During an 8-hour shift, Conterra sees removal rates of 600 to 1,000 square feet (55.7 to 92.9 square meters) with the Aqua Cutter 710V.
Just Porciello, Conterra Restoration Ltd.

With decades of experience in new construction and commercial renovation, Ontario-based general contractor and construction manager Arguson Projects Inc. understood the logistical challenges posed by a multiyear, multi-million-dollar parking garage renovation in Toronto’s East End. The 39-year-old structure—an open-air parkade with a roof deck, two suspended slabs and asphalt on grade—has needed to remain open while crews remove 200,000 square feet of material from the second and third levels. Building tenants required parking to remain open, as well as continued access to the roof deck, which provides amenities for employees.

Seizing an opportunity to reduce not only the project’s carbon footprint, but also the overall cost, Arguson, in conjunction with the property owner, turned to Ontario-based Conterra Restoration to offer an ecofriendly solution.

Parking problems

The suspended slabs within the parkade were heavily contaminated with chloride ions, or road salt, resulting in significant corrosion-related deterioration and cracking. The concrete needed significant repair and replacement to address structural integrity concerns and overall aesthetics. Working with RJC Engineers, a Canadian-based engineering firm specializing in parking facility design and restoration, Arguson determined hydrodemolition was the only concrete removal option that fit the unique needs of the project.

Part of the adjacent building sits on the garage’s roof deck, meaning vibrations needed to be eliminated wherever possible. The building is also home to a prep school with athletic facilities located just south of the parking structure, requiring both noise and dust control to minimize disruptions to students and faculty. The presence of a nearby hotel also made nighttime noise an issue. The project managers needed a solution that would limit dust and other environmental impacts but that was also quiet enough to proceed with the renovations during normal business hours.

“The main concerns for this project were noise and vibration generated by the construction activity, as well as the vast amount of concrete that needed to be removed to properly rehabilitate the suspended parking slabs,” Philip Sarvinis, managing principal with RJC Engineers, says. “Hydrodemolition allowed the contractor to work through the day without disrupting building tenants or the neighboring properties, while at the same time removing large amounts of concrete. The process works extremely well with the added bonus that it doesn’t physically damage the remaining concrete left in place compared to traditional jackhammering operations.”

Arguson brought on Conterra Restoration, in part because of their extensive hydrodemolition experience. The company presented Arguson with a solution that not only provided the productivity to meet deadlines, but also minimized impact on the tenants and the environment. Conterra sourced an Aqua Cutter 710V—a hydrodemolition robot that could provide 25 times more productivity than a large crew using conventional equipment—supplied by Cor-Blast Services Inc. The 5,181-pound Aqua Cutter 710V uses a 14,500- to 40,000-psi water jet, which removes concrete by widening existing pores and micro cracks in the weakened structure. Since the process is impact-free, there are no vibrations. The result is that there is less risk of microfractures. Hydrodemolition also cleans and descales rebar without damaging it.

The plan also featured an Aquajet 700 Ecosilence high-pressure pump, which is quieter than other high-pressure pump systems while still providing ample power for the project at 56 gallons per minute at 18,700 psi. This would keep noise to a minimum, allowing crews to work during the day without disturbing tenants.

“With the Ecosilence, the pump and diesel engine are inside a container with this machine, which dampens the sound enough you could run it under a window downtown and still be quieter than normal traffic,” David Porciello, general manager for Conterra, says. “We paired a hoarding system with the Ecosilence to get down to 63 decibels at a range of 6 meters.”

Additionally, the Ecosilence allowed Conterra to work throughout the year, even when temperatures hit -4 degrees Fahrenheit.

The contractor also included an EcoClear water treatment system as part of their tender. This unit provides on-site water treatment in real time for less than a cent per gallon. After passing through the EcoClear, wastewater can be released into the sanitary sewer system. With the project requiring in excess of 10 million gallons of water, this presented significant cost and carbon savings compared to alternatives, such as trucking the wastewater out with vacuum trucks.

“Environmental stewardship has always been an important part of the conversation for us,” Porciello says. “With the Aquajet equipment, we saw an opportunity to not only provide fast, high-quality results, we could also drastically reduce our impact on the environment. From eliminating the gas and exhaust of vac trucks to minimizing crews—and the associated emissions getting them to and from the worksite—we were able to present not only an economic solution, but an ecofriendly one, as well.”

The company’s full-service approach to building restoration also gave them an advantage in the bidding process. In addition to hydrodemolition, Conterra bid subsequent phases of the project including pouring new concrete, applying a waterproofing system and painting lines. Additionally, decades of experience, highly skilled crews, specialist subtrades, plus an outstanding record for satisfactory and on-time delivery made their bid stand out.

