Nondestructive Deflection Testing Research Articles

Nondestructive Deflection Testing based Mechanistic-empirical Overlay Thickness Design Approach for Low Volume Roads: Case Studies

Illinois Department of Transportation (IDOT) uses an empirical design approach to conduct thickness designs of structural overlays for low volume roads. Modified layer coefficients for a limited number of material types are utilized to assign the structural capacity of in-service pavements. Despite the ease in use and simplicity, such an empirical approach is outdated and lacking in many aspects to characterize recycled and/or nontraditional construction materials nowadays more commonly used in pavements. As far as the rehabilitation of low volume roads is concerned, the lack of testing for evaluating the structural condition of existing, in-service pavements often results in uneconomical and unreliable practices. This paper presents a mechanistic-empirical approach for overlay thickness designs of low volume pavements through a combination of nondestructive deflection testing and pre-established pavement damage models. Twenty different pavement sections were selected from six counties in Illinois with varying structural and traffic characteristics. Falling Weight Deflectometer (FWD) tests were conducted on these road segments and FWD data were analyzed with appropriate temperature correction procedures to determine and monitor the structural conditions of existing, in-service pavement sections. Then, the corresponding required overlay thicknesses were determined for these twenty case sections using three different methods commonly used by local agencies such as, AASHTO 1993 NDT method, IDOT modified layer coefficient method, and Asphalt Institute deflection approach. The M-E Overlay Design method successfully identified structural deficiencies in the original pavement configurations through FWD tests and subsequently led to more economical or safer and more reliable overlay solutions for low volume roads.

Overlay Thickness Design for Low-Volume Roads

Identifying the appropriate overlay thicknesses is critical to a local transportation agency's ability to maintain its pavement network. Local agencies often use empirical approaches for designing the overlay thickness for low-volume pavements. For example, overlay design for low-volume roads in Illinois is currently carried out using assumed layer coefficients for a limited number of material types. Although such empirical approaches are fairly simple to use, they are often not suitable for considering the effects of recycled and nontraditional construction materials that are more commonly considered in current-day sustainable pavement applications. The lack of mechanical testing for evaluating the pavement structural condition often leads to uneconomical practices in the rehabilitation of low-volume roads. This paper presents a mechanistic–empirical approach for overlay thickness designs of low-volume pavements through a combination of nondestructive deflection testing and preestablished pavement damage models. Five pavement sections, with varying structural and traffic characteristics, were selected from two counties in Illinois. Three sets of falling weight deflectometer tests were conducted over a period of one year to monitor changes in pavement deflection responses. Structural conditions of the pavement sections in their original configuration were evaluated first. Then, the corresponding required overlay thicknesses were determined by using two methods currently used by local agencies. The inability of the currently available methods to properly account for current pavement structural conditions was highlighted. A new mechanistic–empirical overlay thickness design method introduced in this study successfully identified structural deficiencies in the original pavement configurations.

Assessing artificial neural network performance in estimating the layer properties of pavements

A major concern in assessing the structural condition of existing flexible pavements is the estimation of the mechanical properties of constituent layers, which is useful for the design and decision-making process in road management systems. This parameter identification problem is truly complex due to the large number of variables involved in pavement behavior. To this end, non-conventional adaptive or approximate solutions via Artificial Neural Networks – ANNs – are considered to properly map pavement response field measurements. Previous investigations have demonstrated the exceptional ability of ANNs in layer moduli estimation from non-destructive deflection tests, but most of the reported cases were developed using synthetic deflection data or hypothetical pavement systems. This paper presents further attempts to back-calculate layer moduli via ANN modeling, using a database gathered from field tests performed on three- and four-layer pavement systems. Traditional layer structuring and pavements with a stabilized subbase were considered. A three-stage methodology is developed in this study to design and validate an “optimum” ANN-based model, i.e., the best architecture possible along with adequate learning rules. An assessment of the resulting ANN model demonstrates its forecasting capabilities and efficiency in solving a complex parameter identification problem concerning pavements.

Cyclic Approach to Airport Pavement Management Based on Non-Destructive Deflection Testing

The Authors describe the role of non-destructive deflection tests in Airport Pavement Management System (APMS) presenting the experience developed at an Italian Airport. An original approach to APMS implementation is illustrated, based on the PDCA cycle for quality control and continuous improvement of processes. An example application for the management of the runway pavement is described. Deflection test results obtained in four tests campaign carried out over a ten years period were globally analyzed to obtain pavement bearing capacity evolution and demonstrate the effectiveness of cyclic approach to pavement management. It is showed that structural evaluation can be an invaluable tool in pavement management and assist planning activities in the medium and long term.

