Why SRFC Is Important In Precast Elements

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Precast concrete products are susceptible to degradation because of sulphate attack, freeze-thaw cycling, alkali-silica reaction, and corrosion of embedded reinforcing bars, if present. In all these cases, permeability to water plays an important part. Durability of precast concrete products is therefore influenced by the rate at which water may enter. Results have indicated that permeability, in turn, depends largely on cracking in concrete, and an increase in the crack width will produce a highly permeable concrete. Fibre reinforcement improves crack resistance, increases the surface roughness of cracks, and prohibits multiple-crack development, thereby significantly reducing the permeability of concrete in service.
The Figure alongside shows a segmental tunnel lining using steel-fibre-reinforced concrete. Segmental tunnel linings are unique structures to design because of the many different loads they must resist. The segments are exposed to bending within a few hours of casting when they are removed from the production moulds and stacked in curing chambers. Within 24 hours after curing, the segments are stacked in matched rings on top of each other for storage. Double ring stacks can include as many as 14 individual segments weighing more than 50,000 lb (23 tonnes). The segments are then transported to the jobsite, lowered into the tunnel, and placed into position with the tunnel-boring machine. Many segments are reinforced with only steel fibres but reinforcing bar can be used in addition if required to carry large moments. And the figure alongside shows railway track slabs for highspeed trains. The term track slab is used to describe non-ballasted track structures that may have combinations of concrete slab and ties used where strength and durability are required. Precast concrete track slabs for high speed passenger trains in Europe have used steel-fibre reinforced concrete in combination with traditional reinforcement to significantly reduce crack width and/ or the required
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amount of reinforcement leading to durability improvement. A reduction of reinforcing bar up to 50% is possible while keeping crack width constant. The quality of the structure is increased due to better material properties and workability. In addition, significant time savings can also be achieved. The figure alongside shows the precast concrete sewer pipes. Reinforcing precast concrete pipes using only steel fibre is economically advantageous for pipe diameters up to 36 in. (900 mm). Small pipes are almost impossible to reinforce properly with mesh. More efficient crack control is achieved using steel fibre-reinforced concrete than with mesh because the first crack load is increased with fibres and at maximum load the crack width is typically smaller than it is for traditional reinforcement at similar loads. Pipes have been reinforced with steel fibres in Europe for more than 15 years and are now being tested in the United States and Canada. The figure alongside shows precast concrete boundary wall panels reinforced with steel fibres. They are cast and installed vertically to form a continuous wall. These examples and many other products like drains and covers, manhole covers, crash barriers etc show that SFRC is used in a broad range of applications. Thus, care must be taken to suitably match the fibre with the intended purpose. In all cases, the chosen fibre provides select benefits that were not possible either with conventional reinforcement or with an alternate fibre system.
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