CONCRETE REINFORCEMENT
Structural Synthetic F iber Reinforcement
by Matthew Maingay
March 31, 2004
Matthew Maingay is a civil engineer and director for Elastoplastic Concrete. He has been researching alternatives to steel reinforcing for the past 4 years.

Sharp price increases for steel reinforcing in the international market place have resulted in designers, contractors & builders looking for construction solutions that involve using less steel.

Market analysts point to extraordinary consumption of steel by China as reasons for the increased global prices. For example a supplier of steel market information, MEPS International reports price hikes between February 2003 and February 2004 as high as 65 percent in the North American market and the situation is similarly reported in Europe.


Fig #1 European Steel Prices

The market is so volatile at the moment that some steel suppliers are refusing to quote prices until time of delivery and worse still in some areas contractors are simply unable to acquire the steel they need for their projects and lengthy site delays and even complete standstills have been reported.

For those seeking alternatives to steel a solution may be found in innovation. Since 1997 Japanese construction companies have been using Structural synthetic fibres to replace steel mesh and steel fiber reinforcements and the technology has since spread into Australia, Europe and North America.

Originally conceived for the reinforcement of concrete pavements the fibres have also seen use in areas such as sprayed concrete linings in mines and tunnels, marine structures, housing construction and precast concrete.

‘the concrete is reinforced with approximately 1 million little reinforcing bars'


A big reason for the fibres acceptance is its ease of use, you can simply throw the bags into the truck mixer and the concrete is reinforced with approximately 1 million little reinforcing bars, thereby reducing labour costs and also alleviating health & safety issues surrounding the handling and placement of steel reinforcement products. Also the structural synthetics are corrosion free and have proved to outperform steel in long term durability tests on cracked concrete.

 

In the past there has been some negative publicity surrounding plastic fibers purportedly used in concrete for plastic shrinkage reinforcement but the technology surrounding the structural synthetics is quite different.

  
Fig #2 Magnified image of Synthetic Fibre

The post cracking performance of different reinforcements can be accurately compared using the ASTM C-1550 round panel test and indications are that the synthetic fibres can at least hold their own against conventional welded wire mesh or steel fiber and therefore rate as a suitable alternative for many reinforced concrete applications.

Of course the synthetic fibres can't solve every problem and you must do your engineering analysis. Whether or not the synthetic fibers can replace steel reinforcing is largely dependant on the size and spacing of the steel bars and the anticipated loading on the structure.

To compare reinforcements using the ASTM C-1550 round panel test concrete discs of 800mm diameter x 75mm thick are prepared using the different reinforcing materials.

Fig #3 Round Determinate Panel Test

The disc is then supported on 3 radial pivots inside the testing rig and a point load is applied at the centre of the round panel which travels through a total central deflection of 40mm and cracks the specimen.
The energy absorbed by the specimen is obtained as the area under the load-deflection curve.

The load-deflection response typical of panels reinforced with steel mesh, steel fibre and BarChip Structural Synthetic fibre is shown below.

Fig #4 Load vs Displacement graph

Some recent projects using structural synthetic fibre include:

  • Sydney 2000 Olympic whitewater course, AUSTRALIA
  • CSO tunnel Rhode Island, USA
  • Oslo Opera House, NORWAY

    • For more information: www.elastoplastic.com