Laboratory Performance Tests Research Articles

Evaluating the Sensitivity of Intermediate Temperature Performance Tests to Multiple Loose Mixture Aging Conditions Using the FHWA Accelerated Loading Facility’s RAP/RAS Experiment

With the advancement of Balanced Mixture Design (BMD), laboratory performance tests for asphalt materials are being assessed for their relation to cracking performance in the field. However, most BMD applications do not account for long-term aging. This gap limits the appropriateness of thresholds and the potential of BMD to improve pavement performance as more amounts of the additives and reclaimed materials available can behave in drastically different fashions between early, intermediate, and late stages of service. In this study, five mixtures with documented field performance from the Federal Highway Administration’s Accelerated Loading Facility were subjected to long-term oven aging (LTOA) protocols. In addition to reheating loose mixtures containing reclaimed asphalt pavement and shingles, the two LTOA methods were 8 h at 135°C and 3 d at 95°C. The objective of this paper is to compare aging approaches, particularly whether equivalence between long-term aged procedures exists, and to highlight the sensitivity (or lack thereof) of common laboratory mixture performance tests. The Indirect Tensile Cracking (IDEAL-CT), Illinois Flexibility Index, Asphalt Mixture Performance Tester cyclic fatigue, and dynamic modulus tests were employed. The results show a collapse in mixture cracking indices when LTOA is incorporated, raising concerns over BMD implementation using criteria established exclusively with short-term oven aging. Use of [Formula: see text] presented a universal and logic shift in response from the reheated to LTOA state, affirming utility as an aging index. Blending insights can possibly be gleaned from the data, although 95 and 135°C LTOA procedures yield mostly equivalent linear viscoelastic and cracking indices.

Evaluating effect of rejuvenators on high RAP mixtures through laboratory performance tests and construction of field test sections

Although thirty-one US states utilize 20% recycled asphalt pavement (RAP) or greater in asphalt pavements, Iowa limits the usage of RAP to 20%, and 30% with a softer binder in the surface layer. Because high RAP mixtures can cause asphalt mixtures to stiffen due to the hardening effect of the aged binder, rejuvenators should be used to improve the cracking resistance of high RAP mixtures. Due to increasing demand for sustainable, and environmentally materials, two bio-based rejuvenators, Invigorate and Tufftreck, were considered for this study. To evaluate effect of rejuvenators on high RAP mixtures, field test sections were constructed in Cerro Gordo County, Iowa, 2020. The field test consists of six different sections with two rejuvenators and three different RAP contents of 22%, 34% and 45%. Performance grading (PG) of asphalt with rejuvenators adopted for the field test sections lowered both high and low temperatures of the virgin asphalt. Based on the eight cores for each test section, all six test sections with or without rejuvenators exhibited field densities between 93.6% and 95.2%, exceeding the minimum requirement of 93%. First, loose field samples were compacted at the laboratory for Hamburg wheel tracking test, semi-circular bending test, and disc-shaped compact tension test. Second, the laboratory test results were analyzed to determine if rejuvenators were effective in mitigating rutting, moisture damage and cracking. Based on the analysis of limited laboratory test results, Tufftrek was effective in lowering rutting and moisture damage whereas, for minimizing cracking, using a soft binder was most effective. Third, a condition survey on test sections was performed in one year after construction. Based on a condition survey of six test sections, no rutting was observed from all test sections, but some low-severity cracks were observed in sections without rejuvenators. Based on the limited condition survey results, it can be concluded that rejuvenators were effective in delaying the initiation of cracking.

Research on Self-melting Snow Material of Asphalt Pavement

The effects of pozzolan and calcium chloride on the performance of asphalt mixtures were analyzed by laboratory performance tests. Using the maximum bulk density of mixed materials after vibration compaction, Determined the reasonable ratio of calcium chloride to fill the voids of pozzolanic material. The amount of surface modified material was determined based on the precipitation rate of the melting snow component and the effect on asphalt performance under cyclic water immersion conditions. Tested the performance of the asphalt mixture, self-melting snow material can improve the low temperature performance of the mixture. There is a certain reduction in high temperature performance and water stability, but all meet the requirements of normative indicators.

