With decades of experience in new construction and commercial renovation, contractor 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 18,581 square metres of material from the second and third levels. The building’s tenants required parking to remain open, as well as continued access to the roof deck, which provided amenities for employees.
Seizing an opportunity to reduce not only the project’s carbon footprint, but also the overall cost, Arguson and the property owner, turned to Conterra Restoration and a suite of Aquajet hydrodemolition equipment for an eco-friendly solution.
The suspended slabs within the parkade were heavily contaminated with chloride ions from road salt, resulting in significant corrosion-related deterioration and cracking.
The concrete needed significant 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 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 meant nighttime noise was an issue.
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“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,” said P.Eng Philip Sarvinis, managing principal with RJC Engineers. “Hydrodemolition allowed the contractor to work through the day without disrupting building tenants or the neighbouring 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.”
For the demolition, 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 2,350-kg Aqua Cutter 710V uses a 14,500-psi 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, and therefore less risk of microfractures. Hydrodemolition also cleans and descales rebar without damaging it.
The plan also included an Aquajet 700 Ecosilence high-pressure pump, which is quieter than other high-pressure pump systems, while still providing ample power for the project — 5,212 litres 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,” said David Porciello, general manager for Conterra.
“We paired a hoarding system with the Ecosilence to get down to 63dB at a range of 6 metres.”
Additionally, the Ecosilence allowed Conterra to work throughout the year, even when temperatures hit -20 Celsius.
The contractor also included an EcoClear water treatment system as part of their tender. After passing through the EcoClear, wastewater can be released into the sanitary sewer system. With the project requiring in excess of 38 million litres of water, this presented significant cost and carbon savings.
“Environmental stewardship has always been an important part of the conversation for us,” Porciello said. “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.”
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 187 metres away and several stories above the pump system.
Arguson and Conterra dedicated a 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 10 to 13 cm.
“The Aqua Cutter finds what most engineers can’t — every millimetre of bad concrete,” Porciello said. “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 eight-hour shift, Conterra sees removal rates of 55.7 to 92.9 square metres. Porciello estimates manual removal would take a crew of 20 — averaging 2.8 square metre 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.
To minimize disturbances and manoeuvring 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 20 cubic metres per hour — on its way to the sewer.
“The EcoClear system gave us a distinct advantage for this project.,” Porciello said. “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. 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,” said Porciello. “And we know the equipment is capable of meeting storm drain requirements. Now that we’re 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 eco-friendly.”
With a closed-loop system, blast water is treated in the EcoClear. Then 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 per cent of the water used by the hydrodemolition robots.
Like many projects during the global pandemic, the parkade restoration’s timelines have suffered. Conterra lost 13 weeks due to COVID, and 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. While this isn’t a benefit Conterra looked for when drawing up their bid, it has certainly allowed them to keep moving forward.
“Hydrodemolition put us on the cutting edge of industry trends,” Porciello said. “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 eco-friendly solutions to eliminating silica dust to reducing health risks like white fingers and hearing loss, smart equipment developments keep us ahead of the curve.”