Flowable Fill

Flowable fill, a fluid, low strength material, is a cost effective alternative for project owners, specifiers, and contractors to meet a project's backfill or structural fill needs.

A flowable slurry-like material with the consistency of pancake batter, flowable fill is self-leveling, can be placed in one lift with minimal labor and no vibration or tamping, and reaches 95% or more compaction within a few hours of placement, according to Rick Meininger, vice president of research for the National Ready Mixed Concrete Association.

Due to reduced labor, reduced excavation and reduced equipment needs, flowable fill offers lower in-place costs for all your backfill projects.

The editors of Concrete Construction magazine, in their May 1991 issue, included the following 15 reason for owners, specifiers, and contractors to use flowable fill.

  1. Readily Available - Ready mixed concrete producers, using locally available materials, can produce flowable fill to meet most project specifications.
  2. Easy to Deliver - Ready mix trucks can delivery specified quantities of flowable fill to the jobsite whenever the material is needed
  3. Easy to Place - Depending on the type and location of void to be filled, flowable fill can be placed by chute, conveyor, pump, or bucket. Because flowable fill is self-leveling, it needs little or no spreading or compacting. This speeds construction and reduces labor requirements.
  4. Versatile - Flowable fill mix designs can be adjusted to meet specific fill requirements. Add more water to improve violability. Add more cement or fly ash to increase strength. Admixtures can be added to adjust setting times and other performance characteristics. Adding foaming agents to flowable fill produces a lightweight, insulating fill.
  5. Strong and Durable - Load-carrying capacities of flowable fill typically are higher than those of compacted soil or granular fill. Flowable fill also is less permeable, thus more resistant to erosion. For use as a permanent structural fill, flowable fill can be designed to achieve 28-day compressive strengths of as high as 1200 psi.
  6. Can be Excavated - Flowable fill having compressive strengths of 50 to 100 psi is easily excavated with conventional digging equipment yet is strong enough for most backfilling needs.
  7. Requires Less Inspection - During placement, soil backfill must be tested after each lift for sufficient compaction. Flowable fill self-compacts consistently and doesn't need this extensive field testing.
  8. Allows Fast Return To Traffic - Because flowable fill can be placed quickly and can support traffic loads within several hours, it minimizes downtime for pavement repairs.
  9. Won't Settle - Flowable fill does not form voids during placement and won't settle or rut under loading. This advantage is especially significant if the backfill is to be covered by a pavement patch. Soil or granular fill, if not consolidated properly, may settle after a pavement patch is placed and forms cracks or dips in the road.
  10. Reduces Excavating - Flowable fill allows narrower trenches because it eliminates having to widen trenches to accommodate compaction equipment.
  11. Improves Worker Safety - Workers can place flowable fill in a trench without entering the trench, reducing their exposure to possible cave-ins.
  12. Allows all-Weather Construction - Flowable fill will displace any standing water left in a trench from rain or melting snow, reducing the need for dewatering pumps. To place flowable fill in cold weather, heat the material using the same methods for heating ready mixed concrete.
  13. Reduces Equipment Needs - Unlike soil or granular backfill, flowable fill can be placed without loaders, rollers, or tampers.
  14. Requires No Storage - Because ready mix trucks deliver flowable fill to the jobsite in the quantities needed, storing fill material onsite is unnecessary. Also, there is no leftover fill to haul away.
  15. Makes Use of a Waste By-Product - Fly ash is a by-product produced by power plants that burn coal to generate electricity. Flowable fill containing fly ash benefits the environment by making use of this industrial waste material.

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Flowable Fill Specification