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Moisture damage resistance assessment in asphalt mixtures traditionally relies on the tensile strength ratio (TSR) method, which may not capture the complex behavior of asphalt under moisture ingress. This study proposes an innovative multifaceted approach for assessing moisture susceptibility, challenging the overreliance on TSR, and integrating multiple intricate aspects of asphalt behavior. Employing two dense-graded and one gap-graded polymer-modified binder mixtures with nominal maximum aggregate size (NMAS) of 13 and 19 mm, the study defines threshold values for total air voids, effective air voids, indirect tensile strength, and percentage density change. Evaluations were conducted using a device selected for its dynamic capabilities in inducing stresses and creating pore pressure under elevated temperatures. This research proposes a new zone-based approach to classify mixtures as moisture-resistant, partially moisture-resistant, or moisture-susceptible. This innovative method, grounded on maximum effective air voids and percentage density change, offers nuanced insights for more accurate moisture resistance assessments. Furthermore, the study explores the effect of effective air void size on moisture damage resistance by image processing for dense and gap-graded gradation of 13.2 NMAS, unveiling clogging behavior especially in dense-graded mixture due to smallest pore size. In conclusion, the study provides an in-depth understanding of asphalt mixture behavior under moisture ingress. By offering a novel approach that integrates multiple parameters and extends beyond the conventional TSR approach, it contributes a practical solution for mitigating moisture damage in asphalt mixtures. This research sets the stage for a potential paradigm shift in the approach to moisture susceptibility assessment, enriching the asphalt field with critical insights. [ABSTRACT FROM AUTHOR]

Long-term aging of asphalt binder plays a major role in fatigue cracking resistance of asphalt mixes. With the use of polymer-modified binder (PMB) with different polymer concentrations, aging susceptibility of asphalt mixes becomes an interesting area to explore. This study evaluated four types of asphalt mixes prepared with PMB, subjected to compacted mix aging (CMA) (85°C, 5 days) and loose mix aging (LMA) (85°C, 8 days). The aged asphalt mixes were tested for their resistance to cracking using the indirect tensile asphalt cracking test (IDEAL-CT). Furthermore, aged binders were extracted from long-term-aged loose and compacted mixes, and their fatigue resistance was examined using the Superpave fatigue factor (|G*|·sinδ), linear amplitude sweep (LAS) test, and binder yield energy test (BYET) parameters. The results indicated that both asphalt binder and mixes exhibit better cracking resistance in CMA conditions compared to LMA conditions. Mixes prepared using PMB with higher polymer content performed better in cracking resistance and were less sensitive to aging. Furthermore, to evaluate the effect of rheology of aged binder on fatigue cracking resistance of mixes, binder fatigue parameters were correlated to cracking index (CTindex) and postpeak slope (|m75|) of mixtures. Other than the yield energy parameter of BYET, a good correlation was observed between binder fatigue and mix fatigue parameters. Outcomes of this study will potentially help to understand the relationship between mixture cracking parameter and standard binder fatigue parameters and their aging sensitivity. [ABSTRACT FROM AUTHOR]

The recent emphasis on adopting the balanced mix design (BMD) concept has encouraged highway agencies and practitioners to explore simple performance tests to capture the rutting performance of asphalt mixes. Though many researchers have adopted the Hamburg wheel tracking test (HWTT) to evaluate rutting resistance, certain limitations, such as using this test method during quality control/quality assurance (QC/QA) are challenging. Therefore, researchers are exploring ways to implement surrogate simple performance tests, namely the ideal shear asphalt rutting test (IDEAL-RT) and the high-temperature indirect tensile strength test (HT-IDT) to support QC/QA of asphalt mixes. However, establishing limiting threshold values of rutting parameters based on such simple performance tests is still in the research stage. Eight mixes with different types of aggregates, binders [unmodified, polymer-modified binder (PMB), and crumb rubber–modified binder (CRMB)] and gradations having different nominal aggregate sizes (NMAS) were collected from various plants. HWTT, IDEA-RT, and HT-IDT were conducted on samples compacted at 7%±0.5% air voids using the Superpave gyratory compactor. The data analysis showed that the rutting resistance index (RRI) parameter derived from HWTT are promising and advantageous compared with final rut depth, as it incorporates the combined effect of rut depth and number of passes. The study presented correlations of different rutting parameters (shear strength, RTIndex , and HT-IDT strength) derived from IDEAL-RT and HT-IDT with the HWTT RRI parameter. Moreover, to ascertain the pass/fail criteria of asphalt mixes, critical threshold values were proposed and recommended for shear strength, RTIndex , and HT-IDT strength as 1.0 MPa and 65 and 135 kPa, respectively. IDEAL-RT followed by HT-IDT are the most suitable potential surrogate simple performance tests for HWT to screen better and worse rutting performance. [ABSTRACT FROM AUTHOR]

