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Frequently Asked RCC Questions
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FAQs > Proper joint spacing
What is the proper joint spacing for RCC pavements?
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| Cutting joint for RCC pavement at Honda facility
in Alabama |
There have been many RCC pavement projects that have been built
without contraction joints and have performed satisfactorily. In
particular, industrial pavements where appearance is not a major
concern and the design incorporates the random cracking, contraction
joints have been eliminated for economic reasons. Random cracks
will typically form from about 30 ft (9 m) to more than 60 ft (18
m) apart. Since it is impractical to install dowel bars in RCC,
the load transfer is provided through aggregate interlock. Crack
openings that form randomly at long spacings tend to be wide and
consequently will provide less aggregate interlock than closely
spaced cracks.
For projects where crack control is important, contraction joints
are used to control the location of cracking in the concrete. Joint
spacing should follow similar concepts as used for conventional
concrete pavement. Because RCC has less shrinkage than conventional
concrete, the control joints can be spaced further apart. Proper
joint spacing depends on pavement thickness, concrete and subbase
properties, aggregate type and climatic conditions.
Current practice for RCC pavements is to space control joints from
20 ft (6m) to 30 ft (9m). As a rule of thumb, transverse joint spacing
should be about 40 times the pavement thickness with a maximum spacing
of 30 ft (9 m). The reason for the 30 ft (9m) maximum spacing is
to ensure that the shrinkage cracks are narrow enough to provide
adequate load transfer.
It is also important to keep the slabs as square as possible. Transverse
joint spacing should not exceed 125% to 150% of the longitudinal
joint spacing. Joints should be sawn as soon as the concrete has
obtained adequate strength to resist raveling of the joint edges.
Early entry saws work best for this type of work, and can often
be used within 2-3 hours after compaction. The depth of the saw
cut should be at least one-fourth the thickness of the slab (D/4)
and have a minimum width of 1/8 in. (3 mm).
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