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Dispersing Helix® in Concrete

Helix® has a natural tendency to clump or lock together during storage due to its twisted and square cross section. If clumps of fibers are added to concrete they will get coated with concrete and remain as clumps indefinitely. Even rapid and continuous mixing in the ready mix truck will not disperse the clumps.

Clumps of Helix® in the concrete can result in two problems:

  1. The concrete pump may get blocked;
  2. The dosage specified by the Engineer may not be achieved.

To prevent clumping and to ensure accurate dosage, Helix® must always be added at the ready mix plant according to the following method (works with both wet and dry batch plants):

Dry batch plant

Mixing Procedure for Ready Mix Plants (wet or dry)

Helix clumping will NEVER occur if the following procedure is rigorously followed:

  1. Add a minimum of 6% of the mix water (more water is better) into the drum, with the drum turning at charging speed;
  2. Dump all of the Helix® into the truck drum in one go, no need to slowly shake;
  3. Turn truck drum at charging speed for six minutes (as the clumps fall over the mixing fins they are broken up into 2D layers, with the water acting as a lubricant).
  4. Add the sand, aggregate and cement (or concrete for a wet batch) in the normal manner;
  5. Mix an additional 6 minutes to ensure the Helix is completely disbursed throughout the concrete.
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Pumping Helix®

Helix® fibers are 1" long and present minimal pumping resistance as long as the fibers are completely dispersed throughout the concrete without clumps.

A minimum 3" line should be used to pump Helix® reinforced concrete. A 2 1/2" diameter line end is not recommended.

Verification of Helix® Dosage

As Helix® is a structural fiber, it is important that the project engineer verify that the specified Helix® dosage is achieved and that the fibers are completely dispersed throughout the concrete. Tests can be made on fluid or cured concrete:

Fluid Concrete

In Canada the relevant test is CSA A23.2-16C "Standard test method for determination of steel fiber content in plastic concrete".

Three samples are taken from the concrete discharge at 25%, 50% and 75%. Each sample is of a specific volume (from 7 to 15 liters). The testing agency washes the cement fines from each sample and uses a magnet to separate the Helix® from the remaining aggregate. The fibers are dried and weighed, allowing the dosage to be calculated.

Cured Concrete

4" core samples are cut from the hardened concrete and sliced in two along the axis with a diamond saw. The number of fibers are counted on one face and this number can be used to calculate the dosage (contact Helix® for methodology).

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