By Bridget McCrea
Large-scale construction projects mean increased stakes for all parties involved. From research to design, build-out and beyond, every decision is magnified. The foundation from which these decisions are made for architects, engineers and contractors is the choice of which building material to employ. With its flexibility, durability and ease of installation, precast concrete has proven successful on a wide variety of projects, as the examples below illustrate.
Wharf replacement in Massachusetts
When the town of Plymouth, Mass., set out to replace an antiquated commercial fishing pier with a newer, larger structure, it was doing more than just replacing the existing 7,780-square-foot “T Wharf” pier. It was building a stronger, sturdier structure that was more than twice the size (18,360 square feet) of its predecessor, and, in the process, helping area businesses and protecting its resources.
“This is the single most important project we’ve had on the harbor in quite some time,” said David Gould, the town’s director of marine and environmental affairs (1).
According to Gould, the new pier also improves Plymouth’s existing lobster and groundfish industries as well as emerging ones, such as shellfish aquaculture. In addition, the new facility includes amenities and services for visiting boaters and creates a more aesthetically pleasing waterfront for the thousands of tourists who visit every year.
What most of those tourists won’t realize is the important role that precast concrete played in the pier renovation project, officially known as the “Wharf Replacement Project Phase One for the Town of Plymouth.” Phase two is being scheduled for a future date. The long, linear portion of the pier is comprised of six 60-foot-by-2-foot-by-3-foot solid precast beams called pier casts, each of which weighs 55,000 pounds.
A team effort
Produced by Scituate Concrete Products of Marshfield, Mass., the massive precast pieces required special attention and handling, both on the manufacturing side and during delivery and installation.
“This was one of the longest pieces of precast we’ve ever manufactured,” said CJ Scott, production manager. “We had to come up with a heavy-duty rigging solution that incorporated longer spreader bars and a few other elements.”
The project also included numerous smaller precast slabs and pieces. Scott said the pieces were made in Scituate’s new 60,000-square-foot plant. The company worked with site and utility construction firm Robert B. Our Co. Inc. and project engineer Bourne Consulting Engineering to design the new structure.
Once completed, each of the 55,000-pound beams had to be shipped to New Bedford and then placed on a barge to be delivered to the project site in Plymouth. To transport the huge beams, Scituate hired a specialized hauling company that offered an extendable trailer. The logistics were complicated, said Scott, and required Scituate to deliver them to a port that was roughly an hour away from its plant, even though Plymouth is just 20 minutes away.
“We’ve done pier casts and handled complicated logistics in the past, but nothing of this magnitude,” Scott said.
During the production phase, Scituate added a corrosion inhibitor to the mix to ensure that the final product would be able to stand up to the marine environment where it would be installed. The precaster also developed a custom wood and steel mold that it used to fabricate the products.
“We had some issues in the beginning with the pressures from the concrete being exerted on the forms,” Scott noted. “The first ones we poured required some adjustments to compensate for the pressure being exerted and the sheer amount of concrete being poured in a single pour.”
The products were then cured in the form for about five days, and were covered in wet burlap to ensure the right level of moisture content.
Meeting and exceeding expectations
Despite the atypical requirements of the project, Scott said it went very well from start to finish, and that it exceeded his early expectations. He also noted that the design process took slightly longer than anticipated, but the extra time allowed the engineer, contractor and Scituate to iron out the details.
“Once we got the project into production, we stayed on pace in terms of the installation and transport ,” he said. “We had no hiccups or bumps.”
At the job site, he said all the massive precast pieces lined up with all the piers, which had been pre-installed. Coming off this successful project, Scott said Scituate now has the confidence to work on even more large-scale precast projects in the future.
“To evolve as a company and as an industry, sometimes you have to push the limits,” said Scott, who advised engineers and precasters to work together to put a spotlight on precast concrete’s key strengths and attributes on large projects such as this one. “Because the products are made in a controlled environment and in a certified plant, engineers are guaranteed that the products will be made to their specs and standards.”
Precast enables rapid dam construction
Elsewhere in the state, and armed with a $1.7-million grant from the U.S. Department of Energy, Bill French of Billerica, Mass.-based French Development Enterprises LLC set out to create a dam that incorporates non-traditional construction methods with off-site manufacturing and on-site installation. Calling his development “The French Dam,” he wanted to make the entire dam production and installation process both “just-in-time” and weather-independent.
FDE’s patented technology for rapid dam construction was also funded through the Massachusetts Clean Energy Center.
The 24-foot-long, 16-foot-high prototype was designed by GEI Consultants of Woburn, Mass., and Oldcastle Precast of Littleton, Colo. It comprises six 27,000-pound precast concrete 8-foot-by-8-foot-by-8-foot blocks interconnected with each other, forming one monolithic structure. A modular precast impoundment for construction and retrofit of hydroelectric dams, water control systems and powerhouses, the product was assembled on-site in less than four hours, even with a heavy rainstorm occurring during installation.
“Building on Massachusetts’ long history of innovation, this investment advances inventive technologies and strengthens renewable energy infrastructure that powers the Commonwealth with clean resources such as hydropower,” said MassCEC Interim CEO Stephen Pike (2). “By modernizing our energy infrastructure, we are capitalizing on investments that produce cost reductions and economic growth to benefit residents across Massachusetts.”
Precast: The material of choice
Bob Kramer, Oldcastle’s vice president of marketing and product development, said French approached his team with the idea of using precast modular components to build hydroelectric dams. Kramer added that French wanted to build a prototype to commercialize the concept. Oldcastle served as a design-manufacturing partner on the project.
Working with a civil design consultant, a dam expert and other members of FDE’s cross-functional team, Oldcastle spent about a year developing the dam prototype and experimenting with different manufacturing, assembly and connection iterations.
“The main driver was how to manufacture and create mechanical connections that would be suitable in the environment of what’s known as a small head dam,” Kramer said. “So that’s what the team did.”
For example, one condition of the federal grant dictated the manufacture and assembly of the modules in a way that would ensure watertightness and the ability to withstand the hydrostatic pressures. This was in addition to being able to unbolt, remove and replace a piece, if necessary.
“Collectively, we created a design and were successful in building up a prototype that satisfied the requirements of the federal grant,” Kramer said.
Dam of the future?
In total, Oldcastle produced six modules. All were of identical dimensions inside and out and manufactured from rigid steel forms to extremely tight manufacturing tolerances. The specifications weren’t unusual for the precaster, although Kramer said that if the dams were to be commercialized at some point – and then scaled up to make fully assembled, working dams – the project magnitude would increase exponentially.
“The product could be used to replace existing spillways, and would be particularly useful for municipal-owned dams that have fallen into disrepair,” said Kramer, noting that there are more than 80,000 non-electric-producing dams in the U.S. “These need to be retrofitted with a quick-fix, low-cost, high-impact solution.”
Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade-technical feature statewide.