Disk-shaped Compact Tension Test Research Articles

Interfacial characteristics of fiber asphalt mastic and aggregates: Impact on mixture crack resistance performance

The interfacial characteristics between fiber-modified asphalt mastics and aggregates play a crucial role in the performance of asphalt mixtures. To explore these interfacial interaction characteristics, three types of fibers (basalt, glass, and polyester), five levels of fiber content (ranging from 0.1% to 0.5% by mixture mass), and two types of aggregates (limestone and basalt) were selected, and an optimal mixture design was established. Contact angle tests, binder bond strength tests, and disk-shaped compact tension tests were conducted to investigate the impact of fiber type, fiber content, and aggregate type on interface characteristics. The results indicate that the addition of fibers can enhance the interfacial strength, with basalt fibers exhibiting superior reinforcement effects. As fiber content increases, the influence of aggregate type on interfacial strength decreases. Under ambient conditions, a composite failure mode was observed, while at low temperatures, cohesive failures dominated. The incorporation of fibers led to an increase in interfacial cohesion strength. The interfacial interaction strength between fiber asphalt mastic and aggregates exhibits a favorable linear correlation with the fracture energy and peak crack mouth opening displacement of the asphalt mixture. Overall, this study elucidates the microscopic mechanisms involved in fiber asphalt mixtures, laying the foundation for further in-depth research.

Comparative fracture resistance assessment of rubber-modified asphalt mortar based on meso-and macro-mechanical analysis

ABSTRACT This study investigates the effects of ground tire rubber (GTR) on the cracking resistance of asphalt mortar from different analysis scales. Furthermore, the effectiveness of different fracture test methods was compared for GTR-modified asphalt mortar, including the indirect tensile cracking test (IDEAL-CT), disk-shaped compact tension test (DCT) and Illinois flexibility index test (I-FIT). To achieve this, a mesoscopic fracture test based on the SEM-Servo Plus device was proposed firstly to obtain the micro-parameters of constitutive models in discrete-element modelling (DEM). A unified fracture modelling procedure that can avoid any interference factors was carried out for comparative fracture analysis. Results from the tests and simulations show that rubber filler plays a positive role in enhancing the fracture properties of the asphalt mortar. The fracture energy measured by IDEAL-CT is almost 5–6 times of the DC(T) test and 1.5–2 times of the I-FIT test. It is not an inherent attribute of material and can only be regarded as a relative index for fracture resistance evaluation. The FI and CTindex obtained from the I-FIT and IDEAL-CT test show a weak correlation of fracture resistance, especially when comparatively evaluating the GTR-modified asphalt mortar with minor difference in filler content.

Mitigation Strategy Selection for Asphalt Mixtures with High Reclaimed Asphalt Pavement Content

Economics and sustainability goals have driven higher use of recycled asphalt materials (RAMs), such as reclaimed asphalt pavement (RAP) and recycled asphalt shingles, in the pavement industry. Owing to the brittle nature of aged binders found in RAMs, a mitigation strategy is usually needed to ensure adequate cracking performance. Determining a proper mitigation strategy is vital to designing long-lasting asphalt concrete (AC) pavements with balanced performance. This study explored the use of mitigation strategies on AC mixtures with intermediate and high RAP contents, using materials from four mixtures that were part of a mill and overlay project in Milford, Delaware. This project included one standard mixture and three experimental mixtures with 25%–40% RAP. This paper presents performance data for field cores, plant-mixed laboratory-compacted specimens, and laboratory-mixed laboratory-compacted specimens. The effects and benefits of using a softer binder versus a recycling agent and the effects of using both a softer binder and a recycling agent to mitigate the stiff RAP binder are explored. To understand the effects of each mitigation strategy with aging, data from one-year field-aged cores and from laboratory-aged specimens are shown. Adjusting only one variable to mitigate the increased stiffness and brittleness of recycled binders yielded the best results in this study. Additionally, some test parameters were found to be sensitive to aging, including the flexibility index from the semicircular bend test and the cracking test (CT) index from the IDEAL-CT, while others were not observed to be sensitive to aging, including the fracture energy measured by the low-temperature disk-shaped compact tension test.

