CONCRETE Prepared and Presented by Mauricio Campuzano GK-12 Fellow Stevens Institute of Technology What is it good for?
Concrete: “A strong, hard, building material composed of sand and gravel and cement and water” In 1824, English inventor, Joseph Aspdin invented Portland Cement What is it?
Oldest known concrete found in Egyptian pyramids (~500BC) • Romans also used a form of concrete • The dome of the Pantheon is 4,535metric tons of concrete! Ancient Concrete
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
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 How Does it Work?
“Weight” Classification • Lightweight, < 1800 kg/m3 • Normal-weight, 2400 kg/m3 • Heavyweight, > 3200 kg/m3 • Prestressed concrete • Precast concrete • Reinforced concrete Types of Concrete
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
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
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?
LiTraCon • “light transmitting concrete,” this is a translucent concrete • Developed in 2001 by ÁronLosoncziin collaboration with scientists as the technical University of Budapest • Made of fine concrete embedded with optical glass fibers 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 Advances in Concrete
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 References