The performance of cement treated permeable base (CTPB) material under full-scale aircraft traffic is investigated on two dedicated pavement sections during construction cycle 9 (CC9) at the Federal Aviation Administration's (FAA) National Airport Pavement Test Facility (NAPTF). Laboratory and field characterization of the CTPB material was performed during the construction stage. In addition to testing for compressive and flexural strength, measuring resilient modulus on 28-day cured CTPB cylindrical specimens was experimented as part of the laboratory characterization. Although producing specimens of flat and smooth end surfaces was one of the major challenges in measuring reliable vertical deformations, stress-dependency of CTPB material was captured in the resilient modulus test results. The light weight deflectometer (LWD) was identified as a feasible field alternative for the characterization test on the finished CTPB surface. The CTPB modulus measured in the laboratory was approximately 1.8-2.6 times the field modulus derived from LWD testing. This paper discusses laboratory and field characterization results and provides an overall evaluation of CTPB material properties and anticipated performance under full-scale traffic. The implications of test results for future CTPB material FAA specifications are also addressed.

Construction Cycle 7 (CC7) conducted at the FAA National Airport Pavement Test Facility (NAPTF) was aimed to study the effect of hot mix asphalt (HMA) layer thickness and develop perpetual pavement design criterion for airfield flexible pavements. Four fully instrumented perpetual test pavements were designed, constructed, and tested, with all test items trafficked under heavy aircraft loads using a three duals in tandem configuration. Pavement condition was monitored using heavy weight deflectometer tests, distress surveys, and surface profiles. Comprehensive response data analysis revealed that increasing HMA layer thickness significantly reduced the tensile strain at the bottom of the HMA layer, permanent deformation in the unbound layer, and vertical stress at top of the subgrade. Thicker HMA test items exhibited better rutting performance, as evidenced in both multiple depth deflectometer and surface profile data. The interaction between HMA layer temperature and thickness was captured in the pressure cell responses. More tests are planned to determine the threshold HMA strain to prevent fatigue cracking.

Four flexible pavements were constructed on the north side for Construction Cycle 7 (CC7) at the Federal Aviation Administration's (FAA) National Airport Pavement Test Facility (NAPTF) to develop flexible perpetual pavement design criterion and validate/refine/modify the fatigue model for asphalt concrete (AC) .H-Bar asphalt strain gauges (ASG) were installed in four test sections to measure transversal and longitudinal strain at the bottom of the AC layer. Fiber optic strain gauges (FOSG) were also installed in one of the test sections (8-inch thick asphalt concrete layer). Full-scale tests were performed on these pavement test sections under heavy aircraft gear loads using the National Airport Pavement Test Vehicle (NAPTV). Three traffic speeds, four gear configurations and three wheel loads were used to evaluate the mechanical response of the AC layer. It was found that response of fiber optic strain gauges is comparable to the asphalt strain gauge. The effects of traffic speed, gear configuration, and wheel load on the asphalt concrete strain were investigated. Strain basins were established based on five wander positions.

This study presents the results of one of the first attempts to characterize the pore water pressure response of soils subjected to dynamic loading under saturated and unsaturated conditions. The resilient modulus, which captures the soil stiffness under dynamic loading, is a critical parameter for pavement design. It has been recognized that the development of pore water pressure contributes to modulus degradation. Several efforts have been directed to model the effect of air and water pore pressures upon the modulus. However, none of them considered dynamic changes in pressures but rather were based on equilibrium values corresponding to either initial or final conditions. A testing program was conducted to characterize the pore water pressure response of a clayey sand subjected to dynamic loading. Using the results, models capable of predicting the cumulative excess pore pressure under both saturated and unsaturated conditions were proposed. Findings regarding the influence of the controlled variables challenge common beliefs. Upon further research, the proposed models may become a powerful tool not only to overcome unsaturated soil testing limitations, but also to prevent soil failure as a result of excessive pore water pressure development. (C) 2016 American Society of Civil Engineers.

