Airfield and Highway Pavements 2021: Pavement Materials and Sustainability

In this study, an asphalt binder was modified with epoxidized methyl soyate (EMS) that was engineered at Iowa State University. The binder modification was accomplished in an asphalt terminal, and the resulting binder was used for reversing the undesired effects of reclaimed asphalt pavement (RAP) in a mixture containing 30% of this reclaimed material. The modified mixture was produced in an asphalt plant for a pavement demonstration project that occurred in November 2017. The EMS-modified mixture with 30% RAP and a control mixture containing only 18% RAP were used for paving a 7-mile stretch of a high-volume roadway in O’Brien County, Iowa, U.S. About 6.6 miles of the roadway were paved with the control low RAP mixture that is traditionally used for paving roadways in Iowa, and the remaining 0.33 miles were paved with the high RAP EMS-modified mixture. To predict the field performance of the mixtures, the low-temperature cracking and fatigue cracking resistance of the mixtures were evaluated using disc-shaped compact tension (DCT) and push-pull fatigue tests, respectively. The results revealed that the EMS restorative reactive modifier (RRM) used in this study results in reversing the undesired effects of RAP and improving the low-temperature cracking and fatigue resistance of the asphalt mixture containing 30% RAP.

Natural insolation is more severe to asphalt concrete (AC) pavements than standard laboratory aging procedures. However, it affects the asphalt binder until a limited AC depth. Understanding the impact of ultra-violet radiation (UVR) on asphalt binder oxidation could improve the simulation of near-surface asphalt binder aging and enable develop a relatively more realistic accelerated laboratory aging method. A repeatable method to irradiate asphalt binder with ultra-violet light requires mitigating the variability induced by different types of aggregates, moisture conditions, and temperatures. Thus, an accelerated aging procedure of asphalt binder utilizing UVR was developed. After initial trials proving the importance of sample thickness and rate of oxidation, a methodology was developed to age asphalt binder samples after optimizing sample thickness and the effect of temperature-UVR coupling. The methodology may be used to assess asphalt binders’ susceptibility to UVR and select better additives to better control AC cracking related to binder brittleness.

Roller-compacted concrete (RCC) pavements require high-density pavers to distribute, densify, and provide the initial finish. High-density pavers coupled with appropriately proportioned RCC mixture volumetrics should reduce the compactive effort necessary to meet density specifications and increase productivity. Additionally, chemical admixtures may also assist in improving compactability and productivity. The primary test employed for fresh RCC workability is the Vebe test, which is primarily a quality control and consistency test. In this study, the direct shear box apparatus measured the shear properties of RCC mortar mixtures in the plastic state. Multiple RCC mortar mixtures with different paste contents and a rheology-modifying admixture (RMA) were evaluated. Direct shear box tests on the compacted RCC mortar samples using an RMA indicated no significant impact on the friction angle for a given maximum aggregate size. The RCC mixture volumetrics, such as intragranular voids, paste volume, and voids filled by paste, predominantly influenced the apparent cohesion when voids in the aggregate were either underfilled or overfilled. Higher apparent cohesion was generated from negative pore-water pressure built-up from relatively high strain rates and restricted drainage. The RMA did not affect the peak or residual friction angle of the compacted RCC.

The Texas Transportation Institute Overlay Tester (OT) is the most popular equipment to measure the reflective cracking performance of the asphalt mixtures in the laboratory. However, there is a high level of variability associated with the number of cycles to failure (N_OT) determined from this test, and it has been a challenge in dependably predicting the reflective cracking performance of asphalt mixtures. The main goal of this study is to identify the reasons for high variability in OT testing data and results. A thorough literature review of recent studies regarding this issue has been conducted, and the potential causes of variability have been categorized based on different phases of OT testing, including testing procedure, data analysis, and reporting results. Finally, the study concludes with recommendations to help minimize these factors causing variability of the OT results and increase repeatability and thereby increase the overall effectiveness and credibility of OT test.

This research compared two recycled plastic products to conventional polymers commonly used for bituminous binder and asphalt mixture production. Samples of the same penetration grade bitumen were modified with 6% of the recycled plastic products, as well as 2%–6% of conventional elastomeric and plastomeric polymers. Testing included index properties and rheological properties used in the United Kingdom and the United States. The results were compared to determine the dosage of conventional polymer that was equivalent to 6% recycled plastic. It was found that 6% recycled plastic was generally equivalent to 3%–6% conventional plastomeric polymer. Although some properties were also comparable to those associated with 3%–4% conventional elastomeric polymer, the force ductility was significantly lower, indicating lower asphalt crack resistance. It was concluded that these recycled plastic products should be considered as a sustainable source of plastomeric polymer for the modification of bituminous binders, rather than as simple binder extenders.

