Flowable Fill, or Controlled Low-Strength Material (CLSM) as it is more formally known, is a cost effective, self-compacted cementitious material that is used primarily as backfill, replacing the more traditional compacted backfill material. Flowable Fill primarily consists of cement, water, fine aggregate, and fly ash or slag. In addition, admixture companies have developed products that enhance both the flowability and hardening features of flowable fill.
Flowable Fill is used in a variety of applications. Municipalities are specifying Flowable Fill on projects where 100% compaction is of importance or when the labor costs in stacking layer after layer of compacted fill becomes too great. Indeed, several large metropolitan cities now designate Flowable Fill for all major street and backfill projects.
While Flowable Fill may have an upper strength limit of 1200psi, many applications call for a material that can be excavated easily, meaning somewhere around 150psi. In addition to backfill, Flowable Fill has been used under roadways, in bridge repair, to strengthen and stabilize rip-rap, as backfill, as residential sub-footings, as mud mats, and in many other uses where zero settlement is desired.