When talking about unexpected reactions, Feltz adds, “Air entrainers are the worst. They are so sensitive to so many other ingredients, that you are constantly adjusting them to get the air content you want.”
Fly ash is the ingredient that is blamed most for air entrainment problems. The carbon in the ash can eliminate the quantity of air bubbles. When the carbon concentration in the ash varies, producers have difficulties adjusting the dosage of the entrainer correctly to compensate.
Managers spoke of fly ash shortages or high prices. But the real problem was they couldn't get as much low-carbon ash as they wanted, and at a reasonable price. The bottom line: If carbon did not affect their air, they would not have a problem with the ash.
And producers identified other factors that affect the amount of entrained air in unpredictable ways. These include the brand of cement used, the ambient air temperature, how long the mix churned in the truck, and how the concrete was placed.Lowest bidders
Producers have similar stories about field testing problems. Testing labs frequently fail to follow correct procedures. As a result, the managers say the burden of proof of good performance falls on the producer to verify the hardened concrete meets project requirements.
“The building owners hire the testing laboratories, and they often go with the lowest bidder,” according to Calvin Cannon of Teichert Readymix in Sacramento, Calif. “The technicians are under pressure to perform their jobs quickly, so they sometimes get sloppy with sampling the concrete. They leave cylinders at the jobsites that are not cured properly and are not retrieved in the specified time frame. When the lab tests these samples, their breaking strength is low.”
So the supplier gets a notice that the concrete failed to meet strength, and now someone has to pay to core the concrete, Cannon adds. “Ninety-nine percent of the time, the concrete onsite is fine, but we've lost a lot of time and money. And so have the owner and his contractor.”
Another complaint was testing companies do not provide results to the producers. “I have been in meetings where the owner told the testing company that they had to give us their test results,” says Frank Nickolaus of Titan America in Florida.
“And they still didn't send them to us. They only send us the tests that report a failure,” Nickolaus adds. “We could use all those results to spot problems early and head them off, or include in our database of mixes. The problem is, we only get about 5% of the reports.”