Adding reclaimed asphalt pavement (RAP) into asphalt mixes is a common practice and has many merits such as reducing costs and emissions. In the recent decade, many state highway agencies have embarked on investigating asphalt mixes with high RAP content. As the RAP content increases, understanding how well the RAP binder blends with virgin binder becomes more crucial. Lack of knowledge on how much of residual RAP binder actively blends with virgin binder during production is one of the reasons preventing full exploitation of RAP materials. Obviously, the amount of aged RAP binder blending into virgin binder affects properties of asphalt mixes. A study was undertaken to investigate the degree of blending, i.e., the amount of RAP binder blended with virgin binder, through the Superpave volumetric mix design. This research was unique and innovative in the sense that extracted RAP aggregate was blended with virgin aggregate at two different gradation levels to simulate zero blending and full blending. These two scenarios along with actual RAP blending were used in the Superpave volumetric mix design to determine optimum asphalt content and degree of blending. Through volumetric mix design paired with simulated cases, it was estimated that approximately 75% residual RAP binder interacted with the virgin binder in terms of blending and contribution to the final mix.

Rutting or the accumulation of permanent deformations has long been a major mode of failure for the flexible pavements. While researchers have developed multiple tests to characterize this phenomenon in asphalt concrete pavements, little information is available on how each factor or parameter or their combinations from these tests affect the permanent deformation behavior of asphalt concrete pavements when it comes to the prediction of the actual field performance. This paper focuses on the ruggedness testing of the factors affecting the permanent deformation behavior utilizing the modified wheel tracker (MWT). These factors are percentage of air voids in the compacted mix (%VTM), nominal maximum aggregate size (NMAS), binder type, and test temperature. The analysis involved these factors, each at two levels. The study utilized half-factorial design in accordance with ASTM E1169-20. The parameters which have a significant effect on permanent deformation were determined through statistical analysis. All the test parameters except the Mix NMAS were found to be significant with VTM imposing the greatest effect followed by test temperature and binder type. Regression models were proposed to predict the flow numbers based on vertical and horizontal deformations, FN_V and FN_H, respectively. Although the NMAS did not seem to be significant in this analysis, its interaction with binder type proved to be significant. In addition, sensitivity analysis was undertaken as an attempt to provide reasonable tolerance limits for the test parameters.

A two-dimensional (2D) semi-circular bending (SCB) model was constructed with the extended finite element method (XFEM) to investigate the fracture performance of asphalt mixtures. The influence of material properties, which include the tensile strength, fracture energy, and elastic modulus, on the crack development in the I-FIT SCB configuration has been examined through the load–displacement curves. A full factorial of 64 simulation cases varying in material properties was carried out for sensitivity analysis. The simulation results showed that the crack development could be divided into four stages according to the damage evolvement. In addition, it was found that stiffer modulus results in higher peak load and steeper slope of curve. Tensile strength showed a noticeable effect on the peak load, while the fracture energy was highly related with the area under curve after peak load. Linear regression equations have been established between material properties and load–displacement curve parameters.

In the current study, two types of reactive powders, namely calcium sulfoaluminate (CSA) cement and ordinary portland cement (OPC), were incorporated into warm mix asphalt (WMA) at 25% volume concentration replacing asphalt binder. The powder materials were added to replace the binder without changing the volumetry of mix design. The performance of the mixtures was then measured and compared to the control mix using laboratory testing. The tests include the workability using a superpave gyratory compactor (SGC), moisture damage and fatigue resistance using an indirect tensile (IDT) test, and thermal cracking resistance using a semi-circular bend (SCB) test. The research results demonstrated that reactive powder-based mixtures show superior resistance to fatigue and thermal cracking, while the workability and moisture resistance were comparable to the control mixtures. The measured fatigue life and low-temperature fracture energy of CSA-based mixes was improved by 62.20% and 9.30%, respectively, when compared to the reference mix. Based on the reported results, it is concluded that using reactive powders in WMA mixtures not only enables a reduction in asphalt binder content but also can improve the mechanical response of the asphalt concrete.

