CONCRETE - Stevens Institute of Technology

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CONCRETE
What is it good for?
Prepared and Presented by Mauricio Campuzano
GK-12 Fellow
Stevens Institute of Technology
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Concrete: “A strong, hard, building material composed of sand and
gravel and cement and water”
In 1824, English inventor, Joseph Aspdin invented Portland Cement
H20 (l)
Paste
Cement
Concrete
Gravel/
Aggregates
Admixtures
What is it?
Crushed
Stone
Calcium
Silicate, 90%
Corrective
minerals
Calcium
sulfate
(CaSO4)
Sand
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• Oldest known concrete found in Egyptian pyramids
(~500BC)
• Romans also used a form of concrete
• The dome of the Pantheon is 4,535 metric tons of concrete!
Ancient Concrete
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• Additives in Opus caementicium (a.k.a Roman
Concrete)
• Volcanic ash allowed concrete to set under water
• Horse hair made the mixture less likely to crack
during hardening
• Blood was added to strengthen the concrete against
frost
More Ancient Stuff
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• Water and cement combine in a process called hydration,
Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2
• “Inorganic
chemical reaction
where water adds to
the crystal structure of a mineral, usually
creating a new mineral.”
• Cement paste coats & binds
the aggregate; 90% cured by ~ 3 wks.
• Not enough paste:
• Produce rough, honeycombed
surfaces and porous concrete
• Too much paste:
• Produce a smooth surface, but resulting concrete is likely to
shrink more and be uneconomical
How Does it Work?
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• “Weight” Classification
• Lightweight, < 1800 kg/m3
• Normal-weight, 2400 kg/m3
• Heavyweight, > 3200 kg/m3
• Prestressed concrete
• Precast concrete
• Reinforced concrete
Types of Concrete
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• Added before or during mixing of cement, water, and
aggregates to enhance one or more aspects of
concrete
• Air-entraining:
increases durability
& workability
• Water-reducing: more
consistent setting-time
• Retarding: Speed up
hydration; used to counteract
the accelerating effect of hot
weather on concrete
• Accelerating: Slow down hydration; reduce the time
required for proper curing and protection, and speed
up the start of finishing operations. Particularly useful
in cold weather
• Plasticizers: increase the workability of plastic or
"fresh" concrete
• Others include Pigments, Corrosion-inhibitors
Admixtures
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• Developed in the late 19th century to overcome
problems of sheer stresses/strains
• Concrete is strong in compression, but weak with
tension
• Reinforced concrete solves this
problem by adding either steel
reinforcing bars,
steel fibers,
glass fiber, or
plastic fiber to
carry tensile
loads.
Reinforced Concrete
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Reinforced Concrete
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• Everywhere!
• “Concrete can be cast in almost any shape
desired, and once hardened, can become a
structural (load bearing) element.”
• Used in roads, tunnels, sewers, building, etc.
Where is it?
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• LiTraCon
• “light transmitting concrete,” this is a translucent
concrete
• Developed in 2001 by Áron Losonczi in collaboration
with scientists as the technical University of Budapest
• Made of fine concrete embedded with optical glass
fibers
Advances in Concrete
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• Carbon Nano-fiber Reinforced Concrete
• Scientists are looking to embed these fibers in
concrete to strengthen concrete, limit cracks
• CNFs and CNTs are amongst the strongest and
stiffest materials known
Advances in Concrete
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http://en.wikipedia.org
http://www.cement.org/basics
http://www.fhwa.dot.gov/infrastructure/materialsgrp/
http://arch.umd.edu/Tech/Tech_III/Lectures/Concrete_Constru
ction.pdf
http://www.azonano.com/default.asp
http://www.litracon.hu/
http://rip.trb.org/browse/dproject.asp?n=20258
http://web.mit.edu/newsoffice/2007/concrete.html
References
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