Texas Overlay Test Research Articles

Prediction of asphalt concrete energy release rate from Texas Overlay Test using machine learning

This study aimed to apply machine learning (ML) models to predict the energy release rate (ERR) in the Texas Overlay Test (TXOT) for the reflective cracking of asphalt concrete (AC) overlay. The Generalised Finite Element Method model was developed with TXOT experimental results. Subsequently, a TXOT Finite Element database was constructed. Four different cases were formulated, each utilising distinct input variables and the same output variable (i.e. ERR). Five ML models were trained and evaluated for ERR prediction. The model performances were compared across four cases to determine the optimal set of input variables. Shapley Additive exPlanations methods were employed to interpret ML models. The results demonstrated that ML models performed differently across different cases. Artificial Neural Network achieved the highest accuracy in the case which included crack length, crack opening, AC modulus, and sigmoidal function parameters. Therefore, ML models prove to be accurate and reliable for predicting ERR.

Effects of Air Void Content, Crumb Rubber, and Pozzolanic Fillers on OGFC Laboratory Performance

Open-graded friction course (OGFC) is recognized for its ability for rapid stormwater drainage and effective noise reduction. Yet, several state highway agencies have limited its use because of concerns about its durability. The objective of this study was to investigate the impacts of air void (AV) reduction, crumb rubber (CR), and pozzolanic fillers on OGFC durability. Six mixtures were fabricated in the laboratory and their performance was evaluated. A control mix, 9.5-NMAS mix, two mixes incorporating CR, and two mixes prepared with pozzolanic fillers (i.e., Portland cement and fly ash) were evaluated. The test factorial was designed so that each mix would be evaluated at three different stages (i.e., production, construction, and field performance). A suite of laboratory tests was conducted including draindown, prediction of compaction effort, Cantabro abrasion loss, Hamburg wheel-tracking, Texas overlay tester, modified Lottman test, and boiling test to evaluate production, compaction, and OGFC resistance to raveling, permanent deformation, cracking, and moisture damage. Results showed that the reduction in AV and the use of CR and pozzolanic fillers considerably enhanced OGFC durability while maintaining appropriate functional performance (i.e., permeability).

Development of a Laboratory Operations-Friendly Long-Term Loose Mix Aging Protocol for New Asphalt Pavements

New asphalt pavements are often designed to last 15 to 20 years without a major rehabilitation. However, an asphalt mix gets stiffer and more brittle with pavement service life because of aging. As cracking resistance decreases at higher aging levels, pavement structural design and performance verification need to consider the long-term aging characteristics of asphalt mixes. The research presented in this paper developed long-term loose mix aging protocols that are more friendly to routine laboratory operations. Based on a theoretical aging model and the IDEAL cracking test, two aging protocols are equivalent to the 3- and 6-day loose mix aging durations at 95°C provided by NCHRP 9-54, which are 20 h at 110°C and 20 h at 120°C, respectively. These new long-term aging protocols were then confirmed by the Texas Overlay Test and the Illinois Flexibility Index Test. The integration of these protocols into a comprehensive framework for mix design, pavement performance verification, and production testing is discussed. In brief, these new long-term aging protocols would be employed for evaluating cracking resistance only in the pavement performance verification stage, whereas the short-term aging protocol, namely, 2 h at the compaction temperature, would be applied to Superpave volumetric evaluation, balanced mix design (BMD), and production testing. These two new aging protocols combined with BMD rapid performance tests and performance prediction tests make this comprehensive framework very practical and efficient.

Evaluating fatigue resistance based on viscoelastic properties of asphalt mixtures

ABSTRACT In this study, the fatigue resistance of different asphalt mixture types subjected to the same aging condition was evaluated using linear viscoelastic properties of asphalt mixtures. The relaxation spectra were determined from the dynamic modulus test based on the linear viscoelastic theory, and the relationship between the parameters of relaxation spectra and the parameters of the storage modulus master-curves were developed. The Texas overlay test was conducted to evaluate the fatigue resistance with the number of load cycle to failure used as the measure of fatigue resistance. From the corresponding results, it is shown that the inflection point frequency of the dynamic modulus master-curves could be used to assess the fatigue resistance compared to other parameters. The Glover-Rowe parameter also exhibited a fair relationship with the fatigue resistance of the asphalt mixtures. The effect of the shape parameter (γ) of the dynamic modulus master-curves was quantified but seemed not very sensitive to fatigue resistance for the asphalt mixtures evaluated. In the study, a new parameter (VECIndex) was developed to evaluate the fatigue resistance, which considered the inflection point frequency and shape of the dynamic modulus master-curves, both of which influence the linear viscoelastic properties and fatigue resistance of asphalt mixtures.