Knowledge discovery and data mining in pavement inverse analysis

Abstract This paper describes the use of data mining tools for predicting the non-linear layer moduli of asphalt road pavement structures based on the deflection profiles obtained from non-destructive deflection testing. The deflected shape of the pavement under vehicular loading is predominantly a function of the thickness of the pavement layers, the moduli of individual layers, and the magnitude of the load. The process of inverse analysis, more commonly referred to as ‘backcalculation’, is used to estimate the elastic (Young's) moduli of individual pavement layers based upon surface deflections. A comprehensive synthetic database of pavement response solutions was generated using an advanced non-linear pavement finite-element program. To overcome the limitations associated with conventional pavement moduli backcalculation, data mining tools such as support vector machines, neural networks, decision trees, and meta-algorithms like bagging were used to conduct asphalt pavement inverse analysis. The resul...

Validation of Backcalculated Modulus Values from Falling Weight Deflectometer through Instrumentation on I-35 in Oklahoma

Several state departments of transportation evaluate the modulus of pavement layers from nondestructive deflection tests such as the falling weight deflectometer (FWD). Although the FWD is a widely used nondestructive testing device, it still does not fully represent the loading conditions generated by moving vehicular traffic. Therefore, the modulus values backcalculated from FWD data may be different from those values backcalculated from vehicular traffic loading data. A comparison is presented of modulus values backcalculated from FWD and strain gauge measurements collected on a 1,000-ft-long instrumented section of I-35 in central Oklahoma. The FWD data were captured at different temperatures with different loading configurations. Meanwhile, longitudinal and transverse strain data were captured from May 30, 2008, through October 28, 2009, over a wide range of middepth pavement temperatures (40°F to 110°F) under actual vehicular traffic loading. The influence of different backcalculated modulus values is demonstrated through the prediction of remaining life in terms of number of equivalent single-axle loads of the existing pavement. Also presented is a description of the testing program, data collection efforts, and subsequent analysis for the I-35 instrumented section. Overall, modulus values backcalculated from the FWD and from longitudinal strain gauges showed close agreement at temperatures above 50°F.

Necessary Assessment of Use of State Pavement Management System Data in Mechanistic–Empirical Pavement Design Guide Calibration Process

Calibration and validation of the Mechanistic–Empirical Pavement Design Guide (MEPDG) for state department of transportation (DOT) networks requires detailed information for a variety of pavement inputs. The biggest database resource that most states possess is their pavement management system (PMS). It is understandable for any DOT to maximize the use of this resource to the greatest extent possible. However, before any state uses PMS data in MEPDG calibration, it is important that a careful comparison be made of the equality of the measurements, data, and so forth in the PMS database with national Long-Term Pavement Performance (LTPP) values. The purpose of this paper is to review possible differences between several key data found in a state PMS database and the LTPP database. Arizona Department of Transportation (ADOT) PMS data are used for this purpose. The specific variables examined in this paper deal with distress type (rutting, cracking, and roughness) and nondestructive deflection testing (NDT) backcalculated moduli to predict in situ pavement layer properties. It was concluded that significant differences did exist between the ADOT PMS values and LTPP measurements. Differences were found between ADOT's NDT measurements and LTPP data in rut measurements, asphalt cracking, international roughness index, and all layer backcalculated moduli. Consequently, ADOT may incur significant expense to calibrate the MEPDG to Arizona conditions. The paper discusses several possible reasons for differences between the PMS data of a specific agency and those in the LTPP database.

Backcalculated and Laboratory-Measured Resilient Modulus Values

The resilient modulus ( MR) of roadbed soils is a necessary parameter in pavement design. The MR of roadbed soils is dependent on the soil type, water content, dry density, particle gradation, Atterberg limits, and stress states. Several procedures can be used for the determination of the MR: laboratory testing, backcalculation with nondestructive deflection testing (NDT) data, and correlations to other soil parameters such as the California bearing ratio, density, and water content. The first procedure is time-consuming and expensive and requires substantial resources to cover the various roadbed soils under the road network. The second is relatively inexpensive and fast and can be designed to cover representative soils under the pavement network. The third procedure is approximate and may be used for the Level 2 design of the Mechanistic–Empirical Pavement Design Guide. The Michigan Department of Transportation (MDOT) sponsored a research project for the development of a systematic procedure to determine the MR values for all soil types encountered under the pavement network in the state of Michigan. The procedure includes laboratory testing of representative disturbed and undisturbed soil samples, NDT with the MDOT falling weight deflectometer, and developing correlations between the MR values obtained from the two tests and between the MR values and other soil parameters that can be obtained using simple tests. The developed correlation equations between the MR measured values and the other soil parameters are presented elsewhere, whereas the correlations between the laboratory-obtained and the backcalculated MR values are discussed in this paper.

