Two test columns measuring 4x5x10 feet were cast at the jobsite. Coastal Carolina Pumping Inc. of Charlotte was the concrete pumper. The independent testing laboratory, S&ME of Charlotte, was also involved in all the test pours. This gave both of us a chance to obtain comparative testing data on the mixes.
The mock-up pours gave everyone the opportunity to familiarize themselves with the mix. Three more test columns were cast at our yard before the first jobsite pour.
We also conducted training classes for our quality control technicians, drivers, batchers, and dispatchers to ensure everyone understood that they were working with an engineered material that behaves differently then conventional concrete.
I repeated, “You can't treat this like 3000 psi concrete. The mixes have an increased mix time at the plant and are extremely sensitive to fluctuations in moisture contents of aggregates.” The drivers must have a clean and empty drum before receiving high-strength concrete, and they must never add any water to mix. The drivers were initially concerned the concrete would set up in the drums, but they soon saw this would not be an issue because of the hydration-stabilizing admixture.
Each plant will check and verify the fine aggregate moisture probes before a pour is started. We check coarse aggregate moisture about 30 minutes before the first load is batched. Aggregate moisture contents and sand probes are rechecked on larger pours or anytime something has changed.
QC technicians will check the temperature and measure the spread, air content, and unit weight of the first three loads of concrete at each plant. They will then visually check every load that is batched and will take random samples for temperature, spread, air content, and unit weight.
Technicians at the jobsite inspect the concrete and redose it with high-range water reducer, if necessary. They also will cast a set of companion cylinders every time the independent lab takes a sample. A set of 12 cylinders is cast every 50 yards. Once cast, they are immediately submerged in a temperature-controlled curing tank onsite.
We initially underestimated the amount of time and effort of our QC department, but it has stepped up to the task. Without the technicians' hard work and effort we would not have had the success we've had thus far. It took us a few weeks to become accustomed to batching high-strength concrete daily, but now it's second nature. Everyone knows and understands his role to ensure each pour is a success.
“Teamwork is critical in projects like these,” says Randy Thompson, project executive with Batson-Cook. I couldn't agree more. Teamwork throughout the planning stages and now construction has been the key.
As 2008 started, the building was only a few stories tall, and there will be more hurdles to overcome. But working as a team, the Wachovia Corporate Center will be our project of a lifetime.
— Adam D. Neuwald is technical engineer with Concrete Supply Co., Charlotte, N.C. Visit www.concretesupplyco.com.Related Articles & Links