Building in a bubble

by Clair D. Urbain

Controlled environment helps assure crack-free concrete and offers other construction benefits.

Hobbyists build ships in bottles; factory workers build products in buildings; but it is unusual for a contractor to construct a $60 million building inside a bubble.

That’s precisely what’s happening at the United States Department of Agriculture’s (USDA) National Animal Disease Center, National Veterinary Services Laboratories and Center for Veterinary Biologics in Ames, Iowa.

It’s building a state-of-the-art facility for animal research at this location and McCarthy Building Companies is in the process of building the highly secure Biosafety Level 3–Ag Biocontainment Laboratory.

The facility is one of four projects of the $460 million USDA Department of Agriculture Ames Modernization Project. The facility replaces many smaller, inadequate research barns with a totally contained facility that can house animals ranging in size from chickens to bison.

The totally controlled and ultra-secure environment will be used to research highly contagious and economically damaging livestock diseases such as bird flu and bovine spongiform encephalopathy (mad cow disease). It will also be used to develop international standards for biocontainment, animal health, safety and quality of the nation’s – and the world’s – food supply.

Totally contained facilities
Because researchers will research potentially dangerous and contagious pathogens in the facility, extreme isolation requirements must be met. Once built, workers entering the 140,224 sq. ft. facility must shower in and out of containment suites. Any air, feedstuffs and water going in and any air or waste coming out of the containment areas must be free of contaminants. This will assure the research isn’t skewed by possible contaminants going into the facility; it will also control any pathogens within the facility from being released into the environment.

“The rooms are similar to the hoods researchers use in laboratories where they stick their hands through ports and into gloves to work on materials inside. However, in this biological safety level – 3 ag-rated facility, the rooms are actually the containment chamber,” says Eric Torkildson, McCarthy senior project manager on the site.

The building will have 22 totally isolated animal housing suites of various sizes and two research labs that are totally sealed to the outside world. The pen doors, which resemble airlocks on submarines, can withstand a 1,500 lb. hit at 35 mph.

Constructing a facility that contains potentially dangerous pathogens starts with extremely detailed design, continues with contractors speaking the same language and working toward the same goal using very high-quality building materials, then finishes with super-controlled work environments closely monitored by a variety of inspectors.

The most visible part of this job is the enormous air-filled structure that envelops the jobsite. McCarthy chose to cover the project in a translucent bubble during the construction to protect it from the Alberta Clippers that sweep across the plains of Iowa and make winter concrete work nearly impossible.

The 450' long x 250' wide x 125' tall bubble encloses 11 million cu. ft. of space. Two 30,000 cfm blowers keep it inflated and provide fresh working air.

Unique work environment
Working in a bubble has its idiosyncrasies. With the air locks and limited space, contractors must stage deliveries to keep building supplies in the bubble to an as-needed level. With only two entrances, all deliveries must be staged. “We had complaints from contractors at first about scheduling the airlock for deliveries, but when the weather turned cold, their attitudes changed,” he says.

The bubble offers ample space to operate cranes and other large equipment such as telescopic handlers. “We have two 65'-long vehicle airlocks that are big enough to accommodate a semitrailer, cement truck or pumper. Workers enter through a revolving door and emergency exits are located around the perimeter that are small sections cut in the fabric and held shut with Velcro-type strips,” he says.

With many engines running inside the bubble, air quality is a concern. Sensors monitor for levels of carbon monoxide and sound alarms if they reach preset levels. Cranes (as many as five working at one time) as well as other material handling equipment inside the bubble are equipped with exhaust scrubbers to help reduce emissions.

“We connect the exhausts of cement trucks to flexible tubing to carry their fumes outside while they are working in the bubble,” says Torkildson. The sensors have never triggered for air quality problems.

Inside the bubble, sound travels in strange ways. “We have workers say they hear tools dropping next to them when they are standing near one wall of the bubble, but when they look, they realize the sound traveled across the roof of the bubble from the other side,” he says.

The bubble offers enough weather protection that crews can control temperature so the concrete cures correctly. Unfortunately, last November, the first bubble on the site collapsed from high winds, exposing some concrete to uncontrolled curing. That meant some concrete already in place had to be removed to assure concrete quality. A new, sturdier bubble was erected and work continued through the winter months.

“In the coldest weather, we can heat the area near the forms effectively to maintain concrete temperature to about 55 F. Even on the coldest days, the temperature never went below 45 F in the bubble and there was no wind, even though it was blustery outside. That’s great working conditions for a construction project in the middle of an Iowa winter,” he says.

Having this type of control allows several trades to work on the building in a sequence not normally followed in a building exposed to the elements.

“Plumbers and mechanical installers can work on the heating and cooling systems even though there is not a complete roof on the facility. Electricians can run wire in parts of the building even though concrete finishers are working only a few feet away. It has really made scheduling interesting because we don’t have to follow the normal course of construction,” he says.

