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CFCC Slab, a precast PC floor system using carbon fibre composite cable

News International-French

3 May 2019

Tokyo Rope International and Oriental Shiraishi jointly developed a precast PC floor system – the CFCC Slab – using carbon fibre composite cable (CFCC).

To date, they have confirmed the product’s fatigue endurance and completed all tests regarding structural performance. Now they are at a stage where the system can be applied to actual bridges.

The use of precast PC floor systems for the construction of new, renovated floor slabs for steel bridges has been expanding recently to shorten the construction period or improve durability or productivity. The CFCC Slab, using carbon fibre composite cable (CFCC), which is a non-corrosive structural material, as a tendon, is a precast PC floor system prestressed in two directions. Adopting short fibre-reinforced concrete also made it possible to reduce reinforcements other than tendons and to reduce costs.

The CFCC Slab uses materials that have no deterioration effect when considering durability against salt damage as specified in road bridge standards. As CFCC does not corrode, there is no need to increase the cover thickness in environments subject to salt damage. Furthermore, although the previous solution used a continuous fibre tendon, the fixing part of the post-tensioning system was made of metal, while the CFCC Slab is a fixing structure that does not feature any metal when completed. Consequently, it is expected to be used in intense saline environments, for example near coasts or in areas where antifreeze agents are applied, where it will offer reliable durability and reduced lifecycle costs (LCC).

The CFCC Slab uses short fibre-reinforced concrete to reduce reinforcing materials such as rebar. Experiments confirmed that its bending fracture characteristics (yield strength and toughness) and punching shear strength are equivalent to those of two-way PC slabs using PC steel and rebar. Furthermore, the wheel load running fatigue test confirmed that even if loaded up to about 300 times – the index value equivalent to 100 years of service life – no destruction occurs.

The CFCC Slab also offers a weight reduction of about 6% for the same slab thickness, and the tendon can be placed in the vicinity of the composite girder’s slippage hole, where there is concern about the penetration of deterioration factors, and in the vicinity of drainage ditches. In addition, floor replacement work can be reduced by about 15% in floor renewal projects compared to general one-way PC floor systems. On the other hand, compared with one-direction PC floor slabs, the overall construction cost is increased by about 13 to 22% (compared to the salt damage area, bridge length 240m).

In the future, in addition to the construction and renewal of steel bridge floor slabs in Japan, the development of further technologies will be considered with a view to expanding in other countries, such as the USA, where the deterioration of infrastructure is also a problem.