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2 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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3 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