Harmonizing Flexible Pavement Rutting Design with Balanced Mix Design

The state-of-the-practice in asphalt concrete mix design and pavement structural design are two divergent concepts. The simulative laboratory performance tests such as Hamburg Wheel Tracking (HWT) and Asphalt Pavement Analyzer (APA) that are used primarily for balanced mix design are pragmatically accelerated surrogate tests developed to ensure the stability or ranking of mixes. Pavement structural design methods, being empirical or mechanistic-empirical, do not consider these laboratory test results in their analyses, in favor of other fundamental mechanical parameters such as dynamic modulus. As such, the selection of the type of mix to be placed on a project is based on the local experience, and a set of consensus limits, rather than the demand of the pavement section. A harmonized strategy that integrates the results from mix tests with the pavement structure, material properties, environmental conditions, and traffic levels can lead to an optimized pavement system. A framework is proposed to incorporate the laboratory HWT and APA device results into the rutting analysis associated with most mechanistic-empirical structural design algorithms. The proposed framework was applied to the results from two accelerated pavement testing facilities and six in-service pavement test sections to demonstrate its feasibility. The proposed strategy can be potentially used to predict the rutting life of the pavement reasonably well. By balancing the rutting demand of an asphalt layer with the rutting capacity of a given mix, the proposed method can potentially lend itself to the use of local materials for a more economical and sustainable pavement structure.

Statistical Analysis Framework to Evaluate Asphalt Concrete Overlay Reflective Cracking Performance

The purpose of this paper is to provide a robust process to statistically analyze reflective cracking field performance data. There is often a lack of consistency and transparency in statistical analysis of pavement field performance data, which may not satisfy ANOVA or regression modeling assumptions. Twelve full-scale asphalt concrete (AC) overlay pavement test sections located at the MnROAD test facility are used to demonstrate the statistical framework. The percentage of cracking reported at joint locations (%RC) is used to represent reflective cracking performance, and its relationships to pre-overlay load transfer efficiency (LTE), truck traffic, overlay thickness, and common performance indices determined from laboratory tests are investigated. The three laboratory tests considered in this study are the disk-shaped compact tension (DCT), semi-circular bend (SCB) and overlay tester (OT). Logistic regression models are used for estimation. Predictive abilities of various models are compared in relation to the percentage odds (%odds) of reflective cracking. Model output is binary: it estimates not the relative amount of reflective cracking but instead the probability of a given pavement structure cracking. Varying ability to perform asphalt mixture laboratory performance testing is assumed. One such model, where no laboratory performance testing variables are included, shows that a one-unit increase (1-in.) in AC overlay thickness may result in approximately a third decrease in the %odds of reflective cracking. A logistic regression model developed that considers laboratory performance data from DCT, SCB, and OT results in the optimal model balancing best fit and best prediction properties without overfitting.

Application of percent within limits concepts on a balanced mix design of asphalt mixtures

ABSTRACT Many agencies have incorporated rutting, and more recently cracking laboratory tests in the design process of asphalt mixtures with the objective to produce a balance between the stability and durability of the final product. Although this performance-engineered mixture design (PEMD), called here balanced mix design (BMD), offers compelling benefits, it raises a number of questions regarding its compatibility with construction practices. The objective of this work is to relate a BMD method with realistic binder content construction tolerances by applying concepts of a percent-within-limits (PWL) approach to field QC/QA, accounting for the variability of both the laboratory performance tests and construction. Four Arkansas mixes were evaluated using the Illinois flexibility index test (I-FIT) and the asphalt pavement analyzer (APA), for which binder content (Pb) and compaction level (%Gmm) were varied in the laboratory. Monte Carlo simulations were employed to generate binder content variability distributions based on BMD diagrams. New approaches for setting PWL lower and upper specification limits (LSL and USL respectively), as well as a criterion for defining the constructability of a BMD are proposed.