The Virginia Department of Transportation (VDOT) is currently taking steps toward incorporating performance-based criteria into asphalt mixture design in an effort to build more durable and longer-lasting pavements. As part of this effort, the indirect tensile (IDT) conducted as per ASTM D8225-19 has been selected as a test method for evaluating the cracking susceptibility of asphalt mixtures. VDOT also requires that the susceptibility of asphalt mixtures against moisture-induced damage be evaluated by means of the AASHTO T283 standard. Apart from the difference in data analysis methodology, specimen thickness is the major difference between the two tests. For a 150-mm-diameter specimen, the IDT cracking test procedure specifies a specimen thickness of 62 mm, while the AASHTO T283 procedure requires a 95-mm thickness. The objective of this study was to investigate if the test procedure in AASHTO T283 can be modified by reducing the specimen thickness such that only one test can be performed for assessing the resistance of asphalt mixtures to moisture and crack-related damage at the same time. In addition, the cracking tolerance (CT) index was evaluated to quantify the cracking and moisture susceptibility of asphalt mixtures. The test results from five plant-produced asphalt mixtures indicated that the moisture damage test as per AASHTO T283 can be performed on asphalt concrete specimens with a thickness of 62 mm and a diameter of 150 mm. The analysis also indicated that the CT index was unable to provide the expected performance trends for asphalt mixtures subjected to a freeze-thaw cycle.

This study explores the interactions and compatibility of different types of cement as reactive powders with bitumen binders to evaluate the rheological performance of warm mix hybrid mastic systems. The binders were modified with a warm mix asphalt (WMA) additive. Two types of portland cement Type I (LF and SM), calcium sulfoaluminate cement (CSA), oil-well cement (OW), and high alumina cement (HA) were blended with asphalt binder and their physical and chemical properties were characterized. The cement properties include Rigden voids, specific gravity, particle size distribution, and chemical composition. The cement powders were incorporated into asphalt mastics at 5% (low), 15% (intermediate), and 25% (high) concentration by volume of the mastic. Fourier transform infrared spectroscopy (FTIR) test was performed to assess the chemical interactions between the cement powders and asphalt binder. The effects of cement type and filler volume concentration on the properties of mastics at high and low temperatures were studied using complex modulus, phase angle, high temperature creep and recovery, low temperature creep stiffness, and relaxation ability. Laboratory results indicate that using cement powders at 15% and higher filler volume concentrations the enhancement of high-temperature response can be attained. According to the Superpave specification, the low-temperature performance of cement-based mastics with 5% replacement of cement was acceptable.

In asphalt foaming process, water is added into the hot asphalt binder at high air pressure to create foam in the binder. The added water, also termed as foaming water content (FWC), turns into water vapor and get encapsulated into the binder in form of numerous water bubbles during the foaming process. These water bubbles are expected to be evaporated out of the foamed warm mix asphalt (WMA) during mixing and compaction. However, all the bubbles may not be completely evaporated out, rather some of the bubbles might be entrapped in the foamed WMA even after compaction. These residual waters might contribute to damages characteristics of the foamed WMA. To this end, this study determined the effects of foaming on fatigue damage characteristics of foamed WMA. Foamed asphalt binders were designed by varying FWCs and they were tested using linear amplitude sweep (LAS) test. The simplified viscoelastic continuum damage (S-VECD) modeling of the LAS test data were utilized for the damage evaluation. The study reveals that foaming softens the binder, which results in slightly lower stiffness, however, an equivalent or slightly improved fatigue characteristics compared to the regular unfoamed binder.

The performance of styrene-butadiene-styrene (SBS) modified asphalt binder deteriorates in the service life possibly because SBS polymer degrades due to aging. Currently, there is no specific test method for the determination of SBS polymer degradation. In this study, a novel dynamic shear rheometer (DSR)-based extensional deformation test was performed to determine the SBS degradation in the asphalt mixture with SBS modified binder due to laboratory aging. AASHTO R30 mixture aging and 1-Day forced-draft oven mixture aging at 135°C were performed in the laboratory to simulate the field aging. Sentmanat extensional rheometer (SER) was inserted inside the DSR host system to perform the extensional deformation test. Two peaks were obtained from the novel test: first peak elongation force (F₁) indicated binder’s stiffness, and second peak elongation force (F₂) indicated elastomeric polymer characteristics. After obtaining the F₂ value from the mixture extracted SBS modified binder, it was compared to an equally stiff SBS modified asphalt binder. The reduction in the SBS polymer’s elongation force (F₂ value) was considered as the degradation. This study found that the SBS polymer degraded when the asphalt mixture with SBS modified binder was being aged in the laboratory. Also, the aging temperature played a significant role in the degradation of SBS polymer.

