Grout, while having the same materials as concrete, has much greater plasticity, giving it the ability to flow better. This increased fluidity makes grout acceptable for filling in gaps and sealing joints. Grout is also useful in fill situations, much like controlled low-strength material (CLSM).
CLSM is a self-compacted material that is often used for backfill when high-strength material is not required, such as filling old tunnels or unused sewer lines. While not designed to resist intense freeze-thaw cycles, CLSM often excels at getting a job done quickly thanks to its high fluidity.