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.

Relating Ndesign to Field Compaction: A Case Study in Minnesota

High field density helps in increasing the durability of asphalt pavements. In a current research effort, the University of Minnesota and the Minnesota Department of Transportation (MnDOT) have been working on designing asphalt mixtures with higher field densities. One critical issue is the determination of the Ndesign values for these mixtures. The physical meaning of Ndesign is discussed first. Instead of the traditional approach, in which Ndesign represents a measure of rutting resistance, Ndesign is interpreted as an indication of the compactability of mixtures. The field density data from some recent Minnesota pavement projects are analyzed. A clear negative correlation between Ndesign and field density level is identified, which confirms the significant effect of Ndesign on the compactability and consequently on the field density of mixtures. To achieve consistency between the laboratory and field compaction, it is proposed that Ndesign should be determined to reflect the real field compaction effort. A parameter called the equivalent number of gyrations to field compaction effort (Nequ) is proposed to quantify the field compaction effort, and the Nequ values for some recent Minnesota pavement projects are calculated. The results indicate that the field compaction effort for the current Minnesota projects evaluated corresponds to about 30 gyrations of gyratory compaction. The computed Nequ is then used as the Ndesign for a Superpave 5 mixture placed in a paving project, for which field density data and laboratory performance test results are obtained. The data analysis shows that both the field density and pavement performance of the Superpave 5 mixture are significantly improved compared with the traditional mixtures. The results indicate that Nequ provides a reasonable estimation of field compaction effort, and that Nequ can be used as the Ndesign for achieving higher field densities.

Sarcopenia in patients with multiple sclerosis

Background: Multiple sclerosis (MS) is an autoimmune neurodegenerative disease of the central nervous system. Sarcopenia, which is characterized by the loss of physical performance and poor outcomes, has recently become the focus of research. However, the relationship between sarcopenia and MS has not yet been investigated. This study aims to determine the prevalence of sarcopenia in MS patients and investigate the factors associated with sarcopenia.Methods: One hundred and one MS patients who can walk without assistance and 55 healthy controls were included. Handgrip strength (HGS) and gait speed tests were applied to all participants. Additionally, anterior thigh muscle thickness (anterior TMT) and skeletal muscle mass index (SSMI) were estimated by ultrasound and bioelectrical impedance analysis (BIA), respectively. According to these tests, MS patients were grouped as either sarcopenic or non-sarcopenic. The groups were compared using clinical and laboratory data, handgrip strength and performance test, Modified Fatigue Impact Scale (MFIS), and the Godin leisure-time exercise questionnaire (GLTEQ).Results: HGS, gait speed, fat free mass (FFM), SMMI, anterior TMT, and sonographic thigh adjustment ratio (STAR) values in patients with MS were significantly lower than healthy controls for both sexes (for female, p:0.001, p:0.001, p:0.010, p:0.049, p:0.001, and p:0.101, respectively; for male, all p:0.001). Compared with healthy controls, MS patients had a significantly lower GLTEQ score (p:0.001), while the MFIS score (p:0.001) was higher. According to STAR, HGS, and gait speed, sarcopenia was diagnosed in 12 (17.64%) female and 7 (21.21%) male patients with MS. Whole-body sarcopenia was diagnosed in only 11 (10.9%) of the patients by BIA. HGS, gait speed, FFM, anterior TMT, and STAR values in sarcopenic MS patients were significantly lower than in non-sarcopenic for females (p:0.001, p:0.001, p:0.004, p:0.001, and p:0.001, respectively) and males (p:0.001, p:0.001, p:0.011, p:0.003, and p:0.001, respectively). MFIS score was significantly higher in sarcopenic patients than non-sarcopenic for both females (p:0.001) and males (p:0.036), but only the physical fatigue subscale was significantly higher. While the physical fatigue score was negatively correlated with GLTEQ in MS patients (r:-0.276, p:0.005), it was positively correlated with the expanded disability status scale (r:0.409, p:0.001).Conclusion: We detected that approximately one-fifth of MS patients have sarcopenia. Regional sarcopenia was more prevalent than whole body sarcopenia. We found a high degree of fatigue and lack of exercise in sarcopenic MS patients.

