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Soil cement, a compacted
mixture of native soil, portland cement, and water, has a
number of uses in today’s construction industry. The
more common uses today are for stream bank protection,
grade control (drop) structures, and pond liners. Soil
cement has been proven in all of these uses to be cost
effective, aesthetically pleasing, performance and time
tested. Other uses for soil cement are retaining walls,
streets, shoulders, airports, parking and storage areas. As the soil cement is placed and
compacted, the cement hydrates and the mix becomes a
structural slab-like material. After construction and
curing, soil cement is hardly affected by water or the
freeze thaw cycle, therefore does not pump under
construction traffic or rut during spring thaws, and can
bridge over soft sub grade.
Almost any native soil can
be used for soil cement, but for optimum production
through our continuous mixing pugmills, a 2" minus
material is recommended (2" minus or less is usually
specified for soil cement projects). One cost savings can
be obtained from the utilization of on site material.
Well graded sandy and gravelly materials with 30-45%
retained on the No. 4 sieve work best for soil cement.
Material that is deficient in fines or has a high
silt/clay content still works well for soil cement but
may require a higher cement content.
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Portland Type I or II
cements are used the majority of the time for soil
cement; other types may be used if they comply with the
latest ASTM and AASHTO standards. Water is important in
soil cement for two reasons. First, it helps obtain
maximum density, and, second, it is necessary for cement
hydration. |
The three fundamental
requirements for strong and durable soil cement are
proper moisture content, minimum cement content, and
laboratory determined densities. A continuous mixing
plant is recommended over the mix-in-place technique when
accuracy and homogeneous mix is necessary in order to
adhere economically to the specifications.
Gears, Inc. and PEI
utilize an Aran portable continuous mixing plant whose
production is rated between 100 and 1,000 tons per hour
contingent upon the engineering properties of the
material being used, speed of excavation, and speed of
placement.
The production of the
mixing plant is monitored by the use of instruments which
display the speeds of various feeds to the mixer. Feed
rates for soil, cement, and water are variable and are
metered with a computerized system based on the weight
and density of the native soil.
Since all of the
ingredient feeds are volumetric and the mix density is
generally specified in terms of weight, it is necessary
to calibrate each feed. The purpose of this calibration
is to establish an accurate relationship between
speed/gate setting and the resultant throughput in tons
per hour.
The soil is loaded in the
feed hopper by means of a front-end loader or conveyor. A
fixed or variable speed belt feeder draws that material
from the hopper at a uniform rate and transfers it into
the Aran twin shaft mixer.
The cement is metered from
the overhead storage silo by means of a cleated belt
feeder and enters the same zone as the native material.
Water is drawn from the
lower storage tank and metered by a variable speed
positive displacement pump system. It is delivered to the
mixing chamber which minimizes the potential for escape
of dust during the mixing process.
For a list of
Gears, Inc. & PEI
Soil Cement Projects,
up to 1998 click here:
For a list of
Gears, Inc. & PEI
Soil Cement Projects,
after 1998 click here:
For contacts, phone
numbers and e-mail addresses, please click here:
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