City of Troy, MI
GeoSpray®: Twin Arched CMP Culvert Repair

Project Overview

The City of Troy, MI is located among Metropolitan Detroit’s northern suburbs in Oakland County. They currently maintain a network of over 350 miles of local, major and county roads under the jurisdiction of their Public Works department. The city has a regular inspection program for their storm culverts and bridges. During recent inspections in 2013 and 2015 severe corrosion of the inverts of twin arched CMP culverts, built in 1967 under Wattles Road and extended in 1983, was observed and the city began to investigate solutions to ensure that the culverts remained structurally sound. The 127 mile Rouge
River runs through the culverts on its path to the Detroit River and can flow full in times of heavy rains and snow melts. The twin culverts were designed as CMP steel arch pipe with a nominal size of 12 ft 10 in wide by 8 ft 4 in tall. The combined length of the two pipes was approximately 170 linear ft.
When the city began to explore its options for the structure, they originally planned to replace the twin culverts with a span bridge because most conventional rehabilitation solutions such as CIPP or Slip-Lining typically aren’t done on pipes that large due to significant costs.


The city decided that the use of a sprayed on geopolymer mortar lining would be an effective rehabilitation solution that would significantly reduce the cost of the final product and allow the road to remain open during installation, minimizing disruption to the public. They specified spray applied cementitious or geopolymer material as their rehabilitation solution. Ultimately, Milliken Infrastructure's GeoSpray was the material selected. Because the culvert has a span of greater than 10 feet the structure is considered a bridge in the State of Michigan and required that all MDOT design specifications and truck loadings be considered in the design of the structural lining. An engineering analysis was completed and the professional engineer determined based on actual site conditions that a minimum liner thickness of 2.5” would be sufficient to structurally repair the culverts.


Because the projected consisted of twin structures, an internal by-pass through one of the pipes was constructed while the other was rehabilitated minimizing traffic disruption. Once the by-pass was established, the first pipe was cleaned and pressure washed and then repaired using a hand spray method due to the large diameter of the pipe. The work was executed in late November and December and thus the pipes were isolated and heated to
prevent freezing of the material during the first 6 hours of curing. The application of the liner was done over a period of approximately 3 weeks with multiple passes with 0.5" to 1.0" inch of mortar applied at a time to optimize the work process and efficiency. A local third party certified laboratory sampled material during most of the spray applications for quality control and adherence to the project specification. The completed project allowed the city to both save money and avoid a dig and replace construction that would have disrupted the local traffic and closed the road for an extended period of time.

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