Three-level performance evaluation of high RAP asphalt surface mixes

To support an increased use of reclaimed asphalt pavement (RAP) and innovative materials, appropriate laboratory performance tests are required. There exists a wide selection of performance tests with varying complexity, reliability, and cost. However, there is no consensus on which tests are best suited to support the design and quality assessment of asphalt mixtures. The main purpose of this effort was to assess the impact of testing complexity on the estimated performance of asphalt pavements through a comprehensive evaluation of four different highly recycled surface mixes produced and placed in Virginia. For that purpose, the research team defined a three-level testing framework herein referred to as basic, intermediate, and advanced. Each level was characterized by an increasing degree of complexity and cost and included tests to characterize both the cracking resistance and the rutting resistance of the evaluated mixtures. Under the performance evaluation process, it was possible to investigate the features of the various laboratory tests. Through the review of the theoretical background, the evaluation of the test procedures, and statistical analysis of the results, it was possible to identify the strengths and weaknesses of each test. Based on the test results, recommendations were provided on the design of highly recycled surface mixes. Also, it was possible to provide guidelines to develop appropriate quality assessment criteria and mix design methodology.

Application of Adaptive Materials and Coatings to Increase Cutting Tool Performance: Efficiency in the Case of Composite Powder High Speed Steel

The paper proposes a classification of adaptive materials and coatings for tool purposes, showing the ability to adapt to external heat and power influences, thereby improving tool life. Creating a cutting tool made of composite powder high speed steels containing refractory TiC, TiCN, and Al2O3 compounds for milling 41CrS4 steel demonstrated the effectiveness of the adaptive materials. The tool material characteristics under the external loads’ influence and the surface layer adaptation to the heat–power exposure conditions were shown by the temperature field study using a semiartificial microthermocouple method (the level of fields is reduced by 20%–25% for 80% HSS + 20% TiCN), frictional interaction high-temperature tribometry (the coefficient of friction did not exceed 0.45 for 80% HSS + 20% TiCN at +20 and 600 °C), laboratory performance tests, and spectrometry of the surface layer secondary structures. Spectral analysis shows the highest spectrum intensity of TiC2 after 5 min of running in. After 20 min of milling (V = 82 m/min, f = 0.15 mm/tooth), dicarbide decomposes and transits to thermally stable secondary phase films of good lubricity such as TiO (maximum) and TiN (partially). There was an increase in tool life of up to 2 times (>35 min for 80% HSS + 20% TiCN), and a decrease in the roughness of up to 2.9 times (Ra less than 4.5 µm after 25 min of milling).

Performance Evaluation of Asphalt Mixtures Modified with Recycled Polyethylene via the Wet Process

The plastics and asphalt pavement industries have shown increasing interest in recycling waste plastics in asphalt because of potential environmental benefits. One approach to incorporating recycled plastics in asphalt is the wet process, which requires mechanical blending of recycled plastics into the asphalt binder as polymer modifiers. This study was aimed at exploring the use of recycled polyethylene (rPE) and a reactive elastomeric terpolymer (RET), which was used as a potential compatibilizer to rPE, for asphalt modification. Moreover, the study evaluated the impact of both modifiers on the bond strength characteristics of asphalt-aggregate systems as well as on the rutting and cracking resistance of asphalt mixtures. To this end, a battery of laboratory performance tests was conducted on asphalt mixtures containing binders: one neat; two rPE modified; and one styrene-butadiene-styrene modified. One rPE modified binder was formulated by adding 3% rPE to a PG 58-28 neat binder, while the other was modified with 3% rPE, RET, and polyphosphoric acid. Test results indicated that the rPE-plus-RET modified binder yielded an asphalt-aggregate system with enhanced moisture resistance, before and after oxidative aging. When compared with the control mixture, using rPE alone or rPE plus RET for asphalt modification significantly improved the rutting resistance. However, the rPE and rPE-plus-RET modified mixtures were found to be more susceptible to intermediate-temperature fatigue cracking at both short-term and long-term aging conditions. Finally, adding rPE or rPE plus RET did not have a significant impact on the mixture reflective cracking and thermal cracking resistance after long-term aging.

