Transcript Document

The Future
FORWARD
THE FUTURE
Material properties, such as
corrosion resistance, fire
resistance and durability are
being continuously improved
and exploited.
These inherent qualities of
precast prestressed concrete
and its considerable design
flexibility also make it ideal
for a wide variety of other
applications: poles, piles,
culverts, storage tanks,
retaining walls, sound
barriers and even
railroad ties.
BACK
FORWARD
THE FUTURE
The benefits of High
Performance Concrete are
already beginning to be
applied. These include
reduced initial construction
costs that result from wider
girder spacing and longer
spans as well as reduced
long-term costs due to fewer
replacements and fewer
repairs. High Performance
Concrete is being increasingly
specified for the nation’s
bridges and structures.
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FORWARD
THE FUTURE
One form of HPC is high
strength concrete. A strength
of 14,000 psi was specified
here for the beams of the
Louetta Road Bridge, a
demonstration project,
located in Houston, Texas.
High strength concrete was
also used in this bridge for
the stay-in-place deck
panels, the cast-in-place
concrete deck and precast
segmental piers.
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FORWARD
THE FUTURE
The Giles Road Bridge in Sarpy
County, Nebraska also was
constructed using High Strength
Concrete. Completed in 1996,
it is another example of a
bridge with 12,000 to 14,000
psi concrete girders and a
5,000 to 8,000 psi concrete
deck. The Federal Highway
Administration, together with
PCI and several states,
continues to promote the use
of High Performance Concrete
in bridge applications. For the
precast industry, High
Performance Concrete often
involves higher than average
compressive strength.
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FORWARD
THE FUTURE
However, other factors, such as
low permeability and
resistance to freeze-thaw – not
just strength – may be features
of High Performance Concrete
depending on the geographic
location of the bridge and the
component for which it is used.
Lightweight aggregate concrete
with strengths in the 7,000 to
10,000 psi range is also being
used on some newer bridges.
Lightweight concrete provides
reduced dead-loads and
seismic forces.
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FORWARD
THE FUTURE
0.7"?
Corrosion-resistant coatings
Stainless-clad
Corrosion-resistant steel
BACK
Strands of larger diameters and
higher strengths are becoming
more common as higher
strength concretes are used
and the demand for higher
tensile force increases. When
0.6 inch diameter strands are
used in conjunction with high
strength concrete, in the
10,000 to 12,000 psi range,
standard I-beams and other
products are able to reach
significantly longer spans never
thought possible before. Even
larger and stronger strand are
on the horizon. Corrosionresistant steels and coatings
promise unlimited durability.
FORWARD
THE FUTURE
Nonmetallic reinforcement
such as glass, carbon and
aramid fiber composites will
be increasingly used for
special applications. A
recent demonstration project
has shown the compatibility
of carbon fiber strands for
prestressing a bridge girder.
Both, internally bonded
prestressing and external
unbonded prestressing
systems are used.
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FORWARD
THE FUTURE
Synthetic, organic and steel
fibers have been shown to
improve toughness and
shrinkage cracking. Recent
developments in high
performance fiber-reinforced
concrete hold promise in
terms of performance and
cost-effectiveness.
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FORWARD
THE FUTURE
Reinforcing steel corrosion
Degree of Corrosion
Migration of chlorides, H20
and O2 into the concrete, no
corrosion and no damage to
concrete
Corrosion of the steel
reinforcement and
cracking and/or spalling
of concrete
Initiation
Propagation
(corrosion)
Critical chloride
threshold
I
Time
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FORWARD
THE FUTURE
Corrosion mechanism of
steel
Corrosion Mechanisms Can be Minimized By
Avoiding Microgalvanic Cell Formation Present
in Conventional and Micro-Alloyed Steels
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FORWARD
THE FUTURE
MMFX is not a stainless steel
but Step 1 of its production
adds chromium and reduces
the carbon content.
Benefits of adding chromium
to reduce the steel’s
corrosion rate.
