Going around a column, the laser screed passes nearby, a finisher hand-strikes concrete the laser screed can’t reach, followed closely by a finisher bull-floating the surface. The concrete mix is easy to work with.
Joe Nasvik Going around a column, the laser screed passes nearby, a finisher hand-strikes concrete the laser screed can’t reach, followed closely by a finisher bull-floating the surface. The concrete mix is easy to work with.

Batching quality concrete is really a numbers game. There are measurements for ingredient weights, water, and mixing times. Producers know that when all numbers fall in the prescribed constraints, their customer can be assured of a quality product.

When the project requires adding ingredients on the jobsite, special care is taken. When the concrete order includes fibers, producers and contractors have guidance on how keep the numbers right.

ACI 304R00, Guide for Measuring, Mixing, Transporting, and Placing Concrete, gives guidance on the inclusion of fibers into a concrete mix. The document advises, “Appropriate equipment should be used to disperse the fibers into the mixer to minimize the potential for the development of fiber balls.”

When ordering, it’s important to remember there’s a special ASTM product specification for concrete containing fibers. ASTM C1116, Standard Specification for Fiber-Reinforced Concrete, covers all forms of fiber-reinforced concrete. While it heavily references ASTM C-94, ASTM 1116 offers guidelines to ensure the product is delivered to a purchaser with the ingredients uniformly mixed, and that it can be sampled and tested at the point of delivery.

In section 8 of the fiber-concrete product standard, there’s guidance on how the fibers should be measured into the truck delivered concrete mixes: Fibers shall be batched by mass or volume with an accuracy of –3?% and +5?% of the amount required per batch.

  • Fibers shall be measured by mass when fiber-reinforced concrete is produced in accordance with Specification C94/C94M, and by volume when produced in accordance with Specification C685/C685M.
  • When the fibers are to be measured by mass, bags, boxes, or like containers are acceptable when provided that the containers are sealed by the fiber manufacturer and have the mass contained therein clearly marked.
  • No fraction of a container delivered unsealed or left over from previous work shall be used unless weighed.
  • A new tool exists for contractors, producers, and design engineers who desire tighter control of steel fiber dosage rates. Baekert, a manufacturer of steel reinforcement fibers for concrete, has released a new app to help in the mix design and batching process. Dramix #Bags is an easy calculation tool designed to help engineers, producers, and contractors define how many bags of steel fiber reinforcement are needed to get the right dosage per concrete truck mixer.

    Users provide the required fiber dosage and concrete volume and the app reports the number of bags the technician must add mixer. The app is flexible, as users can change country, bag weight, measuring unit and language in the settings.

    Rick Yelton is editor at large at World of Concrete-Informa Exhibitions and is the former editor in chief of TCP. E-mail rick.yelton@informa.com.