Gradation plays significantly towards the amount of active binder in hot mix recycling, as a function of exposed specific surface of aggregates. Existing procedures do not explicitly consider gradation of the Reclaimed Asphalt Pavement (RAP) mixture in the determination of active binder content (RAb). In this investigation, two types of RAP reclaimed after six and eight years of service life are used to quantify RAb. The RAP material is sieved into three different sizes representing coarse, fine, and filler fraction and the corresponding binder content is determined. Gradation of extracted aggregate obtained from centrifuge and ignition oven is determined. The RAb mobilized is quantified based on a mechanical mixing procedure with the virgin aggregate of a threshold sieve size. The variation in RAb in the different size fractions is identified, and the need of varied mixing time and rejuvenator dosage for beneficial binder mobilization among the different fractions is also identified.

High early strength concrete (HESC) materials are frequently used for concrete pavement repair since the rapid strength gain permits reopening to traffic in as little as a few hours. Anecdotally, these materials and repairs have often demonstrated durability worse than the adjacent pavement slabs. The rapid strength gain of HESC is associated with strongly exothermic cement hydration that may lead to high repair slab temperatures and or temperature gradients. To explore these phenomena, several candidate HESC mixtures were prepared and tested with semi-adiabatic calorimetry to characterize the time evolving thermal characteristics. These data were used to calibrate several finite element-based heat transfer models which in turn predict the maximum repair slab temperature and temperature gradient. Predicted slab temperatures as high as 138°C and thermal gradients ranging from 63°C/m to 253°C/m were observed. These findings will help to guide experimental validation of the phenomena.

The temperature-sensitive characteristic of the bitumen plays a critical role in the performance of the bituminous binder. The accumulation of distress over a range of temperature depends on the proportion of elastic and viscous behavior of the binder. This paper attempts to separate the elastic and viscous behavior of binder at different temperatures and aging conditions using large amplitude oscillatory shear (LAOS) testing. A binder of VG30 grade as per Indian standard specification was used for this study. The material was sheared using constant strain amplitude for 10 min using a dynamic shear rheometer. Unaged, short-term aged, and long-term aged VG30 binder were subjected to 1% and 5% strain amplitude and the test was conducted at 5 Hz frequency. The test was conducted at the temperatures of 30°C, 45°C, and 60°C. The stress, strain, and strain rate waveform data were used to separate the elastic and viscous stress. The elastic and viscous stress was further used in studying the elastic/viscous behavior dominance at a specific temperature.

Ground Tire Rubber, or GTR, is gaining popularity as a recycled mixture component and performance-enhancing asphalt mix modifier in multiple U.S. states. This noticeable increase in usage has been driven by recent advances in production technologies, material specifications, modern asphalt mixture performance testing, cost-savings, and favorable field performance comparisons with polymer modified asphalt mixes. This paper details laboratory and field investigations of recent GTR designs, demonstration projects, and routine construction projects in Georgia, Virginia, Texas, Wisconsin, Illinois, and Missouri, including high-profile interstate and Tollway paving projects with up to 15 years of performance experience. Both terminal blend and dry process rubber asphalt modification techniques are investigated, with the latter involving a chemically engineered, dry GTR system designed to impart workability and performance characteristics beyond that achieved with simple GTR addition. Mix lab testing methods and procedures will be discussed, and recommendations will be presented regarding BMD with dry process rubber. Mixture performance and field tests indicate that GTR-modified, stone-mastic asphalt (SMA), open graded, and dense graded mixes can perform similarly to polymer-modified mixtures, but at significantly lower modification costs. Field data, economic data, and contractor feedback from several states will be presented, along with brief discussion of the application of an engineered crumb rubber (ECR)-modified mix used at ASCE Headquarters in Reston, VA.

