Conventional fiber reinforced concrete, sometimes called FRC, is concrete that has been strengthened by adding shreds of other materials to the wet mix. Concrete is quite brittle; it has very good compressive strength but comparatively little tensile strength, which makes it likely to crack under many conditions. This leads to further damage. Concrete that is reinforced 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 into mud bricks and horsehair included in mortar. In the early years of the 20th century, asbestos fibers were added to concrete. By the 1960s a variety of materials, such as polypropylene, glass, and steel fibers, were used.
Current research suggests that microfibers, rather than long fibers, best increase tensile strength. Adding these fibers causes relatively little improvement in impact resistance, however. Polypropylene fibers reduce damage from freeze-thaw cycles and reduce the chances of spalling or explosion if there is a fire. Cellulose fibers from genetically modified pine trees have also shown promise in testing.
Glass fiber reinforced concrete, which contains alkali-resistant glass fibers, is especially resistant to ordinary deterioration caused by environmental conditions. It is also an ecologically friendly material because the glass fibers are made from natural materials and take comparatively little energy to produce.
This form of concrete is commonly used at ground level for things like pavements and floors. It can also be used in foundations, pillars, precast forms, and beams, especially in combination with traditional reinforcements like rebar or steel mesh.
The most recent research in fiber reinforced concrete has been in the development of engineered cement composites (ECC). These composites are flexible, both because of the fiber included and because of 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 subject to cracking. It has been used for construction in Japan, Korea, Switzerland, Australia, and the U.S.