Published: 21/12, 2021
Hydrodemolition Suite Provides Ecological and Economic Benefits for Garage Restoration
With decades of experience in new construction and commercial renovation, general contractor and construction manager Arguson Projects Inc. understood the logistical challenges posed by a multi-year, 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 — needed to remain open while crews removed 200,000 ft2 (18,581 m2) 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 provided amenities for employees.
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/replacement to address structural integrity concerns and overall aesthetics of the suspended slabs. 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 building sits on the 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. A nearby hotel also made nighttime noise an issue. The project managers needed a solution that would limit dust and other environmental impacts but was also quiet enough to proceed with the renovations during normal business hours.
Arguson brought on Conterra Restoration, a Canadian-based contractor with extensive Hydrodemolition experience. The company presented Arguson with a cutting-edge solution that not only provided the productivity to meet deadlines, but also minimized impact on the tenants and environments. Conterra sourced an Aqua Cutter 710V — a Hydrodemolition robot which could provide 25 times more productivity than a large crew using conventional equipment — supplied by Cor-Blast Services Inc. The 5,181-lb (2,350kg) Aqua Cutter 710V uses a 14,500- to 40,000-psi (1,000- to 2,758-bar) 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, and therefore 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 — 56 gallons/min (212 liters/min) at 18,700 psi (1,290 bar). This would keep noise to a minimum, allowing crews to work during the day without disturbing tenants. Additionally, the Ecosilence allowed Conterra to work throughout the year, even when temperatures hit -4° F (-20° C).
The contractor also included an EcoClear water treatment system as part of its tender. This unit provides on-site water treatment in real time for less than a penny 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.
The project was broken into two phases over two years, commencing in December 2019. 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 ft (187 m) away and several stories above the pump system. Arguson and Conterra have 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 up to 5 in (13 cm). deep.
During an 8-hour shift, Conterra sees removal rates of 600 to 1,000 ft2 (55.7 to 92.9 m2). Had they opted for manual removal, Porciello estimates it would take a crew of 20 — averaging 30 ft2 (2.8 m2) 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 maneuvering equipment around the jobsite, 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 (20 m3) per hour — on its way to the sewer. With the EcoClear, Conterra can reduce blast water pH from 12.5 to between 7.5 and 8.5. 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 50ppm or less.
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% of the water used by the hydrodemolition robots. Depending on application, some contractors have seen recapture rates up to 90%.
As with 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.
Images courtesy of Just Porciello, Conterra Restoration Ltd.