This work uses computational mechanics modeling to study the influence of the air void (AV) content in the mechanical response of permeable friction courses (PFC). Multiple geometries representing realistic microstructures of 10 × 10 cm PFC specimen were randomly generated using gravimetric techniques through discrete element (DE) modeling. The target AV content of these microstructures was 15%, 20%, and 25%. The dynamic modulus of the PFCs was quantified through finite element (FE) techniques using the commercial software Abaqus. The results corroborated that PFCs with higher AV values—which are promoted by agencies in order to guarantee high permeability—have lower stiffness, weaker internal microstructures and, consequently, they are expected to have durability issues.

Scarcity of available natural resources, high cost of virgin materials, and land depletion caused by the disposal of waste materials, has led to the need for sustainable alternatives in road construction. One such industrial waste emanating from the paper industry is the paper sludge. This paper sludge ash (PSA) can be used as an alternative construction material. The present study envisages the use of PSA in making interlocking concrete block pavements (ICBP). It uses PSA as a replacement to cement in the concrete used for the ICBP, by varying percentages viz., 0%, 5%, 10%, and 15% of cement. All the tests were conducted as per IS: 15658-2006. It was observed that the compressive, split tensile, and flexural strength increased by 15.7%, 6%, and 35.7%, respectively. The water absorption is less for 10% replacement. Overall a 10% replacement is recommended.

Very fine coal combustion products (CCPs) are a by-product of burning coal when generating electricity. Fly ash has generally been used in portland cement concrete. However, some CCPs have been used in hot-mix asphalt (HMA) as mineral fillers. Due to current changes of Environmental Protection Agency (EPA) emission requirements, large volumes of fly ash containing sulfur cannot be used in traditional concrete. Therefore, this research was undertaken to investigate if some of the finer CCPs can be used beneficially in HMA. In this project, fly ash was blended with PG 58-28 asphalt binder at various percentages (5%, 10%, and 15%). A rotational viscosity test was performed on the blend to see what percentages of fly ash by mass of asphalt binder would be workable. All percentages were found to be viable. Hamburg wheel tracking tests were then conducted on these Superpave HMA mixtures. Based on the Hamburg test results, the best performing mixture with 15% of fly ash was selected to conduct further tests, such as, modified lottman, dynamic modulus, and S-VECD test, and compare with the control group (without fly ash). This paper presents these results.

Bitumen—a by-product of crude oil—is a rheological material whose properties undergo deforming changes caused not only by the effects of physical loads and loading duration but also by exposure to environmental factors and variations of temperature. The typical properties of the ultimate bitumen in-service differ greatly from those of the initial bitumen in terms of getting more viscous, stiffer, and more fragile as a result of the age-hardening, and worse still, this process is almost inevitable. Excessive aging may cause the binder to partially lose its adhesion and cohesion, and subsequently it may cause some detrimental distresses in bituminous pavements such as raveling and graveling. The current study represents an elaborate investigation into the pivotal phenomena provoking bitumen aging. Furthermore, several quantitative indicators to determine the level of hardening are discussed and a state of the art on past and current protocols to emulate aging in laboratory environment is provided. Finally, this paper highlights the inclusion of various anti-aging agents to palliate the aging of binder in order to improve the resistance of bituminous mixtures.

Mechanical stabilization of unbound aggregate layers involves creating a geogrid-aggregate stiffened zone with higher confinement. This paper presents findings from a laboratory study with the objective to quantify stiffness increases in geogrid-stabilized aggregate systems. A bender element (BE) field sensor was utilized to evaluate the local stiffness of unbound aggregates in the vicinity of an installed geogrid. A dense-graded crushed stone aggregate material was compacted in a large-scale laboratory testbed over a soft but uniform support, with and without a geogrid placed at the bottom of the aggregate layer. Static surcharge loading providing different confinement levels was applied to all tests including geogrid stabilization and control section. The BE field sensor measured shear wave velocities were then used to estimate the local stiffness and the extent of the stiffened zone at three different locations above the geogrid. Two punched and drawn geogrids with different aperture sizes were evaluated under the static surcharge loading scenarios. The small strain moduli and the extents of the stiffened zones on top of the two geogrids with different aperture sizes were quantified. The extents of the stiffened zone generated by geogrid stabilization were between 15.2 cm (6 in.) and 25.4 cm (10 in.) above the geogrid, and geogrid with a smaller aperture size was a better match and therefore more effective for the dense-graded aggregate material. The effectiveness of geogrid stabilization depends on the level of confinement of the aggregate layer, geogrid aperture size, and gravel to sand ratio, which was also observed from the stiffened zone characteristics from repeated load triaxial tests in a previous study.

