CONCORD – Inspection of a culvert under N.C. 200 in Cabarrus County that was scheduled to be replaced this summer led to an extraordinary discovery.

Crews inspecting the culvert found it contains an unusual combination of materials: about a third each of cut granite, arched terra-cotta block (also called tile), and more conventional corrugated metal pipe – interestingly the most deteriorated section despite being the most modern of the materials.

N.C. Department of Transportation Bridge Maintenance Engineer Robert Plyler knew this discovery, located within the Bost Mill Historic District, a property listed on the National Register of Historic Places, was special.

“The original structure is terra-cotta glazed tiles, which is a unique structure, “ Plyler said. “This one also has a granite extension, so hand-split granite rocks were added in order to widen (N.C.) 200. We knew it was almost this wide in 1937.”

Plyler said it is remarkable that the structure has lasted this long. Accordingly, the NCDOT’s Environmental Analysis Unit confirmed that the N.C. 200 culvert is indeed special – a rare example of a short-lived construction method based on hollow structural masonry block used by some North Carolina road builders during the early years of the 20^th century. The block was manufactured by the Pomona Terra-Cotta Company (1886-1975) near Greensboro.

NCDOT archaeologists and architectural historians have been investigating Pomona block culverts since 2010, identifying only eight so far. Since functional and safety concerns do not allow preservation of these structures, they prepare documentation, including extensive research and photography, ensuring that each resource is well represented in the state archaeological and architectural record.

Representative samples of the tile blocks have been retained for comparative purposes and will be kept at the Office of State Archaeology’s Research Center in Raleigh.  Like other examples, the N.C. 200 culvert was removed with great care by hand and a skillfully operated backhoe. It also offered an unprecedented bonus.

“We’re going to recycle material that’s at least 100 years old into this modern structure so that adds more of a construction aspect, as opposed to a typical pipe replacement,” Plyler added. “There’s enough granite for us to build a 25-foot long and 10-foot-tall headwall to maintain some historical presence.”

To work on something of this nature doesn’t come along often.

“It’s a once-in-a-lifetime DOT chance due to the size of this structure,” added Plyler. “In our careers, we’ll never another get a chance to do something like this.”