The suitability of the Superpave Gyratory Compactor (SGC) to replicate field performance of aggregates during construction and trafficking of airfields was assessed. The subbase materials used at the National Airport Pavement Test Facility (NAPTF) of the Federal Aviation Administration (FAA) were evaluated. SGC test results at different moisture contents were compared to field performance. The SGC was found to be capable of achieving higher densities than the Modified Proctor method. The SGC densities were similar to that achieved by modern field compaction equipment. The use of the SGC over the Modified Proctor method for determining the compaction characteristics of aggregates is recommended. New SGC-based construction specifications will contribute to minimize trafficking compaction in the field. Material performance test results suggest that excessive trafficking compaction is, in part, due to abrasion and attrition of the aggregate. A comparison of laboratory results with field performance indicates the SGC may not be suitable to reproduce trafficking compaction.

This paper discusses various strategies for characterizing three-dimensional particle morphology of granular media for use within the Discrete Element Methods (DEM) framework. The method utilized for three-dimensional shape characterization was performed on rounded Michigan Dune sand and more angular Daytona Beach sand. The feasibility of using Optical Microscope images for particle reconstruction, since these are the most inexpensive images to acquire, are validated against results from Optical Tomography and X-ray Tomography methods, which are more accurate. The particles reconstructed using this methodology can be captured in DEM by a clustering technique where several circular particles are clumped together. Numerical simulation of dry pluviation are performed to study the effect of grain shape obtained using the clustering algorithms on soil fabric and as validation of the process. Daytona Beach sand, Michigan Dune sand and glass beads are modeled in DEM and it is observed that soil fabric obtained from dry pluviation is strongly dependent on particle morphology.

This study presents results of one of the first in situ assessment studies on the use of the Mechanistic-Empirical Pavement Design Guide (M-EPDG) methodology applied to the design of airfield pavements. The M-EPDG’s Enhanced Integrated Climatic Model (EICM) introduces unsaturated soil modeling techniques into the prediction of moisture changes in the unbound materials throughout the life of pavements for highway conditions. Field soil moisture content changes measured at several Air Force bases in the U.S. were collected from historic studies and compared to MEPDG predictions. Details and outcomes from this comparative study are presented herein. Despite significant differences in structural dimensions and geometric design, this study showed that the EICM promises to be a suitable predictive methodology to be adapted for airfield pavement conditions and has the potential to become a tool for the incorporation of unsaturated soil modeling for the design of airfield pavements, provided that several enhancements are made to the model applied to highway design. Also, a discussion on possible sources of uncertainty in the predictions of the MEPDG and a series of alternative revisions and enhancements required to incorporate the EICM with current airfield pavement design methodologies are presented.

The database developed under NCHRP Project 9-23A, Development of a National Catalog of Subgrade Soil–Water Characteristic Curves (SWCC) Default Inputs to Use in the MEPDG, included not only measured soil index properties needed in all hierarchical levels of the enhanced integrated climatic model but also SWCC parameters, which are key in the implementation of Level 1 analyses. A set of maps in portable document format displaying the location of every soil unit identified within the continental United States, Hawaii, Alaska, and Puerto Rico and a simple interface in MS Excel to aid in querying of data were also developed for the project. Under NCHRP Project 9-23B, Integrating the National Database of Subgrade Soil–Water Characteristic Curves and Soil Index Properties with the MEPDG, a second research effort was directed to integrate an enhanced version of the geographic information system–enabled database with the Mechanistic–Empirical Pavement Design Guide. Specifically, NCHRP Project 9-23B aimed at the implementation of an interactive tool that allows the design guide users (currently DarWin-ME users) to retrieve both appropriate soil unit maps and soil properties relevant to a particular user-specified location by entering either state milepost information or geographical coordinates. The final product was integrated into a public website that can be accessed by design guide users, agencies, industry, and academicians through a simple link. Details of the development of this useful search tool and its main features are presented.