Performance Assessment of Bioasphalt Mixtures Containing Guayule Resin as an Innovative Biobased Asphalt Alternative

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of 0.65–0.69 kJ/m2 compared to 0.46 kJ/m2 for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, 400 J/m2). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered 591 J/m2 at its performance grade low temperature (−16°C) and 409 J/m2 at −22°C compared to 429 J/m2 for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Disk-shaped compact tension test for fracture analysis on pharmaceutical tablets

Pharmaceutical tablets must meet a number of requirements and among them, the mechanical strength plays an important role. The diametral compression test is generally used to evaluate it but can generate unstable failures. Thanks to load-unload cycles applied to the tablets subjected to a DCT test, it was shown that the concept of equivalent linear elastic fracture mechanics usually, can be successfully applied to the Mode I fracture behavior. Within this framework, the equivalent elastic crack growth resistance, commonly called resistance curve (R-curve), of the studied material was obtained and revealed the development of a Fracture Process Zone (FPZ) which is symptomatic of a quasi-brittle behavior. Moreover, the cyclic loading applied during the fracture test revealed the existence of a second dissipative mechanism leading to residual crack opening which seems to be mainly caused by friction phenomenon in the FPZ. • Fracture behavior of pharmaceutical tablets is a key issue for their manufacturing. • An alternative to the diametral compression test is proposed here. • No instability issues using the notch opening displacement controller. • A quasi-brittle behavior identified through equivalent LEFM theory. • Presence of dissipative mechanisms like micro-friction inside the process zone.

Application of Balanced Mix Design Strategies to Missouri Dense-Graded Asphalt Mixtures

This study focused on the improvement or redesign of dense-graded mixtures in Missouri by applying various strategies typified by a balanced mix design (BMD) approach. Briefly, the BMD approach involves designing mixtures using appropriate thresholds of mixture performance tests to control major distresses. In this study, two existing dense-graded mixtures from Missouri were adopted with 33% binder replacement by recycled asphalt pavement (RAP). Appropriate thresholds from three commonly used cracking tests, namely the disk-shaped compact tension test, or DC(T), the Illinois Flexibility Index Test (I-FIT), and the indirect tensile asphalt cracking test (IDEAL-CT), were paired with the Hamburg wheel track test (HWTT) toward the improvement or rebalancing of mixes designed before the availability or specified use of these tests. Preliminary test results showed that the existing mix designs did not satisfy the cracking thresholds adopted in this study, and thus the following modifications were made to the mixtures: (a) replacing the base binder with a softer grade binder, (b) adding a rejuvenator, and (c) adding ground tire rubber (either 10% or 20% by weight of base binder). According to the results, modification with rubber and softer binder was the most efficient strategy for improving and balancing DC(T) fracture energy and HWTT performance. On the other hand, the use of a softer binder or rejuvenator led to the best success in meeting semicircular bend (SCB) (I-FIT) and IDEAL-CT test requirements in balance with HWTT requirements.

Comprehensive Laboratory Evaluation of Recycling Agent Treated Plant-Produced Asphalt Mixtures

Recycling agent (RA) is typically used to restore or rejuvenate the properties of aged asphalt to desired properties. This study was motivated to comprehensively characterize the performance of asphalt mixtures treated with RA. The overarching goal of the research project is to provide guidance to agencies for revising asphalt mixture specifications to include RAs. Ten plant-produced mixtures were evaluated including three control mixtures (with 30 and 40% reclaimed asphalt pavement [RAP]) and seven 40% RAP mixtures treated with different RA products. Mixture testing was conducted with and without laboratory conditioning of loose mixture for 6 h at 135°C. Testing included the mixture Complex Modulus (E*) test for viscoelastic characterization, Direct Tension Cyclic Fatigue test for fatigue performance evaluation, Tensile Strength Ratio test for moisture susceptibility evaluation, and Semi-circular Bending test, Cracking Index Test and Disk-shaped Compact Tension test for mixture cracking and fracture behavior at different temperatures. In addition, the Hamburg Wheel Track Testing was conducted for rutting performance characterization on the unaged mixtures. Results show that addition of different RAs can improve the properties of asphalt mixtures by softening the mixtures with RAP and improving the cracking performance as compared with the control mixtures. However, addition of RA could severely deteriorate the rutting performance of mixtures and increase the moisture susceptibility as compared with the control mixtures. In addition, addition of certain RAs can also decrease the aging resistance of asphalt mixtures, specifically in context of cracking performance.