The 5,181-pound (2,350-kilogram) Aqua Cutter 710V uses a 14,500- to 40,000-psi water jet. The robot’s high-pressure water jet removes concrete by widening existing pores and micro cracks in the weakened structure.

Record removal

The project, which commenced in December 2019, has been broken into two phases. At the beginning of the project, Conterra set up a staging area outside the parkade for the Ecosilence and EcoClear. Depending on the day, the Aqua Cutter robot could be up to 615 feet away and several stories above the pump system during operation.

Arguson and Conterra have had a dedicated crew of workers and subcontractors on-site with a small contingent running the Aqua Cutter and support equipment. The hydrodemolition removal process is monitored by one operator/technician with some assistance monitoring the EcoClear. Additionally, a team follows up behind the robot to remove the demolished concrete. Other crews are employed removing through-slabs, forming and other tasks throughout the site. For the most part, the robot removes concrete to a depth of 4 to 5 inches.

“The Aqua Cutter finds what most engineers can’t—every millimeter of bad concrete,” Porciello says. “The robot can be programmed to remove a certain depth; however, the removal could be deeper in certain areas if the strength of existing concrete is not adequate. This assures that all deteriorated concrete is removed and a sound substrate remains for superior bonding of the new concrete overlay. This gives us a clean slate of good concrete for stronger, longer-lasting repairs.”

During an 8-hour shift, Conterra sees removal rates of 600 to 1,000 square feet. Had they opted for manual removal, Porciello estimates it would take a crew of 20 averaging 30 square feet per person per day to achieve the same productivity for removal only. Plus, the project would have been limited to overnight shifts to avoid noise disruptions for the building’s tenants.

Working with water

To minimize disturbances and having to maneuver equipment around the job site, Conterra works on a designated section of the first suspended slab and continues down to ground level. This also allows the team to take advantage of gravity in its wastewater collection plan. Water is routed through existing drains and a system of clear stone filtration to a catch pit near the staging site. From there, it is pumped through the EcoClear, which can process as much as 5,283 gallons per hour on its way to the sewer.

“The EcoClear system gave us a distinct advantage for this project.,” Porciello says. “We’re the only group in Ontario with equipment that can provide documented, quantifiable results on-site and on-demand. With these amounts of water, we didn’t even consider alternative treatment methods. The carbon cost was just too great.”

With the EcoClear, Conterra can reduce blast water pH from 12.5 to between 7.5 and 8.5, and the system uses carbon dioxide rather than mineral acid to reduce pH. This eliminates the risk of acidifying the water and requires less in the way of oversight, training and PPE. The EcoClear also reduces suspended solids to 50 ppm or less.

“We’ve gotten as low as 15 ppm,” says Porciello. “And we know the equipment is capable of meeting storm drain requirements. Now that we’re [more than] a year in, we’re more comfortable with the process and have plans to incorporate a closed-loop system that will make the process even more efficient and ecofriendly.”

With a closed-loop system, blast water is treated in the EcoClear. Then the clean water is reused in the Ecosilence. Conterra plans to begin running this setup in the near future. A small percentage of the water is lost to evaporation, but Conterra estimates the process can collect, treat and recirculate up to 75 percent of the water used by the hydrodemolition robots. Depending on application, some contractors have seen recapture rates up to 90 percent.

Powering through

Like many projects during the global pandemic, the parkade restoration’s timelines have suffered. Conterra lost 13 weeks due to COVID. Thankfully the work ethic of the dedicated project team and the productivity of the Aquajet equipment has minimized the shutdown’s impact. Final completion is now scheduled for late spring 2022.

The use of robotic hydrodemolition equipment also makes it easier to enact social distancing protocols going forward, should they be needed. While this isn’t a benefit Conterra looked for when drawing up their bid, it has certainly allowed them to keep moving forward while other job sites had to reorganize.

“Hydrodemolition put us on the cutting edge of industry trends,” Porciello says. “No one saw a global pandemic coming, but with hydrodemolition robots, we’ve been able to adapt quickly. This speaks to how manufacturers like Aquajet listen to their customers and plan for the future of construction. From ecofriendly solutions to eliminating silica dust to reducing health risks like white fingers and hearing loss, smart equipment developments keep us ahead of the curve.”

The author is the business development manager for Aquajet’s North American subsidiary, Brokk Inc. He can be reached at keith.armishaw@brokkinc.com.