Full-scale Test Sections Research Articles

Laboratory Characterization of Additive-Modified Asphalt Concrete Mixtures

There is a need for a more rapid system of evaluation and implementation for new and existing asphalt additives, especially because of the prohibitive cost of full-scale performance evaluations. To help to meet this need, the Additive Group (AG) experiment at the National Center for Asphalt Technology (NCAT) was developed and began in 2021. A comprehensive laboratory evaluation of six mixtures, each modified with a popular additive type selected by the AG state DOT sponsors, was conducted. Simultaneously, full-scale test sections were constructed at the NCAT test track to evaluate the field performance and structure behavior of each modified mixture. Trafficking of these test sections is currently underway, and estimated to be completed in 2024, at which point an investigation linking the laboratory and field results will be done. This paper presents the completed laboratory evaluation of each AG mixture via complex dynamic modulus (E*), direct tension cyclic fatigue, and bending beam fatigue testing. The wet-process rubber modified mixture was found to have reduced E* and initial flexural stiffness, but increased fatigue resistance, relative to the styrene-butadiene-styrene (SBS)-modified control mixture. The dry-process rubber-modified mixture displayed similar trends, though to a lesser degree. Conversely, the dry-process plastic-modified mixture was found to have increased E* and initial flexural stiffness, but reduced fatigue resistance, relative to the SBS-modified control mixture. The other AG mixtures—a dry-process fiber and a wet-process plastic-modified mixture—were found to display E*, initial flexural stiffness, and fatigue resistance similar to that of the SBS-modified control mixture.

Stress-Dependent Behavior of Lightly Stabilized Industrial Waste Subbase Using Falling Weight Deflectometer

Abstract Pavement layers exhibit stress-dependent behavior, characterized by using a laboratory resilient modulus (Mr) test. However, the field behavior of such materials seldom matches with the laboratory because of changes in the state of stress, material matrix, and loading patterns. In this study, the nonlinear behaviors of three innovative fly ash-based lightly stabilized industrial waste mixes that are proposed to replace the granular subbase of flexible pavement are characterized and compared in the laboratory and field for the first time. Nine full-scale pavement test sections were constructed with three varying thicknesses of waste mix subbase layers, namely, fly ash + 5 % lime (FAL), 70 % copper slag + 30 % fly ash (CFA) and 80 % fly ash + 20 % granulated blast furnace slag (FAG). Repeated load triaxial tests on lab samples and multiload falling weight deflectometer (FWD) tests (40 kN, 55 kN and 70 kN) on test sections conducted for three years post-construction were used to extract the nonlinear behavior of Mr and the FWD backcalculated modulus (EFWD) of subbase layers. Effects of curing and traffic damage on the nonlinear parameters of EFWD were investigated. Stress-dependent conversion factors based on two different constitutive models were established to convert Mr to EFWD at different points of the subbase service life. Stabilized waste mixes exhibited stress hardening with increasing bulk and deviatoric stresses both in the field and laboratory. Curing increased EFWD and reduced the effect of stresses on the EFWD. In contrast, traffic damage imparted the opposite effect, as the stabilized waste mixes transformed into a cracked and blocky mass. The results of this study will allow practitioners to predict the field performance of waste mix subbase with great accuracy, resulting in a reliable design and possible cost savings.

Evaluation of Airport Pavement Base Layer Stiffness Characteristics via Embedded Field Sensors