Quality planning, quality materials
All metal inside the containment areas must be stainless steel to withstand the corrosive nature of heavy-duty disinfectants. “Construction processes must control dust that could contaminate HEPA filters that clean air moving through HVAC and waste management systems – even vent pipes in the plumbing system,” he says.

Instead of burying plumbing in soil below the facility, a crawl space provides a run for all piping systems. All waste pipes contain ports that allow cleaning solutions and steam to be pumped through them for disinfection. All wastes from the containment area will be treated in high-temperature cook tanks before leaving the facility.

The 22 containment sites and two research areas are built on 50,000 sq. ft. of floor area. Linearly, the 12"-thick walls of the containment areas run nearly a mile. “Some of this was poured in batches as small as 6 cu. yd. per day,” he says.

The containment areas are built much the way a corrugated box folds together, says Torkildson. “McCarthy has developed coordination drawings for each containment area section that specifically defines exact placements of rebar and penetrations.”

To minimize the number of wall penetrations, special heavyweight forms were used that do not need form ties. “These forms are only held in place at the top and the bottom. Before each concrete pour, the forms, reinforcements and penetrations are fastidiously cleaned, then inspectors check the forms before the pour takes place. “We do this because exact rebar placement will help prevent cracking while curing. We closely check penetrations because we don’t want to jackhammer any of this concrete. It is very expensive to patch!” says Torkildson.

Throughout any single pour, at least 10 inspectors must okay the work before it proceeds to the next step.

Concrete pours are in batches that allow workers to effectively manage the pour. The mix uses as little water as possible and uses admixtures that allow for easier placement and to allow workers to consolidate it in the forms. “It’s not an easy mix to work with. But our concrete finisher, Story Construction, has become very good at it,” he says.

Inspectors continue to monitor the cure rate of the concrete. Surfaces are kept damp for at least 14 days, the most critical time for the cure. “If we didn’t have the bubble, we couldn’t pour concrete in the winter. That wouldn’t have been economically possible,” Torkildson says.

Precision form work
Forms are stripped only when the concrete reaches 7,000 psi strength. “The calcium chloride readings are taken after the forms are removed and are an indication whether the epoxy coatings can be allpied. Forms usually can be stripped in seven days but it can take up to 60 days to cure enough so work can continue,” he says.

Monitors wait until tests show the concrete has stabilized, which can take from 60 to 280 days. Once it reaches this point, workers drill holes every 12" along the inside perimeter where the wall meets the ceiling and floor and inject an epoxy to seal unseen gaps in the containment area.

In the final construction step, the room is cleaned thoroughly and a rolled- or troweled-on layer of 3/8" thick resilient epoxy is applied. “The concrete, for all intents and purposes, is architectural concrete quality. Any blemish in it will show through the epoxy and could create pock marks that could harbor a pathogen,” he says.

Speaking apples to apples
The tight tolerances require all contractors and planners to work in unison, says Torkildson, and he and other contractors have found training through the Army Corps of Engineers gets everyone speaking the same language.

“Each contractor on this job must have their quality control people, foremen and management go through the Army Corps of Engineers quality control program. It is a three-phase quality process that gets everyone talking apples to apples,” he says.

The Initial Phase of the process is a meeting where all parties discuss the scope of the work, checking over submittals and making sure materials are ordered. “It assures all the pieces are ready to go,” he says.

 The second or Preparation Phase is a meeting with all of the trades involved with the process. “We share the scope of the project and identify all of the inspection requirements and timelines of this part of the project,” he says.

The third phase is called the Inspection Phase, where all completed work is checked to make sure it meets the specification.

“This sounds like added expense, but I think everyone involved with this process agrees it probably saves money because everyone understands the project from the very beginning. We have found if contractors aren’t making deadlines, it’s because of poor planning. This process heads off many of these problems,” he says.

Program helps on government jobs
Although McCarthy developed a specific training program for this site, the Army Corps of Engineers offers one to the general public that covers the same material. “Anyone bidding government work should go through this training. The cost is very reasonable and makes it easier to bid and complete government jobs,” he says.

Torkildson says building this facility is much like building clean rooms in a factory, and the company employs many of the same building principles. “We have modified the clean room building process. Once we get to the point of applying the epoxy, we want the rooms already to be as clean as possible.

“Contractors can only bring in the tools and building supplies they need to work on the job at hand. We have a separate changing area for work clothing outside of the bubble. We don’t allow smoking, chewing or eating inside the bubble. To keep dust to a minimum, we limit access to areas after a certain point in the construction process. Those entering must have a reason for being there and must scrape and dust their work boots,” he says.

“This keeps debris down on the jobsite and makes it a more productive, pleasant place to work. We have adopted these rules on more of our jobsites,” he says.

Published in the July/August 2005 issue of Contractor Tools and Supplies magazine.

back to top