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