Pumping concrete for a 5-foot wide sidewalk may sound straightforward, but accomplishing it in an environmentally protected area while reaching the farthest point 1,644 feet away definitely presents unique challenges.
To complete the job, which was located within the 217-acre Yamato Scrub Natural Area in Boca Raton, Fla., pumping contractor M&M Concrete Pumping recently used two Putzmeister Thom-Katt trailer-mounted concrete pumps. Used in an unusual pump-to-pump arrangement, the Thom-Katts placed 80 cubic yards of concrete to construct the long and curving sidewalk.
"The job was brutal," says M&M owner Mike Moberg. "It's incredibly rare to use two trailer pumps in a pump-to-pump approach, especially when pumping a harsh 3/8-inch pea rock mix such an enormous distance. Plus, we had to be extremely careful not to damage any vegetation while pumping along a looping sidewalk path."
On a normal pour, a trailer pump from M&M's 12-unit fleet uses about 200 feet of delivery system. At eight times that distance, this job was an exceptional and complex endeavor.
In addition, keeping ready mix trucks from driving over and disrupting the vegetation was key. Thus, the concrete (supplied by Maschmeyer Concrete of Lake Park) was discharged at the scrub's edge, where the first trailer pump, a model year 1998 TK 50, was positioned. With its maximum 950-psi pressure, that unit pumped concrete 700 feet through 2-inch steel pipe and hose to a second pump, which was set up on a narrow access road inaccessible to ready mix trucks. That second high pressure unit, a bigger TK 70, pumped the mix another 944 feet through larger 3-inch line that tapered to a 2-1/2-inch size, while snaking around sharp bends before reaching the furthest point of concrete placement 1,644 feet away.
Delivery line size proved to be a significant aspect of the complex pumping equation.
"The smaller the line size, the higher the pressure needed," notes Jim Henegar, co-owner of Miami-based Thomas Machinery, the Putzmeister equipment dealer in the area. "As higher pressures force water into the rock, the mix tends to dry out and makes pumping more difficult at such far distances." He adds, "As the concrete would already be stiff from going the long distance from the first pump to the second, M&M's use of a larger line size for the last 944-foot stretch was a key factor in effectively pumping the concrete the final distance."
And all of this had to be accomplished while protecting the environment.
"As the area was environmentally protected, the plants could not be disrupted in any manner," says Moberg. "We could have avoided about 250 feet of delivery system if allowed to make a beeline straight through the scrub."
To address these concerns, the delivery system had to remain within the curving sidewalk forms. In addition, crews could only venture 18 inches outside the forms on either side, paying special attention to ensure no foliage was harmed during the construction.
There were also environmental concerns with priming the pump with grout. As a grout primer was a critical aspect, two yards of a high strength 6,500-psi mix were eventually proposed and allowed. To dispose of the primer without placing it within the scrub's natural habitat or compromising the sidewalk's integrity, crews placed the strong mix as a low 1-inch layer within the overall 5-inch thick concrete walkway.
Constructed under the direction of concrete contractor West Construction of Lake Worth, Fla., the challenging sidewalk was just one portion of a contracted construction project for various sidewalks, small parking lots and informational kiosks for three different scrubs within Palm Beach County. Ultimately, these construction feats will enable visitors to more conveniently view the natural and exotic plant species along with the protected wildlife of this rare ecosystem.