Laboratory Evaluation of Warm-Mix Asphalt Open-Graded Friction Courses

This study aimed at evaluating the laboratory performance and physical characteristics of warm-mix asphalt (WMA) open-graded friction course (OGFC) mixes prepared with three warm-mix additives (two chemical additives and an organic additive). To achieve this objective, four mixes were prepared including a control mix (CM) prepared with a PG 76-22 binder and two sources of aggregate (i.e., # 78 limestone and # 67 sandstone). Air voids and coefficient of permeability ( k) were used to evaluate the functionality of the OGFC mixes. In relation to constructability, the compaction energy index was used to compare the required compaction effort during construction. Furthermore, the Cantabro test, Hamburg wheel-tracking test, Texas overlay test, Modified Lottman, and boil tests were conducted to evaluate durability, permanent deformation, cracking, and moisture-damage resistances of the evaluated mixes. Results indicated that the use of WMA technologies enhanced OGFC durability and performance. Among the evaluated mixes, the organic additive-OGFC met all Louisiana Department of Transportation and Development and NCHRP 01-55 requirements, as it notably enhanced OGFC durability, cracking, and moisture-damage resistance. Furthermore, the use of WMA notably reduced the required compaction effort and mixing temperature needed during production and construction as compared with the CM.

Evaluation of Full-Depth Reclamation and Cold Central-Plant Recycling Mixtures for Laboratory Compaction, Mechanistic Response, and Performance Properties

Cold recycled mixtures (CRM) are gaining wider acceptability in the United States for rehabilitating existing pavement or new construction while reducing construction costs, environmental impacts, and construction time. However, the technology is still in development owing to inconsistency in design and limited research on mechanistic and engineering properties. To this end, this study evaluates full-depth reclamation (FDR) and cold central-plant recycling (CCPR) materials for evaluating (i) laboratory compaction protocols, (ii) mechanistic properties, and (iii) engineering performances. Two compaction methods—the Superpave gyratory compaction and the modified proctor—were developed for designing test specimens with adequate design properties. The mechanistic properties resilient modulus ( MR) and dynamic modulus (| E*|) were evaluated. Laboratory performance testing such as Texas overlay tester, semi-circular bending, and a modified Hamburg wheel tracking (HWT) were performed. This study also proposed a new parameter, loading limit ( Nmax), based on the modified HWT test configuration. The study found that the FDR exhibits less temperature dependency compared with the CCPR while subjecting to loading. Based on damage properties such as critical fracture energy, J-integral, crack propagation index, and Nmax, the CCPR exhibits more flexibility and damage resistance than FDR.

Evaluation of cracking performance of fiber reinforced and polymer enhanced microsurfacing mixtures using conventional asphalt laboratory testing

This study evaluated the potential for improving the cracking resistance of microsurfacing mixtures using polymer and fiber additions. Three mixtures were evaluated in this study: a fiber reinforced mixture using 1/4″ glass fibers, a polymer (SBR) enhanced emulsion, and a mixture using a combination of polymer and fibers. The polymer enhanced samples and the combination samples showed improvements for the Texas Overlay Tester and the Semi-Circular Bend Test. The greatest improvements in performance for the Texas Overlay Tester were obtained from the polymer enhanced sample, whereas the greatest improvements in the Semi-Circular Bend Test were obtained from the combination samples.

