70% Slag Cement Used In Tremie (Underwater) Concrete
When the Southwest Florida Water Management District (SWFWMD) realized that low water levels had caused a fundamental shift in design parameters affecting a dam on the Kissimmee River north of Lake Okeechobee, Florida a decision was made to construct a tail weir. This weir would, in effect, be a monolithic block of approximately 5000 cubic meters of concrete placed underwater. It was imperative to have the structure in place before the 2008 hurricane season in Florida affected water levels.
Responding to this challenge contractor American Bridge, working with Maschmeyer Concrete Company of Florida, looked for innovative ways to complete the project in a timely fashion. One of the critical issues was temperature control to mitigate thermal cracking in the concrete. With this in mind Maschmeyer Concrete looked to utilize a high level of slag cement to accomplish low heat while still achieving sufficient early strength.
Hanson Slag Cement, part of Continental Florida Materials and Lehigh Hanson, responded by assisting in temperature modeling which indicated that replacing 70% of the portland cement in the mix with CAMCEM™ a slag cement, would be optimum and potentially eliminate the need for ice or other cooling media. Maschmeyer Concrete working with the engineer of record, Waterfront Engineering Group and American Bridge, was able to demonstrate on a six foot by six foot by six foot test underwater test block that the concrete mix using 420 pounds of slag and 180 pounds of portland cement met specification requirements
In fact the three day strength was in the range of 2500 -2700 psi and 28 day compressive strength was approximately 5600 psi which was well in excess of the specified 3000 psi. The contractor was very pleased with the pumping and performance through the tremie pipe. Another benefit was that they were able to prove that there was no need for special anti-washout admixtures and that a standard high range water reducer and slag cement performed flawlessly. Recorded temperature through embedded thermal couples indicated that temperatures ranged from 140 – 159 degrees F.
The project was completed in two placements in June of 2008. It is regarded as a great success by all involved and an innovative use of slag cement to mitigate thermal heat while still meeting early strength requirements.