15 Dec 98
considered a type of low strength concrete, but rather as an alternative to compacted fill. Indeed,
long-term compressive strengths of 50 to 300 psi are very low when compared to concrete.
However, in terms of allowable bearing pressure, which is a common criterion for measuring the
capacity of a soil to support a load, 50 to 100 psi strength is equivalent to a well-compacted fill.
Although CLSM generally costs more per cubic yard than most soil or granular backfill materials,
its many advantages often result in lower in-place costs.
Generally CLSM mixtures are not designed to resist freezing and thawing, abrasive or erosive
forces, or aggressive chemicals.
b. Applicability. The primary application of CLSM is as a backfill or structural fill in lieu of
compacted soil. Because CLSM needs no compacting and can be designed to be very fluid, it is
ideal for use in tight or restricted-access areas where placing and compacting fill is difficult.
Specific application areas include backfills, structural fills, insulating and isolation fills, pavement
bases, and conduit and culvert bedding.
Backfills CLSM can be readily placed into a trench, hole or other cavity. Compacting is not
required, hence the trench width or size of excavation may be reduced. When backfilling against
retaining walls, consideration should be given to the lateral pressures exerted on the wall by
flowable CLSM. Where the lateral fluid pressure may be a concern, CLSM may be placed in
layers with each layer allowed to harden prior to placing the next layer.
Structural fills CLSM may be used for foundation support. Compressive strengths may vary
from 100 to 1200 psi depending upon application. In the case of weak soil it can distribute a
structure's load over a greater area. For uneven or non-uniform subgrades under foundation
footings and slabs, CLSM can provide a uniform and level surface. Compressive strengths will
vary depending upon project requirements. Because of its strength, CLSM may reduce the
required thickness or strength requirements of the slab.
Insulating and isolation fills Low density CLSM material made with preformed foam is
generally used for these applications.
Pavement bases CLSM mixtures may be used for pavement bases, subbases and subgrades.
The mixture may be placed directly from the mixer onto the subgrade between existing curbs.
Good drainage is required when using CLSM mixtures in pavement construction. Freezing and
thawing damage could result in poor durability if the base material is frozen when saturated with
water. A wearing surface is required over CLSM since it has relatively poor wear resistance
Conduit and culvert bedding CLSM provides an excellent bedding material for pipe, electrical,
telephone and other types of conduits, and culverts. The flowable characteristic of the material
allows the CLSM to fill voids beneath the pipe or culvert and provide uniform support. Bedding
can also provide erosion resistance by preventing water from getting between the pipe and
bedding, eroding the support. Encasing the entire conduit in CLSM also serves to protect the
conduit from future damage. If the area around the conduit is being excavated at a later date, the
obvious material change in CLSM versus the surrounding soil or conventional granular backfill
would be recognized by the excavating crew, alerting them to the existence of the conduit.