Higher volume percentages 04 to 07 percent of fibers

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ume of relatively low modulus synthetic fibers. Higher volume percentages (0.4 to 0.7 percent) of fibers have been found to offer significant property enhancements to the SNFRC, mainly increased toughness after cracking and better crack distribution with reductions in crack width. Chapter 4 de- tails the current technological advancements in SNFRC in sep- arate sections that discuss each specific fiber material. As described in Chapter 5 , natural fiber reinforced con- cretes vary enormously in the sophistication by which they are manufactured. Treatment of the fibers also varies consid- erably. In less developed countries, fibers are used in a min- imally treated state. In more advanced countries, wood pulp fibers are used. These fibers have been extracted by an ad- vanced industrial process which significantly alters the char- acter of the fibers and makes them suitable for their end uses. 1.6—Applications As more experience is gained with SFRC, more applica- tions are accepted by the engineering community. ACI Com- mittee 318 “Building Code Requirements for Reinforced Concrete” does not yet recognize the enhancements that SFRC makes available to structural elements. As more expe- rience is gained and reported, more data will be available to contribute to the recognition of enhanced SFRC properties in this and other codes. The most significant properties of SFRC are the improved flexural toughness (such as the abil- ity to absorb energy after cracking), impact resistance, and flexural fatigue endurance. For this reason, SFRC has found many applications in flat slabs on grade where it is subject to high loads and impact. SFRC has also been used for numer- ous shotcrete applications for ground support, rock slope sta- bilization, tunneling, and repairs. It has also found applications in plant-produced products including concrete masonry crib elements for roof support in mines (to replace wood cribbing). SIFCON is being developed for military ap- plications such as hardened missile silos, and may be prom- ising in many public sector applications such as energy absorbing tanker docks. SFRC applications are further sum- marized in Chapter 2 . GFRC has been used extensively for architectural clad- ding panels due to its light weight, economy, and ability to be formed against vertical returns on mold surfaces without back forms. It has also been used for many plant manufac- tured products. Pre-packaged surface bonding products are used for dry stacked concrete masonry walls in housing ap- plications and for air-stoppage walls in mines. Chapter 3 dis- cusses the full range of GFRC applications. SNFRC has found its largest commercial uses to date in slabs on grade, floor slabs, and stay-in-place forms in multi-story buildings. Recent research in fibers and composites has opened up new possibilities for the use of synthetic fibers in construc- tion elements. Thin products produced with synthetic fibers can demonstrate high ductility while retaining integrity. Chapter 4 discusses applications of SNFRC for various fiber types.

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