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Chapter 5
Controlled Low-Strength Material
(CLSM) Containing We Energies
Fly Ash
Introduction
During the past two decades fly ash has been increasingly used in the
manufacture of controlled low-strength material (CLSM). CLSM is defined by
ACI Committee 229 as a “self-compacted cementitious material used
primarily as a backfill material in lieu of compacted fill with a compressive
strength of 1200 psi or less.” However, where future excavation is anticipated,
the ultimate compressive strength of CLSM should be less than 300 psi. This
level of strength is very low, compared to concrete, but very strong when
compared to soils. The composition of CLSM can vary depending on the
materials used in the mixture. CLSM has the unique advantage of flowing and
self-leveling. Hence, in applications like filling abandoned underground tanks
or voids under pavements, CLSM may be the only viable method of
completely filling the void. Additionally, there is no cost associated with
vibrating or compacting the material in place.
CLSM may be known by such names as: unshrinkable fill, controlled density
fill, flowable mortar, plastic soil-cement, soil-cement slurry and K-Krete (36).
We Energies uses the registered trademark, Flo-Pac® for its CLSM. The
range of strength required varies with the type of application. However,
CLSM is normally designed to develop a minimum of at least 20 psi strength
in 3 days and 30 psi at 28 days (ASTM C403 penetration resistance numbers
of 500 to 1500).
A compressive strength of 100 psi is equivalent to the load bearing capacity of
a well compacted soil with a capacity of 14,400 psf which is comparable to a
densely compacted gravel or hard pan type soil. Where CLSM is used as a
support layer for foundations, a compressive strength of 300 psi to 1200 psi is
sometimes used. However, applications involving CLSM with strength in this
range are very limited and often not necessary.
129 We Energies
Coal Combustion Products
Utilization Handbook