Real-time stiffness monitoring of unbound aggregate layers using embedded field sensors is crucial for advanced airport pavement design and management. This paper describes research findings on monitoring base layer stiffness characteristics for airport pavements using an embedded bender element (BE) field sensor, inductive coil sensors, and pressure cells. A full-scale pavement test section was constructed at the Federal Aviation Administration (FAA)’s National Airport Pavement Test Facility (NAPTF). A BE field sensor, inductive coil sensor pairs, and pressure cells were installed in the unbound aggregate base to evaluate the layer stiffness, applied load stress, and deformation characteristics. A triple dual tandem gear loading module applied 58,000 lb per wheel to the tested section with a wander pattern consisting of 66 passes arranged in nine lateral wander positions. Dynamic responses of coil sensors and pressure cells were collected during the traffic test, whereas BE signals were collected after completing each wander pattern. Laboratory repeated load triaxial tests with BE instrumentation were also conducted to establish a correlation for converting BE field sensor readings to layer modulus properties. The in situ modulus characteristics of the aggregate base layer were evaluated during full-scale testing using two methods: shear wave velocities from a BE field sensor, and strain and stress measurements from coil sensors and pressure cells. The moduli estimated using both approaches fell into typical ranges of crushed aggregate bases and were highly comparable. The moduli from the dynamic sensor measurements clearly showed the effect of vehicle wander on aggregate base layer measured responses.

The free swell potential of expansive clays stabilized with the shallow bottom ash mixing method

An expansive clay is considered a geological material and classified as problematic soil because its high free swell potential (FSP) after water absorption often damages light buildings or structures. Stabilizers such as cement and lime have been extensively used to improve the swelling characteristics of expansive clays. Bottom ash (BTA), a waste material obtained from coal lignite electric power plants, is considered a noncohesive coarse-grained soil without undesirable swelling characteristics. Thus, BTA can be applied as a suitable alternative stabilizer in cost-effectiveness and waste management to reduce the FSP of expansive clays. This paper investigates the FSP of expansive clays partially replaced with BTA by the shallow mixing method, which creates composite materials with a reduced FSP. FSP tests were performed on conventional and composite expansive clay samples using kaolin-bentonite mixtures with low to very high FSP levels to determine the optimal BTA content and study the effect of the stabilized thickness ratio (STR) on the FSP. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques were applied to analyze the microstructural and mineral changes in the samples. Finally, FSP tests were conducted on natural expansive clay layers using six full-scale test sections to study the influence of STR on the field FSP. The main results show that when stabilized at the optimal BTA content, the montmorillonite reflection intensity and sodium (Na) amount of the stabilized expansive clay mixtures decreased, while the calcium (Ca) amount increased. This phenomenon was caused by the replacement of Na in montmorillonite with Ca in BTA, resulting in decreasing FSP values. A correlation was proposed between the FSP and STR of the composite samples based on the laboratory tests. However, such correlation overestimated the FSP values of the full-scale tests due to the effect of the overburden pressure caused by the actual thickness of the stabilized layer under field conditions. Hence, a modification factor related to increasing the overburden pressure induced by the upper stabilized layer was included in the correlation to derive an accurate prediction of the field FSP values.

Experimental and numerical studies of the geosynthetics reinforced platforms laid over soft subgrade soil

Six full-scale unpaved test sections were constructed to investigate the benefit obtained from inclusion of geosynthetic layer. Two geotextiles were placed at the interface between the base layer and the subgrade. The results allowed the estimation of reinforcement efficiency. In addition, a numerical model coupled between the discrete element method and the finite element method has been calibrated based on the experimental results.

Comparison of asphalt mixtures containing polymeric compounds and polymer-modified bitumen based on the VECD theory

