Flowable Fill

The safe, economical backfill material

Flowable Fill (also known as Controlled Low Strength Material) is a flowable mixture which contains cement, sand, flyash, water and/or foam admixtures.

Your local ready-mix producer may suggest mixes varying from these components, depending on their availability and the specified project requirements. The versatility in design of the flowable fill mixtures offers numerous advantages to the specifying engineer.

Other advantages include:

  • Readily available - Ready-mixed concrete producers, using locally available materials, can produce flowable fill to meet project specifications.
  • No settlement - Flowable fill does not form voids during placement, and won't settle or rut under loading. This advantage is especially significant if the backfill in a utility trench 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.
  • Easy to deliver - Ready-mix trucks can deliver specified quantities of flowable fill to the job site whenever the material is needed.
  • Versatile - Flowable fill mix designs can be adjusted to meet specific requirements and a variety of performance characteristics.
  • Improves worker safe - Workers can place flowable fill in a trench without entering the trench, reducing their exposure to possible cave-ins.
  • 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.
  • Allows fast return to traffic - Because flowable fill can be placed quickly and can support traffic loads within several hours, it minimizes road closures for pavement repairs.
  • Strong and durable - Load-carrying capacities of flowable fill typically are higher than those of compacted soil or granular fill.
  • Can be excavated - Flowable fill, having a compressive strength of less than 150 psi, is excavatable with conventional excavating equipment, yet is strong enough for most backfilling needs.
  • Requires less inspection - During placement, soil backfill must be tested after each lift for sufficient compaction. Flowable fill self-compacts consistently and doesn't require this extensive field testing.
  • Reduces excavation - Flowable fill allows narrower trenches because it eliminates having to widen trenches to accommodate compaction equipment and laborers in the trench.
  • Reduces equipment needs - Unlike soil or granular backfill, flowable fill can be placed without rollers, loaders, or tampers.
  • Requires no on-site storage - Because ready-mix trucks deliver flowable fill to the job site in the quantities needed, storing fill material onsite is unnecessary. Also, there is no leftover fill to haul away.
  • Allows all-weather construction - Flowable fill will displace standing water left in a trench from rain or melting snow, eliminating the need for dewatering pumps. To place flowable fill in cold weather, the material temperature can be altered using the same methods in heating ready-mixed concrete.
  • Makes use of a waste by-product - Fly ash is a by-product from the power plants that burn coal to generate electricity. Flowable fill containing fly ash benefits the environment by making use of these materials. Other waste products have also been used with success.

Flowable Fill Documents

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