Laboratory Performance and Field Case Study of Asphalt Mixture with Sasobit Treated Aramid Fiber as Modifier

The use of fiber in asphalt mixtures can improve the mixture’s tensile strength and increase its cracking resistance, but the clumping of fiber in the mixture can weaken the improvement effect. The aim of this research is to assess the properties of Sasobit treated aramid fiber modified asphalt mixture and to validate the field case study. The rutting and stripping resistance of the fiber-modified mixture was identified with the Hamburg wheel tracking device. The low-temperature cracking characteristics of the asphalt mixture were quantified with the disk-shaped compact tension test. Moreover, the dynamic modulus test was adopted to reflect the response of the mixture to different loads and frequencies. The creep slope and stripping slope decreased by 67%, and the number of passes to stripping point and fail point increased by more than 250% after fiber modification. The fracture energy, peak load, and maximum crack mouth opening displacement (CMOD) of the mixture increased more than 10% after fiber modification. The dynamic modulus, rutting parameter, and fatigue parameter of the mixture were improved after fiber modification. The fiber in the mixture improved the stiffness of the mixture at high temperatures. The tensile strength improvement at low temperatures promoted the cracking resistance of the mixture. The cracking number in the fiber modified asphalt pavement was less than that in the control asphalt pavement. Thus, fiber modification could significantly restrict the propagation of cracking in the asphalt mixture. The implementation of fiber in the project can provide experience for future fiber application in asphalt pavement.

Evaluation of the Effects of Engineered Crumb Rubber (ECR) on Asphalt Mixture Characteristics

This study examined the effects of modification of dense-grade asphalt mixtures with chemically engineered crumb rubber (ECR) via the dry process. The ECR mixtures were compared to unmodified and polymer-modified mixtures in various criteria. The study mainly had three objectives: (1) comparison of mixture performance, (2) investigation of warm mix equivalence, i.e., to determine if the chemical coating on the ECR resulted in benefits similar to warm mix additives, and (3) to determine the effects of ECR on mixture draindown. For the first objective, the disk-shaped compact tension test was conducted to determine resistance to thermal cracking, and the Hamburg wheel tracking test was performed to determine resistance to permanent deformation (rutting) and moisture damage. To fulfill the second objective, the mixtures were prepared with warm mix asphalt (WMA) additives wherever necessary, and for the third objective, a stone mastic asphalt (SMA) was employed instead of the dense-grade mixture that was used for the rest of the study. Findings showed that modification with ECR greatly improved resistance to rutting and cracking, indicating that ECR pavements will exhibit longer service life. In terms of warm mix equivalence, a comparison of volumetrics data showed that ECR without WMA additive compacted in a similar manner as a polymer (PG 76-22) mixture containing WMA additive. Additional mix cost savings may be realized with ECR modification because of the ability to avoid the cost of WMA additive for the goal of achieving mix workability and compaction at lower temperatures. Finally, an ECR-SMA mix was used for draindown assessment and was found to pass the draindown test without the need for fibers, nearly matching the draindown resistance of the polymer-WMA mix containing cellulose fibers, thereby presenting another cost-saving avenue for contractors. The study also includes details of three field projects that used ECR and reported excellent field performance.

Mesoscale modeling of fracture in cement and asphalt concrete

In this paper, mesoscale modeling is performed to simulate and understand fracture behavior of two concrete composites: cement and asphalt concrete using disk-shaped compact tension (DCT) tests. Mesoscale models are used as alternative to macroscale models to obtain better realistic behavior of composite and heterogeneous materials such as cement and asphalt concrete. In mesoscale models, aggregate and matrix are represented as distinct materials and each material has its characteristic properties. Disk-shaped compact tension test is used to obtain tensile strength and fracture energy of materials. This test can be used as a better alternative to other tests such as three points bending tests because it is more convenient for both field and laboratory specimens in addition to its accurate results. Comparing the numerical results of the mesoscale models of cement and asphalt concrete specimens with experimental data shows that these models can predict the behavior of these composite materials very well as seen in the curves of load-crack mouth opening displacement (CMOD). Also, the mesoscale modeling highlights the variability of crack direction where it is dependent on the random distribution of aggregate.