Evaluation of Asphalt Mixture Performance Using Cracking and Durability Tests at a Full-Scale Pavement Facility

In the asphalt materials community, the most critical research need is centered around a paradigm shift in mixture design from the volumetric process of the previous 20-plus years to an optimization procedure based on laboratory-measured mechanical properties that should lead to an increase in long-term pavement performance. This study is focused on advancing the state of understanding with respect to the value of intermediate temperature cracking tests, which may be included in a balanced mix design. The materials included are plant-mixed, laboratory-compacted specimens reheated from the 2013 Federal Highway Administration’s (FHWA’s) Accelerated Loading Facility (ALF) study on reclaimed asphalt pavement/reclaimed asphalt shingle (RAP/RAS) materials. Six commonly discussed intermediate temperature (cracking and durability) performance testing (i.e., Asphalt Mixture Performance Tester [AMPT] Cyclic Fatigue, Cantabro, Illinois Flexibility Index Test [I-FIT], Indirect Tensile Cracking [ITC, also known as IDEAL-CT], Indirect Tensile Nflex, and Texas Overlay Test) were selected for use in this study based on input from stakeholders. Test results were analyzed to compare differences between the cracking tests. In addition, statistical analyses were conducted to assess the separation among materials (lanes) for each performance test. Cyclic fatigue and IDEAL-CT tests showed the most promising results. The ranking from these two tests’ index parameters matched closely with ALF field performance. Furthermore, both showed reasonable variability of test data and they were successful in differentiating between different materials.

Evaluating the laboratory cracking performance of pavement preservation materials using the Texas overlay tester

This paper introduces a laboratory and fabrication procedure for evaluating the cracking performance of chip seal and microsurfacing under various distress conditions using the Texas Overlay Tester. Three damage severity levels were evaluated as part of this study: excellent condition with no cracks, low severity cracks, and medium severity cracks. The data was evaluated using OT cycles to failure, a pseudo-tensile work indicator, and ANOVA to capture the differences among the various samples. The results show the test is sensitive to treatment type and show a decrease in performance with increase in crack severity.

A parametric study to understand the adhesion failure mechanism of asphalt sealant

Adhesive strength of sealant was investigated by utilizing a new test setup developed from modification of Texas Overlay Test. Direct tension to sealant- asphalt concrete substrate was applied without any specialized sealant testing machine. Type I and Type IV (recommended for use in hot and cold climate respectively) sealants were tested at four temperatures on two different joint thicknesses. Type IV sealant fails in adhesion irrespective of temperature or thickness. Depending on the temperature, the failure pattern of Type I is cohesive or mix mode. A correlation between dynamic shear modulus of sealants and adhesive strength for both the sealants at each thickness were established with R2 values over 0.90. A general trend of the effect of thickness was observed and was explained by proposing a hypothesis that there exists a certain modulus for each sealant type at which the bond strength remains same irrespective of its thickness.

Laboratory characterization of temperature induced reflection cracks

Abstract A hot-mix asphalt (HMA) overlay is one of the primary strategy for rehabilitating existing HMA pavements and Portland cement concrete (PCC) pavements. The current design program, FAARFIELD, does not address reflective cracking for asphalt-overlaid concrete pavements due to its mechanism complexity. The bending, shearing, and thermal are three crucial factors to successfully model reflective cracking. To implement this failure mode in flexible over rigid design procedure, a series of full-scale test pavements were constructed, instrumented, and tested in the condition of extreme cooling temperature at the FAA National Airport Pavement Test Facility. The purpose was to assess cooling effects on the propagation of reflection cracks for airport AC over PCC pavements. In preparation for reflective cracking phase VI test, the FAA is conducting laboratory experiment on field extracted hot mix asphalt (HMA) cores. In order to test these field HMA cores, the Texas Overlay Tester (OT) was customized to get data similar to the full-scale tests. This paper discusses finite element analysis on the full-scale testing, development of the customized Texas OT, and a laboratory testing suite using the customized Texas OT, including preliminary tests, instrumentation, experiment design, and test results. Data obtained from this research effort will be used to develop a rational testing procedure to simulate extreme cooling cycles through full-scale testing.