• Under the same volumetrics, the mixes have similar stiffness and fatigue resistance. • In the field, the mixtures modified with the dry method show a workability issue. • The mixtures modified with the dry method can be more prone to thermal damage. • An intermediate stiffness can ensure limited bottom-up cracking and thermal damage. • The polymer compounds improve the performance of a mixture with neat bitumen. The ‘dry’ method that can be used to produce modified asphalt mixtures is a less expensive, less energy-consuming, and faster process than the well-established ‘wet’ method. Moreover, the dry method allows the incorporation of hard plastics, even those plastics obtained from waste products. Although researchers agree that the dry method can improve the stiffness and rutting resistance (i.e., high-temperature performance) of asphalt mixtures, they have conflicting opinions regarding mixture fatigue and cracking resistance. In this regard, this paper aims to evaluate, through the application of viscoelastic continuum damage theory, the fatigue behavior of two compound asphalt mixtures that have been modified using the dry method. One of the studied compounds is composed of plastomeric polymer and the other is composed of waste plastic with the addition of graphene. A reference mixture containing polymer-modified bitumen (representing the wet modification method) was used for comparison. The experimental program involved dynamic modulus tests and uniaxial cyclic fatigue tests of laboratory-compacted specimens and cores extracted from full-scale field test sections. The test results from the laboratory-compacted specimens and field cores were input to FlexPAVE TM for pavement performance simulations. Under the same volumetric conditions, the three dense-graded mixtures broadly had comparable stiffness and fatigue resistance values at the material level. However, in the pavement-level simulations, the reference mixture exhibited much less damage after 30 years of service than the compound mixtures. Concerning the field test track, the air void contents of the mixtures varied due to workability issues related to the presence of the compounds. Optimum performance was obtained for asphalt layers that could be characterized by an intermediate stiffness level that ensured an adequate load distribution without negative consequences for the mixture’s fatigue resistance and thermal resistance.

Comparison of Relative Structural Characterization Methods for Additive-Modified Asphalt Mixtures

The evaluation, adoption, and efficient deployment of asphalt additives in flexible pavements has historically been a relatively slow process, requiring years of testing and evaluation before a new product may be fully and readily used in pavement cross-sections. However, the fast-paced and innovative nature of the additive marketplace produces numerous products that have the potential to improve performance, reduce costs, or both, but have been hindered by slow deployment. To address the need for a more rapid set of evaluation tools, the National Center for Asphalt Technology Test Track initiated an Additive Group experiment in 2021 to build full-scale pavement test sections modified with several asphalt additives, including recycled tire rubber, recycled plastics, reactive polymers, and aramid fibers. Data will be collected from these test sections to develop a framework for evaluating asphalt additives in the future. Phase 1 of the investigation was to conduct limited laboratory testing and structural analysis from which a group of additives would be selected for full-scale construction and evaluation. Focused on fatigue cracking, this paper details the laboratory testing conducted for Phase 1 and two different structural pavement analysis methods using FlexPAVE™ and WESLEA. Even though the two structural pavement analysis methods are very different, the FlexPAVE and WESLEA analyses provided strongly correlated predicted cracking performance, remarkably similar predictions of equivalent pavement thicknesses, and nearly identical structural layer coefficients. It is recommended that these two approaches be further evaluated against laboratory and field performance data that will be collected from the Additive Group experiment.

Quantifying the Benefits of Geosynthetics Reinforcement in Flexible Pavement Design Using Cyclic Plate Load Testing

Development of pavement design over the past decades has focused on moving from empirical design equations to more powerful and adaptive design schemes. The AASHTO mechanistic–empirical pavement design guide (MEPDG) has been developed to model pavement structure and predict its service life more accurately. Although MEPDG has been widely implemented to design conventional pavement, it is not yet capable of predicting the service life of pavement reinforced with geosynthetics. Given the above concerns, seven full-scale test sections that were constructed at Louisiana Transportation Research Center-Pavement Research Facility (LTRC-PRF) were devoted to a structural experiment to investigate the performance of geosynthetic reinforced pavements. The benefits of using geosynthetics to enhance the performance of pavements constructed over soft subgrades was evaluated using cyclic plate load testing. Cyclic load at a frequency of 0.77 Hz was applied through a 305 mm diameter steel plate. The test results clearly show the benefits of geosynthetics in significantly reducing pavement rutting. The test section with double geosynthetic layers performed better than the other six sections studied. After eliminating the effect of variations in construction, the benefits of geosynthetic reinforcement are quantified within the context of the AASHTOWare Pavement ME Design Guide. The developed design procedure is capable of quantifying the contribution of geosynthetics in pavements to base reinforcement as well as subgrade stabilization. A design methodology is proposed that falls within the context of MEPDG.

