Bridging the Gap

Published: 13/4

Innovative Robotic Solution Provides Productivity for Philippine Bridge Project

Construction is currently underway in the Philippines on a massive bridge system connecting Cebu City with Cordova on the southern end of Mactan Island. The 5.3-mile (8.5km) Cebu-Cordova Link Expressway, slated for completion in 2021, will span the Mactan Channel to ease congestion and boost economic activities throughout the region by providing additional access to the island and the Mactan-Cebu International Airport for an estimated 50,000 vehicles a day.

As one of the largest infrastructure projects in the country, the new bridge relies on a carefully choreographed plan of simultaneous operations to meet strict deadlines. When a bad batch of concrete threatened to derail progress on one of the bridge’s first pylons, project managers needed a creative solution that could quickly remove the poor-quality concrete without damaging the rebar or putting the project behind schedule. Hydrodemolition was the only process with the precision and productivity to keep the project on track.

Cebu Link Joint Venture (CLJV) contacted Singapore-based Asia Waterjet Equipment, the region’s premier hydrodemolition experts. Access and site conditions presented quite a challenge, but with decades of experience in some of the most hazardous applications, Asia Waterjet Equipment was more than up to the task. With the clock ticking and monsoon season in full swing, the team arrived onsite with an Aquajet Aqua Cutter 710V Hydrodemolition robot and Jetstream HP Waterjetting Pump.

 

Troubled Water

Access was the primary problem. CLJV was conducting construction on several bridge pylons simultaneously. To minimize disruptions to the local community, the project’s primary staging area, as well as the initial pylon, were only accessible from the coast. This meant the concrete had to be mixed 1.6 miles (2.5km) down the coast then transported by barge to the jobsite. From there, the barge was grounded, and the trucks disembarked directly onto the beach. The pylon was nearly 100 ft (30m) inland.

Overall, the transportation delay had no negative impacts on the concrete, and 52.5x45.9-ft (16x14 m) pylon quickly grew to 13 ft (4m) tall. However, a complication with a single delivery threatened to throw the entire project behind schedule and over budget.

Crews knew there was a problem immediately. The concrete was already setting as they pumped. Vibrating and other correctional methods failed, and the pour was ultimately unsuccessful. Even worse, the concrete fell 13.8 in (350mm) short, leaving a mesh of exposed rebar.

For CLJV and Asia Waterjet Equipment, the challenges were adding up, making for a very difficult repair. The pylon was nearly complete. While CLJV had budgeted time and money for small complications, it could not afford to demolish the whole pylon and start over. Crews with handheld breakers or excavators could remove the poor-quality concrete, but only by destroying the rebar. They would have to cut the exposed rebar at the top of the pylon to access the concrete a foot below. More rebar would be damaged as the poor-quality concrete was removed, and microfractures from the vibration of jackhammers or excavators would weaken the remaining concrete, jeopardizing the pylon’s integrity.

“There was no option; the rebar and existing good concrete had to be protected,” says Chris Parkhill, Asia Waterjet Equipment Sales Director for Southeast Asia. “Had CLJV gone with traditional demolition methods, they’d have to open, pry apart where possible or cut the rebar and manually jackhammer out the bad concrete. There’s no guarantee a man using a jack hammer could gauge what’s good and what’s bad, so they’d end up removing extra. Then they’d have to bend the rebar back into place without breaking it, or weld or cut new threads and join with it threaded couplers. It would add weeks to the project and a significant cost to the budget. They simply couldn’t afford it.”

Asia Waterjet Equipment knew hydrodemolition was the only solution. The non-intrusive method uses high-pressure water jets as powerful as 40,000 psi manipulated by an automated robot to remove layers of deteriorated and damaged concrete. The Aqua Cutter 710V’s high-pressure water jet leaves a rough, irregular profile after removing the initial layer of concrete that results in a better bonding strength. The robot also cleans and descales the exposed rebar and removes non-visible contaminants such as dirt, mud, foundation mud, salts, chlorides and sulfates.

 

Building Bridges

Productivity was also a concern. With simultaneous construction continuing on several other pylons in the area, crews needed to remove the poor-quality concrete and complete repairs quickly — with minimal labor.

With the ability to complete concrete removal tasks up to 25 times faster than a hand lance, the Aqua Cutter provided the necessary solution to keep the project on schedule. Asia Waterjet Equipment brought in Aquajet Special Application Manager Kjell Isaksson to support the operation.

“There were a lot of variables and no room for error,” Parkhill says. “To minimize the risk of delays, we decided it would be best to have an Aquajet specialist on site.”

Like the cement trucks, the Aqua Cutter and all support equipment, including a high-pressure waterjet power pack with a 4200 series Jetstream pump, had to access the site from the Mactan Chanel. Proximity to the water and the frequent, heavy rains of monsoon season made ground conditions difficult. However, since the Aqua Cutter is self-propelled with tracks, the uneven, muddy terrain presented no problems for Asia Waterjet Equipment. This minimized necessary site preparations and helped accelerate repairs.

 

Crossing the Bridge to Success

This mobility was also necessary for tackling the demolition itself. Once lifted onto the pile cap by a crane, the Aqua Cutter was able to easily maneuver over the rebar. The high-pressure pump was set up 23 ft (7m) away and connected to the hydrodemolition robot by a high-pressure hose. To help reduce cost and increase production, Asia Waterjet Equipment opted to use seawater for the majority of the demolition rather than bring in fresh water. The company continually filled two 5,283-gallon (20 m3) night tanks directly from the Mactan Chanel. Fresh water was only used during the last two days of the project to remove salt and other impurities that could impact bonding. Using the Hydrodemolition robot, operating at 15,000 psi (1,000 bar), and two employees, Asia Waterjet Equipment needed just days to remove 13 yd3 (10 m3) of poor-quality concrete at a depth of 6-10 in (150-250 mm).

“With the Aquajet Aqua Cutter, we increased productivity to a point where construction was back on schedule,” Parkhill said. “Without Hydrodemolition, there’s no way CLJV would have been able to do that.”

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