Relationship between laboratory and full-scale fatigue performance of asphalt mixtures containing recycled materials

Use of recycled materials in asphalt mixtures is an important sustainability practice, and yet the oxidized asphalts introduced may compromise the cracking performance of pavement. This study evaluated the fatigue crack resistance of ten asphalt mixtures containing reclaimed asphalt pavement or recycled asphalt shingles. The materials were acquired from the full-scale test lanes constructed at the Federal Highway Administration Accelerated Loading Facility in McLean, Virginia. Three simple performance tests were employed given their simple testing procedures and analysis approaches: semi-circular bend, indirect tension, and Texas overlay tests. The test data were analyzed to obtain the corresponding fatigue parameters following the latest test standards and relevant literature. A new parameter named corrected crack progression rate (CCPR) was proposed for the Texas overlay test considering the viscoelastic nature of asphalt mixtures. Statistical comparison was performed on the laboratory results to assess the potential of each parameter in discriminating mixtures. This study further investigated the relationship between the laboratory results and fatigue performance of the full-scale lanes. It was found that the proposed CCPR parameter for the Texas overlay test provided the strongest correlation with field performance. Additionally, the fatigue life parameter determined from the same laboratory test, although relatively more variable, demonstrated the highest potential in detecting differences in mixture compositions.

Influence of bitumen type on cracking resistance of asphalt mixtures used in pavement overlays

Cracking is one of the predominant distresses occurring in flexible pavements, especially in old pavements that were rehabilitated with an asphalt overlay. In such cases asphalt mixtures should be designed to ensure high resistance to reflective cracking because new asphalt layers are exposed to existing cracks of the old pavement. The nature of these cracks can be various (transverse, longitudinal as well as crazy cracking). One factor that minimizes this type of distress is the proper mix design process, which should involve selection of specific bitumen binder and mineral mix gradation. However, still there is no universally adopted laboratory test method that would allow to clearly assess resistance of asphalt mixtures to reflective cracking. This paper describes the usage of one of the devices developed to test asphalt mixtures in terms of such distress – Texas Overlay Tester. For this test, samples prepared in laboratory conditions (i.e. compacted with the use of Superpave Gyratory Compactor) as well as obtained in the field (by core drilling) can be used. The results are obtained not only quickly and easily, but also with sufficient repeatability. The described method characterizes both crack initiation and crack propagation properties of asphalt mixtures. In this work one type of mineral mixture was tested with 4 different types of bitumen (one neat bitumen, two ordinary polymer-modified and one polymer-modified with high polymer content). For selected cases extra additives (rubber and loose fibres) were also tested. In total, six asphalt mixtures were tested. A ranking of the used binders was created on the basis of the results in order to conclude which bitumen would ensure the best performance characteristics in terms of reflective cracking. The results have clearly shown that deliberate choice of the binder used in the asphalt mixture for the overlay will significantly improve its reflective cracking resistance or even fatigue resistance.

Comparison of Asphalt Mixtures Crack Resistance at Intermediate Temperatures using Advanced Test Methods and Theories

Due to the increased use of recycled materials in pavement, the crack resistance of asphalt mixtures has become a major concern. This study evaluated the crack resistance of asphalt mixtures containing up to 40% reclaimed asphalt pavement (RAP) at intermediate temperatures. Three groups of materials consisting of seven plant-produced hot-mix asphalt mixtures were evaluated. A suite of test methods with various mechanistic backgrounds were employed, namely: semi-circular bend, simplified viscoelastic continuum damage, indirect tension, Texas overlay, and Illinois flexibility index tests. The corresponding parameters obtained for assessing crack resistance were: critical strain energy release rate Jc, material fatigue sensitivity, dissipated creep strain energy, number of cycles to failure Nf,OT, the interaction plot of critical fracture energy versus crack progression rate, and the flexibility index, respectively. Test results indicated that mixtures with higher RAP content exhibited higher stiffness and indirect tensile strength with lower compliance than the counterpart materials. In addition, all evaluation parameters, except for the use of the interaction plot from the Texas overlay test, provided consistent observations that incorporation of more RAP deteriorated the materials’ crack resistance. The mixture-discriminating capabilities of all test methodologies were also investigated using the paired t-test on the experimental data of each mixture group. The results presented herein were part of Pooled Fund TPF-5(294) study titled Develop Mix Design and Analysis Procedures for Asphalt Mixtures Containing High-RAP and/or RAS Contents.

