Washington, D.C., utility rehabilitates crumbling pipeline using geopolymer mortar
DC Water’s engineering group implemented a pipe entry inspection after receiving an alert from the District Department of Transportation (DDOT) to verify the integrity of a 72-in. diameter brick sewer located at the F Street NW block between 12th and 11th streets. DDOT performed a bore-hole inspection at a street depression, which revealed a 20-in. deep void under the pavement.
Prior to entering the sewer, DC Water evaluated its records and noted the Metro subway tunnel runs below the length of 12th Street while the 72-in. brick sewer runs above the tunnel. In addition, in the 1970s, a 188-ft section of the 72-in. brick sewer was offset and replaced with 205 ft of 72-in. reinforced concrete pipe (RCP). The entry inspection showed the replaced 72-in. RCP was in good shape—however, the original brick sewer was a different story. Starting at the interface with the RCP, the brick crown was cracked and propagating east toward 11th Street and west toward 13th Street. The cracking likely developed after the construction of the Metro subway system.
The most severe damage was located between 12th and 11th streets, where the crown was cracked and missing bricks. Fortunately, there was no significant oval deformation, and there were not many open mortar joints, which would be typical of an impending pre-sinkhole collapse scenario.
DC Water evaluated several repair options, including cured-in-place pipe (CIPP) and tunnel plate. The CIPP option was eliminated due to the need to remove manholes in a busy intersection and issues with reinstating flow daily; the tunnel plate was eliminated due to cost considerations. In the end the city specified two different spray-applied applications and awarded the project to Inland Pipe Rehab to line with GeoSpray geopolymer mortar.
The rehabilitation required:
- Full structural repair to a 50-ft section that was missing bricks and showing signs of advanced crown deterioration.
- Attention to a 125-ft-long partially deteriorated section that needed to stop inflow and infiltration and provide some structural support to the bricks and missing mortar.
After further inspection, DC Water requested a change order for a full structural repair of the entire 175 ft of pipe.
GeoSpray geopolymer was used as a solution for this damaged brick sewer in downtown Washington, D.C.
Because the F Street thoroughfare is a heavily trafficked business and tourist district, all work was completed at night to minimize traffic disturbances, and bypass was released during the day. The design developed by the district required a 2.5-in. minimum thickness of the geopolymer mortar with 4-in.-by-4-in. welded wire reinforcements (type W2xW2) to stabilize the crack at the crown. Specifications for the other spray-on technology also included rebar that was not required with Geospray. The cover over the reinforcement was 1.5 in.
The work was completed over a two-week period with no interruption of service during the day in the downtown business district. An inspection by DC Water was conducted nearly eight months later and no issues were observed. DC Water is currently pursuing other opportunities to install geopolymer linings within its system.