What Started Out as a Small Concrete Pumping Job…
What Started Out as a Small Concrete Pumping Job…A long 10 hours required to place just 110 yards at nuclear power plant
Sometimes the smaller the concrete pumping job — at least in total yardage — the more complicated the process.
That's what Luther Stem Concrete Pumping of Fort Smith, Ark., found out when they were called upon to look at a small job for Bechtel Power Corporation, the general contractor for Energy Operations. According to Howard Yates, the superintendent, the job didn't involve a lot of yardage but was a little complicated because it was at the Arkansas Nuclear Power Plant in Russellville — halfway between Fort Smith and Little Rock.
According to Luther Stem, owner of the pumping company, "Initially, I didn't give this job much thought until Ed Miller, my office manager, and I were going through metal detectors and background checks just to get into the nuclear facility to look at the project."
As part of a $175 million upgrade, the steam generator in Unit One of the nuclear plant was being replaced. In order to accomplish this task, a hole 25 by 30 feet (7.6 by 9.1m) in the side of the 4-foot (1.2m) thick reactor wall was cut out a lofty 90 feet (27.4m) above the ground. A massive steel and concrete structure was erected just to handle moving the enormous 110-ton (99.8 metric ton) generator, which was basically the size of a huge dump truck. It was lifted out of the building and carefully replaced with a new one inside the reactor.
Free-flow hydraulics a "must"
Luther Stem's job was to pump concrete back into the forms to close up the hole. Because of the erected steel structure, the full 140-foot reach of the company's Putzmeister 43+Meter was needed to reach up and over it to safely access the one-foot-square holes (30.5cm2) located at 5-foot (152.4m) intervals up and down the face of the slip forms. Because of the unusual conditions of the nuclear job site, the exclusive free-flow hydraulics of the Putzmeister unit was also a "must" for an extremely smooth pour without boom bounce.
Plus, strict time limits were placed on each mixer or it would be rejected for temperature control reasons. This time limit had to take into account 20 minutes of drive time, 10- to 15-minute security checks of every vehicle, a slump test and the adding and mixing of admixtures on the job site.
Because this delicate pour at a nuclear plant was so crucial, absolutely every contingency was addressed at a pre-pour meeting. Once the pour started, it couldn't stop for any reason or the risk of cold joints would result.
Although the total pour was only 110 yards (100.6m), it would take at least 10 hours to complete. This was because the specs called for an extremely slow 3-foot-per-hour rate (91.4cm), which resulted in an unusually long process just to unload one mixer truck.
All equipment had backups
At the pre-pour meeting, 35 people discussed everything from safety and chain of command to backup equipment. Every piece of equipment had at least one backup, from cranes to lift the skip pans of test concrete off the platform to vibrators and a backup pump.
In this case, Luther chose his 36-meter Putzmeister as the standby. However, it was not needed due to the reliability of the 43+Meter doing its job flawlessly.
The day before the pour, the Putzmeister 43+Meter was brought in to do a trial run on placement procedures and to go through a highly scrutinized security check. This consisted of inspecting everything from the oil in the truck to confiscating the cab's duct tape and WD-40 for unexplained reasons. All this defense hype was due to a heightened alert after the terrorist bombing of a U.S. warship overseas.
The morning of the pour began by again checking all equipment and personnel through security. Every construction worker had an escort by his or her side at all times, even when going to the bathroom. A guard also sat in the cab of the boom pump at all times as a precautionary measure.
Guards escort trucks
When the first mixer truck arrived, it was thoroughly checked and escorted by a guard to the site, as was every mixer thereafter. After basically "everybody and their brother" witnessed the first slump test, the pour began.
The mix consisted of 1300# rock, 1600# sand, 620# cement, 155# fly ash and about 30 gallons (113.6 L) water. Although it appeared to be a typical mix design, the rock, sand and cement were not "local" ingredients. Scientists had recommended that these different aggregates be brought in from various parts of the country to ensure no reactive mix problems at the nuclear site.
Because of the water reducer added on the job site, the actual pumping was easy. Again, the problem proved to be time. Using a slip-form process, the concrete was required to set long periods of time before moving the forms up with each pour. At times, the mix would start to tighten up before actually unloading each truck, as the slump would go from a 6 to 2 inches (15.2 to 5.1cm) to in no time.
Although the Putzmeister pump could handle the tough mix, it was necessary to bring the boom pump to the ground and pump the mix out because of it being too stiff to flow around all the steel and cables in the wall. Fortunately, this occurred only once.
Minimal amount of concrete discarded
Otherwise, whenever the mix started setting up, the truck was quickly pulled out and a fresh batch brought in. Of the eleven trucks brought in within the ten hours, only four to five yards needed discarding. Meanwhile, the pour progressed at its planned snail's pace.
Luther noted that "To make sure we didn't have problems, I stayed at the back of the pump to back up the ready-mix trucks and monitor the mix consistency while pump operators Greg Cox and Chris Stafford were positioned on top of the work platform. One worked the unit's radio remote and one expertly motioned the end hose directions to avoid any mishaps in this tense situation.
"When the last truck pulled away from the pump late at night," recalled Luther, "the general contractor came over to me, smiled and said, 'Luther, that went just like I hoped it would. Let's go home.' I knew how much pressure had been lifted off his shoulders because the same amount had just been lifted off mine."
Thankful the job was done to full satisfaction and without problems, a relaxed Luther said, "When you undertake a project of this serious nature, prepare your best, follow through on those plans, have good reliable equipment and highly trained personnel. However in the end, even the small job that turns into a big one is really just another job chalked up to experience."
The new generator is expected to last another 30 years, at which time Luther Stem Concrete Pumping confidently plans to handle the project again.
Owner: Energy Operations, Inc., Russellville, Ark.
General contractor: Bechtel Power Corporation, Phoenix
Pumping contractor: Luther Stem Concrete Pumping, Fort Smith, Ark.
Ready-mix supplier: Mobley, Dardanelle, Ark.
Equipment: Putzmeister 43+Meter with Putzmeister 36-Meter on standby