TM 5-822-7/AFM 88-6, Chap. 8
f. Placement of forms and string lines. Forms and
strength used for the design of the pavements will be
string lines should be installed well in advance of
obtained and that an economical mixture is being used.
concrete paving operations so that the required
14. Subgrade, base, forms, and string lines.
checks and necessary corrections can be made
a. General. The setting and protection of forms and
without stopping or hindering concrete placement.
string lines and the final preparation of the
The same reasoning applies to the final preparation
subgrade, base course, or filter course require close
of the underlying material, which should not be less
than one full day's operation of the paving equip-
attention to all details to assure that the pavement
ment ahead of paving.
will have the required thickness and the surface will
beat the required grade.
g. String line. The string line will be of high-
b. Subgrade. Subgrade is the natural soil or fill
strength cord or wire. The choice will depend on the
upon which the base and concrete pavement are placed.
type of automatically controlled slipform paver used.
Special procedures may be necessary when dealing
Certain manufacturers recommend that high-tensile-
with frost-susceptible soils, expansive soils, pumping-
strength wire be stretched tautly between supports.
susceptible soils, lateritic soils, or organic soils.
Other manufacturers recommend a large-diameter
Removing soft or troublesome soils that occur in
cord and do not require the tautness that is recom-
pockets may be desirable, where possible.
mended for the wire. The use of wire requires firmly
c. Base. A base may perform many functions, such
anchored supports. As a result, the wire is less likely
as drainage, construction platform, and structural
to be disturbed than is the cord whose supports do
strengthening of the pavement. A base may be a
not have to be so firmly anchored. The wire is
granular material or lime, cement, or an asphalt-
difficult to see, and flagging should be attached
stabilized material. Also a lean concrete, sometimes
between the supports to reduce the chance that it
referred to as "Econocrete," is sometimes used as a
will be disturbed during construction. The cord does
base. There is no clearly accepted definition, but
not require supports to be as firmly anchored as for
cement contents are typically lower, and sometimes
the wire, and as a result, the cord is easier to install
and maintain. However, the chance of sagging between
poorer quality aggregates are used. The lean concrete
base should meet the strength and durability require-
the supports is greater. The cord is easy to see, and
ments of cement-stabilized materials and can be
as a result, the chances of its being knocked out of
treated as a high-quality stabilized material in
alinement are less than for the wire. However, the
design.
cord is more easily disturbed than the wire and
d. Form materials. Steel forms will be used for all
should be checked frequently.
formed pavement construction. Wood forms generally
h. Removal of forms. Pavement forms generally
are unsatisfactory for paving work, and their use will
may be removed 12 hours after the concrete is placed.
not be permitted except for such miscellaneous areas
A longer period will be necessary when the strength
as bulkheads and curved fillets. To avoid the excessive
gain of the concrete is retarded because of delayed or
cost of pavement construction for small j ohs, wood
inadequate protection during cold weather. In some
forms may be allowed for pavements less than 8 inches
instances, earlier removal of forms maybe permitted
thick in noncritical areas, such as open storage areas,
so that the transverse joints may be sawed completely
helicopter parking pads, and vehicle parking.
through to the edge of the slab without leaving a
small fillet of concrete adjacent to the form.
e. Construction of forms. Provisions relating to
built-up forms may be omitted from contract specifi-
15. Batching and mixing.
cations when the contract plans require constant slab
a. General. There are three types of plants: auto-
depth for each paved area. When this provision is
retained in a contract specification, the contractor is
matic, semi-automatic, and manual. For paving
required to furnish steel forms equal to the edge
projects, either automatic or semi-automatic plants
thickness of the majority of pavement slabs for each
will be acceptable. Specifications will be prepared to
paved area. Built-up forms will be used only where
allow either type of plant, and the contractor will
have the option as to the type of plant to be used.
edge thicknesses exceed the basic form depth. The
base width of built-up forms will be equal to the
b. Plant capacity. The capacity to be specified for
the batching plant and mixing equipment will be
width required for a comparable full-depth form.
determined in accordance with the concrete-placement
Side forms on sl.ipform pavers will be the full depth
requirements for the project. Since the pavement
of the pavement.
15
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