Field Performance Evaluation of Class C Fly Ash in Full-Depth Reclamation: Case History Study

Class C fly ash is a coal combustion product from lignite or subbituminous coal obtained as a result of the power generation process. In recent years, efforts were taken to incorporate self-cementing fly ash into fulldepth reclaimed (FDR) material to improve the structural capacity of asphalt pavement base layers. In this study, existing asphalt pavement in County Trunk Highway (CTH) "JK" in Waukesha County, Wisconsin, was pulverized in place and mixed with fly ash and water to function as a base course. To evaluate the contribution of fly ash to the structural performance of the pavement, nondestructive deflection tests were performed with a KUAB 2m falling weight deflectometer on the outer wheelpath 4 days and 1 year after construction. The modulus of fly ash- stabilized FDR base course increased by 49% 1 year after construction. The structural capacity of the fly ash-stabilized FDR base course in CTH JK also has increased significantly as it ages, because of the pozzolanic reaction. The results of this study indicate that the FDR mixes with selfcementing fly ash may provide an economical method of recycling flexible pavements and reduce the need for expensive new granular base courses for road reconstruction.

Evaluating Potential for Reflection Cracking with Rolling Dynamic Deflectometer

A common rehabilitation strategy used for repairing aged concrete pavement is to place a hot-mix asphalt (HMA) overlay on the existing concrete pavement. However, reflection cracks are often found to propagate from the underlying cracks and joints through the HMA layer. As such, much reflection cracking is believed to be caused by differential vertical and horizontal movements in the concrete pavement. A common method of determining the differential vertical movements is by measuring the load transfer efficiency (LTE) at the joints by using nondestructive deflection testing devices. A study was conducted with a rolling dynamic deflectometer (RDD) to evaluate the movement of joints in concrete pavements. Evaluation of joint movements by RDD testing permits estimation of the LTE of each joint or transverse crack. On the basis of the assumption that reflection cracks are more likely to form at joints or cracks with low LTE than with high LTE, pavement engineers can use the results to identify areas with low LTE and perform necessary repairs at these locations to reduce the potential for creating reflection cracking. Field data collected before rehabilitation work on US-82 near Gainesville, Texas, are presented as a case study, and the benefits of continuous deflection profiling for use in the district’s rehabilitation strategy are discussed.

Investigation of Performance of Asphalt Pavement with Fly-Ash Stabilized Cold In-Place Recycled Base Course

Class C fly ash is a coal combustion product from lignite or subbituminous coal obtained as a result of the power generation process. In recent years, efforts have been made to incorporate self-cementing fly ash into cold in-place recycled (CIR) asphalt material to improve the structural capacity of asphalt pavement base layers. In this study, asphalt pavements in County Trunk Highway JK in Waukesha County, Wisconsin, were pulverized in place and mixed with fly ash and water to function as a base course. To evaluate the contribution of fly ash to the pavement’s structural performance, nondestructive deflection tests were performed with a KUAB 2m-FWD falling weight deflectometer (FWD) on the outer wheelpath right after construction. The MICHBACK program was used to backcalculate the material properties of pavement layers from FWD measurements of deflection. The average moduli of the materials in the hot-mix asphalt layer, fly ash–stabilized base course, and subgrade were backcalculated. The structural capacity and structural number were also obtained from FWD test data. The structural coefficient of 0.16 was obtained for the fly ash–stabilized base course in the highway. The results of FWD testing indicate that CIR stabilization with self-cementing fly ash is an economical method of recycling flexible pavements and eliminates the need for expensive new granular base courses for road reconstruction.

Parameters Back-Calculation for Concrete Pavement with Two Slab Layers

This paper presents a new procedure for back-calculating the properties of a concrete pavement with two slab layers using deflection measurements from nondestructive deflection testing. The two slab layers are first represented by an equivalent single slab layer based on the principle of equivalent flexural rigidity. In the back-calculation analysis, the pavement deflection response under load is evaluated using an analytical model for a slab supported on an elastic foundation. Employing a closed-form back-calculation algorithm, it is shown that the back-calculated equivalent radius of relative stiffness and subgrade modulus are unique and independent of the characteristics of the two slab layers. It follows that the equivalent flexural rigidity for the two slab layers is also unique. The next step employs a trial-and-error algorithm to back-derive the moduli of the two slab layers by matching the equivalent flexural rigidity. An upper bound and a lower bound to the modulus can be established for the slab layer with the higher modulus. Similarly, an upper bound to the modulus can be found for the slab layer with the lower modulus. Four numerical examples are presented to demonstrate the use of the proposed back-calculation method.