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CHAPTER 2
Research Methodology
2.1 Introduction (initially placing the dowels in an incorrect position or saw
cutting at the incorrect location), displacement (movement
This section describes the purpose of transverse joints and during or following the paving operation), or both.
dowels in concrete pavements, introduces dowel misalignment The following major categories of dowel misalignments
terminology used in this study, and gives an overview of the were identified by Tayabji (1986) (see Figure 2.2):
dowel misalignment specifications used by various transporta-
tion agencies. · Longitudinal translation;
· Vertical translation;
2.1.1 Joints and Dowels in · Horizontal skew; and
Concrete Pavements · Vertical tilt.
Joints are introduced in PCC pavements to allow for Vertical translation refers to the deviation of the position
thermal expansion and contraction, as well as shrinkage after of the dowel relative to the reference mid-depth position. How-
construction. To improve load transfer across the transverse ever, because concrete cover describes the distance between
joints (thus minimizing faulting and corner breaks), many the dowel and slab surface, it also reflects the vertical positions
transportation agencies place dowels at mid-depth between the of the dowel and its vertical translations.
pavement slabs using either basket assemblies or an automated
dowel bar inserter (DBI) (McGhee, 1995). The load transfer
concept is illustrated in Figure 2.1 (PCA, 1991). When a wheel 2.1.3 Current Specifications
load is applied to an undowelled joint, greater edge and corner Different states have adopted different requirements for
deflections (and corresponding stresses) are experienced. Dowel dowel bar tolerances with respect to longitudinal and vertical
bars reduce the critical deflections and stresses by transferring translation, horizontal skew, and vertical tilt (see Table 2.1).
the load between the slabs. Several studies, including Yu et al. These tolerances can be expressed as absolute maximum
(1998), Khazanovich et al. (1998), and Hoerner et al. (2000), measures or as percentages of the length of the dowel or thick-
concluded that properly designed and installed dowels greatly ness of the concrete. Many states have adopted the FHWA-
reduce transverse joint faulting and corner cracking. Dowels recommended limits for horizontal skew and vertical tilt of
should maximize vertical load transfer, minimize longitudinal 1
/4 in. over 12 in. (6.3 mm over 305 mm) or 2% (FHWA, 1990).
restraint, and be durable (Lechner, 2005). FHWA recommended further studies to determine the validity
of this 2% tolerance (FHWA, 1990). The American Concrete
Pavement Association (ACPA) recommends limits of 3/8 in.
2.1.2 Terminology
over 12 in. (9.5 mm over 305 mm) or 3% based on NCHRP
Ideally, dowel bars should be placed such that the longitu- Synthesis 56 (ACPA, 2004; NCHRP, 1979).
dinal axis is parallel to both the surface and centerline of the The data provided in Table 2.1 were obtained from literature
hardened PCC slab, and the geometric center of the dowel bar review (MCC, 2004; Lechner, 2005) and communications with
is directly below the joint. If dowel position in the hardened state department of transportation (DOT) representatives.
concrete deviates from this ideal position, it is said to be Table 2.2 gives the dowel bar alignment tolerances permitted
misaligned. Misalignment may result from misplacement in the construction specifications of the Ministry of Trans-
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Figure 2.2. Types of dowel misalignment
Figure 2.1. Effectiveness of load transfer (adopted from Tayabji, 1986).
(PCA, 1991).
Table 2.1. Specified dowel misalignments limits.
Longitudinal Vertical
Vertical Tilt Horizontal Skew
Agency Translation Translation
in. per 18 in. in. per 18 in. in. per 18 in. in.
Arkansas
Connecticut
Federal Aviation
Administration
Hawaii
Idaho
Kentucky
Minnesota 0.25 0.25 N/A N/A
Texas
Utah
Wisconsin
Nebraska
Iowa
Michigan
Montana 0.25 0.25 0.50 0.50
North Dakota
0.25 0.25 0.25 0.25
Tennessee
Ontario 0.24 0.24 0.59 0.59
Nevada 0.50 0.50 N/A N/A
Missouri 0.50 0.50 0.50 1.00
1/10 Pavement
Kansas 0.38 0.38 N/A
Depth
Indiana
0.38 0.38 N/A N/A
North Carolina
Illinois
0.19 0.19 N/A N/A
Delaware
South Carolina 0.56 0.56 3.00 0.75
Georgia 0.562 0.562 N/A N/A
Germany 0.75 0.75 2.00 N/A
Alabama 0.25 0.69 N/A N/A
Great Britain 0.39 0.39 N/A N/A
New York N/A 0.16 0.25 0.26
Ohio N/A N/A 0.50 0.50
Pennsylvania 0.23 0.23 1.00 1.00