A limited number of equations have been proposed to incorporate moisture variation effects on resilient modulus; however, the models available are in general based on empirical correlations and not on a fundamental stress state analysis. The suitability of the currently available resilient modulus test protocol for its application on unsaturated soils was assessed. Several modifications in the stress state conditions of the “Harmonized Test Methods for Laboratory Determination of Resilient Modulus for Flexible Pavement Design” NCHRP 128A protocol are necessary when measuring matric suction due to the axis-translation needed during the test. This study presents the results of a preliminary exploration into the response of the resilient modulus of unbound materials subjected to a full stress state for unsaturated soil conditions. Two different materials were tested, one granular base and one subgrade material. The granular base material was tested under both, measured (drained conditions) and controlled (undrained conditions) matric suction modes. The subgrade material was tested under measured matric suction mode. The results were used to enhance the widely known Universal Model for resilient modulus prediction by incorporating matric suction as a fundamental variable within the stress state for unsaturated soils. This model predicts the resilient response of unbound materials at different stress states and matric suction levels. Thus, a unique set of regression constants independent of moisture variation can be obtained for any material.

A newly developed mechanistically based design procedure for airfield hot-mix asphalt pavement is studied. The pavement performance is calculated in terms of critical strains on the basis of multilayer theory. Rutting failure criteria from the Asphalt Institute, Shell Oil, and the revised U.S. Army Engineer Waterways Experiment Station (USACE-WES) are used to calculate the thickness requirements necessary for a range of design input variables. The program has been implemented in ZAPRAM, an event-driven, user-friendly educational computer program that runs in the Excel 2007 environment, coupled with Visual Basic programming. Results of the design comparison indicate a significant difference between the three common airfield pavement design procedures used. Differences between the Asphalt Institute procedure and the revised USACE-WES procedure are relatively moderate for all design situations. The greatest deviation is found between the Shell Oil approach and the other two criteria. The design difference depends heavily on several major factors. An analysis of heavy aircraft (B-747) operating on a low-support subgrade foundation may yield pavement design differences of 2 to 3 ft of granular subbase material. A major effort to enhance the state of the art for airfield pavement design models is recommended.

Evaluation and calibration of the Mechanistic–Empirical Pavement Design Guide (MEPDG) has been attempted by various agencies throughout the United States. Agencies interested in adopting the MEPDG procedure must prepare a practical implementation plan that fits local conditions. The first step in the implementation plan is collection of design input data and establishment of a database for inputs. A 3-year study was conducted at Arizona State University to establish a database to support MEPDG implementation for the Maricopa County, Arizona, Department of Transportation. The implementation program included testing of asphalt binders, hot-mix asphalt dynamic modulus, and unbound-materials resilient modulus; development of climatic weather stations and training material; and collection of traffic data. The collected information can be used to calibrate the MEPDG distress models to county conditions and verify such models. The input parameters can serve as a framework for similar highway agencies and help ensure the successful implementation of the MEPDG.

The suitability of the current resilient modulus test protocol (NCHRP 1-28A) for its application to unsaturated soils was assessed. Modifications to the stress state conditions of the protocol are necessary due to the axis-translation needed during the test when measuring matrix suction. This study presents the modulus of unbound materials resulting from tests performed under unsaturated soil conditions. Two different materials were tested. The base material was tested under drained and undrained boundary conditions, while the subgrade was tested under drained boundary condition. The results allowed for the enhancement of the Universal Model for resilient modulus prediction by incorporating suction as a stress state. This model predicts the resilient response of unbound materials as a function of external stress state and matrix suction levels and therefore, it is independent of moisture variation.

A limited number of equations have been proposed to incorporate moisture variation effects on resilient modulus; however, the models available are in general based on empirical correlations and not on fundamental stress state analysis. The suitability of the current available resilient modulus test protocol for its application on unsaturated soils was assessed. Several modifications in the stress state conditions of the Harmonized Test Methods for Laboratory Determination of Resilient modulus for Flexible Pavement Design, NCHRP 1-28A protocol are necessary when measuring matric suction due to the axis-translation needed during the test. This study presents the results of a preliminary exploration into the response of resilient modulus of unbound materials subjected to a full stress state for unsaturated soil conditions. Three different materials were tested, one granular base and two subgrade materials. The granular base material was tested under both, measured (drained conditions) and controlled (undrained conditions) matric suction modes. The two subgrade materials were tested under measured matric suction mode. The results were used to enhance the widely known Universal Model for resilient modulus prediction by incorporating matric suction as a fundamental variable within the stress state for unsaturated soils. This model predicts the resilient response of unbound materials at different stress states and matric suction levels. Thus, a unique set of regression constants independent of moisture variation can be obtained for any material.

