The key feature of Helix® is the TWISTED profile. This drives the failure mechanism from a frictional mode to untwisting, setting Helix® apart from other fibers. Helix® behaves more like conventional steel reinforcement than other fibers because of this mechanism.
This 'untwisting' requires six times more pull out force compared with a non-twisted steel fiber of equivalent area. Furthermore Helix® maintains a constant resistance regardless of how far it has been untwisted. This differs from other fibers that fail when the cross sectional area is reduced as the fibers pull out of the concrete.
Furthermore the pull-out resistance of Helix® is not dependant on the inclination angle of the micro rebar with respect to a crack.
For more detailed technical information, go to the manufacturer's website: Polytorx LLC.
The graph to the right compares the stress strain curve of Helix® to conventional steel reinforcement. Note that with rebar the stress increases with minimal strain until the first dominant crack occurs (at about 120,000 kN). At this point there is a drop in stress, and a large increase in the strain (from 0% to approximately 5%), as the rebar engages and starts to resist the load.
Helix® begins to engage soon after loading as micro-cracks form in the concrete. This behaviour may be attributed to the short development length of Helix®: 1/4” compared with 24” for 15M rebar. Therefore the strain in the Helix® reinforced concrete can be seen to increase gradually with increasing stress. This improves the performance of the concrete and prevents the formation of a single dominant crack.
The bending moment capacity and shear strength of Helix® reinforced concrete is dependant on the dosage in the concrete. Dosage is measured in pounds per cubic yard or kilograms per cubic meter.
For example, consider a 6" thick concrete wall with #4 bar at 20" on center in both directions. Substituting a Helix® dosage of 20 lbs./yd3 will achieve:
The procedure for determining the correct dosage for your project is as follows:
Wicke Herfst Maver Consulting Inc. have been conducting due diligence on Helix® since late 2012, researching the many tests and corroborating with other engineers across North America. They are well qualified to answer any technical questions you may have. Call (604)484-2859 or visit www.whmengineers.com.