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34 CHAPTER 4 Conclusions and Suggested Research 4.1 Conclusions Using the data derived from the laboratory tests, a finite ele- ment model was calibrated and used to analyze a broader range This report documents the field evaluation, laboratory of dowel misalignment combinations and magnitudes. The field testing, finite element modeling, and methodology used to evaluation indicated no strong links between small amounts develop mechanistic-based dowel alignment guidelines suit- of dowel misalignment and performance in terms of faulting, able for use by highway agencies, consultants, contractors, and spalling, or panel cracking. However, the laboratory testing others involved in the design and construction of concrete and analytical modeling determined that dowel misalignment pavements. could reduce dowel shear capacity and its ability to transfer a Measurement of misalignment (and associated distress) of load and can have the following effect on pavement distresses: more than 35,000 dowels in more than 2,300 transverse joints of 60 projects in 17 states indicated the following ranges for Transverse cracking. Dowel misalignment is not a primary dowel misalignment of most joints: cause or contributor to the development of transverse crack- ing. The increase in longitudinal stresses caused by dowel Longitudinal translation: 2 in. [51 mm] over 18 in. misalignment has a smaller effect in cracking than variabil- [457mm] dowels. ity in other parameters (concrete slab thickness, concrete Vertical translation: 0.5 in. [13 mm] for pavements 12 in. strength, joint spacing, dowel-concrete friction, etc.). [305 mm] or less in thickness. Joint faulting. Any type of dowel misalignment (translational Rotational components (horizontal skew and vertical tilt): or rotational) above a certain magnitude contributes to an each less than 0.5 in. [13 mm] over 18 in. [457 mm] dowels. increase in faulting potential. The dowel shear capacity and joint stiffness decreases as the level of misalignment increases. These levels of misalignment generally have no significant Dowel misalignment has a similar effect on joint perform- effects on pavement performance. ance as a reduction in the diameter of dowels. Therefore, the Extensive laboratory testing was conducted to evaluate the equivalent dowel diameter concept is appropriate for predict- effect of dowel misalignment on performance parameters such ing performance for pavements with misaligned dowels. as pullout force, shear capacity, and shear stiffness. These tests Joint spalling. A reduction in concrete cover because of indicated the following: vertical translation and/or tilt beyond a critical level increases the potential for spalling development. Extreme longitudinal and vertical translation can cause IRI. Because dowel misalignment increases faulting and significant reductions in shear capacity. spalling potential, it will affect ride quality and IRI. A combination of low concrete cover and low embedment length has a more adverse effect on dowel performance An MEPDG-based procedure was developed to quantify than either one of the two misalignments. the effect of dowel misalignment on pavement performance. Dowel rotations of up to 2 in. over 18 in. [51 mm over In this procedure, an equivalent dowel diameter is calculated 457 mm] length have a negligible effect on pullout and shear for the joint based on type and level of dowel misalignment performance measures. in a joint. The mean equivalent dowel diameter is calculated Pullout of ungreased dowels requires a significantly higher for each section and is used in MEPDG analysis to predict force than for greased dowels, suggesting that a lack of grease pavement distresses. may restrain a doweled joint from opening and closing and Guidelines for dowel alignment have been prepared and cause joint lockup. are included as Attachment A to this report. These guidelines