260 Beyond Validation Testing: A Sleep Tracker for Longitudinal Data Collection in Operational Environments

Abstract Introduction Sleep tracking wearables are increasingly being validation tested against polysomnography (PSG) and actigraphy, but they may not be ideal for long-term epidemiological sleep studies, or for use in operational environments. A given device’s short battery life, limited data storage capacity, inability to detect naps or estimate sleep architecture, or privacy concerns may discourage researchers from using wearables to collect objective sleep data in real-world settings. The Zulu watch (Institutes for Behavior Resources) is designed to collect longitudinal sleep data in operational populations with irregular sleep patterns, such as long-haul pilots or shift workers. It is capable of on-wrist sleep-wake determination, nap detection, on-wrist sleep depth scoring (i.e., interrupted sleep, light sleep, or deep sleep), on-wrist data storage up to 80 sleep intervals, and year-long battery life. Laboratory testing is an important initial step toward establishing the performance of a device for longitudinal real-world sleep evaluation; therefore, the Zulu watch sleep tracking was subjected to testing against gold-standard PSG and actigraphy. Methods Eight healthy young adult participants (30.4±3.2 years; mean±SD) wore a Zulu watch and Philips Respironics Actiwatch 2 simultaneously over a 3-day laboratory PSG sleep study, with 8 hours time-in-bed each night. Overall epoch-by-epoch agreement of sensitivity (for sleep), specificity (for wake), and accuracy of Zulu watch data were tested against PSG and Actiwatch 2. Results Compared with either PSG or actigraphy, both accuracy and sensitivity for Zulu watch sleep-wake determination were >90% while specificity was low (~26% vs. PSG, ~33% vs. actigraphy). Accuracy for sleep scoring vs. PSG was ~87% for interrupted sleep, ~52% for light sleep, and ~49% for deep sleep. Conclusion The Zulu watch showed mixed results but may be a viable candidate for sleep evaluation based on initial laboratory performance testing in healthy adults. The next steps will be to compare the Zulu watch against self-report of sleep in operational and substance use disorder populations. Longitudinal epidemiological sleep studies can become more feasible if technology is tailored to the specific needs of the real-world environment. Support (if any) Medical Technology Enterprise Consortium award MTEC-17-08-Multi-Topic-0104; Office of Naval Research, Code 34.

Recycling of low-value packaging films in bitumen blends: A grey-based multi criteria decision making approach considering a set of laboratory performance and environmental impact indicators.

