Engineered Cementitious Composite
Encyclopedia
Engineered Cementitious Composite (ECC), also called bendable concrete, is an easily molded mortar
-based composite reinforced with specially selected short random fibers, usually polymer
fibers. Unlike regular concrete
, ECC has a strain capacity in the range of 3–7%, compared to 0.1 % for ordinary portland cement (OPC). ECC therefore acts more like a ductile metal
than a brittle glass
(as does OPC), leading to a wide variety of applications.
, is a micromechanically
designed material. This means that the mechanical interactions between ECC's fiber and matrix are described by a micromechanical model, which takes into account material properties and helps predict properties and guide ECC development.
ECC looks similar to ordinary portland cement-based concrete, except that it does not include coarse aggregate and can deform (or bend) under strain. A number of research groups are developing ECC science, including those at the University of Michigan
, Delft University of Technology
, the University of Tokyo
, the Czech Technical University, and Stanford University
. Traditional concrete’s lack of durability and failure under strain, both stemming from brittle behavior, have been a pushing factor in the development of ECC.
, ease of processing on par with conventional cement, the use of only a small volume fraction of fibers (~ 2 %), tight crack width, and a lack of anisotropically weak planes. These properties are due largely to the interaction between the fibers and cementing matrix, which can be custom-tailored through micromechanics design. Essentially, the fibers create many microcracks with a very specific width, rather than a few very large cracks (as in conventional concrete.) This allows ECC to deform without catastrophic failure.
This microcracking behavior leads to superior corrosion
resistance (the cracks are so small and numerous that it is difficult for aggressive media to penetrate and attack the reinforcing steel) as well as to self-healing. In the presence of water (during a rainstorm, for instance) unreacted cement particles recently exposed due to cracking hydrate and form a number of products (Calcium Silicate Hydrate
, calcite
, etc.) that expand and fill in the crack. These products appear as a white ‘scar’ material filling in the crack. This self-healing behavior not only seals the crack to prevent transport of fluids, but mechanical properties are regained. This self-healing has been observed in a variety of conventional cement and concretes; however, above a certain crack width self healing becomes less effective. It is the tightly controlled crack widths seen in ECC that ensure all cracks thoroughly heal when exposed to the natural environment.
When combined with a more conductive material (metal wires, carbon nanotubes, etc.) all cement materials can increase and be used for damage-sensing. This is essentially based on the fact that conductivity will change as damage occurs; the addition of conductive material is meant to raise the conductivity to a level where such changes will be easily identified. Though not a material property of ECC itself, conductive ECC for damage-sensing applications are being developed by a number of research groups.
Note: FRC=Fiber-Reinforced Cement. HPFRCC=High-Performance Fiber Reinforced Cementitious Composites
Mortar (masonry)
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
-based composite reinforced with specially selected short random fibers, usually polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
fibers. Unlike regular concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
, ECC has a strain capacity in the range of 3–7%, compared to 0.1 % for ordinary portland cement (OPC). ECC therefore acts more like a ductile metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
than a brittle glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
(as does OPC), leading to a wide variety of applications.
Development
ECC, unlike common fiber reinforced concreteFiber reinforced concrete
Fiber-reinforced concrete is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers...
, is a micromechanically
Microelectromechanical systems
Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...
designed material. This means that the mechanical interactions between ECC's fiber and matrix are described by a micromechanical model, which takes into account material properties and helps predict properties and guide ECC development.
ECC looks similar to ordinary portland cement-based concrete, except that it does not include coarse aggregate and can deform (or bend) under strain. A number of research groups are developing ECC science, including those at the University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
, Delft University of Technology
Delft University of Technology
Delft University of Technology , also known as TU Delft, is the largest and oldest Dutch public technical university, located in Delft, Netherlands...
, the University of Tokyo
University of Tokyo
, abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is considered to be the most prestigious university...
, the Czech Technical University, and Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
. Traditional concrete’s lack of durability and failure under strain, both stemming from brittle behavior, have been a pushing factor in the development of ECC.
Properties
ECC has a variety of unique properties, including tensile properties superior to other fiber-reinforced compositesFiber reinforced composite
A fiber-reinforced composite consists of three components: the fibers as the discontinuous or dispersed phase, the matrix as the continuous phase, and the fine interphase region, also known as the interface. This is a type of advanced composite group, which makes use of rice husk, rice hull,...
, ease of processing on par with conventional cement, the use of only a small volume fraction of fibers (~ 2 %), tight crack width, and a lack of anisotropically weak planes. These properties are due largely to the interaction between the fibers and cementing matrix, which can be custom-tailored through micromechanics design. Essentially, the fibers create many microcracks with a very specific width, rather than a few very large cracks (as in conventional concrete.) This allows ECC to deform without catastrophic failure.
This microcracking behavior leads to superior corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
resistance (the cracks are so small and numerous that it is difficult for aggressive media to penetrate and attack the reinforcing steel) as well as to self-healing. In the presence of water (during a rainstorm, for instance) unreacted cement particles recently exposed due to cracking hydrate and form a number of products (Calcium Silicate Hydrate
Calcium silicate hydrate
Calcium Silicate Hydrate is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials.-Preparation:...
, calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
, etc.) that expand and fill in the crack. These products appear as a white ‘scar’ material filling in the crack. This self-healing behavior not only seals the crack to prevent transport of fluids, but mechanical properties are regained. This self-healing has been observed in a variety of conventional cement and concretes; however, above a certain crack width self healing becomes less effective. It is the tightly controlled crack widths seen in ECC that ensure all cracks thoroughly heal when exposed to the natural environment.
When combined with a more conductive material (metal wires, carbon nanotubes, etc.) all cement materials can increase and be used for damage-sensing. This is essentially based on the fact that conductivity will change as damage occurs; the addition of conductive material is meant to raise the conductivity to a level where such changes will be easily identified. Though not a material property of ECC itself, conductive ECC for damage-sensing applications are being developed by a number of research groups.
Types
There are a number of different varieties of ECC, including:- Lightweight (i.e. low density) ECC have been developed through the addition of air voids, glass bubbles, polymer spheres, and/or lightweight aggregate. Compared to other lightweight cements, lightweight ECC has superior compressive and tensile strength, crack-width control, and damage tolerance. Applications include floating homes, barges, and canoes.
- ‘Self compacting concrete’ refers to a concreteConcreteConcrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
that can flow under its own weight. For instance, a self-compacting material would be able to fill a mold containing elaborate pre-positioned steel reinforcement without the need of vibration or shaking to ensure even distribution. Self-compacting ECC was developed through the use of chemical admixtures to decrease viscosity and through controlling particle interactions with mix proportioning.
- Sprayable ECC, which can be pneumatically sprayed from a hose, have been developed by using various superplasticizing agents and viscosity-reducing admixtures. Compared to other sprayable fiber-reinforced compositesFiber reinforced compositeA fiber-reinforced composite consists of three components: the fibers as the discontinuous or dispersed phase, the matrix as the continuous phase, and the fine interphase region, also known as the interface. This is a type of advanced composite group, which makes use of rice husk, rice hull,...
, sprayable ECC has enhanced pumpability in addition to its unique mechanical properties. Sprayable ECC has been used for retrofitting/repair work and tunnel/sewer linings.
- An extrudable ECC for use in the extrusion of pipes was first developed in 1998. Extruded ECC pipes have both higher load capacity and higher deformability than any other extruded fiber-reinforced composite pipes.
Field Applications
ECC have found use in a number of large-scale applications in Japan, Korea, Switzerland, Australia and the U.S.[3]. These include:- The Mitaka Dam near HiroshimaHiroshimais the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
was repaired using ECC in 2003. The surface of the then 60-year old dam was severely damaged, showing evidence of cracks, spalling, and some water leakage. A 20 mm-thick layer of ECC was applied by spraying over the 600 m2 surface.
- Also in 2003, an earth retaining wall in Gifu, Japan, was repaired using ECC. Ordinary portland cementPortland cementPortland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
could not be used due to the severity of the cracking in the original structure, which would have caused reflective cracking. ECC was intended to minimize this danger; after one year only microcracks of tolerable width were observed.
- The 95 m (312 ft.) Glorio Roppongi high-rise apartment building in TokyoTokyo, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
contains a total of 54 ECC coupling beams (2 per story) intended to mitigate earthquake damage. The properties of ECC (high damage tolerance, high energy absorption, and ability to deform under shear) give it superior properties in seismic resistance applications when compared to ordinary portland cementPortland cementPortland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
. Similar structures include the 41-story Nabeaure Yokohama Tower (4 coupling beams per floor.)
- The 1 km (0.621372736649807 mi) long Mihara Bridge in HokkaidoHokkaido, formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island; it is also the largest and northernmost of Japan's 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaido from Honshu, although the two islands are connected by the underwater railway Seikan Tunnel...
, Japan was opened to traffic in 2005. The steel-reinforced road bed contains nearly 800 m3 of ECC material. The tensile ductility and tight crack control behavior of ECC led to a 40 % reduction in material used during construction.
- Similarly, a 225-mm thick ECC bridge deck on interstate 94 in MichiganMichiganMichigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
was completed in 2005. 30 m3 of material was used, delivered on-site in standard mixing trucks. Due to the unique mechanical properties of ECC, this deck also used less material than a proposed deck made of ordinary portland cement. Both the University of MichiganUniversity of MichiganThe University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
and the Michigan Department of TransportationMichigan Department of TransportationThe Michigan Department of Transportation is a constitutional government agency in the US state of Michigan. The primary purpose of MDOT is to maintain the Michigan State Trunkline Highway System which includes all Interstate, US and state highways in Michigan with the exception of the Mackinac...
are monitoring the bridge in an attempt to verify the theoretical superior durability of ECC; after 4 years of monitoring, performance remained undiminished.
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 |
Note: FRC=Fiber-Reinforced Cement. HPFRCC=High-Performance Fiber Reinforced Cementitious Composites