The rising cost of conventional steel reinforcement has dramatically increased the demand for synthetic, as well as steel, fibers as an alternative to wire mesh in shotcrete applications. More importantly, with the shift to the shotcrete industry is discovering that reinforcement yields significant economic advantages, as well as definite engineering benefits for long-term shotcrete durability.
Significant economic benefits result from the elimination of placing wire mesh. In addition, the use of fibrous reinforcement in lieu of wire mesh reduces rebound from the receiving face by up to 20%.
Suitable shotcrete applications include slope stabilization, tunnel liners and water diversion channels, structural repairs, swimming pools, arti-ficial rock, waterscapes, and thin overlays. These applications benefit from the three-dimensional network of reinforcement formed by the fibers, which reduces plastic shrinkage cracking and drying shrinkage cracking. The fibers also provide quanti-fiable toughness and enhanced durability, including increased surface abrasion resistance and impact resistance. Performance is predicated on the proper selection of the fiber type, length, configuration, and addition rate. Elimination of potential voids created by the wire mesh pattern is just one more advantage of using fiber.
General Product Information
There are three fiber types that contribute to the physical properties of shotcrete: steel fibers, micro- synthetic fibers, and macro-synthetic fibers.
Although the price of steel fibers has risen, the fact remains that the in-place cost of steel fiber-reinforced shotcrete is less than the cost of fixing and placing conventional steel. In general, steel fibers must meet the requirements of ASTM A 820 and may be manufactured from either drawn wire or slit sheet steel. Steel fibers, first introduced in the mid 1970s, are generally available in four lengths: 3/4, 1, 1-1/2, and 2 in. (20, 25, 38, and 50 mm). The standard unit of sale is typically 50 lb (22.7 kg) boxes or bags.
Micro-synthetic fibers can be nylon mono-filament or polypropylene monofilament and fibrillated fibers. They have been in use since the early 1980s for secondary temperature-shrinkage