Change in the Latest 15 Years in Strength, Composition and Crack Behavior of Ultra High Strength Fiber Reinforced Concrete Used in Sakata-Mirai Footbridge

Abstract

 The use of ultra high strength fiber reinforced concrete (UFC) has been increasing since the publication of the recommendations on design and construction of UFC structures by the Japan Society of Civil Engineers in September 2004. UFC is a unique cementitious composite with a high tensile strength which enables concrete structure designs without reinforcing bars. Its durability is also very high compared to conventional concrete. UFC has been applied mainly to bridges, taking advantage of its high strength. Sakata-Mirai Footbridge completed in October 2002 was the first bridge in Japan constructed with UFC. In this paper, the durability and the mechanical properties of the 15 year old UFC bridge have been studied by using the specimens exposed to the field inside the box girder. The main results obtained are as follows: (1) The compressive strength of the field specimens has gradually increased until the age of 15 years; (2) The flexural strength of the field specimens has increased almost linearly until the age of 15 years; (3) Chloride penetration depth after 15 years of exposure was less than 3.0mm from the surface; and (4) Delayed reaction of unhydrated cement grains richly contained in UFC with external water allowed the initial cracks to close gradually.