Abstract
The use of ultra high strength fiber reinforced concrete (UFC) has been increasing since the publication of recommendations on the design and construction of UFC structures by the Japan Society of Civil Engineers in September 2004. 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 has been mainly applied to bridges, taking advantage of its high strength. The Sakata-Mirai Footbridge was the first bridge of UFC in Japan completed in October 2002. In this paper, the durability and the mechanical properties of the ten year old UFC bridge have been studied by using exposed specimens from the girder and core test pieces from the web. The major results obtained are shown below. (1) The compressive strength of the field specimens showed a gradual increase until the age of 10 years. (2) The flexural strength of the field specimens showed an almost linear increase until the age of 10 years. (3) The chloride ion diffusion coefficient obtained from the field specimens was much lower than that of laboratory immersed specimens. (4) The chloride ion diffusion coefficient in the test cores was lower than that of the field exposed specimens from the girder. (5) Examination of the exposed specimens and core test pieces by scanning electron microscopy revealed the presence of many unhydrated cement particles. (6) These findings suggest that UFC footbridges can retain good condition and mechanical properties for at least ten years even against severe environments, thus verifying the sustainability of UFC structures for the period of ten years.
