Crack Happens: N4 at NCAT finally cracks

While it is said, “all good things must come to an end,” it is bittersweet to announce VTRC’s Section N4 at the NCAT Test Track has finally cracked (see picture). Before you let depression set in, here are a few facts to keep in mind. First, N4 was the thinnest of the three structural sections sponsored by VDOT in 2012. All three sections were a variation of the 2011, I-81 rehabilitation/reconstruction concept. N4 was comprised of a 6-inch granite aggregate sub-base, a 5-inch central cold plant recycled (CCPR) base layer, a 2-inch IM-19.0D intermediate layer, and a 2-inch SMA-12.5 (PG 76-22) surface. Section N3 was identical to N4 but had a 4-inch IM-19.0D layer. Section S12 had the same surface, intermediate and base layer materials and thickness but consisted of a stabilized full-depth reclamation layer. Second, the first crack did not appear until nearly the end of the third cycle of testing, or nearly 30 million ESALs. While the section’s structural monitoring and testing at the end of the second cycle indicated the pavement’s structural condition was changing, no cracking was present. Third, currently, no one knows where the crack initiated. Did it start in the classical bottom-up fashion or somewhere else in the bound layers? And finally, the section was designed and expected to fail at some point. To see the section perform for nearly 30 million ESALs exceeded everyone’s expectations. But again, no forensic investigation has been completed to identify the origin of the cracking.

So, what is next? VTRC is evaluating what’s to be done with Section N4 and the other structural section at the Test Track (S12). Depending on the reason the cracks formed, VTRC can evaluate approaches to rehabilitate the pavement. VTRC could choose to sponsor a new experiment or not sponsor the section in the 2021 NCAT cycle.

More information on Virginia’s test sections at NCAT and the 2018 Test Track Cycle’s overall results will be presented at the NCAT Test Track Conference June 22-24, 2021. Mark your calendars to attend this important conference. For those unable to attend in person, NCAT will have an online option available.

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