TM 5-822-7/AFM 88-6, Chap. 8
j. Placing of small areas. For vehicular parking and
the bottom of the overlay as the concrete hardens.
paving projects of 1,600 cubic yards or less, machine
This cracking may occur when the concrete is too
spreading, finishing, and floating will not be required
green to saw. Often the crack is not visible at the
if the benefits derived from the use of the equipment
surface of the pavement when the sawing is done. To
are not commensurate with the cost of using the
prevent such cracking, it may be necessary to use
machines. In this case, hand spreading, finishing,
inserts in the plastic concrete to form contraction
and floating will be specified.
joints.
k. Overlay pavement construction.
1. Control of cracking in pavements placed on lean
(l.) General. Where overlay pavement construction
concrete and cement-stabilized bases. Occasional
is required, contract specifications will contain
problems have developed when relatively thin
special provisions for preparation and treatment of
concrete pavement has been placed directly on lean
the existing surface before placing concrete in the
concrete bases or stabilized bases with high cement
overlay pavement. Criteria herein pertain to
contents. Uncontrolled contraction cracks in the
base material have on occasion reflected through the
construction of rigid overlays on existing rigid
pavement. Construction of rigid overlays on existing
new pavement. If a thin pavement less than 9 inches
flexible pavement or on existing rigid pavement with
thick is to be placed directly on a cement-stabilized
or lean concrete base, it may be desirable to either
a bond breaking course is treated as new construction.
place a bond-breaking material between the pave-
Construction of thin bonded overlays is discussed in
ment and base or to saw cut contraction joints in the
appendix B.
(2.) Bond between layers of pavement. Overlay
base to match those in the pavement surface. If a
pavements generally are designed on the assumption
bond breaker is used between the pavement surface
that a partial bond will develop between the two
and the base, the design engineer must be aware of
concrete layers. Concrete surfaces to receive partially
the lack of bond since this can affect the required
design thickness of pavement. If contraction joints
bonded overlays will be thoroughly cleaned of dirt
are to be sawed in the base to control cracking, it
and other foreign material, loose or spalled concrete,
extruding joint seal, bituminous patches, and
must be done at an early age just as discussed in
material that would break the bond between the
paragraph 22d for concrete pavements.
m. Appendix D describes the methods and pro-
concrete layers. Different areas of pavement will
require different treatment. The condition of the
cedures for the construction of roller compacted
existing pavement will determine the cleanup
concrete pavements.
measures necessary. Normally, sandblasting or
17. Field test specimens.
surface-abrading equipment will be required to
a. General. Field tests other than those called for
remove material adhering to the surface, and hand
by contractor quality control will be conducted by
scaling of loose or spalled material will be required.
the Government to determine the slump and air
No special treatment such as an acid wash of the
prepared surface or the use of a grout bonding course
content of freshly mixed concrete, and specimens
will be molded to test for flexural strength of hardened
will be required for partially bonded overlays. In
concrete. All tests will be performed under the super-
areas where oil or grease is present on the surface,
vision of the contracting officer. However, since the
scrubbing with a detergent and a wire brush may be
contractor will be required to furnish concrete
required. Cleaning of surfaces to receive the overlay
samples, labor, and facilities for molding and curing
with rotary grinding equipment will be permitted,
test specimens, specifications must indicate the
but the surface must be swept clean prior to placing
extent of testing required. Equipment for making
the concrete overlay.
air-content and slump tests will be furnished by the
(3.) Control of cracking in overlay pavements.
contracting officer when the Government is respon-
Considerable difficulty has been experienced with
sible for testing and by the contractor when the
uncontrolled cracking of overlay pavements at
contractor is responsible for testing. Beam molds
contraction joints. This cracking is likely to occur
will be made of steel and will be rigid and watertight.
during hot weather when the temperature of the
Beam molds will be supplied by the contracting
existing pavement is appreciably higher than that of
officer except when the contractor is responsible for
the concrete being placed in the overlay. Contraction
due to cooling of the base pavement results in move-
testing. When molds are required to be furnished by
ment at the existing joint, which may start a crack in
the contractor, details necessary to assure that the
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