15 Dec 98
Coloring agents have been used in mixtures to help identify the presence of CLSM.
c. Mix Components. Conventional CLSM mixtures usually consist of water, portland cement,
fly ash or other similar by-products, and fine or coarse aggregates or both. Some mixtures consist
of water, portland cement and fly ash only. Special low density CLSM mixtures consist of
portland cement, water and preformed foam.
Although materials used in CLSM mixtures may meet ASTM or other standard requirements,
the use of standardized materials is not always necessary. Selection of materials should be based
on availability, cost, specific application and the necessary characteristics of the mixture including
flowability, strength, excavatability, density, etc.
Cement provides the cohesion and strength for CLSM mixtures. Increasing cement content
while maintaining other components equal will normally increase strength and reduce hardening
time. For most applications, Type I or Type II portland cement conforming to ASTM C 150 is
normally used. Fly ash is sometimes used to improve flowability. The quantity of fly ash used
will be determined by availability and flowability requirements of the mix. Its use may also
increase strength and reduce bleeding, shrinkage and permeability. Most fly ashes used conform
to either Class F or Class C as described in ASTM C 618. However, fly ashes not conforming to
ASTM C 618 may be used. In all cases, whether or not fly ashes conform to ASTM C 618
specifications, trial mixes should be prepared to determine whether the mixture will meet the
Water serves as a lubricant to provide high flowability characteristics and promote
consolidation of the materials. Water that is acceptable for concrete mixtures is acceptable for
CLSM mixtures. ASTM C 94 on Ready Mixed Concrete provides additional information on
water quality requirements.
Air-entraining chemical admixtures can be valuable constituents for the manufacture of CLSM.
Air takes up space and improves flowability, assisting performance while enhancing economy. It
can also be used to enhance insulating characteristics and provide for reduced density, and may
also be used as a means of limiting the maximum strength of CLSM. Although chemical
admixtures have been used successfully in CLSM mixtures, pretesting should be performed to
determine acceptability. Also, air-entraining agents may not be cost effective unless they are
needed to satisfy specific requirements.
Aggregates are often the major constituent of a CLSM mixture. The type, grading and shape
of aggregates can affect the physical properties such as flowability and compressive strength.
Granular excavation materials with somewhat lower quality properties than concrete aggregate
are a potential source of CLSM materials, and should be considered. However, variations of the
physical properties of the mix components will have a significant effect on the mix performance.
Silty sands with up to 20 percent fines (minus #200 sieve) have proven satisfactory. Also, soils
with wide variations in grading have been shown to be effective. However, soils with clayey fines
have exhibited problems.
Non-standard materials, which may be available and more economical, can also be used in
CLSM mixtures depending upon project requirements. Examples of non-standard materials that