Influence of bitumen type on cracking resistance of asphalt mixtures used in pavement overlays

Cracking is one of the predominant distresses occurring in flexible pavements, especially in old pavements that were rehabilitated with an asphalt overlay. In such cases asphalt mixtures should be designed to ensure high resistance to reflective cracking because new asphalt layers are exposed to existing cracks of the old pavement. The nature of these cracks can be various (transverse, longitudinal as well as crazy cracking). One factor that minimizes this type of distress is the proper mix design process, which should involve selection of specific bitumen binder and mineral mix gradation. However, still there is no universally adopted laboratory test method that would allow to clearly assess resistance of asphalt mixtures to reflective cracking. This paper describes the usage of one of the devices developed to test asphalt mixtures in terms of such distress – Texas Overlay Tester. For this test, samples prepared in laboratory conditions (i.e. compacted with the use of Superpave Gyratory Compactor) as well as obtained in the field (by core drilling) can be used. The results are obtained not only quickly and easily, but also with sufficient repeatability. The described method characterizes both crack initiation and crack propagation properties of asphalt mixtures. In this work one type of mineral mixture was tested with 4 different types of bitumen (one neat bitumen, two ordinary polymer-modified and one polymer-modified with high polymer content). For selected cases extra additives (rubber and loose fibres) were also tested. In total, six asphalt mixtures were tested. A ranking of the used binders was created on the basis of the results in order to conclude which bitumen would ensure the best performance characteristics in terms of reflective cracking. The results have clearly shown that deliberate choice of the binder used in the asphalt mixture for the overlay will significantly improve its reflective cracking resistance or even fatigue resistance.

Relationships between simple asphalt mixture cracking tests using Ndesign specimens and fatigue cracking at FHWA’s accelerated loading facility

Current methods and criteria for asphalt mix design and quality assurance testing are unable to discern the true impact of recycled materials such as RAP, recycled shingles, ground tyre rubber, re-refined engine oil bottoms, or products aimed at enhancing performance such as polymer-modified binders, fibres, or even WMA. There is an urgent need to implement reliable tests to assess the cracking resistance of asphalt mixtures. This study used test specimens compacted to Ndesign in four simple tests: the Cantabro test, a modified version of the Texas Overlay test, the Semi-Circular Bend test, and the Indirect Tensile test from which IDT strength and two other index parameters were obtained. The relationships between results from these tests and the fatigue cracking of the FHWA’s ALF test lanes were used to assess how well test methods could differentiate actual performance. The study also examined variability data for test results and how that impacted the utility of the tests to discern mixtures from one another. Results of this study indicate that the IDT Nflex Factor and the Cantabro test provide the strongest relationship to fatigue cracking in the field and are able to detect differences among common mixture variables. Both tests are simple, quick, and have very low costs to implement.

Selection and preliminary evaluation of laboratory cracking tests for routine asphalt mix designs

Cracking has become a primary mode of distress in recent years that frequently drives the need for rehabilitation of asphalt pavements. Meanwhile, asphalt mix designs are becoming more and more complex with the increasing uses of recycled materials, recycling agents, binder additives/modifiers, and multiple warm mix asphalt technologies. Thus, there is an urgent need to identify reliable cracking tests that can be used for routine mix design to eliminate brittle mixes. This paper critically reviewed cracking mechanisms and laboratory tests. A total of 12 cracking tests were discussed at a cracking test workshop held as part of the National Cooperative Highway Research Program Project 9-57. Seven cracking tests were selected for further laboratory evaluation and field validation. Four of the simpler cracking tests from the seven were evaluated in this paper, these being the Texas Overlay Test (OT), Disk-shaped Compact Tension (DCT) test, Semi-Circular Bend test from the Louisiana Transportation Research Center (SCB-LTRC), and SCB test at room temperature from Illinois (SCB-IL). A laboratory sensitivity study was performed, and the results showed that all four cracking tests were generally sensitive to asphalt mix components. However, there were some concerns with the DCT, SCB-LTRC, and SCB-IL. Both the DCT and SCB-IL were found to be not sensitive to asphalt binder content; and both the DCT and SCB-LTRC showed an unexpected increase in cracking resistance when adding RAS to the mix. Additionally, two sets of field test sections were used for preliminary validation of these four cracking tests. It was found that the OT, DCT, and SCB-IL provided rankings which matched the measured field performance for the two sections on US62, Texas; and the OT and SCB-LTRC were valid for six APT test sections. Further validation with different mixes, traffic, and climate is needed.