The present study deals with the revision of the current model in the Mechanistic–Empirical Pavement Design Guide (MEPDG) used to predict the environmental factor for unfrozen unbound materials (F U ), which is used to adjust the resilient response of soils resulting from seasonal changes. A large database with data from the existing literature and studies at Arizona State University was developed to evaluate the model. The results suggest that the environmental factor is underestimated for fine-grained materials with high plasticity under dry (arid) conditions. However, insufficient data were available to enhance the F U models for wetter conditions. Three fundamental factors that may have impacts on the F U values were evaluated in this study: stress state, compaction energy (soil density), and soil type. The stress state was found to have little to no impact on the predictions of F U . But density changes and soil type were found to be important. The potential for soil index properties to be predictive variables was assessed. Models dependent on enhanced moisture content accounting for the effect of soil type are proposed for nonplastic and plastic materials. The range of predicted F U values is in close agreement with the actual measured F U values found from laboratory studies. It is recommended that the new models be adopted in the revision of the MEPDG model for the drier conditions described in this report and that research be conducted to enhance the F U approach in the current MEPDG for wetter conditions brought on for a variety of reasons (e.g., groundwater table change, increased rainfall, and frost effects).

The modulus backcalculation from Falling Weight Deflectometers is one of the primary means for evaluating in-situ resilient properties of pavement materials. When evaluating material moduli from the same location by using deflection data from different sources, it is highly probable that different methodologies will lead to differing results. This study presents a comparative analysis of backcalculated moduli results performed to quantify the differences between the historic Arizona Department of Transportation - Pavement Management System (ADOT-PMS) and the Strategic Highway Research Program – Long Term Pavement Performance (SHRP-LTPP) databases. Pavement sections were selected from numerous SHRP sites in Arizona, having both forms of deflection data available at the same location and in the same general time frame. The results of this study indicated that there was a poor correspondence between backcalculated layer moduli from both databases. As a general rule, the degree of layer correspondence improved as layer depths gradually increased (subgrade was the most accurate comparison). On the other hand, fairly good correspondence was obtained for all moduli between two differing backcalculation schemes (MODCOMP v4.2 and MODULUS v6.0). Finally, it was found that the use of the simple, closed form solution to estimate subgrade moduli from the outer geophones, gave comparable answers to the more complex backcalculated solutions based upon total deflection basin results. This gives rise to the possibility that significant reductions in cost and labor can be achieved in maintaining PMS systems and by utilizing the outer geophone equation as an implementation approach for the Mechanistic-Empirical Pavement Design Guide (ME-PDG).

Pavement damage is heavily influenced by seasonal variations in the environmental regime and by externally applied loads. The state of the art methodology currently evaluated by pavement engineers focuses upon coupling the effects on pavement performance of moisture content/matric suction properties of unbound materials with the external stresses. The literature review showed that several equations have been proposed to incorporate moisture variation effects on resilient modulus; however, the limited models available lack fundamental principles or have not been properly validated. A feasibility study on cohesionless granular base material is presented, whereas matric suction was controlled during drained and measured during undrained resilient modulus tests. It is apparent that certain modifications in the recommended stress state conditions of the NCHRP 1-28A protocol may be necessary when measuring matric suction due to the axis-translation needed during the test. Difficulties associated with the test include the current confinement fluid, which allows for air diffusion during the suction equilibration stage. Preliminary results show that the k1-k2-k3 parameters used in the approved AASHTO Mechanistic Empirical Pavement Design Guide (ME-PDG) may be functions of the suction applied to the specimen during the test protocol.