CONCRETE - Stevens Institute of Technology

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29 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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CONCRETE

What is it good for?

Prepared and Presented by Mauricio Campuzano

GK
-
12 Fellow

Stevens Institute of Technology

1

What is it?

Concrete
: “A strong, hard,
building material composed of sand and
gravel and cement and
water”


In
1824, English inventor, Joseph
Aspdin

invented Portland Cement


Concrete

Paste

H
2
0 (l)

Cement

Calcium
Silicate, 90%

Corrective
minerals

Calcium
sulfate
(CaSO
4
)

Aggregates

Gravel/

Crushed
Stone

Sand

Admixtures

2

Ancient Concrete


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!


3

More Ancient Stuff


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

4

How Does it Work?


Water and cement combine in a process called
hydration,
Ca
3
SiO
5

+ H
2
O


(CaO)∙(SiO
2
)∙(H
2
O)(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



Cement

Aggregate

Air

Concrete

H
2
0

Cement

Paste

5

Types of Concrete


“Weight” Classification


Lightweight, < 1800
kg/m
3


Normal
-
weight, 2400
kg/m
3


Heavyweight, > 3200
kg/m
3


Prestressed

concrete


Precast concrete


Reinforced concrete

6

Admixtures


Added before or during mixing of cement, water, and
aggregates to enhance one or more aspects of
concrete


Air
-
entraining
:

increases durability

& workability


W
ater
-
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

7

Reinforced Concrete



Developed in the late 19
th

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.

8

Reinforced Concrete

9

Where is it?


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.


10

Advances in Concrete


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


11

Advances in Concrete


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



12

References



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

13