Where corn and concrete meet: a producer meets the challenge of a continuous pour at a new ethanol plant

Concrete Producer, The, Nov, 2004 by Allan Anderson

There's not much that's easy about a continuous, five-day pour. Everything has to go right and there's little margin for error. There are no second chances.

Things were touring along swimmingly last December for Kevin Murray, general manager at R&I. Ready Mix in Robinson, Ill. R&L was pouring concrete for the two 125-foot-tall towers of the new Lincolnland Agri-Energy ethanol plant near Palestine, Ill., just a statue's throw away from the Wabash River in rural southern Illinois. But then Mother Nature lowered the boom by lowering the thermostat.

A continuous 24-hour supply of concrete was needed until the pour was completed. The pour was started in the middle of December, so weather conditions were a prominent factor in whether concrete temperatures at the jobsite would he warm enough. Murray also had to schedule and utilize his staff 24 hours a day, not only to meet the delivery schedule at the ethanol plant, but also to service his regular customers.

Pumping 1402 yards

Two silos were poured simultaneously in a slip form fashion. R&L supplied concrete at a rate of 24 yards an hour, allowing the placed concrete to set up enough to keep the slip forming moving up. A pump placed all of the 1402 yards.

The mix design for the project called for 4000 psi concrete. Buzzi Unicem Cement USA Inc. supplied the cement from its Greencastle, Ind., plant.

Four ready-mix trucks were on the job each and every hour. The timing of the concrete placement was critical as the concrete needed to be in the setting process when it went into the forms. This allowed the slip forming to stay on schedule.

"We not only had to maintain a set mix time before leaving for the job, but we had to battle traffic getting on and off the road, maneuver around a hectic and congested jobsite, and keep the loads consistent," says Murray.

Each driver mixed his load 20 minutes before driving to the jobsite, providing the initial set times that the concrete needed for the slip forming requirements, the general manager explains.

Timing was critical. "We had to keep everything efficient and consistent in loading the trucks for the pour," says Murray, "My office manager kept the load schedule on the mark so we were able to coordinate the ethanol plant scheduling with our regular customer scheduling without conflict or delay."

Cold front

Weather is very changeable this time of year in this part of the Midwest, as Murray and his crew were about to find out. The temperature was above average the first two days of the pour, with highs in the mid-50s during the day and lows in the upper 30s. It all changed abruptly the third day, as daytime highs dropped into the upper 30s and the nighttime lows dipped into the lower teens.

This made it difficult to maintain the required 80[degrees]F concrete temperatures. Murray constantly checked his hot water system to make sure it was keeping up, as they were using it not only on the ethanol plant silos but also on regular customers' concrete. "We had to keep a close eye on our hot water system as it was running 24 hours a day for over six days without a break," he explains.

Murray also monitored the concrete temperatures before each truck left the plant to see if any adjustments had to be made. "The change in the temperatures presented a challenge not only in the concrete temperatures but also in keeping the pace of delivery on line with what the customer required," he says.

The concrete temperatures became a major concern by the fourth day as the cold kept the aggregate temperatures progressively lower. This challenged the ability of R&L to attain the required 80[degrees]F concrete temperatures. "We simply could not maintain 80[degrees]F by Friday," says Murray. "The best we could get was concrete temperatures in the upper 60[degrees]F range."

Fortunately, most of the job was complete by the time the concrete temperatures started to drop. "We had maxed out our capabilities to get the concrete temperatures that were required," says Murray. "If the pour had lasted two more days, we would have struggled to keep the concrete temperatures at an acceptable level."

Manpower Issues

R&L was faced with stringent staffing needs. A night shift was created for the pour where one had not existed before. Drivers and the batch operation staff volunteered for this challenge. "Everybody sacrificed to keep the pour on schedule and also to keep regular service to our daily customers," says Murray. "Everybody from the drivers to the office staff pitched in."

To meet the requirements of this large job and the producer's regular customers, Murray used two 12-hour shifts. This allowed the plant to meet production schedules, be watchful of the hot water system and aggregate supplies, as well as aggregate temperatures. "We were concerned with keeping production online as well as the plant and equipment running at peak levels," Murray adds. "Everyone monitored all the equipment and the amount of testing we did to keep an eye on the concrete and aggregate temperatures throughout the pour."