The early work of the Pentagon Memorial design-build
team has focused on researching the fabrication and performance
criteria for the 184 Memorial Units that comprise the heart
of the memorial. Each Memorial Unit is a complex, yet elegantly
simple, element that performs several tasks and is several
things at the same time. It is an individual reflecting
pool of water that glows with light at night, the place
for the permanent inscription of each individual victim's
name and a place to sit and place mementos. Its slender
cantilevered form and the Memorial Unit's multidimensional
integrity are rooted in the fabrication of its cast metal
form.
The design-build team developed performance criteria for
the Memorial Unit to aid in determination of the appropriate
alloy to cast the benches. The criteria established the
need for a metal that would last a hundred years or more,
maintain structural integrity, and be compatible with other
park materials and the water circulation system. Requirements
for machinability, castability, and durability were also
determined.
Corrosion became one of the team's most critical concerns.
Based upon the original concept design, researchers began
a search for an aluminum alloy that led them to contact
Dr. Edgar A. Starke, Jr., Oglesby Professor of Materials
Science and Engineering and Director of the Light Metals
Center at University of Virginia's School of Engineering
and Applied Science. Dr. Starke and colleague Robert G.
Kelly, Associate Professor of Materials Science and Engineering
and Co-Director of UVA's Center for Electrochemical Science
and Engineering met with the team to discuss metal selection
and corrosion considerations. This workshop established
that aluminum could not meet the performance criteria, as
corrosion was inevitable. The team began intensive research
into stainless steel, titanium, and other metal options
that included literature searches, extensive interviews
with metals and corrosion experts and engineers, exhaustive
discussions with fabricators, and visits to three representative
foundries.
The research resulted in a decision by the design-build
team and representative family members of the victims to
produce the Memorial Units using a Super Duplex stainless
steel alloy with a high pit resistance equivalent (PRE).
The specific alloy is used extensively in offshore oil and
gas facilities and increasingly in naval applications as
it offers high strength and excellent corrosion resistance.
Notably, the metal was recently used in the restoration
of the Statue of Liberty, where constant exposure to salty
air had corroded the monument. While more expensive than
aluminum, it is significantly less expensive than titanium
and offers the life cycle cost benefit of a less intensive
maintenance regime. Critical to design performance, the
engineered alloy meets or exceeds the metal performance
criteria established for the specific application of the
Pentagon Memorial - a place designed for a lifetime.
