Transverse Cracking Model. The structure of the NCHRP 1-37A transverse cracking model is the same as that of the HDM model. The major difference from the HDM cracking model is that the estimated cracking increases as the slab joint spacing increases, as shown in Figure 19. The figure also indicates that shorter joint spacings result in less transverse cracking. Transverse cracking is the only type of cracking modeled by NCHRP 1-37A; however, WSDOT records all types of cracking by severity levels instead of types, and the major cracking type in Washington State is longitudinal. Figure 20 shows WSDOT cracking of all types and the default NCHRP 1-37A transverse cracking estimation. WSDOT cracking data were averaged in each 10-year period. The averaged values were used to develop the cracking progression trend. The trend is similar to the default NCHRP 1-37A estimation. Using the typical WSDOT design parameters, the default NCHRP 1-37 software model always overestimated transverse cracking (Figure 20). The transverse cracking model needs to be roughly calibrated to 1/3 of the actual cracking of all types in the WSPMS because the longitudinal cracking was approximately 2/3 of all types of cracking, according to the historical WSDOT PCC pavement images. 100 Slabs with transverse cracking (%) 80 20 0 10 20 30 40 Time since Original Construction (year) 19 ft 18 ft 17 ft 16 ft 15 ft Figure 19 Default NCHRP 1-37 estimated transverse cracking under varying contraction joint spacings (9–in. undoweled slab, 9–in. granular base, 1.6 million ESALs/year/design lane, Seattle). 100 Slabs cracked (%) 20 Time since Original Construction (year) WSDOT data (274 sections) WSDOT 10-year interval average Default 1-37A transverse cracking model WSDOT cracking trend Figure 20 Percentage of cracked slab by age based on WSDOT data and the default NCHRP 1-37A transverse cracking prediction.
Transverse Cracking Model. The default HDM model estimated almost no transverse cracking for WSDOT. In addition, when the slab joint spacing increased, the HDM model estimated less transverse cracking. This is unreasonable. Furthermore, because WSDOT does not record transverse cracking, the cracking model could not be effectively calibrated.
Transverse Cracking Model. Calibration results: The calibrated estimates for undoweled pavements are shown in Figure 30, and estimates for DBR sections are shown in Figure 31. Results showed very small amounts of transverse cracking, which match well with WSPMS data. WSDOT data: WSPMS data do not distinguish between transverse and longitudinal cracking. Instead, it is the total of cracking of all types. Therefore, the NCHRP 1-37A model’s predictions of transverse cracking should have been lower than or equal to WSPMS data. Attempts at direct comparison were confounded by WSPMS’s inclusion of longitudinal cracking. Despite this, the NCHRP 1-37A estimated transverse cracking curve showed the same trend as the WSPMS data-generated curve shown in Figure 20. Key assumptions: On the basis of observation and analysis for WSDOT-recorded PCC pavement images, it was assumed that 2/3 of all cracks were longitudinal. Therefore, the estimated transverse cracking was calibrated to 1/3 of WSPMS measured values. Key observations: Longitudinal cracking is significant in WSDOT PCC pavements but is not modeled in the NCHRP 1-37A software. To accurately predict PCC pavement performance, especially in urban areas where high levels of longitudinal cracking are observed, a longitudinal cracking model is needed. 100 Slabs with transverse cracking (%) 80 60 1 Granular, high traffic, MP 2 Granular, high traffic, EW
