Conventional repair of pavement base layers using compacted lifts of crushed aggregate requires specialized labor and equipment, contributes significantly to total construction time and is very difficult to perform, particularly in restricted access areas. This often results in a poorly constructed repair and loss in performance, they say. Adding flowable fill technology has shown some success when used for backfilling patches and utility cut repairs.

“Flowable fill is a viscous, grout-like material used in place of traditional compacted aggregate in backfilling operations,” they say. “Flowable fill is also referred to as controlled low-strength material, controlled density fill, soil-cement slurry, soil-cement grout, unshrinkable fill and K-Krete.”

Common applications of flowable fill include backfill, structural fill, pavement base, void fill, pipe bedding and in-closure projects for tanks, pipes and culverts, Griffin and Brown write. The material is commonly a blend of portland cement, fine aggregate, water and waste materials including fly ash, foundry sand and bottom ash. Chemical admixtures commonly used in PCC, such as air-entrainers, water reducers, set accelerators and retarders, can be used to modify the performance characteristics of flowable fill.

“The material is self-leveling, self-compacting and possesses other desirable properties, including flow under gravity, rapid hardening capability, strength selectability, material uniformity and reduced construction requirements,” they say.

Griffin and Brown present the performance and cost advantages of using preblended flowable fill for rapid repair of damaged areas in highway and airfield pavements. Eleven commercially available flowable fill blends were evaluated using both laboratory and field testing methods. The laboratory evaluation consisted of standard material characterization, including compressive strength, flowability, hardening time and what they call “excavatability.”

“Field testing included constructing- and trafficking-simulated utility cuts and full-depth patches in existing pavements,” they write. “An examination of structural capacity, surface deformation and visible surface distress was conducted for each repair at regular traffic intervals. Additionally, construction time, difficulty and cost were compared to a traditional aggregate repair.”

Testing results indicate that backfilling utilities and patches in pavements using flowable fill reduces the potential for premature failure, reduces construction time and reduces total project cost while increasing repair performance, they conclude.