Assessment of Asphalt Mixture Disk-Shaped Compact Tension Test Indexes for Reflective Cracking Performance

Abstract Disk-shaped compact tension (DCT) testing is a commonly used low-temperature fracture test to determine the cracking resistance of asphalt mixtures. The current testing specification only considers the fracture energy (Gf) from load-crack mouth opening displacement test data. However, Gf does not directly take into consideration the behavior of the post peak region of the curve, which may indicate the mixture’s ability to resist crack propagation and provide insight into fracture processes (e.g., crack growth velocity). It is possible to have two DCT specimens with similar Gf values but dramatically different load-displacement responses. The main focus of this paper is to make a comparative evaluation of various performance indexes developed for DCT fracture testing with respect to field reflective cracking performance of 10 full-scale asphalt concrete overlay test sections. This study evaluates Gf in addition to three other indexes: fracture strain tolerance (FST), rate-dependent cracking index (RDCI) and a proposed DCTIndex from Minnesota Department of Transportation that considers the post peak load-displacement behavior. An equivalent performance index approach is adopted to make comparisons of test sections with varying overlay structures in terms of thickness and material properties. Results from this study showed there was relatively good agreement between all equivalent laboratory performance indexes in identifying the best and worst performing overlay sections, according to normalized field performance indexes after approximately three years of service. In general, the equivalent FST and RDCI laboratory indexes rank test sections similarly, while equivalent Gf and DCTIndex have comparable ranking.

Evaluation of Hexagonal Multi-Shape, Multi-Axial Geogrids in Unsurfaced Road Applications

A full-scale unsurfaced test section was constructed to evaluate the performance of two recently developed innovative geogrids, referred to as NX-1 and NX-2, having a unique combination of hexagonal, trapezoidal, and triangular aperture shapes, rib aspect ratios greater than 1.0, and a coextruded, composite polymer sheet designed to improve aggregate and geogrid interaction. The test section consisted of a 25-cm-thick crushed aggregate surface layer placed over a weak clay subgrade. Simulated truck traffic was applied using a load cart outfitted with a single-axle dual-wheel truck gear. Rutting performance and instrumentation response data gathered from earth pressure cells and single-depth deflectometers were monitored at multiple traffic intervals. It was found that the geogrids improved rutting performance when compared with an unstabilized test item, and NX-1 was found to be the best performer of the two geogrids. Calculated traffic benefit ratios ranged from approximately 1.2 at low levels of rutting up to approximately 13.0 at higher levels of rutting. Instrumentation response data indicated that the geogrids reduced measured pressure and deflection near the surface of the subgrade layer. Pressure response data in the aggregate layer suggested that the geogrids redistributed applied pressure higher in the aggregate layer, effectively changing the measured stress profile with depth.

Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils

An evaluation of deep soil mixing (DSM) technology in stabilizing expansive soils was conducted by designing and constructing two full-scale test sections. The test sections were instrumented and installed with different numbers of DSM columns and area ratios. Their performance was evaluated by comparing the test sections with two untreated test sections. The performance of the DSM test sections was measured by addressing the shrink and swell behaviors using vertical and lateral soil movements and the swell pressures within the treated soil mass. This paper discusses the construction of the test sections, the instrumentation details, and comprehensive analyses of the field monitored data. The untreated test sections experienced absolute vertical soil movements on the order of 35 mm or greater, whereas the treated test sections had movements in the range of 10 to 25 mm. Similar observations were recorded for the lateral soil movements and swell pressure changes in both the untreated and treated sections. Unlike the DSM-treated test sections, the untreated test sections showed repeated soil movements with field moisture content changes due to periodic dry/wet climatic conditions. Results from nondestructive testing (NDT) revealed that the overall stiffness of the DSM-treated test sections was superior to that of the untreated sections. This study showed that DSM technology is a viable option for stabilizing expansive soil formations with moderate to deeper active depths.

