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Controlled low-strength material (CLSM) is a self-consolidating cementing material used primarily as an alternative to compacted fill (ACI 229R). It is intended to result in a compressive strength of 1200 psi or less.
CLSM mixture usually consists of water, portland cement, fly ash or similar products, fine aggregates, coarse aggregate, or both. The material is selected based on the availability, project specification, and requirement for flowability, strength, excavatability, and density.
CLSM is a material designed to be very fluid, and that requires no compaction, which is used in tight or restricted-access areas where placing and compacting is difficult.
CLSM is described in various terms like flowable fill, plastic soil-cement, slurry, K-Krete, unshrinkable fill, flowable mortar, controlled density fill, etc.
This article describes the various applications of CLSM in the construction industry.
Applications of CLSM in Construction
1. CLSM for Backfilling
CLSM is used for backfilling into the trench, holes, or cavities with a higher uniformity than achieved from granular or site excavated backfill. As CLSM does not require compaction, the trench width or size of excavation can be reduced.
CLSM is placed in layers, with each layer allowed to harden before placing the next layer.
2. CLSM for Structural Fills
CLSM is used to strengthen foundation supports. On sites with weak soil, CLSM fills help to evenly distribute the load from the superstructure over a greater area. It also helps to provide a uniform and level surface for footing and slabs.
The compressive strength achieved by using CLSM as structural fills varies from 100 to 1200 psi. The required strength varies based on the project requirements.
3. CLSM For Thermal Insulation
CLSM is used by the departments of transportation and local municipalities to backfill trenches with gas pipes, electrical cables, conduits, waste, and sewer mains instead of gradual fills. The backfilling process is easy and provides guaranteed performance.
CLSM is used for thermal-insulation-conductivity fills, especially for high-voltage underground transmission line projects. This backfilling method is cost-effective and performs better than conventional trench filling.
4. CLSM for Pavement Base Construction
CLSM mixtures are used to construct pavement bases, subbases, and subgrades. The mixture is placed directly onto the subgrade, between the existing curbs.
The structural coefficient of a CLSM layer can range between 0.16 to 0.28 for compressive strength from 400 to 1200 psi. (Reference: Report on Controlled Low-Strength Material, ACI Committee 229).
CLSM surfaces have poor wear resistance unless specially designed for a traffic load. Hence, it always requires a wearing surface when used as a pavement base.
5. CLSM for Conduit Bedding
CLSM is used as a bedding material for different conduits, as they fill the voids beneath the conduit and provide uniform support. It is a bedding material for pipe, electrical, telephone conduits, etc.
6. CLSM for Erosion Control
Different studies and field performance indicate that CLSM is a better erosion control material than other sand or clay fill materials.
CLSM is used for embankment protection as riprap and below dam spillways to hold rock pieces in place. They are also used to fill the voids under the pavement, bridges, sidewalks, and other structures where there is extreme soil erosion.
7. CLSM for Filling Voids
The high flow characteristics of CLSM are used to fill the voids of abandoned structures like tunnels, basements, underground structures, mines, and sinkholes.
8. CLSM for Nuclear Facilities
CLSM is used for backfilling operations in nuclear facilities and other special activities like encapsulating decommissioned pipelines and tanks, encapsulating waste-disposal sites, and stabilizing waste. It is also used to address chemical and radio-nuclide-stabilization requirements.
FAQs
Controlled low-strength material (CLSM) is a self-consolidating cementing material used primarily as an alternative to compacted fill.
CLSM is used for backfilling operations in nuclear facilities and other special activities like encapsulating decommissioned pipelines and tanks, encapsulating waste-disposal sites, and stabilizing waste. It is also used to address chemical and radio-nuclide-stabilization requirements.
The high flow characteristics of CLSM are used to fill the voids of abandoned structures like tunnels, basements, underground structures, mines, and sinkholes.
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