1. CONCRETE What is it good for? Prepared and Presented by Mauricio Campuzano GK-12 Fellow Stevens Institute of Technology 1

2. 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 PasteH20 (l)Cement Calcium Silicate, 90% Corrective minerals Calcium sulfate (CaSO4) Aggregates Gravel/ Crushed Stone SandAdmixtures 2

3. 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

4. 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

5. 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 5

6. 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

7. Admixtures 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 7

8. 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

9. Reinforced Concrete 9

10. 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

11. 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

12. 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

13. 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://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