Peru, IN
GeoSpray® Geopolymer Mortar: Highway Culvert

Project Overview

INDOT had a series of culverts along US Highway 31 in north western Indiana in need of rehabilitation. The INDOT specified various pre-approved options based on the physical state of the culverts, the access to the inlet and outlet, and hydraulic concerns. One of these culverts was a 78-inch CMP segmented pipe installed in the late 1970s. The pipe had at one point been lined with asphalt and the invert had cracked and worn. From this damage, it was showing severe ovality under one of the traffic lanes of the highway. The decision by INDOT was originally to slip line the pipe. While the solution did meet the structural needs of the road, the loss of water way created a secondary hydraulic concern. Part of the project proposed a second 36-inch culvert be bored under the highway so the expected hydraulic flows could be properly handled and not cause additional problems to the roadway.


The second 36-inch pipe made the project much more challenging and costly to the DOT. The contractor that had won the bid made an alternative proposal to the state to line the pipe with GeoSpray® geopolymer mortar. This could provide both the needed structural capacity and have significantly less effect on the hydraulic flow of the pipe than the slip-line solution. Additionally, this would allow them to avoid drilling under the highway and install a second parallel culvert. The state reviewed the hydraulic calculations and agreed on a GeoSpray mortar lining that would be centrifugally cast to a thickness of at least 1.5 inches. The active flow through the pipe could not be by-passed around the busy highway. An internal by-pass pipe was set up at the center of the pipe invert so that the pipe could be dewater and the geopolymer could be applied without flowing water.

First, the pipe was prepared by cutting any hanging or lose sections of the existing asphalt coating. Then it was pressure washed to remove lose debris. The pipe had a few areas of infiltration near the spring-line under the highway median that we plugged using hydraulic cement and a water-activated grout.

Once the pipe was prepared, the GeoSpray liner was applied over three passes with approximately 0.5 inches being applied during each pass. Each pass of the 310 linear foot culvert took approximately 5 hours. Once the full liner was applied, the by-pass line was moved out of the center of the invert and additional material was filled into any areas that were shielded by the by-pass pipe.

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