This study focused on evaluating the rutting performance of three different highly polymer-modified asphalt (HiMA) binders (i.e., O, T and B) using binder-based [i.e., multiple stress creep recovery (MSCR) and force ductility (FD)] and mix-based [flow number (FN) and Hamburg wheel tracking test (HWTT)] rutting performance tests. The binder-based rutting indicators were compared with mix rutting performance to determine a parameter that can help in the correct prediction of HiMA rutting resistance. In addition, the study looked into application of a simple performance test, the indirect rutting tolerance index (IDEAL-RT), for HiMA mix rutting prediction. The MSCR test revealed different rankings of recovery at 0.1- and 3.2-kPa stress levels. Moreover, the T and B binders did not satisfy the stress sensitivity criteria (Jnr_difference) of Max 75%. The force ductility tests revealed that the peak force observed for polymer network phase in HiMA was significantly higher than base binder stiffness, which is in contrast with force distribution in polymer-modified binders (PMBs). The mix rutting resistance ranking (O>T>B) was similar in all the tests (i.e., FN, HWTT, and IDEAL-RT). Although IDEAL-RT can be used to compare the rutting resistances of HiMA mixes, detailed future work is required to establish its acceptability in comparing various types of mixes and the minimum requirements of RTIndex. The comparison between binder and mix rutting indicators demonstrated that MSCR testing on binder at stress levels of 6.4 kPa and higher can be used to predict the rutting resistance of HiMA binders. Parameters like slope and cohesion energy and a newly introduced parameter—work done for polymer activation (WPA)—from FD tests can be used to determine the polymeric phase dominance in HiMA binders. Overall, this study provides pavement stakeholders with a framework for rightly predicting the rutting resistance and polymeric phase dominance of HiMA binders and mixes using MSCR, FD, and IDEAL-RT tests. [ABSTRACT FROM AUTHOR]

Fillers are known as dust fractions in asphalt mixes having a predominant particle size less than 75 micrometer (μm). Typical filler concentration in an asphalt mix varies from 4% to 12% (by aggregate weight). The effects of filler intrinsic properties on mastic behavior can get magnified with the concentration of filler. Thus, in filler-rich mixes like stone matrix asphalt (SMA), the filler characteristics and concentration can be sensitive factors, playing significant roles in the performance of asphalt mastic and mix. The study considered six different types of fillers to capture the effect of filler characteristics on mastic. The mastics were prepared with a constant filler concentration by volume (F/Bvol=0.49), which was determined by a typical SMA mix design. The fillers were characterized based on their surface area, size distribution, shape, Rigden voids (RV), clay content, and chemical composition. The filler effects on mastic were evaluated based on the stiffness (complex modulus) and stiffness ratio. The weak correlation observed between the mastic stiffness and the fixed and free binder reveals that the RV and filler fixing factor (FFF) can mislead regarding the stiffening potential of filler material. The surface areas by Brunauer–Emmett–Teller (BET) and Blaine's methods were insufficient to represent the stiffening potential while the stiffness showed a better correlation with the concentration of finer gradations in the filler evinced by a higher coefficient of P10 (percentage passing 10 μ sieve size) and fineness modulus (FM) parameters. Further, the micromechanics based understanding of mastic behavior explains the mastic stiffening phenomenon as the combined effects of adsorbed asphalt layer thickness and interparticle interaction. The linear relation observed between stiffness ratio and newly derived micromechanism stiffening factor (MMSF) indicates that in filler-rich mastics, the stiffness may be improved with a finer sized filler (lower FM) and higher volume concentration. However, the adsorbed layer thickness didn't show correlation with any of the filler properties considered. The study recommends a limiting value for mastic stiffness in terms of stiffness ratio which is established based on MMSF factor. A limiting value for stiffness of mastic could be significant to avoid dry mixes and subsequent poor fatigue performance. [ABSTRACT FROM AUTHOR]

