The Lone Star Northwest, Inc. dry bulk powder cement storage terminal in Portland, Ore., sits less than 100 miles from the Pacific Ocean on the banks of the Columbia River in a city that has a climate far wetter than most. In fact, ships can off load cement powder from the dock directly into the storage area.

Some skeptics might question the wisdom of locating a facility used to store dry bulk powder cement so close to the water. After all, any moisture seepage can cause cement powder to adhere to the nearest storage surface, rendering it useless. But the Lone Star Northwest facility is as unique as its location. The building is a monolithic dome-a round, one-piece structure made of steel-reinforced concrete and known for its insulation and moisture-proofing characteristics.

Lone Star Northwest General Manager of Cement Operations Gary Madson admitted that selecting a dome facility went a little against the industry grain. "The industry has long-standing methods for cement storage, and we looked at several possibilities," he said. "We visited another cement storage dome facility in Missouri before we made our decision."

Although monolithic domes have been around for more than 25 years, there has been a recent resurgence in their use as bulk storage facilities. Lone Star Northwest's experience illustrates some of the reasons for this boom in popularity.

Keeping the powder dry was just one of the problems the dome facility solved for the operation. Dollars and common sense made up the rest of the picture. "It came down to plain old economics," says Barry South, owner of Dome Technology, Inc., and the builder of the dome at the Portland operation. "Traditional silo and flat storage buildings are more expensive to load and unload, and they usually cost more to build."

The economies of constructing a dome storage facility verses a silo are not hard to figure out. "To build a silo with the same capacity as a dome, it would have to be very tall," South said. "Of course the higher you go, the more expensive it is."

Lone Star Northwest Terminal Manager Dale Martin echoes that sentiment. "The dome gives you the most bang for the storage buck," he said. "The density requirements for the foundation on a silo are huge. We had the foundation for the dome poured in no time."

The building process itself is also simple and straightforward. The circular foundation features special anchors around the perimeter that hold the Airform, an inflatable balloon made of single-ply roofing material.

When inflated, the Airform creates the shape of the dome. On its inside, the Airform is sprayed with a polyurethane insulation material in several stages, totaling about 3 in. in thickness. A grid of steel rebar is then placed into the insulation, making the inside of the dome look like a giant birdcage. Finally, the rebar grid is embedded in a 2- to 3-in. layer of Shotcrete. The Airform remains in place to serve as the structure's waterproof outer shell.

Domes are insulated with high-efficiency polyurethane, which minimizes condensation. The shot-in-place concrete used in construction is of a higher density than conventional "poured" concrete, making it nearly impervious to chemical attack.

Since most of the construction process takes place on the interior, crews are rarely hampered by weather delays. The end result is a super-strong building that can withstand direct hits from a tornado or hurricane and is designed to last for centuries, according to its makers.

In addition, the cost savings continue long after completion. For example, loading and unloading is more efficient in the circular domes than in flat storage buildings. "Because they are round and load from a single point at the top, it is always going to be cheaper to load and unload a dome," explained South. "To get even close, a flat storage building would have to have multiple entry points or a moveable conveyor, and there are costs associated with both of those."

Unloading at the Lone Star Northwest dome is a detail Martin doesn't worry much about. "We're fully automated," he said. "We unload with a gravity reclaim system and mechanical auger. The cement goes out a hole in the center of the floor and is pneumatically transported."

Martin concedes that because of the automation, the dome is slightly more expensive to operate than the silos that the company still uses for storage. "But so far it hasn't required a lot of maintenance," he said.

Other advantages of domed bulk storage facilities stem from the bulk products often streaming off a conveyor, making a cone-shaped pile. That cascading effect happens to be a perfect fit for a monolithic dome, and there is seldom any time required to spread the material around inside the facility.

Domes are adaptable to storing more than one type of product. Concrete partitions, usually 20-ft high, serve to segregate different materials within the facility. In addition, equipment can be suspended above the bulk pile out of the weather and high enough to be out of the way.

Since domes are round, a center-pivoting circular conveyor can be mounted on the outside. Adding an electric shovel or slide to the conveyor makes it possible to deposit specific materials at pre-determined points inside the building. Also, the center load-out area cuts down on the time needed to pick up loads. All bins are the same distance from the loading point. A center dump can use a conveyor to either a mixer or a load-out station.