Effects of Laboratory Compacted Asphalt Mixtures Air-Void Variations on Fracture Properties at Low Temperatures

Abstract Asphalt mixtures contain several constituents, among which air void content has a significant effect on pavement performance. In this research, the impact of laboratory compaction air-void variations for asphalt mixtures was investigated on asphalt-mixture fracture energy and peak load, as two primary outcomes of the disk-shaped compact tension test. Two groups of asphalt mixtures with air void contents of 7 ± 1.0 % were selected, and comprehensive statistical analyses, such as Pearson’s correlation coefficient, analysis of variance (ANOVA), Welch’s test, and Tukey’s test, were conducted to explore any possible impacts of specimen-to-specimen air-void variation on fracture energy and peak load. Statistical analyses have been carried out on individual asphalt mixtures in groups and all asphalt mixtures together as a group, as well. Results showed that there is a weak-to-negligible relationship between air void, fracture energy, and peak load. In addition, results of the ANOVA at the significance level of 0.05 revealed that air void content does not have any significant effect on asphalt mixtures’ fracture energy and peak load, except for peak load data when all asphalt mixtures are grouped as single population. Finally, results of Tukey’s test demonstrated that in a range of 7 ± 1.0 %, air void does not have a significant effect on fracture energy at the significance level of 0.05. The findings of this study can help researchers and agencies extend the air-void variation tolerance to 1 % in asphalt mixtures with target of 7 % air void content to assess low temperature cracking resistance.

Comparison of Fracture Test Methods for Evaluating the Crack Resistance of Asphalt Mixture

For the better understanding of fracture test method to evaluate the crack resistance of asphalt mixtures, the current test methods and evaluation indexes were theoretically and experimentally compared, including the indirect tensile test, single edge notch beam test, semicircular bending test (SCB) and disk-shaped compact tension test. The stress intensity factors for different tests were compared, and the appropriate range of notch depth was determined. The SCB was finally selected as the test method for evaluating the crack resistance of the asphalt mixtures. According to the relationship between the fracture energy and notch depths, the essential fracture energy of asphalt mixtures was calculated, and it was recommended as the evaluation index of asphalt mixtures for crack resistance. Furthermore, the failure process of the SCB was analyzed, and the contraflexure point on the load–displacement curve was found and defined. The fracture energy at the contraflexure point could be used to evaluate the ultimate crack resistance of the asphalt mixtures. The application of the essential fracture energy and the contraflexure point can correspond to the actuality of the asphalt pavement, which provides a reference for the crack resistance research of asphalt mixtures in the future.

Recycled asphalt shingle modified asphalt mixture design and performance evaluation

The inclusion of recycled asphalt shingles (RAS) in asphalt mixtures has become increasingly common; however, the underlying design principles vary significantly by agency. The primary objectives of this study included: (1) evaluating the ‘binder availability’ concept for RAS mixtures through a carefully designed laboratory experiment; (2) demonstrating a balanced mixture performance testing approach for the design of RAS mixtures; and (3) evaluating the field data of RAS mixtures placed in the Midwest region of the U.S. Three asphalt mixture designs with RAS contents of 0, 2.5% and 5.0%, which were designed to have nearly identical volumetric characteristics, were investigated. The binder availability was determined to be approximately 100% in the two RAS mixtures considered. In addition, Hamburg wheel tracking and disk-shaped compact tension tests were conducted to evaluate the high- and low-temperature mixture performance. As expected, the addition of RAS significantly improved the rutting resistance. Disk-shaped compact tension (DC(T)) test results demonstrated that a soft base binder effectively permitted the design of thermal-crack-resistant RAS mixtures. Field investigations indicated that the performance of pavement surfaces containing RAS was similar to that of surfaces containing only reclaimed asphalt pavement or virgin materials. This study also highlights a performance-engineered mix design approach, which is currently being adopted by several agencies in the Midwest (e.g., Illinois Tollway, Missouri DOT, etc.) and can provide mix designers a reliable approach for designing innovative asphalt mixtures with higher recycling levels and a modern, heterogeneous composition. Furthermore, the proposed approach may prove to be a simpler, more mixture-centric alternative to the primary method suggested in AASHTO PP78-17, which recommends arbitrary VMA bumping plus binder extraction, recovery, and advanced binder testing. • Study aims at determining binder availability from RAS material in asphalt mixtures. • Virgin and RAS mixtures were designed with identical volumetric parameters and asphalt contents were compared. • Binder availability was determined to be approximately 100% for RAS mixtures. • Performance-based tests were used to characterize RAS mixtures. • Field observations of mixtures with RAS were reported.

