100% Positive Material Identification

Poster Session Scholars at TITANIUM EUROPE 2016 (continued)
reducing atmosphere or acid deaerated
environments) instead of more expensive
alloys.
Anodic oxidation of titanium
produces a compact, protective and
almost insulating oxide (mainly TiO2) on
titanium surface; this technique is fast,
easy and satisfactorily applied to other
metals so it represents the first natural
choice for this investigation.
In order to find the best anodizing
treatment three main parameters were
identified: anodizing electrolyte, applied
potential and anodizing current density.
The anodic oxidations were carried out in
H2SO4 (because of the wide knowledge
available on this electrolyte), and then
in Na2SO4, (NH4)2SO4 and NH4BF4,
trying to find a neutral electrolyte with
good oxide growth times. The applied
potential is directly linked to the final
thickness of the oxide obtained. A
higher potential produces thicker film
that is expected to behave better from
the corrosion point of view, but leads to
oxide crystallization that is known to be
detrimental. Thus, in order to investigate
a proper range and to avoid conditions
of difficult industrial implementation,
the potentials were kept from 10V to
80V. Anodizing current density was also
expected to have effects on crystallization
of the oxide, a current density of 20 mA/
cm2 was taken as a reference but also 5
mA/cm2 and 50 mA/cm2 were analyzed.
All the surfaces finishing obtained
were tested with potentio-dynamics
analyses carried out in different
electrolytes. NaCl35 g/L was initially
chosen for the common use of titanium
in marine environment; then, in order
to simulate more severe industrial
environment, after a screening on
different concentration from 1 g/L to 35
g/L, the electrolyte was substituted with
NaF3.5 g/L.
The results obtained so far don’t
highlight any preferable treatment. Each
anodizing sample provided insulation
and the consequent lower current density
circulating during the potentio-dynamic
tests. The results concentrate in the
region corresponding to a current density
one order of magnitude lower than the
one circulating in non-treated samples,
and didn’t show any better or more
reliable behavior with respect neither of
used electrolyte nor of applied potential
or current density.
For economical reason and a better
applicability, the suggestion is to apply
a treatment at low potential (10-20V)
and to perform it in Na2SO4, which is
the cheapest and easier to handle tested
electrolyte. Further investigation is
required: alloyed titanium is often used
to control localized corrosion and this
form of attack will be the next method
to distinguish the best of the available
treatment.
Jonathan Knudtsen, Oregon State
University Civil and Construction
Engineering, Corvallis, OR
Knudtsen received his bachelor of
science degree in Civil Engineering from
the Colorado School of Mines in Golden,
CO. He is currently working towards his
master of science degree in Structural
Engineering at Oregon State University.
His research is focused on the use of
titanium for strengthening concrete
bridge girders deficient in shear. His
advisor is Dr. Chris Higgins.
Abstract:
Aging and obsolete infrastructure has
become a major problem throughout
the world. This is particularly evident
in the case of concrete bridges. The cost
of completely replacing these bridges is
often prohibitive, meaning engineers
must find ways to strengthen them.
Many older bridges predate our modern
understanding of shear in bridge girders,
and were thus built with insufficient
internal stirrups. These bridge girders
often display diagonal tension cracks in
the high-shear zones near the columns.
One method commonly used to
strengthen these bridge girders is called
near-surface mounting (NSM), which
involves epoxying bars into vertical
grooves cut on the surface of the girder.
Although this method was first
developed for use with steel bars, it is
now most commonly implemented using
carbon fiber rods, due to steel’s corrosive
properties. The goal of this research is to
establish titanium as a viable alternative
to steel and carbon fiber for NSM shear
strengthening applications.
Titanium has several advantages over
the other materials. It’s noncorrosive,
so it does not need to be protected like
steel. Titanium bars can easily be bent
at the ends to provide anchorage. This is
titanium’s main advantage over carbon
fiber, since carbon fiber rods cannot
be bent, and thus rely solely on epoxy
for shear transfer. This means that the
ultimate strength of carbon fiber is rarely
reached, making it an inefficient repair
material. Titanium’s low modulus of
elasticity allows for large deflections,
giving advance warning of impending
failure. Due to titanium’s high yield
strength, small diameter bars can be
used. This significantly reduces the
costs associated with time, labor, and
materials, resulting in an overall cost
savings when compared to other retrofit
materials.
For this research program, seven
realistically proportioned T-shaped
concrete girders were constructed.
These girders were intentionally underdesigned
to force diagonal tension failure,
even after being strengthened with NSM
titanium bars. The girders were tested
in four-point bending. Failure occurred
when the titanium bars ruptured at the
main diagonal tension crack, meaning
their full strength was achieved. This
indicates that the method used is highly
efficient. To date, four of the seven girders
have been tested. Research is ongoing on
the effects of fatigue loading and harsh
environmental conditions.
Our research has conclusively
demonstrated the effectiveness of NSM
titanium bars in shear strengthening
applications. Titanium has many
advantages, including cost, over the
methods and materials currently used,
and we expect to see it established as a
viable repair option for bridges.
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