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 CASE P2 - Granular Interlayers in Pavement Overlays, M. Jones
Improper use of granular interlayers in construction of overlays.
Problem:
Pavement cracking.
Symptoms:
Collection of Facts: When thick overlays have been required for increased
load capacity, or where pavement grade must be raised, an interlayer of sand
or gravel was frequently used between the existing and the new pavement
wearing surface. Many pavements which were constructed this way cracked very
badly due to water entrapment and high pore water pressure in the interlayer.
Solution/Alternative: The use of granular interlayers should be avoided when
designing pavement overlays. When, for economy, their use is desirable, an
open graded interlayer, with subdrains should be used. A preferred
alternative is to stabilize the granular material with either asphalt or
cement.
CASE P3 - Steel Fiber Reinforced Concrete - Airfield Pavements, M. Jones
Problem:
Excessive cracking in new SFRC overlay pavements.
Corner cracking.
Symptoms:
Collection of Facts: Steel fiber reinforced concrete costs from 30% to 50%
higher than plain concrete. In order to be competitive with plain concrete on
a square yard basis, SFRC airfield pavements have been designed to a thickness
of three-fourths the thickness of plain pavements. Joint spacing has ranged
from 25 to 50 feet.
Field surveys of SFRC overlay pavements has indicated that extensive corner
cracking is occurring under load.
Solution/Alternative: When thin overlay pavements with long joint spacings
are placed on rigid foundations, the corners tend to warp and lose contact
with the base slab. Cracking then occurs under the aircraft wheel loads.
Indications are that the thickness design criteria is unsatisfactory. The
thickness of SFRC pavements should not be reduced from that given by
Westergaard theory and conventional overlay design methods. In no case should
an unbonded concrete overlay of a concrete airfield pavement be thinner than 6
inches.
CASE P4 - Asphalt Slurry Seals on Airfield Pavements, M. Jones
Loss of cohesion in asphalt slurry seal mix.
Problem:
Loose aggregate on pavement surface.
Symptoms:
Collection of Facts: In August of 1976 the Atlantic Division of the Naval
Facilities Engineering Command awarded a contract for approximately 1.4
million square yards of asphalt slurry seal on runways and taxiways at the
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