Employment of Mechanical Testing to Evaluate the Effect of Density on Asphalt Pavement Performance

Abstract Considering the budget allotted to construct and maintain roadway surfaces, a 5 to 10 % increase in their performance could potentially yield annual savings of billions of dollars. Considering this, the Kentucky Transportation Cabinet (KYTC) launched a project to better understand the effect of in-place density on the durability of their hot-mix asphalt (HMA) pavements. In-place density is known to be a crucial factor in HMA performance. The Asphalt Institute in cooperation with the KYTC embarked upon the research and collected numerous HMA samples from five pavement construction sites in Kentucky. An experimental laboratory plan was developed to examine potential improvement in the mixtures’ performance if they were compacted to a desired higher density. The laboratory test plan consisted of flow number, flexural beam fatigue, and disk-shaped compact tension tests to evaluate the mixtures’ performance with respect to rutting, fatigue cracking, and low-temperature cracking. A statistical analysis of the results was performed to evaluate the effect of density on the durability of each of the pavements. The results showed that the service life of the pavements could improve considerably by achieving a target density of 92 %. The compactibility of the HMA mixtures was also investigated through their compaction characteristic curves by using the Superpave gyratory compactor. Based upon the compactibility analysis, the mixtures could be better compacted in the field by increasing their lift thickness.

Model I cohesive zone models of different rank coals

The present work develops cohesive zone models (CZM), i.e. cohesion-separation laws, for mode I fractures in different rank coals, including weakly caking coals, gas coals, fat coals, meager-lean coals and anthracite, through disk-shaped compact tension tests. Firstly, the experiments show that with the coal rank rising, the critical crack separation displacements and the degrees of the nonlinearity of the softening function decline gradually. By fitting the experimental data with the four commonly used cohesive zone models including the power law, the exponential law, the bilinear law and the linear law, the best-fitted model for each rank of coals was identified and the corresponding parameters were found. Secondly, to arrive at a general CZM formulation for the different rank coals, Karihaloo’s polynomial law was employed, which also gave better fit to the experimental data compared with the aforementioned four CZMs. After obtaining the CZM for coals, fracture energy was evaluated which is equal to the area under the softening curve. With the increase of the coal rank, the fracture energy reduces but its coefficient of variation increases. Thirdly, the geometric characteristics of fractures in different rank coals are studied. The lower rank coals have more tortuous crack propagation paths and larger roughness coefficients, whereas the higher rank coals possess wider average fracture apertures. Lastly, in order to further test the applicability of the obtained cohesion-separation laws, we implemented the Karihaloo’s polynomial CZM and the bilinear CZM into the cohesive elements of ABAQUS® using the user-subroutine VUMAT, and thereby simulated the crack propagation in single-edge notched beams made of weakly caking coals, fat coals, and meager-lean coals, respectively. It is found that the numerical results based on Karihaloo’s polynomial CZM have a better agreement with the experimental data than the bilinear CZM.

Performance Evaluation of Asphalt Mixtures with Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Missouri

This study investigates the performance of eighteen different dense-graded asphalt mixtures paved in Missouri. The sections contain a wide range of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS), and different types of additives. The large number of sections investigated and the associated breadth of asphalt mixtures tested provided a robust data set to evaluate the range, repeatability, and relative values provided by modern mixture performance tests. As cracking is one of the most prevalent distresses in Missouri, performance tests such as the disk-shaped compact tension test (DC[T]) and Illinois flexibility index test (I-FIT) were used to evaluate the cracking potential of the sampled field cores. In addition, the Hamburg wheel tracking test (HWTT) was employed to assess rutting and stripping potential. Asphalt binder replacement (ABR) and binder grade bumping at low temperature were found to be critical factors in low-temperature cracking resistance as assessed by the DC(T) fracture energy test. Six sections were found to perform well in the DC(T) test, likely as a result of binder grade bumping (softer grade selection) or because of low recycling content. However, all of the sections were characterized as having brittle behavior by the I-FIT flexibility index. Service life and ABR were key factors in the I-FIT test. Finally, a performance-space diagram including DC(T) fracture energy and HWTT rut depth was used to identify mixtures with higher usable temperature interval (UTImix), some of which contained significant amounts of recycled material.