Fluid Migration Characterization of Full-Scale Annulus Cement Sections Using Pressure-Pulse-Decay Measurements

Abstract Fluid migration behind casings is a well integrity problem that can result in sustained casing pressure, undetected leaks to the environment, and potentially very challenging remediation attempts. Understanding the geometric dimensions and extent of annular migration paths is important for diagnosing and effectively treating fluid migration and sustained casing pressure problems in wells. In this study, permeability and micro-annuli sizes in two full-scale cemented annulus test sections are measured using transient pressure-pulse-decay and steady-state seepage measurements. One of the studied sections is a cemented 9 5/8-in. and 13 3/8-in. casing section from a 30 years old Norwegian North Sea production well. A model for predicting the transient pressure decay in annular sections with non-uniform permeability is presented and the permeabilities of the two sections are determined by fitting the transient model to pressure measurements at either side of the test sections and at selected axial positions. For both sections, measured micro-annulus sizes are within the range of effective wellbore permeabilities based on sustained casing pressure records and previous vertical interference tests from other wells. The test sections display measurable axial permeability variations with the bottom part of these vertical sections having the lower permeability. For the retrieved casing section, the axial permeability variation occurs close to the middle of the test section and is attributed to the top-of-cement. Increasing internal casing pressure is found to slightly reduce the equivalent micro-annulus size, indicative of fracture-like response of the migration paths. Using two independent test protocols, we have measured effective permeabilities as well as local permeability variations in full-scale test sections and found consistent results. The study suggests that the transient test procedure can be used to more effectively characterize low-permeable annular cement where it is otherwise time-consuming or difficult to establish steady-state flow conditions.

Utilization of Cold Central Plant Recycled Asphalt in Long-Life Flexible Pavements

Long-life flexible pavements are well documented and used widely across the U.S. Found in every climate zone and traffic classification, long-life pavements do not experience deep structural distresses such as bottom-up fatigue cracking or substructure rutting. Full-scale test sections, built in 2003 at the National Center for Asphalt Technology (NCAT) Test Track, provided the basis for an optimized design approach that utilizes strain distributions for long-life thickness design. These sections, containing only virgin materials, were subjected to 30 million standard axle loadings with excellent performance in terms of rutting, cracking, and roughness. In 2012, three new sections were built at the Test Track using cold central plant recycled asphalt materials as the base layer. These layers, made from nearly 100% reclaimed asphalt pavement (RAP), supported hot mix asphalt layers that also included RAP with one section featuring in-place stabilization of the existing aggregate base. This paper provides a direct comparison between the sets of sections to compare and contrast their performance histories and structural characterization, and consider their economic and environmental impacts. None of the recycled sections are exhibiting any surface deterioration, despite heavy trafficking, and the section with a stabilized base is exhibiting lower strains than established long-life pavement thresholds. The economic analysis suggested that the recycled sections can deliver similar performance at a lower average structure normalized section cost than the non-recycled sections. Furthermore, the section with the stabilized base and 76% recycled material is likely a long-life pavement and can potentially outperform the sections with no recycled content.

Performance of Polypropylene Fiber-Reinforced Solidified Soil

Urgent repair and construction of airstrips is a research hotspot in global airport engineering. Selecting the proper structural materials is a key component of the airstrip repair process. First, with unconfined compressive strength and splitting tensile strength, the fiber length and content of polypropylene (PP) fiber-reinforced solidified soil were optimized. Then, using a scanning electron microscope, the reinforcing mechanism of PP fiber on soil and the influence mechanism of fiber parameters on fiber-reinforced soil were discussed and analyzed. Lastly, a full-scale test section was paved, on which static and dynamic loading tests were performed to verify the carrying capacity and deformation characteristics of the full-scale test section. The above research provides a theoretical foundation and data support for the urgent repair and construction of airstrip. Results indicate that PP fiber with length of 12 mm and fiber content of 0.3% has optimal performance and economic cost. The reinforcing mechanism of fiber-reinforced soil can be summarized to be the effect of a one-dimensional lacing wire and the effect of a three-dimensional network structure. Fibers show two failure modes of pull-out and tensile failure. After 20000 dynamic loading cycles, the stress at the bottom of each structural section varies less, the graded plastic deformation is stable, and the cumulative plastic deformations of the fiber-reinforced soil base, solidified soil base, and cemented soil base pavement structures are 0.83 mm, 0.93 mm, and 1.2 mm, respectively. Pavement structure composed of fiber-reinforced solidified soil can meet the load capacity requirements for use in airstrips under the characteristics of time-sensitive application.

