1

CONCRETEWhat is it good for?

Prepared and Presented by Mauricio CampuzanoGK-12 FellowStevens Institute of Technology

2What 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

H20 (l)

Cement

Calcium Silicate, 90%

Corrective minerals

Calcium sulfate (CaSO4)Aggregates

Gravel/Crushed Stone

SandAdmixtures

3Ancient 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!

4More 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

5How Does it Work?

• Water and cement combine in a process called hydration, Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2

• “Inorganic chemical reaction where water adds tothe 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

H20Ceme

nt Paste

6Types of Concrete

• “Weight” Classification• Lightweight, < 1800 kg/m3

• Normal-weight, 2400 kg/m3

• Heavyweight, > 3200 kg/m3

• Prestressed concrete• Precast concrete• Reinforced concrete

7Admixtures

• 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

8

Reinforced Concrete

• 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.

9

Reinforced Concrete

10Where 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.

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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

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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

13References

• 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_Construction.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