HWD Test Procedure and Results
HWD Test Procedure
Heavy Weight Deflectometer (HWD) measurements were taken at the slab centers on the TT sections. The HWD testing was conducted with a four-drop loading sequence beginning with an approximate 12,000-lb seating load. The subsequent loads were approximately 6,000, 9,000, and 12,000 lbs. At each load level, surface deflections were measured using eight geophones positioned at: -12, 0, 12, 24, 36, 48, 60, and 72 inches, respectively. The HWD loading plate was offset from the slab center by two feet (in the South direction) to facilitate measurements on all geophones within the slab dimensions.
HWD Test Results
The P-401 AC overlay modulus values reduced between RCOD Phase I and RCOD Phase II. Specifically, the average P-401 modulus value from RCOD Phase I was approximately 985 ksi, whereas the RCOD Phase II pre-trafficking and post-trafficking values were 848 ksi and 626 ksi, respectively. This reduction in stiffness may have been a result of the cracking that had occurred between RCOD Phase I testing (10/21/2019) and RCOD Phase II testing. In total, 43 cracks were initiated between these two time periods due to non-traffic related loading as documented in the visual observation section. The P-154 subbase layer experienced some densification between RCOD Phase I and RCOD Phase II. This may have been a result of some preliminary compaction in this layer after exposed to traffic loading in RCOD Phase I. Regarding the other pavement layers (P-501 and Subgrade), all backcalculated modulus values were relatively similar between RCOD Phase I, RCOD Phase II pre-trafficking, and RCOD Phase II post-trafficking. It was also observed that the subgrade modulus values appeared greater than expected.