Center for Transportation Research
The University of Texas at Austin
Project Summary Report 0-4382-S Project 0-4382: Establish an Acceptable Pavement Thickness Tolerance to Allow for Non-Destructive Continuous Concrete Pavement Thickness Measurements Authors: Seong-Min Kim and B. Frank McCullough October 2002
ACCEPTABLE CONCRETE PAVEMENT THICKNESS TOLERANCE
This research project was conducted to investigate if the current thickness tolerance for concrete pavements can be loosened and to provide TxDOT with the acceptable thickness tolerance so that non-destructive testing (NDT) methods can be used with conﬁdence for thickness measurements. TxDOT’s current tolerance limit for concrete slab thickness was developed in the 1950s based on engineering judgment and experience; no additional study on tolerance limit has been conducted since. The tolerance limit is currently 5 mm (0.2 in.) for full payment. This tolerance limit is too tight to allow use of existing NDT methods for slab thickness determination because these methods are not as accurate as direct measurement from coring. If the current tolerance can be shown Number of load application (ESALs)
to have minimal impact on the pavement performance, then the tolerance limit can be loosened so that NDT methods can be used for thickness determination. NDT methods are less time-consuming and more cost-effective than coring. Moreover, the slab thickness measured continuously by NDT methods will represent the pavement more adequately than spotchecking by coring. In this research, the sensitivity of pavement performance to slab thickness has been investigated based on various models including the AASHTO model, a mechanistic distress prediction model, and fatigue failure models. The controlling performance indicator from the sensitivity study has been compared with the measured variability of pavement thickness in the ﬁeld, and to the accuracy of the NDT devices. From these
comparisons, a reasonable tolerance limit of the slab thickness has ﬁnally been obtained.
What We Did …
This research was conducted with four different phases as follows: • Review of current thickness tolerance limits for concrete pavements in Texas and other states. • Sensitivity analysis of concrete pavement thickness based on various models such as the AASHTO model, mechanistic distress prediction model, and fatigue failure models. • Investigation of ﬁeld variability of concrete pavement thickness and accuracy of NDT devices. • Determination of acceptable thickness tolerance. The thickness tolerance
Design life Thickness tolerance
AASHTO equation Design life Allowable loss of life
Allowable loss of life
Allowable design life AASHTO equation
Figure 1: Thickness Tolerance Determination with AASHTO Equation Thickness tolerance
Project Summary Report 0-4382-S
mechanistic models. The concept of determining pavement thickness sensitivity to pavement Pavement stress life by using the AASHTO equation is illustrated in Figure 1. The pavement design life can be obtained from the Stress level pavement design thickness by using the Fatigue failure equation AASHTO equation. Then, an allowable Design life loss of the pavement life is selected, and the allowable design life is obtained by Allowable loss of life subtracting the allowable loss of life Allowable design life from the design life. The correspondFatigue failure equation ing allowable pavement thickness can then be obtained by using the AASHTO Allowable stress level equation inversely, and ﬁnally the thickness tolerance for the allowable loss of Allowable stress life can be obtained by subtracting the allowable thickness from the design Westergaard equation thickness. Allowable thickness The concept of determining pavement thickness...