When not adequately processed, the construction and demolition waste, CDW, and green coconut shell tend to end in landfills. The big volume of material to be deposited in landfills poses an environmental problem. This work aims to promote circular economy principles under a perspective of waste valorization, by stimulating the use of recycled concrete aggregate (RCA) derived from crushed concrete of CDW, and coconut fibers (CF) coming from green coconut shell. An RCA was characterized and used to produce a cement bound granular mixture (CBGM) for the base/subbase layers reinforced by CF. In laboratory, an experimental program was developed to evaluate the performance of the CBGM incorporating RCA and CF against a traditional CBGM. Mechanical performance was assessed through unconfined compressive strength and indirect tensile strength tests, and the durability was evaluated through the wet-dry durability method. The results indicated an adequate performance underlying the effectiveness of GBGM with RCA and CF to be used in pavement layers.

Cold recycling has globally lifted foamed bitumen and emulsion stabilization technology to unprecedented levels. From humble beginnings of five decades ago, where bitumen stabilization provided sustainable solutions for road rehabilitation under light to moderate traffic, cold recycling has evolved into a technology that addresses the demands of heavily trafficked highways with a high percentage of recycled asphalt. The key to the success of road recycling is reliable pavement performance evaluation (including durability) of recycled materials through the identification of the critical parameters, their tests defined by well-defined protocols, a reliable structural design function to estimate their service life as well as sound specification limits to measure against. This paper uses reclaimed asphalt pavement (RAP) as an increasingly important component of cold recycling to highlight the technological advances that have taken place in the last two decades. The development and standardization of mix and structural design processes for bitumen stabilized materials have enabled optimization and reliable application of the technology.

Geogrid type and aperture size of the grid openings play a significant role in the performance of mechanically stabilized pavements. In the present study, three types of biaxial geogrids were used to quantify the influence of aperture size on the corresponding benefit quantifiers. Large-scale model pavement experiments (LSMPE) were conducted to study the behavior of geogrid stabilized unbound model pavements overlying a wide range of subgrades with California bearing ratio (CBR) equal to 1%, 5%, and 7%. Pavement sections were prepared in a test chamber measuring 1.5 m (length) × 1.5 m (width) × 1.0 m (height), and the load was applied through a rigid 300-mm-diameter circular plate using a 100 kN actuator. The influence of aperture size ratio (ratio of the size of the grid opening to the nominal size of aggregate) on load-settlement behavior was studied. The optimum aperture ratio for effective interlocking and particle strike-through mechanisms was proposed by varying the ratios from 1.0 to 2.0. Lastly, the benefit factors, i.e., modulus improvement factor (MIF) and layer coefficient ratio (LCR) of geogrid stabilized pavements, were presented. LSMPE test results showed significant geogrid-aggregate interaction when the ratio of the equivalent aperture size of geogrid to aggregate particle size ranged from 1.0 to 1.63. This could be attributed to the effective interlocking of aggregates within the apertures of the geogrids. The overall MIF and LCR values ranged from 1.38 to 2.2 and 1.19 to 1.46, respectively, for the tested cases of the study.

Traditionally, variations of Proctor compaction method by means of an impact hammer have been used for the fabrication of cement-treated specimens in the laboratory. There are several systematic errors and practical concerns associated with compacting cement-treated aggregate base materials in cylindrical rigid molds. Issues pertaining to the quality, uniformity, and internal pore-structure of laboratory prepared specimens greatly influence the reliability of data and confidence in the material properties for the analysis and design of transportation infrastructure. Therefore, this study was designed to investigate the influence of compaction techniques on the pore-structure distribution, as well as compressive strength properties of cement-treated materials. The experiment design incorporated cement treated virgin aggregates and reclaimed materials to better understand the synergistic interactions between different aggregate sources, cement contents, and compaction methods on the mechanical behavior of cement stabilized base materials. X-ray computed tomography results revealed the superiority of the gyratory compactor to achieve uniform porosity distributions in orthogonal directions. The mitigation of boundary effects in gyratory compacted specimens resulted in enhanced compressive strength performance compared to specimens compacted using the impact method. The outcome of this research can be instrumental for the pavement design industry for the refinement of specimen production procedures and the improvement of mixture design protocols in cement-stabilized base layers.