India is witnessing unprecedented growth in its road network. To meet the asphalt binder demand, distillation towers have been loaded with crude oil from different sources. Although the quality system is expected to guarantee reduced variability, a quality system based on traditional indexes may lead to high variability in binders of the same grade. Because India relies on traditional indexes for quality control, we aimed to quantify such variability and its impact specifically on moisture damage resistivity. Additionally, the response of binders from different sources in the short term and long term has also been evaluated. Five binder sources were selected, and they were meant to conform to the same viscosity grade. Thereafter, moisture damage assessment tests such as surface free energy (SFE) measurements, bitumen bond strength (BBS) test, rolling bottle test (RBT), and boiling water test (BWT) were performed in unaged, short-term aged, and long-term aged conditions. Additionally, variations in chemistry of the binders were assessed based on Fourier transform infrared (FTIR) spectroscopy. It was concluded that the chemical and moisture damage characteristics had a strong dependence on the source of the binder. Furthermore, there was substantial variability in the moisture damage performance for binders from different sources. This implied that quality systems based on traditional indexes may not be stringent enough to reduce the variability. The impact of aging on the moisture damage resistivity of the asphalt–aggregate system was also discussed. Given the limited information available in the literature on asphalt binder variability of the traditional grading system, the data reported in this study can serve as reference for future studies dealing with its characterization and assist in developing a strategy for reducing uncertainty related to the performance of asphalt mixes. [ABSTRACT FROM AUTHOR]

Moisture-induced damage of asphalt pavements constitutes a primary distress. To quantify the extent of moisture-induced damage efficiently, a moisture-induced stress tester (MIST) was developed. This study adopts varying stress cycles of MIST to condition the asphalt mixes without and with reclaimed asphalt pavement (RAP) to ascertain their moisture-induced damage resistivity. Hence, the control mix (0% RAP) and mixes containing 10%, 20%, 30%, and 40% RAP by weight were prepared and conditioned using 0, 1,000, 2,000, 3,500, 5,000, and 10,000 stress cycles of MIST. Thereafter, an indirect tensile (IDT) strength test was conducted on the prepared mixes. Using analytical approaches, the biaxial state of stress was defined to compute the static (ES,H) and average modulus (ES,A). Increasing stress cycles of MIST decreased the stiffness of control and RAP mixes. The compressive stress–strain curve (SSC) was plotted and utilized to compute the linearity and toughness index (TI) of control and RAP mixes. Increasing stress cycles of MIST were observed to increase the ductility of control and RAP mixes, whereas prepeak linearity was observed to reduce it. The TI increased with the increase in stress cycles of MIST. New moisture damage ratios (MDRs) were computed by utilizing ES,H and ES,A and compared with the commonly adopted tensile strength ratio (TSR). Based on such MDRs, it was concluded that RAP improves the moisture-induced damage resistivity of asphalt mixes. Statistical analysis indicated that both ES,H and ES,A have the potential to be good indicators of moisture-induced damage of control and RAP mixes. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of six different bitumen film thicknesses (0, 0.2, 0.4, 0.6, 0.8, and 1 mm); four polishing levels of aggregate [220, 400, 600, and 800 Silicon Carbide (SiC)]; three moisture conditioning temperatures (25°C, 40°C, and 60°C); and three different aging levels of bitumen (143°C, 163°C, and 173°C) on interfacial strength of basaltic-unmodified bitumen system using binder bond-strength (BBS) test. Further, two different basaltic aggregates were procured, and their interfacial bond with three different types of bitumen, namely, unmodified (VG30), polymer-modified (PMB40), and crumb rubber–modified (CRMB60) was evaluated. The results showed that basaltic aggregate with higher porosity (and thus higher rate of moisture absorption) showed lower bond strength, although the polishing level of both aggregates was kept at 220 SiC. Further, PMB40 had higher bond strength followed by VG30 and CRMB60, depicting the influence of crumb rubber particles on interfacial bonding behavior of CRMB60. The study showed that 220 SiC polished aggregates having 0.8-mm bitumen film thickness and conditioned at 40°C can provide appropriate results on aggregate-bitumen bond strength using the BBS test, which supports the recommendations provided in AASHTO T 361. Thus, the authors believe that the BBS test may be beneficial in evaluating aggregate-bitumen bond strength in the field. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is a nanomaterial that is characterized by a two-dimensional, atomically thin, honey-combed lattice. Studies over the years have indicated potential applications of GO for improving performance characteristics of asphalt binder. This study attempts to explore the impact of GO on various chemical and rheological characteristics of unmodified asphalt binder (AC30). GO was added to AC30 over varying dosages of 1%, 2%, and 3% by weight. Carbon (C), hydrogen (H), and nitrogen (N) determinations and Fourier-transform infrared (FTIR) spectroscopy aided in understanding the chemical interaction of GO with AC30. Further, the effect of GO on dynamic viscosity was also evaluated. Rutting performance of GO-modified AC30 was studied using the multiple stress creep recovery (MSCR) test, whereas fatigue performance was evaluated based on the linear amplitude sweep (LAS) test. Additionally, yield energy GO-modified AC30 was comprehended using the binder yield energy test (BYET). CHN determination and FTIR spectroscopy indicated that modification of GO is mostly physical in nature. An improvement in aging resistivity was observed due to incorporation of GO. GO was observed to increase dynamic viscosity. Improvement in both rutting and fatigue performance of AC30 was observed but different optimum dosages of GO were obtained: 1% for maximum rutting performance and 2% for maximum fatigue performance. Enhancement in yield energy and recovery potential was also observed. [ABSTRACT FROM AUTHOR]