An adaptive arresting vessel device for protecting bridges over non-navigable water against vessel collision

There is a large number of bridges over non-navigable water, and the safety protection against vessel collision is worthy of attention. In this paper, a new adaptive arresting vessel device (AAVD) was developed to protect bridges over non-navigable water against vessel collisions. The AAVD mainly consists of moored boats, mooring chains and anchors, adaptive buoys, arresting nets, trigger devices and energy absorbing devices with constant resistant force. The motion behavior of the adaptive buoys was analyzed theoretically using rigid-body kinematics. Enormous kinetic energy of the vessel is consumed by the deformation and fracture of a series of cables. Through the scale model experiments, the key parameters of the AAVD on the arresting effectiveness are discussed and determined, and the feasibility of AAVD has been preliminarily verified. The full-scale test section of the AAVD has been constructed, and the arresting vessel collision tests have been carried out. The experimental results show that the AAVD can effectively stop a yaw ship, and verify the feasibility and reliability of the technical principle and engineering design. Hence, the AAVD can achieve the purpose of protecting the safety of bridges over non-navigable water. Numerical simulation of the AAVD has been performed by using hydrodynamic analysis ANSYS-AQWA software. Numerical results are in reasonable agreement with the experimental and theoretical simulation results.

Optimisation and field assessment of poroelastic wearing course bond quality

Compared to typical asphalt mixtures, poroelastic mixtures are characterised by high porosity and high flexibility, which are desirable for traffic noise reduction. However, the same properties increase the risk of debonding from the lower layer, which is a significant source of premature damage. The study investigates which of the factors – tack coat agent, type and texture of the lower layer – have the greatest impact on interlayer bonding quality. From 27 variants of interface bond techniques investigated in laboratory, 8 were selected and constructed on two full-scale test sections. Monotonic direct shear loading and cyclic direct shear loading tests with normal force were used for this purpose. The tests indicated that softer bitumen used for the tack coat and the milled texture of the lower layer improves bond quality. However the appropriate laying compaction has the major influence. Poroelastic mixtures are much more sensitive to technological imperfections than standard asphalt mixtures.

Evaluating the Performance of Wicking Geotextile in Providing Drainage for Flexible Pavements Built over Expansive Soils

The longevity and performance of a pavement section depend on the characteristics of the subgrade soil. A majority of the pavements in North Texas, U.S., are constructed on expansive soils. The deterioration of the pavement performance because of rutting, cracking, and differential heaving is a regular phenomenon in the regions predominantly distributed with expansive soils. The pavements, particularly those built for low-volume traffic conditions, experience distress because of the high swelling and shrinkage characteristics of the underlying problematic soils. Geosynthetics have been traditionally used to improve such poor subgrades because of their many benefits, such as ease of installation, and ample mechanical and hydraulic properties. In the last decade, a newly available wicking geotextile, with a moisture redistribution capacity, has been developed to improve the performance of pavements constructed over expansive and frozen soils. In this study, small-scale laboratory and full-scale field studies were conducted to comprehend the wicking ability of this innovative geotextile in an expansive soil environment. Full-scale test sections were constructed with reclaimed asphalt pavement aggregate and traditional crushed stone aggregates in the base layer near North Texas. Details of the construction and instrumentation procedure are discussed in this paper. A comparative study between the performance of the pavement sections subjected to traffic loads and moisture intrusion was also performed. Furthermore, the rutting life of the sections, estimated using a linear elastic model, was compared and validated using the in situ data. The observations during the initial phase indicated that the wicking geotextile has the potential to improve the long-term pavement performance.