Base course quality has a significant impact on the pavement load-bearing capacity and the layer strength could be improved using stabilization techniques. Asphalt emulsion is one of the commonly used materials for base course stabilization. Cement is usually added as an active filler to enhance the mix properties. Asphaltenes is a waste material derived from Alberta oil-sands Bitumen with no significant application in the industry. This study compares the impact of asphalt emulsion stabilized layers modified by asphaltenes and cement separately. For this purpose, asphaltenes and cement modified mixes with 1% and 2% by the mixes total weight were prepared. Both mixes mechanical properties were investigated through Marshall stability, indirect tensile strength (ITS), and tensile strength ratio (TSR). IDEAL-CT test was also used to evaluate the cracking resistance of the mixes. From the results, it was concluded that asphaltenes had a greater impact on increasing the Marshall stability, tensile strength, and cracking resistance of the mixes compared to cement. However, asphaltenes-modified samples were found to be more susceptible to moisture damages.

Multi-temporal Interferometric Synthetic Aperture Radar (InSAR) is a space-borne monitoring technique able to detect cumulative surface displacements with a millimetre accuracy within the line of sight (LOS) of the radar sensor. Several developments in the processing methods and an increase in the availability of SAR data sets from different satellite missions have proven the viability of this technique in the near-real-time assessment of bridges and the health monitoring of transport infrastructure. This research aims to demonstrate the potential of satellite-based remote sensing techniques in developing an innovative health-monitoring method for structural assessment of bridges and the prevention of subsidence damage, using high-resolution SAR data sets and complementary ground-based (GB) non-destructive testing (NDT) techniques. To this purpose, high-resolution COSMO-SkyMed (CSK) products provided by the Italian Space Agency (ASI) were acquired and processed. A multitemporal InSAR analysis was developed to identify and monitor the structural displacements of the Rochester Bridge, located in Rochester, Kent, U.K. This bridge is composed by four separate bridge decks carrying the A2 Road, a railway, and a service-bridge carrying service pipes and cable. The outcomes of this study demonstrate how multitemporal InSAR remote sensing techniques can be synergistically applied to complement the traditional GB analyses (e.g., ground penetrating radar, laser scanner, and accelerometers) and information on river bridges (e.g., river levels from monitoring stations). This can provide an extended spatial coverage and an effective identification and monitoring of defects and decays at reduced costs, compared to traditional monitoring techniques.

Chip seals are a common pavement preservation technique for maintaining an acceptable roadway condition for vehicles. Chip seals applied in urban areas can alter the optical and thermal properties of the pavement, which affects the Urban Heat Island (UHI). Four field cores were extracted from chip seal roadways that were 6–12 months old and their thermal and optical properties were measured to quantify the impact on UHI. The thermal properties were measured using a transient plane source (TPS) technique for the asphalt substrate layer as well as the combined asphalt and chip seal structure, with similar values found for both sets. Measurements with the combined structure had a higher standard deviation as compared to the asphalt only condition, indicating a higher percentage of air voids in the chip seals. The optical properties were measured only for the chip seal surface. The albedo of the chip seal ranged from 0.04 to 0.06, as compared to 0.15 to 0.20 for typical asphalt that is at least a year old. The emissivity of the chip seal averaged 0.92, as compared to 0.83 for asphalt concrete reported in literature. The UHI impact was quantified in terms of the global warming potential (GWP) as well as the hourly average net surface heat flux and surface temperature. Given the measured optical and thermal properties of field cores, chip seals were found to increase the UHI effect of flexible pavements by a small amount.

The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. The National Center for Asphalt Technology (NCAT) Test Track is a 1.7-mile oval where the accelerated loading research is conducted on experimental asphalt pavements. In this study, six pavement sections with low skid resistance were selected for shotblasting abrasion, which included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four aggregate types (limestone, granite, dolomite, and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking, and surface roughness was periodically monitored. The test results indicated that shotblasting treatment was effective in improving the long-term friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting, and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and aggregate type.

