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4 100 field data that were analyzed in this project is provided in Chapter 2, the section entitled "Reflection Cracking Amount 80 and Severity Model." Appendix L shows how to determine 1 < 1.0 the -value from field data, and makes it possible for a user % Crack Length 60 2 = 1.0 to develop a set of calibration coefficients. By inserting a set 3 > 1.0 40 -1 of calibration coefficients into the software, an agency can e = 36.8% develop a regional or local version of the overlay analysis 20 model. 0 1 2 3 Use in Design - 2,000 4,000 6,000 8,000 10,000 No. of Days The reflection cracking program presented in this report is Figure 2. Parameters in reflection cracking severity a tool for designing an overlay. The output from the program model. shows graphically the rate of reflection cracking length and severity increase with the number of days after construction. The program runs as a subroutine of the MEPDG software, by the scale parameter, . The three sets of coefficients that executes a 20-year set of computations in a relatively short are developed for each type of overlay predict the number time, and allows the trial of a variety of mixture designs, over- of days that a given overlay will require to reach the scale lay thicknesses, and reinforcing or strain-absorbing interlay- points, , on the each of the three distress curves. A detailed ers to determine which combination provides the desired discussion of the S-shaped curve and examples from the service life within acceptable costs.