ABSTRACT
Bridge maintenance in urban highway is becoming increasingly important due to increasing traffic volumes and heavier truck loads (Frangopol et al. 2007, Furuta et al. 2007). In Japan, many urban highway bridges have been constructed over the past 30 years and the reinforced concrete (RC) bridge decks have been severely damaged by fatigue. It is thought that overlaying the aging RC bridge decks with thin fiber reinforced concrete is one of the most effective repairing methods to increase the life-span of highway bridges (Detwiler et al. 1997). However, lots of problems exist to apply this method to urban highway RC bridge decks. For example, it is not allowed by nearby residents to compact overlay concrete with excessive vibration and noise at night. Additionally, it is known that shrinkage cracking which occurs in overlay concrete and debonding between overlay concrete and the existing concrete greatly influence to the durability of the repaired bridge deck. In this study, expansive ultra rapid hardening fiber reinforced concrete has been developed for solving these problems. Firstly, the fresh and hardened properties of this concrete are investigated. Next, the load-carrying capacities of RC members overlaid by this are evaluated. The required specifications and performances for this material are as follows; (1) Thickness of overlay is limited to 40 mm in comparison to the past, 60 mm, considering the composition of pavement and the anteroposterior level on the pavement. (2) Compressive strength of concrete at the age of 3 hours is satisfied with more than 24 MPa under sealed curing at 20C supposing to one overnight construction. (3) The consistency range in slump is within 5-15 cm, which is more workable than that of the existing one to enable to construct the concrete
overlay with low-noise. In order to compact this concrete, smaller and lighter concrete finisher equipped with high-frequency vibrator is being developed. The range of slump has been kept for at least 30 minutes after mixing. (4) Autogenous shrinkage can be remarkably compensated by the effect of expansive additive incorporated in concrete.
