison with the tensile strength ratio test. All compacted mixtures were produced with a newly developed CMA mix design method to maintain air void levels between samples. Results show that image analysis can be effectively applied to quantify the results of the boiling test, and rankings from all three tests are consistent; this efficacy suggests that the evaluation of coating quality with the modified boiling test can be used as an effective initial evaluation of the potential for CMA moisture susceptibility.

Innovative Testing Protocol for Evaluation of Binder-Reclaimed Aggregate Bond Strength

The durability of asphalt mixtures is strongly related to the adhesion properties developed at the interface between binder and aggregates. The loss of adhesion implies a rapid deterioration (e.g., stripping or raveling) of pavement layers under traffic loads, especially when the pavement is affected by the presence of moisture. Adhesion is a complex phenomenon related to the mineralogical and morphological nature of aggregates as well as to the chemical binder composition and the environmental conditions. The evaluation of adhesion has become even more complicated as an increasing percentage of reclaimed asphalt pavement (RAP) is used in the production of new asphalt mixes. Therefore, adhesion properties are also related to the mechanisms developed at the interface between virgin binder and aged binder that coats the RAP aggregate surface. An innovative procedure to evaluate the compatibility of the system virgin binder–RAP aggregate was proposed in this study. This procedure allowed the substrate of a RAP aggregate to be simulated in the laboratory and could integrate the binder bond strength test currently used to investigate bonding properties and water sensitivity of the system binder and virgin aggregates. Tests were performed with various aggregate sources, several modified binders, and two conditioning types (dry and wet). It was found that the procedure was able to discriminate different test configurations and variables. In particular, the artificial reclaimed aggregate substrate ensured higher adhesion performance compared with the virgin aggregate, especially in the wet condition, regardless of the modification level of the virgin bitumen.

Improved durability of recycled porous asphalt

Porous asphalt mixtures are extensively used as highway surface layer due to their benefit in improving skid resistance and reducing spray and splash effects during wet conditions. Moreover, porous asphalts (PA) are also oriented towards the reduction of road traffic noise thanks to enhanced sound absorption capabilities. Nevertheless, the limited durability of porous asphalt layers leads to frequent maintenance and rehabilitation activities. In this study, the use of course reclaimed asphalt (RA), obtained by milling old porous surface layers, as aggregate in new PA mixtures was evaluated. Preliminary, Binder Bond Strength tests on coated and uncoated basalt aggregate substrates showed encouraging results in terms of adhesion properties between unaged polymer modified bitumens and substrates coated with aged bitumens, simulating RA aggregates. Thus, five porous asphalt mixtures prepared with 15% course RA aggregates and different total binder contents were studied in the laboratory. A reference PA mixture containing only virgin aggregates was also investigated for comparison purposes. Indirect tensile strength tests, particle loss (Cantabro) tests, semi circular bending (SCB) tests and repeated indirect tensile tests were carried out in both dry and wet conditions in order to evaluate acceptability, durability, fracture resistance and water sensitivity of recycled mixtures. Results showed that recycled porous asphalt mixtures can perform as well as (or even better than) reference one. In particular, recycled mixtures at equal or higher binder contents than the reference mixture demonstrated an improvement in moisture resistance and durability.

Effect of Water Conditioning for Extended Periods on the Properties of Asphalt Binders

Selecting materials with a low susceptibility to moisture damage (i.e., stripping) is critical to guarantee the performance of asphalt pavements. Stripping in the asphalt mix can accelerate damage and consequently reduce pavement life. Most current research on moisture damage considers the effect of water on the mastic, the aggregate, and the adhesive bond between the aggregate and the binder. However, limited research has been conducted to determine the effect of extended water exposure on the properties of asphalt binders. This study investigated the influence of extensive water exposure on the stripping potential of asphalt binders by measuring the rheological properties, bond strength, and wettability of a Colombian binder before and after immersion. Thin films (2-mm height) of asphalt were immersed in water for 3, 6, and 9 months, and comparisons were made between the experimental results of unconditioned and conditioned binders. Master curves for complex modulus and phase angle were obtained by using a frequency sweep test in a dynamic shear rheometer. The bond strength between the binder and aggregates was measured with the recently developed binder bond strength test. The wettability potential of the conditioned and unconditioned binder was estimated by using the sessile drop method, and dynamic modulus testing of mixes prepared with the unconditioned and conditioned binder was conducted. Experimental results showed significant changes in the properties of the binder after 9 months of water conditioning. Further, dynamic modulus of the mixes prepared with the binder conditioned for 9 months was significantly higher than the modulus of the unconditioned mix.