Pavement evaluations provide airfield management teams with estimates of the structural capacity of their airfields. These pavement evaluations include computation of allowable passes and allowable gross loads using layered elastic analytical techniques. In its airfield evaluation criteria, the Department of Defense recommends the use of the computer program PCASE. Currently, PCASE uses the layered elastic code WESLEA, but future versions of the program will transition to another layered elastic program JULEA. These two LEA codes contain different interface models to describe the bonding condition between pavement layers. The definition of this relationship is important when considering the interface at the bottom of slabs in rigid pavements. The purpose of this study is to quantify the differences in computed bending stresses, allowable passes, and allowable gross loads (AGLs) in the evaluation of concrete airfield pavements using the two interface bonding definitions. The theoretical formulation of these two interface models shows that an essential shortcoming in WESLEA is its lack of consideration for the interfacial shear stresses. Results show that this fundamental difference in the interface definitions leads to noticeable disagreements in estimations of bending stress, allowable passes, and AGLs by the two programs. Findings suggest that the JULEA interface model provides a sounder theoretical relationship for interface bonding and should be used in future versions of PCASE.

This paper investigates the application of surface electrical resistivity measures to assess the durability of concrete pavements containing steel fibers. Electrical resistivity testing has become a popular method to predict the service life of concrete with a good correlation with the chloride penetration testing results. The application of surface resistivity follows the same trends for in-service materials. However, the steel reinforcement in concrete elements, including pavements introduces sources of errors in such measure. Existing literature offers techniques to minimize such errors in conventional reinforcements with the orderly spatial distribution of steel bars. The presented investigation utilized numerical simulations to identify challenges introduced by randomly distributed steel fibers in concrete pavements. Results address expected errors in surface electrical resistivity caused by short steel fibers in standard specimens and analyze these errors with respect to properties and characteristics of steel fibers and their spatial distributions within the body of the concrete. Conclusions include an assessment of errors and offer modification factors for realistic conditions.

A flexible pavement network may be exposed to traffic changes over time because of detours that may cause unusually high traffic loading on some parts of the pavement sections. Such sections, therefore, need to be preserved earlier than their expected service life. This study focuses on incorporating the effectiveness of preservation and rehabilitation techniques, e.g., functional thin overlay and structural asphalt overlay on flexible pavement service life predictions using a machine learning approach. The developed models are capable of estimating the current and future international roughness index (IRI) and of detecting performance recovery after application of preservation treatment, thereby forecasting the remaining service life. The traffic, pavement structural, and performance data were obtained from the pavement management information system (PMIS) of the Iowa Department of Transportation (DOT). This study describes realistic what-if scenarios considering various treatment techniques to provide a better understanding of the effectiveness of treatments on extending flexible pavement service life. Such outcomes will help facilitate better pavement preservation management strategies.

Inaccurate weigh-in-motion (WIM) data may result in significant over-or under-estimation of the pavement performance period, leading to over-or under-design pavements. Therefore, the data collected at WIM systems must be accurate and consistent. The paper presents an approach to estimate WIM system accuracy based on axle load spectra attributes [normalized axle load spectra (NALS) shape factors]. This alternative approach to assess WIM system accuracy is needed to characterize temporal changes in WIM data consistency. The WIM error data collected before and after calibration were related to NALS shape factors for Class 9 vehicles. This analysis’s main objective is to determine WIM system errors based on axle loading without physically performing equipment calibration. This approach can help highway agencies select optimum timings for routine maintenance and calibration of WIM equipment without compromising its accuracy. The results show that the WIM accuracy for the tandem axle (TA) can be estimated with TA NALS shape factors with an acceptable degree of error for bending plate (BP) and quartz piezo (QP) sensors. Further, the results obtained using different statistical methods for model development and validation show reasonable goodness of fit. The use of NALS to estimate the TA WIM accuracy can save a significant amount of time and resources, which are usually spent on equipment calibrations every year.

This paper presents a laboratory evaluation and field verification of the cracking performance of seventeen asphalt mixtures that were placed on pavement test sections. Plant-mixed lab-compacted (PMLC) specimens were produced to assess their mechanical performance, specifically their cracking performance with the crack progression rate from the overlay tester (OT) test. Also, the cracking condition of the pavement test sections was monitored semi-annually with pavement distress condition surveys. Field cores were also extracted from the pavement test sections to assess their cracking properties with the OT test. The cracking performance of the asphalt mixtures obtained from testing the PMLC specimens and field cores was compared and related to the observed field cracking performance as a means of verification. The OT test can delineate between good and poor performing asphalt mixtures in terms of cracking potential and should be considered as a design tool for routine evaluation of asphalt mixtures.