TM
5-822-14/AFJMAN
32-1019
may be exaggerated when the soil-lime is remixed
unloading and obtaining a uniform rate of dis-
over a long period of time, especially at moisture
charge. With the auger trucks, spreading is han-
contents less than optimum moisture. The fluff
dled by means of a portable, mechanical-type
action is usually minimized if adequate water is
spreader attached to the rear (fig 4-27) or through
provided and mixing is accomplished shortly after
metal downspout chutes or flexible rubber boots
lime is added. For soils that tend to fluff with
extending from the screw conveyors. The mechani-
lime, the subgrade elevation should be lowered
cal spreaders incorporate belt, screw, rotary vane,
slightly or the excess material trimmed. Trimming
or drag-chain conveyors to distribute the lime
can usually be accomplished by blading the mate-
uniformly across the spreader width. When boots
rial onto the shoulder of embankment slopes. The
or spouts are used instead, the lime is deposited in
blading operation is desirable to remove the top
windrows; but because of lime's lightness and
0.25 inch because this material is not often well
flowability, the lime becomes distributed rather
cemented due to lime loss experienced during
uniformly across the spreading lane. Whether me-
construction. Excess rain and construction water
chanical spreaders, downspouts, or boots are used,
may wash lime from the surface, and carbonation
the rate of lime application can be regulated by
of lime may occur in the exposed surface. If dry
varying the spreader opening, spreader drive
lime is used, ripping or scarifying to the desired
speed, or truck speed so that the required amount
depth of stabilization can be accomplished either
of lime can be applied in one or more passes. With
before or after lime is added (fig 4-19). If the lime
the pneumatic trucks, spreading is generally han-
is to be applied in a slurry form, it is desirable to
dled with a cyclone spreader mounted at the rear,
scarify prior to the addition of lime.
which distributes the lime through a split chute or
(2) Lime application.
with a spreader bar equipped with several large
(a) Dry hydrated lime. Dry lime can be
downspout pipes. Finger-tip controls in the truck
applied either in bulk or by bag. The use of bagged
cab permit the driver to vary the spreading width
lime is generally the simplest but also the most
by adjusting the air pressure. Experienced drivers
costly method of lime application. Bags of 50
can adjust the pressure and truck speed so that
pounds are delivered in dump or flatbed trucks
accurate distribution can be obtained in one or two
and placed by hand to give the required distribu-
passes. When bulk lime is delivered by rail, a
tion (fig 4-24). After the bags are placed they are
variety of conveyors can be used for transferring
slit and the lime is dumped into piles or trans-
the lime to transport trucks; these include screw,
verse windrows across the roadway. The lime is
belt, or drag-chain conveyors, bucket elevators,
then levelled either by hand raking or by means of
and screw elevators. The screw-type conveyors are
a spike-tooth harrow or drag pulled by a tractor or
most commonly used, with large diameter units of
truck. Immediately after, the lime is sprinkled to
10- to 12-inches being recommended for high-speed
reduce dusting. The major disadvantages of the
unloading. To minimize dusting, all types of con-
bag method are the higher costs of lime because of
veyors should be enclosed. Rail-car unloading is
bagging costs, greater labor costs, and slower
generally facilitated by means of poles and me-
operations. Nevertheless, bagged lime is often the
chanical or air-type vibrators. Lime has also been
most practical method for small projects or for
handled through permanent or portable batching
projects in which it is difficult to utilize large
plants, in which case the lime is weigh-batched
equipment. For large stabilization projects, partic-
before loading. Generally, a batch plant setup
ularly where dusting is no problem, the use of
would only be practical on exceptionally large jobs.
bulk lime has become common practice. Lime is
Obviously, the self-unloading tank truck is the
delivered to the job in self-unloading transport
least costly method of spreading lime, because
trucks (fig 4-25). These trucks are large and
there is no rehandling of material and large
efficient, capable of hauling 15 to 24 tons. One
payloads can be carried and spread quickly.
(b) Dry quicklime. Quicklime may be ap-
type is equipped with one or more integral screw
conveyors that discharge at the rear. In recent
plied in bags or bulk. Because of higher cost,
years pneumatic trucks have increased in popular-
bagged lime is only used for drying of isolated wet
ity and are preferred over the older auger-type
spots or on small jobs. The distribution of bagged
transports. With the pneumatic units the lime is
quicklime is similar to that of bagged hydrate,
blown from the tanker compartments through a
except that greater safety emphasis is needed.
First, the bags are spaced accurately on the area
pipe or hose to a cyclone spreader to a pipe
spreader bar-mounted at the rear (fig 4-26).
to be stabilized, and, after spreading, water is
applied and mixing operations started immedi-
Bottom-dump hopper trucks have also been tried,
ately. The fast watering and mixing operation
but they are undesirable because of difficulty in
4-13
Previous Page
