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

critical, as the restraint forces due to misalignment are
directly proportional to the'amount of slab movement. In
addition, the effect of two slabs acting as one as the result of
a locked or "frozen" joint is not as severe for the shorter slab
lengths.
In order to perform satisfactorily, dowels must also be
reasonably aligned. The prevailing practice is to specify dowel
alignment tolerances on the order of 1 percent, or roughly 1/8inch,per
foot. This frequently results in a high percentage of
the dowels being "out of specs@' and gives the impression that
obtaining proper dowel alignment is very difficult. Studies(6'(7'
suggest that the alignment tolerances can be relaxed. FHWA now
recommends an alignment tolerance of l/4 inch per foot and will
be evaluating the possibility that these tolerances can be
further relaxed. It is recognized that the problems with
misaligned dowels are generally the result of gross misalignment
occurring during concrete placement. Equipment to precisely
measure compliance with alignment tolerances after concrete
placement are not readily available. However, it is recommended.
that the completed pavement joints be inspected using a metal
detector to verify that no significant dowel misalignment has
occurred.
The use of mechanical dowel bar inserters holds promise for the
improved installation of dowel bars. Two manufacturers, Guntert-
Zimmerman and Gomaco, have developed and are marketing new
automatic inserters. It is their claim that these inserters are
capable of placing dowels more efficiently and at less cost than
basket assemblies without sacrificing placement accuracy.
Construction Technology Laboratories was recently retained to
monitor the results of the placement of dowels using these new
machines. The Guntert-Zimmerman inserter was evaluated on
projects in Texas and Wisconsin and the Gomaco inserter was
evaluated on an Idaho project. The placement of dowels using
basket assemblies was also monitored in Texas and Wisconsin,
Preliminary findings indicate that the inserters placed the
dowels with approximately the same accuracy as dowels placed
using basket assemblies. Cost figures from the Wisconsin study
indicate that a savings of approximately $ 0.35 per sq. yd. of
concrete pavement was obtained by using the dowel implanter in
lieu of dowel baskets.
The use of dowels is strongly encouraged on all pavements except
possibly those with very low truck volumes. Dowels can provide a
higher serviceability level over a longer period of time than
pavements relying only on aggregate interlock for load transfer.
Dowels can minimize pavement distress caused by overloads or
heavier loads travelling by permit.
3.2.4