Fly ash is the key for flowable fill, a product that can be used for backfilling or as structural fill which flows into place, but which can also easily be re-excavated as necessary without resorting to jackhammers.
Fly ash is the essential ingredient in flowable fill, which is designed to flow into place and obtain maximum density. Fly ash provides flowability and buoyancy, preventing segregation, even when using concrete pumps to place the material.
Once in place the flowable fill becomes a well-graded superfine aggregate, filling voids without settling, and eliminating the need for mechanical compaction of other fill materials. Fly ash provides maximum density and stability in hardened flowable fill, giving it superior geotechnical properties.
Flowable fill is used extensively in backfilling utility trenches, bridge abutments, and abandoned underground structures (such as fuel tanks, sewer lines, and storm drains.) In new construction it is used as structural fill and as a select fill material to establish new elevation grades. By controlling the amount of water in the mix, flowable fill can be used in a variety of settings, even in standing water.