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Rehabilitating Saskatchewan culverts in record low temperatures

by Angus W. Stocking, L.S.

The smallest culvert rehabilitated was filled with ice, which had to be melted out with hot, glycol-filled hoses.
The smallest culvert rehabilitated was filled with ice, which had to be melted out with hot, glycol-filled hoses.

Cold winters in Saskatchewan aren’t news but even so, January and February in 2014 were special; “Temperatures were ridiculous,” says Doug Cook, general manager of Winnipeg-based MuddRuckers, Inc. “We worked for weeks in one of the worst winters in history, down around -30 degrees C, with wind chill taking that down to -45 degrees C. But, anything we have to do, we can do in winter.”

MuddRuckers took on a winter project for the Saskatchewan Department of Highways and Infrastructure that involved the rehabilitation of four large CMP culverts. They won the bid with an innovative method, CentriPipe, a centrifugally cast concrete pipe (CCCP) solution that is efficient and cost effective. And they completed the project in record low temperatures, heating the culverts and surrounding ground for weeks at a time, and building temporary but effective hoardings and heated staging areas. Like many infrastructure projects, it wasn’t glamorous, but keeping roads running year round often requires hard, skillful work at inconvenient times, and the Saskatchewan culvert rehabilitation project is a good example of a contractor finding ways to do this necessary work in challenging circumstances.

A cost-effective, structural solution

The CCCP process used, CentriPipe, is based on a precisely controlled spincaster that uses high pressure to spray on multiple thin layers of high strength cementitious grout. This creates, basically, a brand new concrete pipe within the old pipe or sewer, a pipe that adheres tightly to the old, failing substrate without relying on it for structural support.

CentriPipe is very advantageous for large diameter pipe; it’s structural, trenchless, waterproof and, if hydrogen sulphide is an issue, the grout can be treated with a permanent anti-microbial agent. Typical CentriPipe applications are about two inches thick, so flow capacity is only minimally reduced.

This last benefit — minimal flow reduction — was a big factor in MuddRuckers’ bidding. “We were bidding against a sliplining proposal,” Cook explains. “But since sliplining would reduce capacity significantly, the contract called for a new push-through pipe run parallel to the existing pipe, to match original capacity.” MuddRuckers’ CCCP solution saved all that additional work, so their bid was about 25 percent less, saving the Department about $200,000. CentriPipe is costeffective for most large diameter pipes and sewers, with significantly lower per-foot prices than CIPP, dig-and-replace, and other rehabilitation techniques.

But good as it is, CentriPipe is a sprayed concrete solution; for effective curing in record low temperatures, MuddRuckers had to raise ground and culvert temperatures by 40-50 degrees C… and keep them there for a few weeks.

Preparing weeks in advance — Total six weeks due to work on multiple sites

“It was like a military operation,” says Cook. “We planned for weeks, and having everything we needed in place at the right time was a major logistical challenge.”

Work began a week before any concrete was sprayed when 350,000 BTU heaters known as “Herman Nelsons” were brought to the sites, along with ground thaw heaters. The Herman Nelsons were set up at each end of the culverts, or hot, glycol-filled hoses from the ground thaw heaters were run along inverts and up culvert walls. The smallest culvert rehabilitated was actually filled with ice, which had to be melted out with the hoses. Over about a week’s time, the heaters and hot hoses gradually raised culvert temperatures to about 20 degrees C, optimum for curing. After rehabilitation was complete, the heaters were kept in place for a week to facilitate proper curing. By rotating the heaters from site to site, and working on multiple sites, the entire project was completed in just six weeks.

Corroded culvert pipe.

Meanwhile, MuddRuckers built 4 foot x 8 foot insulated panel walls that could be assembled onsite and roofed with translucent, insulated tarps. These hoardings let in reasonable amounts of light, and could be sized as needed to support workers running the CentriPipe spincasting equipment. The concrete pump and mixer was kept in an insulated shipping container, two insulated trailers were used to store mix water and tools, and a semitrailer “reefer” unit was used to store bags of dry grout. It made for a large, complicated staging area, with 7-8 vehicles, several trailers and the Sea Can, the panel building, and a skid steer that was used to move material pallets.

In some ways, the cold was helpful. Freezing temperatures meant no special dewatering procedures were needed. And when ground thawing did yield some melt water, a simple ice dam was enough to hold it out.

With everything in place, work proceeded smoothly enough. “The weather didn’t really affect us too much,” says Cook. “Sure, it was hard to get started some mornings, and moving from site to site was difficult, but we were able to work efficiently despite the cold.” Still, big projects in cold weather are always at least a little unpleasant.

Good technique, great rehabilitation

The project consisted of four large culverts in separate locations. One is round, 5-foot diameter and 130 feet long. The other three are arched, about 80 feet long, with one 72 inches wide and 42 inches tall, and two that are 102 inches wide and 72 inches tall. All are of corrugated metal, and the two largest had very deep indentations. And all were failing; they were badly rusted, some sections of invert were rotting out, and some culvert sections were misaligned.

