CEMP-ET
DEPARTMENT OF THE ARMY
ETL 1110-3-496
U.S. ARMY CORPS OF ENGINEERS
Washington, DC 20314-1000
Technical Letter
No. 1110-3-496
15 December 1998
Engineering and Design
CONTROLLED LOW STRENGTH MATERIAL
WITH COAL-COMBUSTION ASH AND OTHER RECYCLED MATERIALS
1. Purpose. This letter provides information and guidance for design and construction of
controlled low strength material (CLSM). CLSM has many applications but has been primarily
used as a flowable, self-compacting fill in place of a compacted fill. An example specification
containing provisions for using fly ash and other recycled materials in the CLSM mix is also
provided.
2. Applicability. This letter is applicable to all HQUSACE elements and USACE commands
having military construction and design responsibility.
3. References. ER 1110-345-100.
4. Distribution. Approved for public release; distribution is unlimited.
5. Background.
a. CLSM is a self-compacting, cementitious material used primarily as a backfill in lieu of
compacted fill. Often called flowable-fill, CLSM should flow easily during construction and gain
sufficient strength to be walked on and buried within a day. CLSM is especially popular as a
excavatable material for backfilling trenches and other hard-to-compact locations. To allow for
future excavation most current CLSM applications require unconfined compressive strengths of
50 to 300 psi. Waste materials can sometimes be recycled by their use in CLSM mixtures. Waste
materials that may be suitable as aggregates for CLSM include bottom ash produced in the coal
combustion process, discarded foundry sand, and reclaimed crushed concrete. In all cases, the
characteristics of the non-standard material should be determined, and the suitability of the
material should be tested in a CLSM mixture to determine whether it meets specified
requirements.
b. This ETL provides guidance and design recommendations for the use of CLSM with coal-
combustion ash and other recycled materials. The information provided is for use of CLSM for
backfill, structural fill, insulating and isolation fill, pavement base and conduit and culvert
bedding.