Modification of asphalt binder with Elvaloy (Elv) and polyphosphoric acid (PPA) has been reported to have better performance. However, such modification may increase mixing and compaction temperatures of asphalt binder. Furthermore, the positive effect of PPA may get neutralized with the addition of lime, which can lead to inferior performance of asphalt binders. Recently, different types of warm mix additives (WMA) are being introduced to reduce production and construction temperatures of asphalt binder. However, the effects of WMA additives with and without lime on various rheological response of PPA + Elv modified asphalt binder is not well understood so far. Therefore, the present study was undertaken to evaluate the rutting and fatigue performance of PPA + Elv modified asphalt binder (referred as Control binder) containing threeWMAadditives (water, chemical, and wax-based) with and without lime. The multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests were conducted to capture the rutting and fatigue performance of asphalt binders, respectively. The results show that rutting and fatigue performance of Control asphalt binder decreased with the addition of chemical and water-based WMA additives. The performance of Control asphalt binder further deteriorated when these WMA additives (chemical and water) were used with lime. Interestingly, the addition of wax showed higher rutting resistance and similar fatigue life as that of Control asphalt binder. The addition of lime with wax additive showed improved rutting resistance and reduced fatigue life compared with Control asphalt binder. Regardless of the type of WMA additives, the addition of lime decreased the fatigue life of Control asphalt binder. The adverse effect of lime was prominent when used with wax compared with water and chemical-based WMA additives. Furthermore, the addition of WMA additives increased the stress sensitivity of Control asphalt binder. The stress sensitivity of asphalt binder further increased when wax and chemical-based WMA additives were used with lime. However, use of water-based WMA additive and lime reduced the stress sensitivity of Control asphalt binder. Overall, it can be concluded that the performance of Elv + PPA modified asphalt binder depends largely on the type of WMA additives and their combination with lime. [ABSTRACT FROM AUTHOR]

The current study compared aggregate shape parameters and laboratory performance of coarse aggregates produced from two different types of crushing operations. The coarse aggregates from two type of crushing operations, (1) a series of jaw (J)-cone(C)-vertical shaft impactors (V), called JCV, and (2) a series of jaw (J) and horizontal shaft impactors (H), called JH, were selected in the present study. The coarse aggregates collected from both crushing operations were separated into five different sizes ranging from 4.75 to 25 mm. The shape parameters [angularity, texture, sphericity, and flatness (F) and elongation (E)] of different sizes of coarse aggregates were measured using the aggregate image measurement system (AIMS) device. Further, the influence of aggregate shape parameters on their packing behavior and stability were evaluated by conducting three laboratory tests: void in coarse aggregate (VCAdrc), angle of repose (AoR), and the direct shear test (DST). The results showed that both the JH and JCV series of crushers produced aggregates with similar angularity; however, significant differences were observed in texture, sphericity, and F and E of aggregates. The aggregates produced from the JH crusher were found to have higher VCAdrc, AoR, and friction angle compared to aggregates from the JCV crusher. The results showed that aggregates obtained from the JH crusher may have better interlocking and stability than aggregates from the JCV crusher. [ABSTRACT FROM AUTHOR]

