15 Dec 98
strength, flowability, density, etc. Adjustments are then made to achieve the desired properties.
Within these specifications cement contents generally range from 50 to 200 lb/yd3, depending
upon strength and hardening time requirements. Class F fly ash contents range from none to as
high as 2000 lb/yd3 where fly ash serves as the aggregate filler. Class C fly ash is used in
quantities of up to 350 lb/yd3. The majority of specifications call for the use of fine aggregate.
Coarse aggregate is generally not used in CLSM mixes as often as fine aggregates. When used,
however, the coarse aggregate content is approximately equal to the fine aggregate content.
More water is used in CLSM than in concrete. Water contents typically range from 325 to 580
lb/yd3 for most CLSM mixes containing aggregate. Water contents will be higher with mixtures
using finer aggregates.
f. Mixing, transporting, placing, and quality control. The mixing, transporting and placing of
CLSM generally follows methods and procedures given in ACI 304. Whatever methods and
procedures are used, the main criteria is that the CLSM be homogeneous and consistent and
satisfy the requirements for the purpose intended. CLSM may be mixed by several methods,
including central-mixed concrete plants, ready-mixed concrete trucks, and pugmills. Most CLSM
mixtures are transported in truck mixers. Agitation of CLSM is required during transportation
and waiting time to keep the material in suspension. Under certain circumstances CLSM has been
transported short distances in non-agitating equipment such as dump trucks.
CLSM may be placed by chutes, conveyors, buckets, or pumps depending upon the application
and its accessibility. Internal vibration or compaction is not required since the CLSM
consolidates under its own weight. Although it can be placed year round, CLSM should be
protected from freezing until it has hardened. For trench backfill CLSM is usually placed
continuously. To contain CLSM when filling long open trenches in stages or open-ended
structures such as tunnels, the end points can be bulkheaded with sandbags, earth dams, or stiffer
mixtures of CLSM. For pipe bedding, CLSM may have to be placed in lifts to prevent floating the
pipe. Each lift should be allowed to harden before continued placement. Other methods of
preventing floatation include sand bags placed over the pipe, straps around the pipe anchored into
the soil or use of faster setting CLSM placed at strategic locations over the pipe. CLSM is not
self-supporting and places a load on the pipe. For large, flexible wall pipes, CLSM should be
placed in lifts so that lateral support can develop along the side of the pipe before fresh CLSM is
placed over the pipe. Backfilling retaining walls may also require the CLSM be placed in lifts in
order to prevent overstressing the wall.
CLSM has effectively been tremied and end dumped directly into the water without significant
segregation. In confined areas the CLSM will displace the water to the surface where it can easily
be removed. Because of its very fluid consistency, CLSM can flow long distances to fill voids and
cavities located in hard-to-reach places. Voids need not be cleaned as the slurry will fill in
irregularities and encapsulate any loose materials.
For most projects CLSM is pretested using the actual raw materials to develop a mix design
having certain plastic (flowability, consistency, unit weight) and hardened (strength, durability,
permeability) characteristics. Following the initial testing program, field testing may consist of