Applications of Controlled Low-Strength Material (CLSM) in Construction

Controlled Low-Strength Material (CLSM), also known as flowable fill, is a remarkable cementing material with a wide range of applications in the construction industry. This self-consolidating material has gained popularity due to its ease of use and unique properties, making it an attractive alternative to traditional compacted fill materials. In this comprehensive article, we will explore the various applications of CLSM, shedding light on its versatility and benefits for construction projects.

What is CLSM?

CLSM is a specialized mixture typically comprising water, Portland cement, fly ash or similar additives, fine aggregates, coarse aggregates, or a combination thereof. The specific components are chosen based on project requirements, availability, and the desired properties of the CLSM, such as flowability, strength, excavatability, and density.

Applications of CLSM in Construction

1. CLSM for Backfilling

One of the primary applications of CLSM is in backfilling. It is used to fill trenches, holes, or cavities with a level of uniformity that is often challenging to achieve with traditional granular or site-excavated backfill materials. Notably, CLSM eliminates the need for compaction, allowing for the reduction of trench widths or excavation sizes. The process involves layering CLSM, allowing each layer to harden before placing the next, ensuring structural integrity.

2. CLSM for Structural Fills

CLSM plays a crucial role in strengthening foundation supports, particularly on sites with weak soil conditions. By distributing the load from superstructures evenly over a broader area, it provides stability and support for footings and slabs. The compressive strength of CLSM can vary from 100 to 1200 psi, making it adaptable to different project requirements.

3. CLSM For Thermal Insulation

Departments of transportation and municipalities turn to CLSM for backfilling trenches containing gas pipes, electrical cables, conduits, and sewer mains. This approach offers simplicity and guaranteed performance. Additionally, CLSM is an excellent choice for thermal-insulation-conductivity fills, particularly in high-voltage underground transmission line projects. It proves to be cost-effective and outperforms conventional trench filling methods.

4. CLSM for Pavement Base Construction

CLSM mixtures find application in the construction of pavement bases, subbases, and subgrades. These mixtures are placed directly onto the subgrade, typically between existing curbs. The structural coefficient of a CLSM layer varies based on its compressive strength, ranging from 0.16 to 0.28. However, it’s important to note that CLSM surfaces have poor wear resistance, necessitating the addition of a suitable wearing surface when used as a pavement base.

5. CLSM for Conduit Bedding

As a bedding material, CLSM offers uniform support and fills voids beneath various conduits, including pipes, electrical, and telephone conduits. This application ensures stability and protection for underground utility systems.

6. CLSM for Erosion Control

Studies and field performance data highlight CLSM’s effectiveness as an erosion control material compared to traditional sand or clay fill materials. It is commonly used for embankment protection, such as riprap, and beneath dam spillways to secure rock pieces in place. CLSM is also employed to fill voids under pavements, bridges, sidewalks, and other structures prone to soil erosion.

7. CLSM for Filling Voids

The exceptional flow characteristics of CLSM make it an ideal choice for filling voids in various structures. Abandoned tunnels, basements, underground structures, mines, and sinkholes can all benefit from CLSM’s ability to efficiently fill empty spaces, providing structural support and stability.

8. CLSM for Nuclear Facilities

CLSM plays a critical role in nuclear facilities and other specialized applications. It is used for backfilling operations, encapsulating decommissioned pipelines and tanks, stabilizing waste, and addressing chemical and radio-nuclide-stabilization requirements. Its unique properties make it a valuable asset in these critical environments.


Controlled Low-Strength Material (CLSM) is a versatile and indispensable component in the construction industry. Its ability to offer strength, stability, and ease of placement without the need for compaction makes it a valuable choice for a wide range of applications. Whether used for backfilling, structural support, thermal insulation, pavement bases, erosion control, or void filling, CLSM consistently proves its worth in enhancing construction projects. Consider incorporating CLSM into your construction plans to experience its numerous benefits firsthand.

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