The present study was undertaken to understand the moisture damage resistance of unmodified and ground tire rubber (GTR)-modified asphalt binders containing three different type of warm mix asphalt (WMA) additives using the surface free energy (SFE) approach. The SFE parameters of unmodified and GTR-modified asphalt binders with and without WMA additives were determined in the laboratory using theWilhelmy plate method. The SFE of two types of aggregate, namely, granite and limestone, were adopted from literature. Thereafter, work of adhesion, work of cohesion, work of debonding, and energy ratio (ER) were estimated for a total of 16 different combinations of aggregate and asphalt binder. An attempt was made to evaluate sensitivity of SFE parameters with elemental composition (carbon, hydrogen, nitrogen, and sulfur) of asphalt binder. The results showed that moisture damage resistance of unmodified and GTR-modified asphalt binder decreases with addition of WMA additives. The control asphalt binder with Rediset (Akzo Nobel, Netherlands) showed better bond with aggregate, followed by Sasobit (SasolWax, Hamburg, Germany) and Advera (PQ Corporation, Malvern, Pennsylvania). The limestone aggregate showed better moisture damage resistance compared with granite aggregate. The elemental composition (CHNS) of an asphalt binder found to have a fair correlation with SFE parameters. [ABSTRACT FROM AUTHOR]

The current study was undertaken to evaluate the effect of aggregate shape parameters (i.e., angularity, sphericity, form, and texture) and gradation on the permeability of commonly used aggregate bases in Oklahoma. Aggregates used in this study were collected from three different quarries. For each aggregate type, upper and lower limits of three different gradations, modified AASHTO #57, Oklahoma Aggregate Association (OKAA) Type M, and Oklahoma DOT (ODOT) Type A, were selected. Permeability of 18 different combinations of aggregate types and gradations (three aggregate types × three gradations × two gradation limits) were tested using a falling-head permeability approach. For a selected gradation, the lower limit exhibited higher permeability values than the upper limit. Also, permeability was found to increase with an increase in effective diameter and void ratio. An increased coefficient of uniformity and fine content resulted in lower permeability, as expected. Further more, the shape parameters of different aggregate types were measured using an aggregate imaging system (AIMS). The coefficient of permeability was found to increase with reduced gradient angularity and increased sphericity. The texture index was found to have minimal impact on the coefficient of permeability. A regression model was developed using aggregate shape and gradation parameters to estimate permeability of aggregate bases. [ABSTRACT FROM AUTHOR]

Over the past few years, many regression-based and artificial neural network (ANN)-based models have been developed to estimate the dynamic modulus of hot mix asphalt (HMA). These models use the gradation of aggregates and the volumetric properties of compacted samples as input variables to the model. However, none of these models use aggregate shape parameters (i.e., angularity, texture, form, and sphericity) in the development of the model. Recently, researchers have expressed concerns that the shape parameters of aggregates need to be considered in the estimation of dynamic modulus. The primary objective of this study was to develop an ANN-based model for the estimation of dynamic modulus of HMA using aggregate shape parameters. The dynamic modulus of 20 different HMA mixes composed of various sources, sizes, types of aggregates, and different volumetric properties were measured in the laboratory. The shape parameters of different sizes of coarse and fine aggregates were measured with an automated aggregate image measurement system (AIMS). An ANN-based model was developed to consider the following input variables: aggregate shape parameters (i.e., angularity, texture, form, and sphericity), frequency, asphalt viscosity, and air voids of compacted samples. A sensitivity analysis of each model parameter was conducted by correlating these parameters with dynamic modulus. It is expected that this study will be helpful in predicting the dynamic modulus of HMA using aggregate shape parameters. [ABSTRACT FROM AUTHOR]