30 June 2001
(b) Preformed compression seals. The reservoir width for preformed compression seals
must be designed to keep the sealant in compression at all times. The depth of the reservoir must
exceed the depth of the seal but is not related directly to the width of the joint. The width of the
compression seal should be approximately twice the width of the joint. The limits on the compression
seal are normally 20 percent minimum and 50 percent maximum compression strain of the original
sealant width. For example, the working range of a 25-millimeter (1-inch) wide neoprene compression
seal is from 13 to 20 millimeters (0.5 to 0.8 inches). If the seal is subjected to compression greater than
the 50 percent level for extended periods of time, the seal may take a compression set, and the webs
may bond to each other. If this happens, the seal will not open as the joint opens, and the seal will no
longer be effective. The joint dimensions for the standard size slab are shown in Figure 12-30. Design
sealant dimensions based on the actual joint spacing. Choose preformed neoprene compression seal
dimensions so that the working range of the joint is within the working range of the sealant.
12. JOINTING PATTERN FOR RIGID AIRFIELD PAVEMENTS. Proper jointing pattern for rigid airfield
pavement is a critical item of design and construction for all services. Not only is it important for a quality
product, but it can and should promote efficiency for the construction contractor, and thus cost savings.
Criteria for type of joints, their location, and maximum allowable spacing have been given in the previous
paragraphs. This paragraph focuses on appropriate and efficient layout of the jointing pattern. Laying
out a good jointing pattern depends on experience working at it and is more of an art than a science.
The designer must learn to play with it and try various combinations until the optimum layout is reached.
Every productive hour spent on this produces appreciable cost savings.
a. General. All project joint layout drawings should have a prominent note on them saying "No
changes in the jointing pattern shall be made without the written approval of the design engineer." The
design engineer must make every effort to provide an efficient layout for construction, consistent with the
limits of criteria. However, once the joint layout is finalized, no change whatever should be made by field
personnel unless examined and approved in writing by the designer to be sure that it does not
compromise his plan or violate criteria.
b. Layout. Joint layouts should be as simple and as uniform as possible and meet all criteria of the
preceding paragraphs. Except for unusual circumstances, all joints should have straight lines with the
longitudinal and transverse joints at right angles. Careful study must always be made to ensure that the
paving lanes (longitudinal construction joints vs transverse joints) are laid out in the right direction for the
contractor's efficient work--particularly where the area has irregular boundaries.
c. Spacing. Longitudinal construction joints should be spaced such that the widths of pioneer
(pilot) lanes are all equal and any variability in total distance is taken care of in a few fill-in lanes, where
setting the paver width is not such a problem. Except where impractical, the jointing pattern should not
require slabs that have one side exceeding the other by more than 25 percent; if any slab exceeds this, it
must be reinforced--an extra expense.
d. Longitudinal Construction Joints. Never should longitudinal construction joints be spaced by
simply dividing the overall distance into a whole number of lanes of equal width, unless that width comes
out to an easily used value for the paving operations. If practical, pioneer lanes should have widths in
multiples of 6 inches, or, if metric is used for the project, multiples of 250 millimeters. Extensions to the
paver are easily made in these intervals. Other, odd intervals can be used, but they are more expensive
for the contractor to adjust. Fill-in lane widths should be reasonably close to the pioneer lanes, and all
fill-in lanes can be made the same width as necessary to accommodate the total distance. However, if
the take-up distance is small, it is usually better to provide it in just one or two lanes and make the rest of
the fill-in lanes uniform in width--simply to reduce the chance of measurement error during construction.