Development of a Simple Fatigue Cracking Test for Asphalt Binders

Current Superpave® PG specification uses parameter | G*|sin(δ) to quantify asphalt binder fatigue resistance. The parameter’s effectiveness has been debated for a long time. AASHTO recently adopted the linear amplitude sweep test as a provisional standard, AASHTO TP 101-12. The authors evaluated the sensitivity of this standard to different aging conditions: unaged original binders, rolling thin-film oven-aged binders, and 20- to 80-h pressure aging vessel–aged binders. Test results showed, in many cases, longer predicted fatigue lives for more-aged binders. Thus this study developed a simple fatigue cracking test for asphalt binders. In this new test, the pure linear amplitude sweep (PLAS) test, peak shear strain was increased linearly from 0% to 30% over a course of 3,000 oscillatory cycles. A new fatigue parameter, the fatigue resistance energy index (FREI), was derived with fracture mechanics. The PLAS test and FREI parameter were sensitive to both binder aging conditions and rejuvenator type and dosage. Four laboratory mixtures were employed to evaluate the correlation between this new binder fatigue test and the two mixture cracking tests: the Texas overlay test and the Illinois flexibility index test. The results showed that the PLAS and FREI correlated well with the mixture cracking tests. Additionally, the proposed method was preliminarily verified with the FHWA accelerated loading facility test, and a fair relationship with the full-scale fatigue test data was observed. It is obvious that the PLAS and associated FREI need further validation through more field test sections.

Laboratory Evaluation of a Plant-Produced High Polymer–Content Asphalt Mixture

Reflective cracking in asphalt overlays placed over jointed concrete pavements is of major concern in Virginia, as well as nationally, and has generated interest in various reflective crack mitigation techniques that are easy to implement. One technique is the use of binder modifiers, such as asphalt rubber, polymer-modified asphalt binders, or high polymer–content (HP) modified binders. In the summer of 2014, the Virginia Department of Transportation placed an HP asphalt mixture produced by using an asphalt binder that contained approximately 7.5% styrene-butadiene-styrene polymer in a trial section within a subdivision as a low-risk means to assess constructability and laboratory performance. The HP mixture was evaluated in comparison with a typical surface asphalt mixture with a 9.5-mm nominal maximum aggregate size, as a control. Testing was performed on specimens fabricated from reheated control and HP mixture samples, as well as on specimens fabricated from site-compacted samples and road cores of the HP mixture. In addition, binder grading was performed on the control binder and modified binder. The HP binder was significantly more elastic than the control binder. Comparable dynamic moduli were found for reheated mixture specimens, although site-compacted and road core specimens from the HP mixture had lower stiffness than the control mixture. The HP mixture performed better in rutting and in fatigue. The Texas overlay test indicated similar crack resistance between the two mixtures; however, measured loads of the HP specimens were nearly half those of the control specimens. The results of laboratory testing indicated that the mixture incorporating the HP binder should have a far greater fatigue life and rut resistance than the control mixture.

The Effect of Aging on the Cracking Resistance of Recycled Asphalt

Fatigue cracking is an important concern when a high percentage of Reclaimed Asphalt Pavement (RAP) is used in an asphalt mixture. The aging of the asphalt binder reduces its ductility and makes the pavement more susceptible to cracking. Rejuvenators are often added to high-RAP mixtures to enhance their performance. The aging of a rejuvenated binder is different from virgin asphalt. Therefore, the effect of aging on a recycled asphalt mixture can be different from its effect on a new one. This study evaluated the cracking resistance of 100% recycled asphalt binders and mixtures and investigated the effect of aging on this performance parameter. The cracking resistance of the binder samples was tested by a Bending Beam Rheometer. An accelerated pavement weathering system was used to age the asphalt mixtures and their cracking resistance was evaluated by the Texas Overlay Test. The results from binder and mixture tests mutually indicated that rejuvenated asphalt has a significantly better cracking resistance than virgin asphalt. Rejuvenated mixtures generally aged more rapidly, and the rate of aging was different for different rejuvenators.