LTPP Data Analysis: Improving Use of FWD and Longitudinal Profile Measurements (2024)
Chapter: 8 Guidelines for Assessing JPCP Curl and Warp from Longitudinal Profile
CHAPTER 8
Guidelines for Assessing JPCP Curl and Warp from Longitudinal Profile
The following describes the proposed guidelines for determining the effects of JPCP curl and warp from longitudinal profile measurements using the 2GCI method (Appendix L provides the proposed stand-alone longitudinal profile guidelines).
Temperature gradient plays a significant role in the daily curl of a JPCP slab. During the warming period of the day, the top of the slab is warmer than the bottom, and the difference in thermal expansion causes the slab to curl downward. In contrast, during the cooling period of the day, the bottom of the concrete slab is warmer than the top, which causes the slab to curl upwards. The degree of curling and warping increases as the temperature gradient increases. Slab curling and warping can result in a loss of support at the slab corners and slab center, and when combined with the weight of the slab and traffic loading, can contribute to cracking or slab failure.
A moisture gradient can also result in JPCP slab volume changes and cause curling and warping. Typically, the top of the JPCP slab is partially saturated while the bottom is close to saturation, which can result in cracking, especially when combined with a negative (daytime) temperature gradient.
The approach includes conducting longitudinal profile testing, at least three visits, over 12 hours (and during different seasons) to capture the variability of changes in slab curvature. Longitudinal profile testing should be conducted in accordance with applicable AASHTO, ASTM, and agency requirements. Longitudinal profile testing should be conducted on a clear, sunny day followed by a clear night, attempting to obtain the maximum temperature gradient. The timing of the passes includes 2 to 3 hours before sunrise, between 8 a.m. to 10 a.m., 1 p.m. to 3 p.m., and 5 p.m. to 7 p.m. The testing location should be accurately identified and repeat testing (at least five consecutive passes) should be conducted at the exact location during each site visit and pass. The ambient air and surface temperature, and non-typical pavement features or events (e.g., bridges, intersections, manholes, project start location, project stop location) should be noted for each site visit and pass.
The effects of curl and warp on JPCP are assessed using the longitudinal profile measurements and the 2GCI method. For each profile run, a high-pass filter with a normalized profile is applied to identify joint locations (Figure 56).
Once the slab locations have been identified, the longitudinal profile slab profile is fitted to an assumed slab shape by detrending the profile and offset so the mean evaluation is zero and applying a curve fitting procedure based on the Westergaard equation (Figure 57).
The average PSG and IRI values are determined for each profile pass to establish the IRI-PSG relationship (Figure 58).
These calculations are conducted for subsequent visits to illustrate the long-term trend in roughness not associated with curling and warping (Figure 59). Examination of Figure 59 may reveal changes in roughness caused by distress more readily than examining overall IRI as shown in Figure 58.