Many road construction and maintenance projects are increasingly using recycled material as pavement material. Most of the times, generic sustainability evaluations are ascribed to recycled products without fully considering their performance. The potential environmental benefits of various alternatives can be analytically evaluated with Life Cycle Assessment while many performance indicators can be found through laboratory and field tests. However, it is highly uncommon for these two approaches to be combined in the same assessment methodology and most of the analyses rely on one or the other. Trading off between environmental advantages and performance and durability in the field is considered of utmost importance when evaluating construction alternatives, especially on large projects. This study utilizes recycled plastic packaging films for bitumen modification. The recycled polyolefin blend is a combination of linear low-density polyethylene and low-density polyethylene (LLDPE/LDPE). LLDPE/LDPE was added in bitumen at various dosages (i.e., from 3% to 12% by weight of the bitumen) to assess the effect of recycled LLDPE/LDPE on the binder physio-chemical, rheological and thermal performance. In addition to the various laboratory performance tests, the environmental sustainability of the alternatives was evaluated through an LCA study. Finally, the outcomes from the two approaches (laboratory performance and environmental impact assessment) were combined via grey relational analysis to identify the best overall alternative. It was found that the storage stability of LLDPE/LDPE modified blends varied from 6°C to 57°C whereas the storage stability value of A35P was 2°C. Softening point of bitumen was 44.1°C which improved to 55.7-104.1°C at different content of LLDPE/LDPE. The melting temperature of LLDPE/LDPE modified blends was 100.22, 101.44, 101.87 and 102.49 for LLDPE/LDPE-3%, LLDPE/LDPE-6%, LLDPE/LDPE-9% and LLDPE/LDPE-12%. The methodology highlighted in the paper can be easily adapted to other scenarios, hence facilitating multi-attribute decision-making processes when incorporating recycled materials in roads and leading to better informed decisions.

Laboratory Assessment of Dense Graded Asphalt Concrete Incorporating Coal Furnace Ash in South of Vietnam

Currently, application of industrial waste or by-product in road construction industrials is a major interest by researchers, government officers and engineers. Coal ashes by-product from industrial parks negatively impact environment, costly in treatment, and require large ground for disposing areas. Therefore, this paper proposes on using the coal ash from furnace products of an industrial park in South of Vietnam to be incorporated into dense graded asphalt concrete using Nominal Maximum Aggregate Size 12.5mm. Laboratory performance tests including Marshall stability, indirect tensile strength, Cantabro loss, and dynamic fatigue test were conducted. The effects of coal ash contents in replacement of fine aggregate which is passing 4.75mm sieve from asphalt mixture into laboratory performance of mixture is also discussed in detail.

Investigation of recycled asphalt mixtures in Missouri: laboratory, field, and ILLI-TC modelling

This study investigates the lab and field performance of four asphalt mixtures placed in Missouri, USA, containing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). Laboratory tests including disk-shaped compact tension fracture (DC(T)), indirect tension (IDT) creep and strength, Illinois flexibility index (I-FIT), indirect tensile cracking test (IDEAL-CT), and the Hamburg wheel tracking test (HWTT) were conducted on field cores and plant-produced, lab-compacted (PPLC) samples. The DC(T), I-FIT, and IDEAL-CT tests showed that all of the mixtures exhibit brittle behaviour and have high cracking potential, while the HWTT indicated that rutting does not appear to be a concern with these mixes. Statistical analysis was performed to examine the capability of the performance tests investigated to distinguish between mixes. The DC(T) exhibited the best ability to distinguish between mixtures, while IDT strength displayed the least ability. Simulations using the ILLI-TC software were conducted to further explore the low temperature cracking behaviour of the mixes. Finally, field data collected using an automatic road analyzer (ARAN) was analyzed to further assess the laboratory performance tests.

Evaluation of Reclaimed Hydrated Fly Ash as an Aggregate for Sustainable Roadway Base Material

This paper summarizes the findings from laboratory and field performance testing of reclaimed hydrated class C fly ash (HFA) stabilized with a triangular aperture geogrid. This phase of testing was performed on HFA laboratory specimens and field test sections. The laboratory test results provided estimates for design input values, while the field testing assessed performance characteristics including the as-constructed modulus of the subgrade reaction, the in situ resilient modulus, and permanent deformation. For the laboratory portion, all results were derived from tests conducted on specimens immediately after sample preparation and after a 7-day cure. The compressive strength of reclaimed hydrated class C fly ash increases with curing. The strength of the HFA material can be further increased when mixed with a chemical stabilizer. For this project, chemical stabilization with lime was not viable because the lime supplier was too far from both HFA source and project site. Based on cyclic plate load tests, the in situ resilient modulus of the HFA and geogrid-stabilized HFA layers were determined on site. This paper reports the findings from the laboratory and field plate load test and highlights the potential use of geogrids in the stabilization of HFA.

