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

INTRODUCTION
Traditionally, the dowel bars at Portland Cement Concrete (PCC,
transverse pavement joints have been placed using wire basket
assemblies, which are staked to the base prior to paving. Dowel
basket assemblies are expensive, and their placement is labor
intensive. For at least three decades, contractors and equipment
manufacturers have been trying to develop a piece of paving
equipment which can accurately place dowels in the plastic
concrete at transverse joints, to eliminate the need for dowel
baskets.
In the days of side form paving, a machine was developed and used
in several states that was doing an acceptable job of vibrating
dowels in ahead of the final finishing machine, but with the
advent of slipform paving this machine proved unsatisfactory. If
the dowels were placed between the spreader and the slipform, the
dowels tended to settle or move horizontally when the slipform
passed over them. If the dowels were vibrated in behind the
slipform paver, there was a depression at the joint location
which could not be removed by hand finishing with a
straightedge.(l)
In recent years many states, including Wisconsin, are specifying
dowels in all transverse joints on heavily trafficked PCC
pavements, due to excessive faulting which has occurred on
existing pavements without dowels. Shorter joint spacings are
now also commonly used, which require many more dowel baskets &
mile of pavement.
These changes in design policy have stimulated
even greater interest in developing a mechanical dowel bar
inserter that will work with a slipform paver.
For several years a mechanical dowel bar inserter made by Guntert
C Zimmerman has been used in Europe with reported success. A
Wisconsin paving contractor purchased one of these machines, and
was granted an opportunity to use it on an experimental basis on
a project on I-90 at Janesville in 1987. Construction Technology
Laboratories, Inc., of Skokie,
IL (CTL) was retained to conduct a
study of the dowel placement accuracy of the inserter versus
baskets on the Janesville project, using a ground penetrating
radar system.
The report from this study was reviewed by WisDOT staff, and the
study results were found to be inconclusive. This was
principally due to sh&tcomings of the ground penetrating radar
technology used in the study. The problems included lack of
precision of the measurements for some of the dowel placement
parameters, and marginal correlation between the radar data and
coring results. Consensus opinion of the WisDOT staff was that
additional investigation was needed before the dowel inserter
could be approved for general use.
Numbers in parentheses denote references given at end of repor
3.5.6