Evaluation of early-age strains and stresses in roller-compacted concrete pavement

Abstract In the structural design of a roller-compacted concrete pavement (RCCP), it is crucial to estimate strain and stress developments in the RCCP slab realistically. Since the RCCP mix uses less cement and lower amount of water, shrinkage strain and concrete temperature during the hardening stage are expected to be reduced as compared to those of conventional concrete mixture, resulting in a reduction of the concrete early-age deformation and stress developments in the RCCP slab. In this paper, early-age concrete strain and stress developments in RCCP slab subjected to environmental loads were evaluated. A full-scale test section of RCCP under real climatic conditions was monitored. The early-age total strains, stress-independent strains, shrinkage strains, and coefficient of thermal expansion (CTE) of the RCCP were measured and analyzed. Using the results of measured strains, in-situ CTE and shrinkage strain, and temperature, the early-age concrete stress development is computed by incorporating a viscoelastic property of the early-age concrete. The results revealed that the shrinkage strain of the RCCP is quite low as compared to that of conventional concrete. The early-age stress developments in the RCCP slab are strongly governed by the thermal-induced stresses. Shrinkage-induced stresses were quite small and might be negligible in a preliminary estimation of early-age stress developments in the RCCP slab.

Structural Performance of Sections Treated with Thin Overlays for Pavement Preservation

Over the last decades, increased efforts have been made to identify cost-effective alternatives to achieve a longer pavement life by applying preservation treatments. The application of thin overlays to restore the surface condition of the pavement is widely practiced across the United States. Benefits include a long service life, a better riding surface, reduced noise, grade and slope geometry preservation, recyclability, and fewer maintenance regimes. Although thin overlays can provide significant improvements in both the immediate and long-term functional performance of the pavement, there is little information on how these treatments affect the structural performance of pavements. Although not expected to significantly improve structural capacity, thin overlays may be able to maintain a structurally sound pavement in good condition for longer. The objective of this study was to evaluate the structural performance of pavements treated with thin overlays as a preservation technique. To accomplish this objective, falling weight deflectometer and field performance data from six full-scale thin overlay test sections and a control section with high cracking were collected and analyzed over a period of nearly 8 years. The results indicated that, based on deflection basin parameters (DBPs), the treated sections had better performance and were projected to reach the “warning” zone much later than the untreated sections. The observed surface condition correlated well with these parameters as, in general, sections with higher DBPs also exhibited more cracking and rutting. The test sections continue to be monitored to fully quantify the extent of the structural benefit obtained from the treatments.

Construction, instrumentation and field performance of geogrid-reinforced unpaved roads

A research study involving full-scale unpaved road test sections was carried out to investigate the performance of unpaved roads reinforced with geogrids. Ten test sections were constructed with two different base course thicknesses. Three biaxial geogrids of different tensile stiffness and one geogrid with triangular aperture were evaluated. Geogrids were placed at the subgrade–base course interface. The sections were instrumented for measuring road response to traffic loading. Traffic loading was provided by a single-axle dump truck. Field measurements of rut depth and surface deformation were recorded at selected traffic intervals. An analysis of the measured performance data indicated that the geogrids effectively reduced surface rutting and improved the performance of unpaved thin base layers and the benefit became more pronounced when a stiffer geogrid was used. The results suggested reductions in the thickness of the base layer by using geogrids of up to 18%. The improvement by geogrids was shown to be less for increasing base layer thickness. In addition, the ability of the design procedure by Giroud and Han to predict rutting performance using the test section parameters as design inputs was assessed. The results indicated that the method underpredicted the required base thickness to support the applied traffic loads.