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FORWARD
THE FUTURE
1 – Untransformed Nano
Sheets of Austenite
The Second Step to
Achieving
Microstructure
Steel
1
MMFX approach to altering
the micro-structure of the
steel: Produce a
Microcomposite Steel that
Eliminates Formation of
Microstructural Galvanic
Cells
2
2
1
2
1
2
Prior
Austenite
Grain
Boundary
1
1
~ 0 .1  m
2
2–
Dislocated
Laths
(Martensite)
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FORWARD
THE FUTURE
Reinforcement
Type
Low
Cost
installation
High
Cost
installation
Chloride
Threshold
(lb/yd3)
Propagation
(years)
Black Steel
$0.38
$0.53
1
6
Epoxy Coated Steel
$0.50
$0.66
1
20
Stainless Steel
$2.75
$2.91
20
12
MMFX 2 Steel (4 X)
$0.70
$0.85
4
12
MMFX 2 Steel (6 X)
$0.70
$0.85
6
12
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FORWARD
THE FUTURE
Reinforcement Type
Installation
Cost
Initial
Cost
($/ft2)
Time to
Initiation
(Years)
Time to
First
Repair
(Years)
Total Life
Cycle
Cost
($/ft2)
MMFX 2 Steel (4 X)
HIGH
$15.01
90
>100
$15.01
MMFX 2 Steel (6 X)
HIGH
$15.01
>100
>100
$15.01
Epoxy Coated Steel
HIGH
$14.93
44
64
$19.02
Black Steel
HIGH
$14.42
44
50
$21.31
Stainless Steel
HIGH
$23.75
>100
>100
$23.75
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FORWARD
THE FUTURE
Self Consolidating concrete is
an extremely cohesive and
flowable material capable of
being placed without
vibration. It can be placed
very fast at a very dramatic
reduction in noise.
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FORWARD
THE FUTURE
The cohesion of the fresh
concrete and no negative
effects from vibration will
result in a more
homogeneous surface layer.
This reduces permeability,
increases resistance to
chloride ingress, carbonation
and other chemical attack
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FORWARD
THE FUTURE
Another development has been
the use of precast deck panels.
Used as stay-in-place forms,
the panels reduce labor for
field placement of reinforcing
steel and concrete for bridge
decks, resulting in considerable
savings. The panels become
composite with the fieldplaced concrete for live loads.
They’re made of high-quality,
plant-produced concrete and
contain the primary tensile
reinforcement between beams.
They remain crack-free,
protecting this important
reinforcing steel.
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FORWARD
THE FUTURE
Full-depth precast deck
panels promise to provide the
solution for extended closings
due to deck replacement.
The technique applies to new
construction as well. Precast
highway paving panels are
being demonstrated in Texas
to speed lane widenings and
reduce traffic closures and
detours. Refined materials
and methods are making
these solution an exciting
new part of the designers
tool box.
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FORWARD
THE FUTURE
Another innovation is the
development of horizontally
curved precast concrete
bridges which is creating
exciting new options in
contemporary bridge designs.
This technique involves posttensioning precast elements
together in the plants before
shipment or in the field
after erection.
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FORWARD
THE FUTURE
Spliced girders give
Prestressed concrete
girders the ability to
reach further and
longer
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FORWARD
THE FUTURE
And yet another solution for
curved structures is
segmental construction.
Working together with the
American Segmental Bridge
Institute (ASBI) and the
AASHTO Bridge
Subcommittee, PCI has
endorsed a family of standard
shapes for segmental bridges
that is intended to reduce
the cost of segmental bridges
for smaller structures such as
urban grade separations.
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FORWARD
THE FUTURE
Prestressed concrete got its
start as the original
composite material and
further developments by the
industry and its suppliers
have continued to refine the
performance of the product
for the bridge market.
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FORWARD
THE FUTURE
Today, it still gives the public
extremely good value for its
money. The reputation of
the precast prestressed
concrete industry has been
built on the strength,
imagination, consistency and
integrity of its people and
products alike. In the future,
it will continue to be the
solution of choice.
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FORWARD
Thank You for
Your Attention
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