Q. When is the best time to introduce the bags of fiber to a transit mixer?
There is no single right way to introduce the bags of fiber to the transit mixer. The important element to success is to consistently introduce the bags at the same point during the mixing cycle, and to mix the conventional ingredients and the fibers for the same amount of time, each and every time.

The concern is really focused on when the bags are added:

• If the bags are added during the introduction and the mixing of the conventional ingredients, timing is very important. The bags can be introduced prior to the coarse aggregate or with the coarse aggregate or with the fine aggregate. Do not add the bags of fiber at the same time as the cement because the bag can become coated with cement paste and will not break down as designed.
• Adding the fibers after all of the conventional ingredients have been thoroughly mixed eliminates the potential of inconsistency that could occur if the bags of fiber were introduced during the cycle when conventional ingredients are added and mixed. This also makes it easier to accurately monitor the mixing time for the fibers.

Again, there is no standard 'best way' to introduce the fibers. Success is predicated on uniformity. If a system works and the results are acceptable, don't change it. On the other hand, if total mixing of the fibers is not achieved then take a hard look at how and when the bags of fiber are being introduced.

Six-Step Approach to Introducing Bags of Fiber to the Transit (Drum) Mixer.

1. Introduce and thoroughly mix the conventional ingredients in the transit (drum) mixer. (This procedure also applies to central batch plants where transit mixers are used to transport concrete to the job site.)
2. Determine the specific type of fiber required in this truckload of concrete.
3. Determine the dosage rate of fiber per cubic yard required.
4. Determine the number of cubic yards of concrete in the transit mixer and the number of bags of fiber required based on the dosage rate of the fiber per cubic yard and the size/weight of bags available.
5. Turn the mixing drum in the discharge direction. Bring the mix up to the point of discharge and stop. Throw proper number of bags of fiber into the mixing drum.
6. Reverse the drum and run at agitation speed for 3-4 minutes.

By following these simple steps, success should be achieved 100% of the time.

If there are any questions regarding this subject or any other technical item, please call Bob Zellers at 724.475.3885.

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