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Alcatraz
is one of the most famed tourist sites in the United States
and welcomes nearly 1.4 million visitors annually. “The
Rock” was made famous as a prison that was virtually
inescapable because of its remote location in the middle
of San Francisco Bay, and its notorious occupants, including
Al Capone, “Machine Gun” Kelly, and others.
Alcatraz Cellhouse, the most visited and prominent building
on Alcatraz Island, was also the largest reinforced concrete
building in the world at the time of its completion in
1912. It was reinforced with square and twisted reinforcing
steel, a style that was sometimes used in the early 20th
century concrete buildings.
Ironically, what made Alcatraz so famous and difficult
for prisoners to escape from was also the cause of its
demise. The cold salt waters of San Francisco Bay and
the windy conditions of the area caused airborne chlorides
to deposit themselves onto the concrete structures, and
after decades of exposure and neglect, ultimately penetrate
through the concrete to the steel reinforcement. In addition,
atmospheric carbon dioxide also caused the concrete to
become carbonated over the years, lowering its pH, and
causing corrosion of the reinforcing steel. The degradation
of the structures on Alcatraz Island, along with the high
operating costs of the prison, caused Alcatraz to shut
down as a penal institution in 1963.
Alcatraz was occupied by various groups over the next
decade with little attention made to maintenance or upkeep.
The structures continued to degrade, and chloride induced
corrosion caused the reinforcing steel to expand, cracking
and spalling the concrete. In 1972, Alcatraz Island was
turned over to the Golden Gate National Recreation Area.
However, due to limited funds from Congress to the National
Parks Service, another 30 years passed before any significant
rehabilitation program took place on Alcatraz. When money
finally became available, a major concrete repair and
seismic strengthening program was initiated.
This was an extremely challenging project for the contractor due to the remote location of the island and the fact that the facility remained open to tourists during construction. In addition, being a landmark building, the appearance of the Alcatraz Cellhouse could not significantly change, including details such as graffiti that were required to remain intact and pipes that could not be relocated.
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Owner
National Park Service
San Francisco, California
Project Engineer/
Designer
Wiss, Janney, Elstner Associates, Inc.
Emeryville, California
Repair Contractor
Watertight Restoration, Inc.
San Francisco, California
Material Supplier/
Manufacturer
Sika Corporation
Lyndhurst, Maryland
General Contractor
Miller/Watts Construction, Inc.
Richmond, California
Construction Manager
Parsons Brinckerhoff
San Francisco, California
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