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Engineered cementitious composite



Engineered Cementitious Composite, (ECC) is an easily molded and shaped mortar based composite reinforced with short random fibers,[1] usually polymer fibers.

ECC, unlike common fiber reinforced concrete, is a micromechanically designed material. This means that the mechanical interactions between ECC's fiber, and matrix are taken into account by a micromechanical model which calculates these elemental properties into a strong and flexible composite material.[1] As a result, guidelines for the selection of fiber, matrix and interface characteristics advantageous to creating ECC, such as the use of polymer fibers instead of pumice, steel or clay become available.

ECC's tensile strain hardening behavior has a capacity in the range of 3-7%,[1] which means that unlike common concrete, which is brittle and breaks under that amount of strain, ECC will bend under the same stress, like a piece of sheet metal. The high ductility is achieved by optimizing the microstructure of the composite employing micromechanical models. ECC looks exactly like regular concrete, but under excessive strain, the ECC concrete bends because the distinctively coated matrix of fibers in the cement is allowed to slide within the cement.[2] ECC is made using the same ingredients of regular concrete but without the use of coarse aggregate.[2]

The University of Michigan has a research team whose ECC technology has been used on projects in Japan, Korea, Switzerland, Australia and the U.S.[2] It has had a relatively slow adoption in the U.S. according to Professor Victor C. Li, who is the leader of U-M’s research team that is developing its own ECC. Traditional concrete's many problems: lack of durability, failure under severe strain, and the resulting expenses of repair, have been a pushing factor in the devolpment of ECC.[2]

Comparison to other composite materials

Properties FRC Common HPFRCC ECC
Design Methodology N.A. Use high Vf Micromechanics based, minimize Vf for cost and processibility
Fiber Any type, Vf usually less than 2%; df for steel ~ 500 micrometre Mostly steel, Vf usually > 5%; df ~ 150 micrometre Tailored, polymer fibers, Vf usually less than 2%; df < 50 micrometre
Matrix Coarse aggregates Fine aggregates Controlled for matrix toughness, flaw size; fine sand
Interface Not controlled Not controlled Chemical and frictional bonds controlled for bridging properties
Mechanical Properties Strain-softening: Strain-hardening: Strain-hardening:
Tensile strain 0.1% <1.5% >3% (typical); 8% max
Crack width Unlimited Typically several hundred micrometres, unlimited beyond 1.5% strain Typically < 100 micrometres during strain-hardening[1]

Note: FRC=Fiber-Reinforced Cement. HPFRCC=High-Performance Fiber Reinforced Cementitious Composites

See also

References

  1. ^ a b c d A brief introduction to ECC and ECC technology network. Engineeredcomposites.com. Retrieved on 2007-11-03.
  2. ^ a b c d U-M researchers make bendable concrete. Umich.edu. Retrieved on 2007-11-03.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Engineered_cementitious_composite". A list of authors is available in Wikipedia.
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