| The “Green” movement
that has been gaining momentum over the past few years has led
to some new innovations in the manufacture of products and the
design of building systems. Building owners and architects who
want to achieve a LEED (Leadership in Energy and Environmental
Design) certification for their buildings have been searching
for more ways and means to score points in the certification
process.
As a result, new products are coming onto the
market. As an example, one that could have a significant impact
on the design of concrete structures introduces a material that
has been used in the aircraft industry for many years, high-strength
carbon fiber.
To understand how this material can be of use,
let me first give you a short lesson in how a common building
component, the concrete beam, works.
Imagine that you have a sponge that is one foot
long by 4 inches deep by 2 inches wide. This sponge has series
of parallel stripes painted on the 4 inch side of the sponge
with the stripes perpendicular to the long dimension of the
sponge.
Place something under the ends of the sponge
so that the sponge resembles a beam. Then place another object
on the center of the sponge “beam”. The sponge will deflect
down under the weight of the object, and when it does, the stripes
will get further apart at the bottom of the sponge, and closer
together at the top. The stripes get closer together at the
top because that part of the beam is in compression; the stripes
at the bottom of the beam get further apart because it is in
tension.
Concrete is very strong in compression, but
very weak in tension. Steel is very weak in compression, but
is very strong in tension. This is why concrete beams must be
reinforced with steel at the bottom of the beam, and the top
of the beam needs very little or no steel. Without the reinforcing,
the beam would simply break in half.
The problem is that both steel and concrete
are very heavy, so the amount of concrete and steel that are
used in structures increase exponentially with the height of
the structure.
The use of carbon fiber for the reinforcing
component instead of steel promises to reduce the size, and
thus the weight, of beams by as much as 66 percent. Considering
that concrete weighs 155 pounds per cubic foot, that is a significant
weight reduction. Reducing the size of the concrete beams reduces
the overall weight of the building, and that will lead to large
reductions in cost.
Another use for carbon fiber is in precast concrete
sandwich panels. These are composed of two thin concrete beams
with an insulating foam board between them. Typically, steel
rods are used to hold all three pieces together, but steel,
being a good conductor of cold and heat, serves as a “leak”
for energy by conducting energy through the panel. Carbon fibers
are not good conductors, so using carbon fibers instead of steel
means that no energy is leaked through the panel.
Environmentalists look at these kinds of innovations
for more than just the cost savings. Initially, they see a huge
reduction in the amount of energy it takes to manufacture the
concrete and the steel reinforcing rods. When the life of the
building is over, they also see a reduction in the amount of
energy required to demolish the concrete, as well as a reduction
in the amount of concrete debris that must be recycled or placed
into a landfill. Reducing the impact on the environment is their
goal, and the reduction of the amount of material and energy
usage fulfills that goal.
The question is, would we have come up with
these kinds of innovations without the environmental movement?
The Greek Philosopher Plato wrote in his dialogue, “Republic”,
“necessity is the mother of invention”. One of the great things
about capitalism (which many environmentalists despise) is that
competition, market demand, and economics encourages innovation.
To be competitive, it is necessary to be inventive.
The real question is, would the innovative use
of carbon fiber in concrete have come about without the environmental
movement? I think that the certain answer is yes, at least in
America and other capitalist countries it would.
The next obvious question is, if capitalistic
forces create innovation, then why do we need the environmental
movement at all?
The answer next week.
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