Building a Concrete Bunker

In a secluded mountainous location within the Carolinas, advanced features of Putzmeister truck-mounted concrete boom pumps are being utilized to pump concrete for a unique application -- an underground bunker to be used should catastrophic disaster strike in 2012 as predicted by Nostradamus.

The large 13,000-square foot bunker is designed to help its occupants escape the major effects from nuclear blasts and radioactive fallout as well as provide protection from natural disasters. The bomb shelter will be used by its anonymous owners for emergencies only, while hidden near the couple's primary residence for quick evacuation.

To ensure the greatest resiliency, the bunker is being built below the earth's surface with concrete, deemed the strongest material for its long-lasting durability. To construct both the underground fallout shelter and its three-story lookout tower in the most time and labor efficient manner, three boom pumps are placing 3,900 cubic yards of concrete to finish the $3.5+ million project by 2011. This targeted completion date is two years after the project's May 2009 start date and one year prior to Nosterdamus' 2012 warning.

The Chosen Ones
Responsible for the unusual project's construction is general contractor Baxter Norris Construction, Inc. of Zionville, North Carolina, and concrete contractor Ocmulgee Concrete Services, Inc. of Morrisville, North Carolina. Chandler Concrete of Burlington, North Carolina, is supplying the concrete, and HFK Corporation (HFK) with locations in Burnsville, North Carolina, and Hollywood, Florida, is providing the concrete pumping services.

To handle precise concrete placement, HFK is putting the compact size of their three-axle truck-mounted concrete boom pumps to the test. This includes a 32Z-Meter, first on the site to handle the footings, and also a 36Z-Meter. However, the bulk of the concrete is being pumped with a 40Z-Meter.

"We specifically purchased a Putzmeister 40Z-Meter for this project because the model offers long reach and an ultra-lightweight design of less than 56,000 pounds (25,400kg), not to mention it's mounted on a more maneuverable three-axle truck," says HFK's vice president Frank Kahn Jr.

"A three-axle truck was a 'must,' because just getting to the job site requires navigating a mile-long gravel road up a steep mountain that has switchbacks with three-point turns," says Kahn Jr. "A four-axle vehicle just wouldn't be able to make those hairpin turns."

Kahn Jr. adds, "Once on the job site, there was limited space so we needed the machine's tight turning radius and compact outrigger footprint to safely set up the boom pump."

Another important feature was the 40Z's long 115-foot two-inch horizontal reach. Kahn Jr. notes, "With the longer reach of the boom pump, we could access all areas of the pour and avoid the labor of dealing with extra delivery line."

Non-Stop Pumping
The first major concrete pour was the footings that were connected to eight massive holes. The process required an exorbitant amount of concrete as the largest of the eight holes was 20 feet square and 10 feet deep.

Having started at seven o'clock in the morning, HFK continuously pumped concrete for 18 hours, as over 750 cubic yards of concrete, more than double the amount initially expected, had to be pumped non-stop to avoid cold joints. Adding to the job's complexity, the restrictive job site's space allowed room enough for only one ready mix truck at a time to be discharged into the pump's hopper. This was further compounded by a one-lane gravel road, which allowed only one ready mix truck at a time to travel its extremely narrow path. Any vehicle that met another on this road would require one or the other to back down.

Distinctive Design
To accommodate the bunker's distinctive design, every subsequent pour had different pumping requirements. The next time a boom pump returned to the job, it was a 36Z-Meter, which placed 300 cubic yards of concrete for the exceptional 16-inch-thick and 10-foot-tall perimeter walls, obviously lacking any window formwork. At a later date, the same boom pump placed a similar amount of concrete for the 8-inch-thick slabs, which involved intricate placement to avoid puncturing heating tubes that were laid for a floor heating system.

Next, interior walls, poured at a 12-inch thickness with 162 cubic yards of 4,000-psi concrete, formed 12 octagonal rooms. The eight-sided shape of the rooms was incorporated into the design for greater strength than square ones offered. This is especially important as 6 feet of dirt along with grass will be placed on top of the structure's roof to conceal the bunker.

