A special group of Olmsted Dam project team members received the Army Corps of Engineers Headquarters Innovation of the Year Award.
They created a “Self-Consolidating Concrete” (SCC) mixture and concrete placement techniques that were used in construction of the Olmsted Dam Project on the lower Ohio River. Team members include David Kiefer, Lakes and Ohio River Division (LRD) regional technical specialist; Matt Whelan, senior geotechnical/concrete engineer; Joe Kissel, senior concrete materials technician; Bill Gilmour, Olmsted constructability engineer; Mick Awbrey, deputy chief, Olmsted Division; Mike Braden, chief, Olmsted Division; and Steve Durrett, former district engineering division chief and deputy district engineer.
The Olmsted Dam is composed of a tainter gate section and a navigable pass section. The dam is being constructed of precast concrete elements called shells that are constructed on the Illinois bank, transported to the river and placed over foundation piles in the riverbed. The shells are individual structural elements that fit together to create the dam. After the shells are set in place, they are filled with concrete and form a permanent segment of the dam.
The team received the headquarters recognition because they came up with an innovative construction technique and SCC mix design to use in the trunion girder anchorage zone within the Lower Pier (LP) shells. David Kiefer, a division regional technical specialist said, “SCC is basically concrete that is very wet and flowable, and doesn’t need external energy or vibration to fill concrete forms; it consolidates on its own.
“It incorporates conventional concrete materials, but in different proportions and with different admixtures than conventional concrete.”
A traditional concrete mix would require workers to access and vibrate the concrete during placement. Due to the geometry of the LP shells, placing concrete traditionally would have required a confined space entry for the workers and equipment. Using SCC for the LP shells significantly reduced contractor WGA and USACE employee exposure and was therefore a safety bonus.
The aspect of the LP shell construction that benefitted the most from the SCC approach was the trunion girder anchorage zone. This area of the shell contained very congested and tightly spaced reinforcing steel, post-tensioning tubes and steel plates. As designed, this concrete would be placed in discrete two-foot-thick horizontal layers with traditional construction joint treatment after every lift had hardened. The lift joint preparation and access in all of the embedded metals would have been extremely difficult, according to Kiefer. Adopting a technique from roller compacted concrete construction, each individual lift was allowed to stiffen, but not harden, before the next lift was placed. This “warm joint” approach allowed the whole trunion girder anchorage zone to be built in one semi-continuous operation.
Extensive testing was conducted for the warm-joint approach. Even a full scale mock-up test was performed at the site to prove that the SCC and warm-joint technique would perform reliably in real world conditions. Proven successful, the warm-joint construction method was ultimately placed into the production cycle.
Mike Braden, chief of Olmsted Division said “It’s this type of critical thinking that is driving significant cost savings while achieving an almost two-year gain on schedule.” He said that an innovative construction project like Olmsted requires innovative thinkers.
“Every time I’ve asked, the project team and our contractor partner WGA, have answered the bell by engineering a way forward that improves cost, schedule, quality and safety performance over the status quo,” Braden said.