chapter 3 rigid pavement - DOT On-Line Publications - Department ...

during the AASHO Road Test. One transverse joint faulted
seriously, but investigation showed that the joint had been
accidently sawed at some distance beyond the end of the dowel.
Over the two-year test period, there were no other cases of
measurable faulting at the joints, all of which were doweled.
Based on road tests performed at the NARDO track in Italy, the
XVIII World Road Congress reported that dowels significantly
increased the pavement service life"'
Dowels reduce deflections at the joint, which in turn reduce the
magnitude of concrete flexural stresses. These deflections and
stresses are reduced due to the load being more effectively
shared with the adjoining slab through shear and bending stresses
in the-dowel itself. Reduced concrete flexural stresses increase
the fatigue life of the pavement and thus extend its service
life. A theoretical analysis indicates that a 10" doweled slab
with 80% load transfer will have the same deflection as a 12"
undoweled slab with only 40% load transfer. Dowels can also
reduce the potential for premature failure due to comer breaking
caused by loss of,subgrade support through pumping.
When dowels are properly designed and installed, they can reduce
faulting and increase the pavement's se-ice life. When they are
not, dowels can cause premature failure of the pavement in the
vicinity of the joint. Dowels too small in diameter to handle
the necessary stresses have resulted in premature joint failures.
Excessive concrete bearing stresses have crushed the concrete
around the dowels and allowed faulting to occur. Considerable
research has been performed recently which supports the use of
larger bars (l-1/4 to l-1/2 inch). The AASHTO Guide for Design
of Pavement Structures recommends a dowel diameter of l/Sth the
pavement thickness, with the dowels placed near the center of the
slab to minimize bending stresses. Most States are currently
using, as a minimum, l-1/4 inch diameter bars, with good results.
Most States are using dowels 18 inches long spaced at 12 inches
and are reporting no problems.
Dowels should also be corrosion-resistant. The use of epoxy-
coated or stainless-steel dowels has been shown to provide the
necessary resistance to corrosion. It is important that a bond-
breaker be applied to the dowels to allow the slabs to freely and
independently expand and contract without developing restraint
forces. This bond-breaker should be applied to provide a thin
but uniform coating.
Many of the past performance problems associated with doweled
joints were the result of excessive joint spacings, ranging from
60 to 100 ft. The trend to plain doweled slabs with joint
spacings of 15 to 20 ft. eliminates many of these problems.
Shorter joint spacings result in smaller crack widths, which
reduce the stresses acting on the dowels. The shorter spacing
also reduces slab movement, which makes dowel alignment less
3.2.3