Microwave-healing performance of modified asphalt mixtures with flake graphite and exfoliated graphite nanoplatelet

This paper computationally and experimentally investigated the microwave healing performance of graphite (flake graphite and exfoliated graphite nanoplatelet (xGNP)) modified asphalt mixture. The original fracture energy and strength were first measured for the modified asphalt mixture through the disk-shaped compact tension test. Then the micro-wave healing performance (recovered fracture energy and strength) were further examined. All these were enhanced with the added carbon materials. The recovered fracture strengths were also compared with FE cohesive zone model (CZM) simulation with digital image correlation (DIC) calibrated parameters. The predicted recovered fracture strength had good agreement with the experimental measurement.

Inverse Estimation of Cohesive Fracture Properties of Asphalt Mixtures Using an Optimization Approach

Tensile cracking in asphalt pavements due to vehicular and thermal loads has become an experimental and numerical research focus in the asphalt materials community. Previous studies have used the discrete element method (DEM) to study asphalt concrete fracture. These studies used trial-and-error to obtain local fracture properties such that the DEM models approximate the experimental load-crack mouth opening displacement response. In the current study, we identify the cohesive fracture properties of asphalt mixtures via a nonlinear optimization method. The method encompasses a comparative investigation of displacement fields obtained using both digital image correlation (DIC) and heterogeneous DEM fracture simulations. The proposed method is applied to two standard fracture test geometries: the single-edge notched beam test, SE(B), under three-point bending, and the disk-shaped compact tension test, DC(T). For each test, the Subset Splitting DIC algorithm is used to determine the displacement field in a predefined region near the notch tip. Then, a given number of DEM simulations are performed on the same specimen. The DEM is used to simulate the fracture of asphalt concrete with a linear softening cohesive contact model, where fracture-related properties (e.g., maximum tensile force and maximum crack opening) are varied within a predefined range. The difference between DIC and DEM displacement fields for each set of fracture parameters is then computed and converted to a continuous function via multivariate Lagrange interpolation. Finally, we use a Newton-like optimization technique to minimize Lagrange multinomials, yielding a set of fracture parameters that minimizes the difference between the DEM and DIC displacement fields. The optimized set of fracture parameters from this nonlinear optimization procedure led to DEM results which are consistent with the experimental results for both SE(B) and DC(T) geometries.

Use of Nonlinear Acoustic Measurements for Estimation of Fracture Performance of Aged Asphalt Mixtures

This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture performance tests and investigated the possibility of estimating the low-temperature fracture properties of aged mixtures by using a nonlinear ultrasonic approach. Asphalt mixture samples, oven aged for 12, 24, 28, 32, and 36 h at 135°C, were compacted, made into test specimens, and evaluated by using a noncollinear wave-mixing approach. In addition, the embrittlement temperature and fracture energy of the replicate samples were assessed by using the acoustic emission test and the disk-shaped compact tension test. Comparison of results from the three testing methods clearly showed similar trends. This finding suggests that the fracture properties of mixtures can be estimated by using the noncollinear ultrasonic wave-mixing approach, which is a nondestructive method which does not require core extraction in the field.

Low Temperature Fracture Properties of Polyphosphoric Acid Modified Asphalt Mixtures

AbstractThe low temperature fracture properties of polyphosphoric acid (PPA) modified mixtures are evaluated and compared with those of polymer modified mixtures. The main objective is to determine whether PPA can partially or completely substitute traditional polymer modifiers, without adversely affecting the mixture’s resistance to thermal cracking. Laboratory compacted and field cored test samples from the Minnesota Road Research Project (MnROAD) were tested using traditional methods as well as newly developed fracture testing protocols: indirect tensile test (IDT), semicircular bending test (SCB), and disk-shaped compact tension test (DCT). The effects of temperature, air-void content, comma and long-term aging on low temperature fracture properties were analyzed; and field performance observations of the test cells from MnROAD were discussed. On the basis of the analysis, the fracture resistance of the PPA modified mixture is less than that of the SBS modified mixture. However, when PPA is used to su...