Since CentriPipe is based on precise spincasting, some preparation was needed for the non-round culverts. After sandblasting to clean out debris and, in one case, jacking some misaligned sections into place, MuddRuckers crews used a simple shotcrete sprayer on large culverts to fill in and smooth out corrugations, then sprayed and trowelled extra material into the “knees” of the arch to bring the culverts closer to round. In future, Cook says a different technique may be used; “We’ve designed a way to move the spincaster through the culvert in four-inch steps, so just the indentations get filled on the first pass,” he explains. “That should be more efficient than the hand work we did on this project.” The material used for this prep work was PL-8,000 UL (underlayment), a self-consolidating mortar supplied by AP/M Permaform, the developers of CentriPipe. PL-12,000, a similar product, was used to repair some inverts. All the ‘PL’ series grouts and mortars are engineered, fibre-reinforced products with high compressive strength and excellent adhesion.

With this work done, actual spincasting could begin. AP/M Permaform provided engineering specifications for thickness, number of passes, and other details, based on initial surveys of the culverts, and the CentriPipe spincaster was pulled through at calculated speeds to meet these specs with multiple layers of PL-8,000. Each layer is a half inch or less, and doesn't require hand finishing. The cure time is just a few hours, so layers can be applied on successive days, or even on the same day. The resulting new pipe is smooth and seamless from end to end.

Design thickness was assured by two techniques. First, measurements were taken of the existing culverts, and then the rehabilitated culvert was measured in several places for comparison. Also, MuddRuckers carefully tracked the amount of material used, and then calculated the volume, and thus thickness, of the final applications based on the amount of material used. These methods were backed up by simple gauges preinstalled along the old CMP, and then covered with material.

The Saskatchewan Department of Highways and Infrastructure had used CentriPipe on previous culvert rehabilitations, and specified it as an alternative on this project. It’s a robust solution that has worked in many challenging situations. It’s cost-effective, completely structural, doesn’t reduce flow… and apparently, it works well in extreme weather conditions!

The rehabilitated culvert pipe is smooth and seamless from end to end.

Meanwhile, MuddRuckers built 4 foot x 8 foot insulated panel walls that could be assembled onsite and roofed with translucent, insulated tarps. These hoardings let in reasonable amounts of light, and could be sized as needed to support workers running the CentriPipe spincasting equipment. The concrete pump and mixer was kept in an insulated shipping container, two insulated trailers were used to store mix water and tools, and a semitrailer “reefer” unit was used to store bags of dry grout. It made for a large, complicated staging area, with 7-8 vehicles, several trailers and the Sea Can, the panel building, and a skid steer that was used to move material pallets.

In some ways, the cold was helpful. Freezing temperatures meant no special dewatering procedures were needed. And when ground thawing did yield some melt water, a simple ice dam was enough to hold it out.

With everything in place, work proceeded smoothly enough. “The weather didn’t really affect us too much,” says Cook. “Sure, it was hard to get started some mornings, and moving from site to site was difficult, but we were able to work efficiently despite the cold.” Still, big projects in cold weather are always at least a little unpleasant.

Good technique, great rehabilitation

The project consisted of four large culverts in separate locations. One is round, 5-foot diameter and 130 feet long. The other three are arched, about 80 feet long, with one 72 inches wide and 42 inches tall, and two that are 102 inches wide and 72 inches tall. All are of corrugated metal, and the two largest had very deep indentations. And all were failing; they were badly rusted, some sections of invert were rotting out, and some culvert sections were misaligned.

Since CentriPipe is based on precise spincasting, some preparation was needed for the non-round culverts. After sandblasting to clean out debris and, in one case, jacking some misaligned sections into place, MuddRuckers crews used a simple shotcrete sprayer on large culverts to fill in and smooth out corrugations, then sprayed and trowelled extra material into the “knees” of the arch to bring the culverts closer to round. In future, Cook says a different technique may be used; “We’ve designed a way to move the spincaster through the culvert in four-inch steps, so just the indentations get filled on the first pass,” he explains. “That should be more efficient than the hand work we did on this project.” The material used for this prep work was PL-8,000 UL (underlayment), a self-consolidating mortar supplied by AP/M Permaform, the developers of CentriPipe. PL-12,000, a similar product, was used to repair some inverts. All the ‘PL’ series grouts and mortars are engineered, fibre-reinforced products with high compressive strength and excellent adhesion.

With this work done, actual spincasting could begin. AP/M Permaform provided engineering specifications for thickness, number of passes, and other details, based on initial surveys of the culverts, and the CentriPipe spincaster was pulled through at calculated speeds to meet these specs with multiple layers of PL-8,000. Each layer is a half inch or less, and doesn't require hand finishing. The cure time is just a few hours, so layers can be applied on successive days, or even on the same day. The resulting new pipe is smooth and seamless from end to end.

Design thickness was assured by two techniques. First, measurements were taken of the existing culverts, and then the rehabilitated culvert was measured in several places for comparison. Also, MuddRuckers carefully tracked the amount of material used, and then calculated the volume, and thus thickness, of the final applications based on the amount of material used. These methods were backed up by simple gauges preinstalled along the old CMP, and then covered with material.

The Saskatchewan Department of Highways and Infrastructure had used CentriPipe on previous culvert rehabilitations, and specified it as an alternative on this project. It’s a robust solution that has worked in many challenging situations. It’s cost-effective, completely structural, doesn’t reduce flow… and apparently, it works well in extreme weather conditions!

Company info

PO Box 555
Johnston, IA
US, 50131

Website:
permaform.net

Phone number:
515-276-9610

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