The initial work performed under this project was designed to advance the state of the practice and to provide tools to help highway agencies and others use controlled low-strength material (CLSM) for backfill, utility bedding, void fill, and bridge approaches. A Phase I Interim Report for this project was completed by the Delaware Transportation Institute. The contract with the Delaware Transportation Institute for this project was terminated when the principal investigator transferred to the University of Texas at Austin. The remainder of the work for this project was conducted under NCHRP project 24-12(1) with the University of Texas at Austin.

CLSM, also known as flowable fill, is a cementitious fill placed without compaction, typically by mixer truck. It is prepared by mixing a variety of materials such as hydraulic cement, fine aggregate, fly ash or other similar by-products, and water. Depending on the specific application, CLSM requirements may include the following: compatibility with different types of utilities, compatibility with different pipe types, absence of undesirable environmental effects, flowability with minimum segregation, strength consistent with easy removal, and rapid but limited strength gain.