Using damage evaluation to assess the fatigue behaviour of cement-treated base material from laboratory and full-scale performance tests

Cement-treated base (CTB) has become the most popular cement-modified road-base material. This study theoretically connects understandings of CTB damage behaviour derived from laboratory and full-scale experiments using the continuum damage mechanics approach. Fatigue-life tests using four-point bending testing were performed on laboratory CTB specimens and compared to test data from full-scale fatigue testing conducted by the Australia Road Research Board. Damage evolution curves developed from both test environments were characterised and compared, resulting in three key findings: (1) damage evaluation through the normalisation technique can be reasonably used to overcome the inherently different conditions of the testing environment; (2) a significant distinction was observed in the final phase of the damage evolution curves; (3) damage evolution of field CTB can be reasonably predicted by the damage evolution of laboratory CTB specimens. Future research should investigate the effects of parent material gradation, testing method, and unforeseen factors to the damage characteristics of CTB.

Mechanistic-based verification of a structural layer coefficient for high polymer-modified asphalt mixtures

Extensive laboratory performance testing and advanced statistical analyses led to the determination of a fatigue-based structural layer coefficient of 0.54 for high polymer-modified (HP) asphalt concrete (AC) mixtures in new pavements. The objective of this paper was to verify, using mechanistic-empirical (ME) analyses, the structural capacity of HP AC pavement sections designed using the 0.54 layer coefficient. The ME analysis for rutting, shoving, and top-down cracking in the AC layer resulted in most of the cases in a better performance for the HP AC mixes when compared with their respective PMA AC mixes. Moreover, the rut depths determined in the unbound layers were observed to be lower than the maximum allowable rut depth indicating an acceptable performance for the HP pavement sections which had a thinner AC layer thickness. In summary, the verification efforts supported the use of a structural coefficient of 0.54 for HP AC mixes in new pavements.

Effects of emulsion types, application rates, and crumb rubber on the laboratory performance of chip seal

Chip sealing is a commonly used pavement maintenance method that aims to delay pavement deterioration by reducing water infiltration and restoring skid resistance. Loss of aggregate and bleeding are considered the major failure mechanisms in chip seal, and therefore, are the main design criteria for this treatment method. The objective of this study was to evaluate the laboratory performance of chip seals prepared with different types of asphalt emulsions, application rates, and aggregate blends. A newly introduced crumb rubber modified asphalt emulsion was evaluated that allows chip seal installation at the same temperature of a standard emulsion. Types of emulsion included a crumb-rubber modified asphalt emulsion (CRS-2TR), an asphalt rubber (AC20-TR), a polymer-modified emulsion (CRS-2P), and a conventional unmodified emulsion (CRS-2). Application rates were selected based on the Louisiana Department of Transportation and Development (LaDOTD) and the Texas Department of Transportation (TxDOT) specifications as well as from the chip seal design method recommended in NCHRP Report 680. A 90-10 aggregate blend of lightweight aggregate (LWA) and rubber aggregate (RA) was also investigated.The loss of aggregate was measured using two laboratory performance tests: the sweep test (ASTM D 7000) and the Pennsylvania Aggregate Retention Test (PART). The strength of adhesion of the four emulsions was also evaluated using the Bitumen Bond Strength (BBS) test. While asphalt rubber was the best performer in terms of aggregate loss, CRS-2P and CRS-2TR performed similarly followed by the conventional emulsion. Results of the BBS test showed a similar rank for the bond strength of the emulsions. It was also observed that the loss of aggregates in chip seal decreased with the increase in application rate. However, incorporation of rubber as aggregate in chip sealing increased the loss of aggregate in the specimens indicating poor adhesion between the emulsions and the rubber aggregate.