Although the bunker will be hidden, three doorways will be exposed. As a result, the entrances are being given extra attention and extra concrete with the help of the boom pumps. At each entry point, a 3-foot-thick slab of concrete sized approximately 15 feet by 20 feet will be placed above heavy-duty blast doors for added protection.

New Addition
After the interior walls were already placed with concrete, construction crews were faced with a change in the bunker's design. A 4-foot-wide and 10-foot-tall tunnel, resembling a hallway attached to the home, was added around the bunker's irregularly-shaped half circle perimeter.

The addition of the tunnel, situated at the greatest distance from the pump's setup, posed the greatest reach challenge for placing concrete. However, the 40Z, specifically purchased for its reach and maneuverability arrived on site with its 115-foot 3-inch horizontal reach and four-section Multi-Z boom to place concrete at the farthest point without additional delivery line. Consequently, it pumped 335 cubic yards of a 5,000-psi concrete mix for the newly added footings and expanded perimeter wall.

"Without the longer reach of the boom pump, pouring the new perimeter wall would have posed a problem. Dragging line over the top of the interior walls that were already in place would have been extremely difficult and time-consuming," says Kahn Jr. "Fortunately, the 40Z had all the ideal features to easily overcome this job site obstacle."

Waterproofing the Bunker
Once crews installed 400 U.S. tons of steel beams atop the poured walls to hold up the deck, the 40Z pumped a 10-inch thick roof cap with 479 cubic yards of concrete. Again, it was crucial to pump non-stop to avoid cold joints; a backup pump was on site but never needed.

Just as unique as the project was the concrete mix for the roof. As the bunker will eventually be covered with dirt, it is paramount to keep water from entering inside. Xypex, a non-toxic, chemical additive for waterproofing was incorporated into the mix at the batch plant. Becoming an integral part of the concrete, this additive generates a non-soluble crystalline formation deep within the pores and capillary tracts of concrete to seal against the penetration of water.

"Like all mixes on this job, we pumped this highly specialized mix with a smooth flow because of the pump's Free Flow Hydraulics," says Kahn Jr. "This also proved beneficial for the longer 18-hour pours because its closed loop system keeps the oil cool for reliable operation."

Technology on the Move
"I've watched concrete pumping technology rapidly advance," says HFK owner Frank Kahn Sr., who started his Hollywood, Florida-based company with a trailer-mounted line pump 27 years ago. "With today's highly-developed equipment, the concrete pumps had the ideal combination of technological features to accomplish this job with greater efficiency than possible just a few years ago."

In fact, it was just a few years ago that Kahn Sr. moved most of his fleet north when Florida showed signs of a slowdown. Kahn Sr. remained in the sunshine state, but sent his young son Frank Jr. with three operators, four boom pumps and two City Pumps to a niche area in the Carolinas. Frank Jr. aggressively began promoting the company's new location by following ready-mix trucks to job sites and knocking on doors. Hard work paid off; and today, the North Carolina branch of the pumping company is known for tackling unique projects. Consequently, once HFK pumps the three-story lookout tower, which is expected to consume 1,500 cubic yards of concrete, their involvement in the extraordinary project will be yet another challenging feat under their belt.

The Ultimate Test
As December 21, 2012, approaches, it is impossible to know whether the varied interpretations of Nostradamus as well as the Mayan calendar and even biblical references will result in a 2012 Doomsday. However, if worldwide catastrophe does occur, the concrete's high strength qualities for this bunker may some day be put to the ultimate test for human survival.

A division of one of the world's most well-recognized and respected heavy equipment manufacturers, Putzmeister Concrete Pumps GmbH, Putzmeister America, Inc. manufactures a complete line of truck-mounted concrete boom pumps, separate placing booms, truck-mounted telescopic belt conveyors, and trailer-mounted concrete pumps as well as mortar, grout, shotcrete, plaster and fireproofing pumps and mixers, industrial pumps, tunneling machinery and pipeline systems. Some of the industry's best known brands such as Allentown Shotcrete Technology, Esser Pipe Technology, Thom-Katt, Powercreter and Telebelt are part of the Putzmeister America family. The company's workforce is dedicated to hands-on customer support and advancing the industry in design and technical innovation.

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