Is CLSM a Grout?
The versatility of Control low strength material
(CLSM) or flowable fill makes it useful in a wide variety of applications. CLSM is gaining
acceptance as a backfill material, particularly for work around pipes and other utility
trench applications and as a void filling material for abandoned underground facilities.
CLSM has inherited many different names throughout the industry including liquid dirt,
controlled density fill, flowable mortar, and lean backfill. General constituents of CLSM
are sand, cement, fly ash and water with flowing consistency and relatively easy
pumpability. This clearly qualifies CLSM as a grout, although the ready mix suppliers or
the ACI 229 committee doesn’t refer to it as a grout.
The key to CLSM’s (a self leveling material) success has
been the ease of placement, no required compaction, reduced trench excavation, use of
locally available material, less labor and safer operations. Because of the nature of
application the component materials need not meet the standards required for concrete
production, typically 28th day unconfined compressive strength of 100 psi is specified for
excavatable fill. The National Ready Mixed Concrete Association has defined excavatable
CLSM as having an unconfined compressive strength of 150 psi in one year. Higher strengths
are used for applications where future excavation is not required.
Performance tests may be required before placement to establish
the rate of strength gain and the potential ultimate strength of the mixture. Besides
compressive strength, flowable fill has many other physical properties that have to be
specified and evaluated before placing the material. Flowability is a measure of the
flowable fill mixtures’ fluid characteristics. Highly flowable mixtures often contain
more water so hydrostatic pressure during backfill placement must be considered; placing
them in lifts will reduce the hydrostatic pressure. When using CLSM, buoyancy is a common
concern because the pipes can be lifted off the foundation/bedding. CLSM unit weight
varies from 70 to 145 pcf.
The permeability of CLSM can range from sand to clay or even
lower, this will also help in selecting the material for different applications. ASTM has
approved a few standards for measuring the properties of CLSM and these are listed below.
CIGMAT researchers are currently working on developing and characterizing various CLSM
mixes using foundry sand, clay and fly ash. |
