Fiber-reinforced concrete (FRC) is concrete reinforced with other materials to increase tensile strength and reduce cracking. Microfibers are found to be the most effective, while polypropylene fibers reduce damage from freeze-thaw cycles and fires. Glass fiber reinforced concrete is environmentally friendly and resistant to deterioration. Engineered cementitious composites (ECC) are flexible and less prone to cracking. The University of Michigan developed a formula that weighs 40% less and is 500 times less prone to cracking, used for construction worldwide.
Conventional fiber-reinforced concrete, sometimes called FRC, is concrete that has been reinforced by adding fragments of other materials to the wet mix. Concrete is quite brittle; it has very good compressive strength but relatively low tensile strength, making it likely to crack under many conditions. This leads to further damage. Reinforced concrete is less likely to crack than standard concrete.
Using fibers to reinforce other materials is not a new idea. In fact it has been practiced for thousands of years, with straw mixed with mud bricks and horsehair included in the mortar. In the early 20th century, asbestos fibers were added to concrete. In the 1920s, a variety of materials were used, such as polypropylene, glass and steel fibers.
Current research suggests that microfibers, rather than long fibers, best increase tensile strength. However, the addition of these fibers results in a relatively small improvement in impact strength. Polypropylene fibers reduce damage from freeze-thaw cycles and reduce the chances of splintering or explosions in the event of a fire. Cellulose fibers from genetically engineered pine trees have also shown promise in tests.
Glass fiber reinforced concrete, which contains alkali resistant glass fibers, is particularly resistant to ordinary deterioration caused by environmental conditions. It is also an environmentally friendly material because glass fibers are made from natural materials and require relatively little energy to produce.
This form of concrete is commonly used at ground level for things like sidewalks and floors. It can also be used in foundations, pillars, precast formwork and beams, especially in combination with traditional reinforcement such as rebar or wire mesh.
The most recent research in fiber-reinforced concrete has involved the development of engineered cementitious composites (ECC). These composites are flexible, both for the fiber included, and for the materials that make up the concrete itself. The University of Michigan introduced a formula in 2005 that weighs 40% less than regular concrete and is 500 times less prone to cracking. It was used for construction in Japan, Korea, Switzerland, Australia and the United States
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