HLJ's first challenge was access issues. The job had to be serviced from one large overhead door 400 feet from the project's starting point. With the manufacturing facility still in use throughout the project, HLJ worked behind 50-foot-high demising walls, and all trucks, machines and equipment had to be outfitted with exhaust scrubbers to operate inside the plant. That meant HLJ had to purchase a $5,000 bolt-on scrubber for its concrete pump truck, and ready mix supplier, Southgate Concrete, had to modify the exhaust systems on 10 of its trucks to accept custom-made exhaust scrubbers.
The project started with HLJ and its demo and excavation subcontractor removing 2,300 cubic yards of old slabs and an old foundation they unexpectedly found under the existing building. The project is planned to pick up LEED certification, so all the demo material was recycled and reused in the subgrade. All demo work was done at night to minimize dust and noise for workers in the facility.
Once the demolition was complete, HLJ began forming the mechanical trenches that created a grid throughout the floor and acted as the slab edge. Quantity and spacing of the reinforcing steel, dowel baskets and access issues prohibited the use of HLJ's Somero Laser Screed to place the 6-inch slab with double-mat reinforcement, leaving crews with the task of placing floors by hand.
HLJ came up with several possible plans for placing the floors, including one that utilized a highway truss screed. Eventually, HLJ reached out to Allen Face Companies for perspective. Over multiple conferences and a site visit to one of Allen Face Companies' clients in Washington, DC, HLJ settled on the latest version of the Screed Rail to help them install the floors.
HLJ utilized two Screed Rails for efficient concrete placement in the 40-foot-wide by 60-foot-long pours. Each rail was placed in pre-determined spacing and the rail guides were set to height by lasers utilizing the adjustable dual jacks at each end. Concrete was placed in each bay between the rails then hand straight-edged into place.
"We tried a power vibrating screed in a few bays but found the concrete was too susceptible to bubbling under the blade and throwing off the levelness numbers," Sean explains. Instead, HLJ crews screeded all the areas by hand using a straight edge, pulling straight back rather than the side-to-side shake technique since they found that movement also created bubbles. Immediately following placement, each area received a straight-edge float, and prior to the initial set the areas were bump-cut twice.
Al Frankeny with Allen Face Companies took the HLJ crew through a dry run before the first day of the pour. He explained to the crew how FF and FL systems work, what affects the numbers and what is required to reach high numbers. "When we do a floor like this, everyone has certain responsibilities and its best not to change them in the middle of a job," Frankeny explains. "When we do a dry run, everyone sees what he has to do throughout the course of the pour. Then when the job starts, everyone has already gone through the job once in their heads."
Sean says Frankeny helped crews tweak their placement methods, resulting in an FF 85 and a FL 40 on the first floor. "By our third pour we were hitting FF numbers over 100 and FL numbers above 50," Sean says. "And in some areas we hit an FF 124 and FL 64." HLJ averaged a 90 FF and a 47 FL on the overall project.
Frankeny says these numbers are very difficult to achieve on a hand-placed floor and can be credited to the HLJ crew's willingness to embrace the new equipment and system. But a lot of it had to do with HLJ's well-trained and experienced craftsmen. "Not everybody could end up with the same results," Frankeny says.