Jeffrey Lee

Application of RDD Continuous Profiling in Maintenance and Rehabilitation of Concrete Pavements

The Rolling Dynamic Deflectometer (RDD) is a nondestructive testing device that is used to evaluate the structural conditions of pavement systems. Unlike discrete deflection measurements such as the Falling Weight Deflectometer and Dynaflect, the RDD provides continuous deflection profiles that enable 100% coverage along the testing lane. The continuous deflection profiles have been used to delineate poorly performing areas to be repaired, develop input for pavement forensic studies, select rehabilitation treatments, and monitor pavement deterioration rates. In this paper, the patterns in RDD deflection data which represent four different structural conditions (with respect to joint load transfer and slab support) in jointed concrete pavements (JCP) are presented and discussed. Then, results from RDD tests used in three project-level studies are presented. The first project involved a continuously reinforced concrete pavement (CRCP) with an asphalt overlay. RDD measurements were used to measure the relative improvement due to the overlay rehabilitation and also monitor the pavement deterioration rate with time. The second project involved a JCP with longitudinal cracking. RDD deflection profiles were used to delineate poorly performing areas due to poor slab-support conditions and identify potential locations of reflective cracking. The third project involved a JCP with faulting. RDD deflection profiles were used to identify locations that needed either dowel-bar retrofit or full-depth repair.

Part 1: Pavement Rehabilitation: Monitoring Pavement Changes in a Rehabilitation Project with Continuous Rolling Dynamic Deflectometer Profiles

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to (a) monitor changes at locations of previously high deflections, (b) evaluate the effectiveness of full-depth repairs, and (c) group different A...

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.

DISCRETE AND CONTINUOUS DEFLECTION TESTING OF RUNWAYS AT HARTSFIELD ATLANTA INTERNATIONAL AIRPORT, GEORGIA

The measurement of deflection characteristics is a key feature in the evaluation of pavements. Deflections are used to evaluate pavement moduli, relative stiffness, load transfer, and, when used periodically, a rate of deterioration and remaining life. The comprehensive deflection testing program conducted on Runways 9L/27R and 8R/26L, both jointed concrete pavements, at the Hartsfield Atlanta International Airport is described. A heavy-weight deflectometer was used to measure deflections at discrete locations on slab interiors, transverse joints, longitudinal joints, and slab corners. A rolling dynamic deflectometer was used to measure continuous deflection profiles along three longitudinal lines on both runways. Before fall 2001, all pavement deflection testing was performed using a falling-weight deflectometer. Comparisons of the equipment, loading mechanisms, and measured deflections are presented.

Monitoring Pavement Changes in a Rehabilitation Project with Continuous Rolling Dynamic Deflectometer Profiles

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to (a) monitor changes at locations of previously high deflections, (b) evaluate the effectiveness of full-depth repairs, and (c) group different AC test sections of the new overlay according to the condition of the underlying concrete pavement. It was found that the continuous deflection profiles obtained at the start of a rehabilitation project can be used to identify high-deflection locations that, if not repaired, will likely deteriorate rapidly after the new overlay is placed. The continuous deflection profile measured on the concrete pavement after milling was particularly helpful in identifying high-deflection locations that were irregularly spaced. Continuous deflection profiles, measured at various times after placement of the new overlay, effectively tracked the zones of deterioration.

EVALUATING 17L-35R RUNWAY AT GRAYSON COUNTY AIRPORT USING THE ROLLING DYNAMIC DEFLECTOMETER

The Rolling Dynamic Deflectometer (RDD) is a state-of-the-art nondestructive deflection testing device that was developed at the University of Texas at Austin. Over the years, it has been used in many different highway and airport project-level studies. Since the RDD is able to collect continuous deflection profiles, nearly complete coverage of a runway system can be accomplished rapidly and cost- effectively. With this information, pavement engineers are able to pin-point critical sections where rehabilitation work is needed. This type of coverage is especially important in airport rehabilitation projects where considerable savings can be made if defective areas can be precisely identified and repaired. In this paper, four longitudinal deflection profiles collected along Runway 17L-35R at the Grayson County Airport are presented. Two of the longitudinal deflection profiles were collected near the centerline of the runway where most of the aircraft loading occurs. The other two longitudinal deflection profiles were collected near the runway edges. Part of the runway was built over 38 years ago and has remained in service to this date. There are a total of 8 different rigid and flexible pavement cross sections along the 17L-35R runway. Jointed Concrete Pavement (JCP) sections were constructed at the runway ends, while the interior of the runway was constructed with Asphalt Concrete (AC). As described herein, the deflection, or stiffness, characteristics of each pavement section are readily identified and evaluated using the RDD continuous profiles.

Superaccelerated Pavement Testing on Full-Scale Concrete Slabs

Several full-scale rigid pavement slabs were constructed and tested under constant cyclic loading for fatigue. To provide the comparable maximum applied stress to number of cycles to failure (S-N) relationships for the full-scale field slabs, laboratory beam fatigue testing was conducted before field testing with the use of the same concrete mix designs. The superaccelerated pavement testing technique that was developed at the University of Texas was used in the field. The stationary dynamic deflectometer (SDD) was used to load the full-scale concrete slabs. To monitor the response of the rigid pavements, accelerometers and linear variable differential transformers were installed, and dynamic and permanent displacements of slabs were recorded during the entire testing period. All test slabs reached fatigue failure under the interior loading configuration using the SDD. This field loading system was found to be a practical and effective tool for testing the full-scale rigid pavement system. During fatigue loading, cracks began at the bottom of the slabs at the loading locations and propagated along the bottom of the slab centerline, which was the maximum stress path. Vertical crack propagation at the edge and stress redistribution occurred for the part of the slabs fatigue life. The concept of equivalent fatigue life was applied to correct the effect of the different stress ratios between the field and the laboratory testing. The laboratory beams and full-scale field slabs showed an almost identical S-N relationship after the correction for the variance of stress ratio.

Part 3: Accelerated Pavement Testing: Superaccelerated Pavement Testing on Full-Scale Concrete Slabs

Several full-scale rigid pavement slabs were constructed and tested under constant cyclic loading for fatigue. To provide the comparable maximum applied stress to number of cycles to failure (S-N) relationships for the full-scale field slabs, laboratory beam fatigue testing was conducted before field testing with the use of the same concrete mix designs. The superaccelerated pavement testing technique that was developed at the University of Texas was used in the field. The stationary dynamic deflectometer (SDD) was used to load the full-scale concrete slabs. To monitor the response of the rigid pavements, accelerometers and linear variable differential transformers were installed, and dynamic and permanent displacements of slabs were recorded during the entire testing period. All test slabs reached fatigue failure under the interior loading configuration using the SDD. This field loading system was found to be a practical and effective tool for testing the full-scale rigid pavement system. During fatigue ...