WSP’s responsibility includes, among other things, ensuring that every aspect of construction, including hundreds of auger cast piles—3-foot-wide holes drilled 140-feet deep and filled with rebar and concrete—are built to last at least the 100-year design life of the infrastructure project.
“The main challenge with the auger cast piles was to maintain proper temperature as the concrete cured,” Baltzer said. “Too hot, which is a constant concern in Miami, and the concrete doesn’t cure properly.”
The piles were successfully completed in 13 months, and then came the more conventional but still massive task of casting the concrete footings. It is the largest concrete placement in FDOT’s history.
After constructing coffer dams to keep out groundwater and tying 1.7 million pounds of steel rebar, the project team began pouring 5,200 cubic yards of 8,000 psi concrete into the 140-foot x 68-foot x 14-foot central pier footing on Friday, July 23.
“Five concrete plants in the region were involved and four pump trucks were used to place the concrete into the foundation,” Baltzer said.
By Sunday morning, 33 hours later, the pour was complete. But the job of maintaining proper cure temperatures in the giant slab continued for the next seven days. Six miles of cooling pipes were placed in the concrete as it was cast.
“Seven large chillers provided cold water that circulated through the pipes,” Baltzer added. “To control uniform temperature during curing, wireless thermometers communicated the temperatures throughout the footing to operators.”
The cooling systems, as well as the testing methods used on concrete samples to measure chloride resistance, are standard construction processes, according to Baltzer. A more customized approach was needed to ensure concrete flowed perfectly into the lowest area of the footing, where rebar was tied so thickly that only inches of space remained between rebar.
“The builders specified a custom concrete mix, then used two mockups to make sure it flowed correctly between all those spaces,” he said.