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ECC, short for Engineered Cementitious Composites, is an ultra ductile mortar based composite reinforced with short random fibers. ECC, unlike common fiber reinforced concrete, is a micromechanically designed material. This means that the mechanical interactions between fiber, matrix and interface are taken into account by a micromechanical model which relates these constituent properties to composite response. As a result, guidelines for selection of fiber, matrix and interface characteristics advantageous for composite properties are made available.
Macroscopically, the most significant characteristics of ECC is its tensile strain-hardening behavior with strain capacity in the range of 3-7%, yet the fiber content is typically less than 2% by volume. The ultra high-ductility is achieved by optimizing the microstructure of the composite employing micromechanical models. A typical direct tensile stress-strain curve of an ECC reinforced with 2% of PVA fiber is shown in Figure 1. During strain-hardening, multiple microcracks limited to about 60 mm in crack-width form along the length of the tensile specimen. Figure 2 shows the ductile behavior of ECC under flexural load. ECC may be regarded as an optimized high performance fiber reinforced cementitious composite (HPFRC).
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Figure 1. Tensile Stress-Strain curve of an ECC material with 2% fiber
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Figure 2: ECC specimen tested under bending load showing ductile behavior
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The ECC Technology Network is a group of organizations involved in the research , development and commercialization of ECC materials and applications. They include academic, industrial and governmental organizations in Asia, Europe and the United States. Industrial organizations are involved in a broad range of concerns, including basic material supplier such as fiber manufacturers, concrete product producers, and design/construction firms. The purpose of this network is to create a platform of knowledge and technology exchange between members of the network, as well as to allow other interested parties to participate in ECC Technology R&D with the latest information. An ultimate goal of ECC Technology is to enhance the health of our civil infrastructures and to mitigate natural hazards such as earthquakes.
A comparison between ECC, FRC and HPFRC is given in the Table below.
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FRC |
Common HPFRC |
ECC |
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Design Methodology
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N.A. |
Use high Vf |
Micromechanics based, minimize Vf for cost and processability
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Fiber
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Any type, Vf usually less than 2%; df for steel ~ 500 mm
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Mostly steel, Vf usually > 5%; df ~ 150 mm |
Tailored, currently polymer fibers most suitable, Vf usually less than 2%; df < 50 mm |
| Matrix |
Coarse aggregates used |
Fine aggregates used |
Controlled for matrix toughness and initial flaw size; fine sand used |
| Interface |
Not controlled |
Not controlled |
Chemical and frictional bonds controlled for bridging properties
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Mechanical
Properties:
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Tensile strain
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Crack width
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Strain-softening:
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0.1%
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Unlimited
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Strain-hardening:
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< 1.5%
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Typically several
hundred mm,
unlimited beyond
1.5% strain
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Strain-hardening:
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>3%; 8% demonstrated
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Typically < 100 mm
during strain-
hardening
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