TM 5-822-7/AFM 88-6, Chap. 8
requiring 2,500 cubic yards of concrete or less.
apply to all paving projects regardless of the type of
e. Transporting plant-mixed concrete. Vehicles for
mixing equipment used. The addition of water to the
transporting concrete from stationary mixers to the
mixture in excess of that required by the mixture
forms will conform to the applicable requirements of
proportions to maintain slump during prolonged
ASTM C 94. Plant-mixed concrete may be trans-
mixing will not be permitted.
c. Slipform paving. Approval of the slipform paving
ported in a truck agitator, in a truck mixer operating
equipment for airfield pavement will be based on satis-
at agitating speed, or in approved non-agitating
equipment. Non-agitating equipment will have
factory performance in the field. Trial sections of
smooth, watertight, metal bodies equipped with
sufficient length and located in low-volume aircraft
gates to permit control of the discharge of the
traffic areas will be used to approve the paving equip-
ment, considering both slipform and another for the
concrete; covers will be provided for protecting
fill-in operation when scheduled by the contractor.
concrete in transit, as required. Concrete transported
in non-agitating equipment will be discharged into
Furthermore, approval shall be based on the ability
the pavement forms or to the slipform paver within
of the machine to consolidate the concrete and form
45 minutes after introduction of the mixing water
the pavement to the desired cross sections. Plan
grade and surface smoothness tolerances must be
and cement to the aggregates at the mixer. The
met. Particular attention should be paid to the ability
major problem in using ready-mixed concrete in
of the machine to form the required edge without
pavement construction is avoiding segregation in
discharging and transferring the concrete from the
excessive slumping or tearing during slipform opera-
tions and to form a suitable longitudinal construction
transporting unit to the final position in the form or
on the subgrade in front of the slipform paver. The
joint during fill-in operations. The machine shall not
use of readymixed concrete requires suitable
damage the surface or edge of the previously placed
transfer and spreading equipment capable of
slab during fill-in operations. The suggested length
depositing and distributing the concrete in an
of the trial section is 1,000 to 2,000 feet. Slipform
unsegregated condition in the final position in the
pavers with a full-width auger are recommended.
Traveling blades have been less satisfactory. If the
forms. When low-slump plant-mixed concrete is
transported, trucks equipped with vibrators are
slipformed pavement is 10 inches or greater in
thickness, some of the lighter slipform pavers may
often required to discharge the concrete and should
have problems properly handling the low-slump
be required unless it is satisfactorily demonstrated
that the concrete can be discharged without delay.
concrete.
d. Spreading. Hand spreading of concrete will be
permitted only when necessitated by odd widths or
shapes of slabs, or in emergencies such as equipment
16. Placing.
breakdown.
a. General. Concrete may be placed between fixed
e. Vibration. Vibration requirements are influenced
forms or using approved slipform paving equipment.
by many factors, such as the type and size of aggre-
Both methods produce satisfactory results, and
gate, mixture proportions, air entrainment, slump,
when possible, the option should be left with the
workability of mixture, and pavement thickness.
contractor as to the method to be used. With
The specified maximum spacing for vibrator units
slipform equipment, the rate of placement can be
and the specified vibrating procedures are based on
significantly increased over the rate with fixed
field experience with the vibration of pavements 12
forms. In addition, the material for forms and the
inches or more in thickness. There has been only
labor for setting forms are eliminated. As a result,
limited use of internal vibration for thinner slabs. If
the cost for large jobs will be less for slipform place-
necessary for proper consolidation of the concrete, a
ment than for placement with fixed forms. However,
closer spacing of vibrator units will be required.
on small jobs or larger jobs with special requirements,
Particular attention should be paid to vibrators
the use of fixed forms may be necessary or may be
more economical than the use of slipform equipment.
along the edge of the paving lane to ensure that the
edge is properly consolidated. General experience
No guidelines can be given as to what size job will
has been that it is more satisfactory to use vibrators
permit the economic use of slipform pavers.
at a closer spacing and for shorter periods of vibra-
b. Placing time. Concrete will be placed before
tion than to attempt to consolidate the concrete by
obtaining its initial set and within 45 minutes after
prolonged vibration at a wider spacing. The duration
cement has been added to the batch. These provisions
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