Abstract
The use of ultra high strength fiber reinforced concrete (UFC) with increased tensile strength has been increasing since the publication of recommendations on design and construction of UFC structures by the Japan Society of Civil Engineers (JSCE). UFC is a unique cementitious composite with high tensile strength which enables concrete structure designs without reinforcing bars. Its durability is also very high compared to conventional concrete. UFC is prepared by mixing pre-mix powder with water and superplasticizer and dispersing short fibers in the mixture. The pre-mix powder consists of cement, silica fume, silica fine powder, silica sand and other materials in the optimum proportion. The standard formulation contains short steel fibers (with a diameter of 0.2mm and a length of 15mm) of 2 volume % mixture.
One of the common problems found with UFC is surface contamination induced by corrosion of the exposed steel fibers on the surface. Corrosion may also occur on steel fibers when they bridge cracks, if present, inside the UFC. In order to provide a solution to this problem, the authors investigated applicability of corrosion-resistant organic fibers with extremely high strength and elasticity, including twisted poly-p-phenylenebenzobisoxazole (PBO) fiber bundles.
The important findings in this study were as follows: (1) tensile and flexural strengths of UFC were increased by using twisted PBO fiber bundles; (2) shrinkage behavior of UFC containing twisted PBO fiber bundles was the same as that of UFC containing steel fibers; and (3) fracture energy and abrasion resistance of UFC were slightly decreased by using twisted PBO fiber bundles.
