Engineered cementitious composite

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ECC showing its flexibility

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

ECC, unlike common fiber reinforced concrete, is a micromechanically designed material. This means that the mechanical interactions between fiber, matrix and its interface are taken into account by a micromechanical model which calculates these constituent properties to a composite response. As a result, guidelines for selection of fiber, matrix and interface characteristics advantageous for composite properties are made available.

One of the most significant characteristics of ECC is its tensile strain hardening behavior with a strain capacity in the range of 3-7%. This 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, although the fiber content is typically less than 2% by volume. 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. ECC is made mainly of the same ingredients of regular concrete minus the coarse aggregate.

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. 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. Li, who holds appointments in the departments of civil engineering and environmental engineering and materials science and engineering, believes most of these problems have been addressed.

[edit] ECC compared to FRC and HPFRCC

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