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Publication Number:  FHWA-HRT-14-092    Date:  February 2015
Publication Number: FHWA-HRT-14-092
Date: February 2015


Long-Term Pavement Performance Automated Faulting Measurement


The performance of jointed concrete pavements depends to a large extent on satisfactory performance of joints. Most jointed concrete pavement failures can be attributed to problems at the joint, as opposed to inadequate structural capacity. The distresses that may result from joint failure include faulting, pumping, spalling, corner breaks, blowups, and mid-panel cracking.(1) This study focuses on faulting on jointed plain concrete pavements (JPCP). Faulting is a common distress type in JPCP and is defined as the difference in elevation across a transverse joint or crack. Faulting can result from a combination of factors such as inefficient load transfer at joints, slab pumping, slab settlements, curling, warping, and inadequate base support conditions. Faulting plays a prominent role in pavement surface roughness over time, affecting ride comfort and driver's safety. Moreover, significant joint faulting has an adverse impact on pavement lifecycle costs for maintenance and rehabilitation as well as vehicle operating costs.(2)


The Long-Term Pavement Performance (LTPP) Program has been collecting longitudinal profile data using high-speed inertial profilers (HSIP) along the wheelpaths (left and right) on concrete pavements since 1989 and along the center of the lane from 1995. Profile data can be used to evaluate the roughness of the pavement by computing a roughness index such as the International Roughness Index (IRI). The change in longitudinal pavement profile over time, which is directly related to the change in roughness with time, is an important indicator of pavement performance. As previously mentioned, faulting is one of several key pavement performance indicators. The LTPP Program collects joint and crack faulting data on a regular basis at each jointed concrete pavement test site using the Georgia Faultmeter (GFM). Manual faulting measurement (MFM) using the GFM is time consuming and entails traffic control, lane closures, safety measures, personnel cost, etc. To replicate MFMs collected using the GFM, this study uses LTPP longitudinal profile data collected using an International Cybernetics Corporation (ICC) MDR 4086L3 profiler to identify joint locations and determine faulting at each joint on a JPCP.


The first objective was to develop, using the LTPP profile data, a new LTPP automated faulting measurement (AFM) algorithm that could be used in the LTPP Program to reduce the need for lane closure and manual data collection using the GFM (the traditional way of measuring faulting at transverse joints and cracks on JPCP). The second objective was to evaluate two existing American Association of State Highway and Transportation Officials (AASHTO) R 36–12 automated faulting methods: ProVAL (Method-A developed by the Transtec Group, Inc., using LTPP 25-mm interval profiler data as the input) and PaveSuite (Method-B developed by the Florida Department of Transportation (FDOT) using the 20.7-mm interval HSIP data).(3)


This section introduces LTPP faulting data collection using the manual GFM and longitudinal profile data using the LTPP profiler.


The GFM was designed, developed, and built by Georgia Department of Transportation Office of Materials and Research personnel to simplify measuring concrete joint faulting and is very light and easy to use. There are two versions of the GFM. The manual GFM uses a dial gage to determine the positive or negative difference at a joint or crack, and the automated GFM uses the Linear Variable Differential Transformer (LVDT) to determine positive or negative faulting at a joint or crack. The unit weighs approximately 3.2 kg and supplies a digital readout with the push of a button located on the carrying handle. It reads out directly in millimeters (e.g., a digital readout of 3 indicates 3 mm of faulting) and shows whether the reading is positive or negative. The legs of the GFM's base are set on the slab in the direction of traffic on the leave side of the joint. The joint must be centered between the guidelines shown on the side of the meter. The measuring probe contacts the slab on the approach side. Vertical movement of this probe is transmitted to an LVDT to measure joint faulting. Any slab that is higher on the approach side of the joint registers a positive faulting number. If the slab on the leave side of the joint is higher, then the meter gives a negative reading.(4) MFMs collected using the GFM may have some potential errors caused by, for example, vertical movement of the probe rod. If the measuring rod does not move freely, then the reading will also be in error. In addition, due to non-linearity of the LVDT, cases where approach and departure slabs are not on the same plane (i.e. slabs are at an angle from each other) can cause errors in the readings. In addition, weak batteries and improper calibration of the equipment could cause erroneous readings. Finally, three measurements are taken at each joint or crack, and a representative reading of the three values average of the three values) is entered into the pavement performance database (PPDB). Thus, data entry errors ± 1 mm reading resolution could occur when recording the three measurements on the data sheet onsite or in the PPDB. Figure 1 shows the MFM using the GFM.

This diagram shows how to do manual faulting measurements using the Georgia Faultmeter (GM). It shows a pavement structure with base, subbase, and subgrade in yellow and slab surface in gray. The pavement has three slabs with two transverse joints. The slab to the left of the transverse joint is called the approach slab, and the slab to the right is called the leave slab. The GFM is placed in the direction of traffic from left to right at the first transverse joint. The unit weighs approximately 3.2 kg and provides a digital readout with a push of a button. It reads out in millimeters and shows whether the reading is positive or negative. The joint must be centered between the guidelines shown on the side of the meter. The probe of the unit is placed on the approach slab, and the legs of the unit’s base are set on the leave slab. The approach slab at the first transverse joint is greater than the leave slab and is shown as positive faulting, but the approach slab at the second transverse joint is less than the leave slab and is shown as negative faulting.
Figure 1 . Diagram. MFM using the GFM.


A profiler is an instrument used to produce a series of numbers related in a well-defined way to a true profile. Profile data obtained by a profiler describe a two-dimensional slice of the road surface taken along an imaginary line.(5) The longitudinal profile along the wheelpaths in a pavement can be used to determine ride quality as well as joint/crack faulting on jointed concrete pavement, which are important indicators of pavement performance. Studies have shown that a strong correlation exists between the rate of change in faulting values and the rate of change in IRI values on JPCP. Faulting is a major contributor to the increased roughness of JPCP.(6) The LTPP Program currently uses an Ames Engineering profiler. The profilers previously used by the LTPP Program were ICC MDR 4086L3 and K. J. Law Engineers, Inc., DNC 690 and T-6600. This study uses the 25-mm interval longitudinal profile data collected using the ICC MDR 4086L3 profiler to detect JPCP joint locations and to determine faulting at those locations.


This section examines the following challenges in detecting JPCP transverse joints using profile data:


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