15 Dec 98
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. In certain cases,
environmental regulations may require prequalification of the raw material or CLSM mixture or
both, prior to use.
d. Properties. The properties of CLSM cross the boundaries between soils and concrete.
CLSM is manufactured from materials similar to those used to produce concrete and is placed
from equipment in a fashion similar to that of concrete. But in-service CLSM exhibits
characteristic properties of soils. The properties of CLSM are affected by the constituents of the
Flowability Flowability is the property that makes CLSM unique as a fill material. It enables
the materials to be self-leveling, to flow into and readily fill a void, and be self-compacting
without the need for conventional placing and compacting equipment. Flowability can be varied
from very stiff to very fluid depending upon requirements. A major consideration in using highly
flowable CLSM is the hydrostatic pressure it exerts. Where fluid pressure is a concern, CLSM
may be placed in lifts, with each lift being allowed to harden before placement of the next lift.
Segregation Separation of constituents in the mixture can occur at very high levels of
flowability when the flowability is primarily produced by the addition of water. With proper
proportioning, a high degree of flowability can be attained without segregation. For highly
flowable CLSM without segregation, adequate fines are required to provide suitable cohesiveness.
Fly ash generally accounts for these fines, although silty or other noncohesive fines up to 20
percent of total aggregate have been used.
Subsidence Subsidence deals with the reduction in volume of CLSM as it releases its water
and entrapped air through consolidation of the mixture. Most of the subsidence occurs during
placement and the degree of subsidence is dependent upon the quantity of free water released.
Typically, subsidence of 1/8 to 1/4 inches per foot of depth is common. This amount is generally
found with mixtures of high water content. Mixtures of lower water content undergo little or no
subsidence and cylinder specimens taken for strength evaluation have experienced no measurable
change in height from the time of casting to the time of testing.
Hardening time Hardening time is the approximate period of time required for CLSM to go
from the plastic state to a hardened state with sufficient strength to support the weight of a
person. When this excess water leaves the mixture, solid particles realign into intimate contact
and the mixture becomes rigid. Hardening time is greatly dependent on the type and quantity of
cementitious material in the CLSM. Hardening time can be as short as one hour, but generally
takes 3 to 5 hours under normal conditions. A load resistance test according to ASTM D 6024
can be used to measure the hardening time or the suitability of loading of the CLSM.
Pumping CLSM can be successfully delivered by conventional concrete pumping equipment.
As with concrete, proportioning of the mixture is critical.
Strength and bearing capacity Unconfined compressive strength is a measure of the load