Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
34 4.1 Conclusions This report documents the field evaluation, laboratory testing, finite element modeling, and methodology used to develop mechanistic-based dowel alignment guidelines suit- able for use by highway agencies, consultants, contractors, and others involved in the design and construction of concrete pavements. Measurement of misalignment (and associated distress) of more than 35,000 dowels in more than 2,300 transverse joints of 60 projects in 17 states indicated the following ranges for dowel misalignment of most joints: ⢠Longitudinal translation: ± 2 in. [51 mm] over 18 in. [457mm] dowels. ⢠Vertical translation: ± 0.5 in. [13 mm] for pavements 12 in. [305 mm] or less in thickness. ⢠Rotational components (horizontal skew and vertical tilt): each less than 0.5 in. [13 mm] over 18 in. [457 mm] dowels. These levels of misalignment generally have no significant effects on pavement performance. Extensive laboratory testing was conducted to evaluate the effect of dowel misalignment on performance parameters such as pullout force, shear capacity, and shear stiffness. These tests indicated the following: ⢠Extreme longitudinal and vertical translation can cause significant reductions in shear capacity. ⢠A combination of low concrete cover and low embedment length has a more adverse effect on dowel performance than either one of the two misalignments. ⢠Dowel rotations of up to 2 in. over 18 in. [51 mm over 457 mm] length have a negligible effect on pullout and shear performance measures. ⢠Pullout of ungreased dowels requires a significantly higher force than for greased dowels, suggesting that a lack of grease may restrain a doweled joint from opening and closing and cause joint lockup. Using the data derived from the laboratory tests, a finite ele- ment model was calibrated and used to analyze a broader range of dowel misalignment combinations and magnitudes. The field evaluation indicated no strong links between small amounts of dowel misalignment and performance in terms of faulting, spalling, or panel cracking. However, the laboratory testing and analytical modeling determined that dowel misalignment could reduce dowel shear capacity and its ability to transfer a load and can have the following effect on pavement distresses: ⢠Transverse cracking. Dowel misalignment is not a primary cause or contributor to the development of transverse crack- ing. The increase in longitudinal stresses caused by dowel misalignment has a smaller effect in cracking than variabil- ity in other parameters (concrete slab thickness, concrete strength, joint spacing, dowel-concrete friction, etc.). ⢠Joint faulting. Any type of dowel misalignment (translational or rotational) above a certain magnitude contributes to an increase in faulting potential. The dowel shear capacity and joint stiffness decreases as the level of misalignment increases. Dowel misalignment has a similar effect on joint perform- ance as a reduction in the diameter of dowels. Therefore, the equivalent dowel diameter concept is appropriate for predict- ing performance for pavements with misaligned dowels. ⢠Joint spalling. A reduction in concrete cover because of vertical translation and/or tilt beyond a critical level increases the potential for spalling development. ⢠IRI. Because dowel misalignment increases faulting and spalling potential, it will affect ride quality and IRI. An MEPDG-based procedure was developed to quantify the effect of dowel misalignment on pavement performance. In this procedure, an equivalent dowel diameter is calculated for the joint based on type and level of dowel misalignment in a joint. The mean equivalent dowel diameter is calculated for each section and is used in MEPDG analysis to predict pavement distresses. Guidelines for dowel alignment have been prepared and are included as Attachment A to this report. These guidelines C H A P T E R 4 Conclusions and Suggested Research
35 provide information on measuring dowel misalignment, quan- tifying the effects of misaligned dowels on pavement perform- ance, determining critical levels of dowel misalignment, and the means for preventing dowel misalignment and mitigating or remedying the effects of misaligned dowels. The finite element analysis confirmed the findings of the laboratory testing that PCC-dowel friction and/or bond strength due to lack of proper bond breaker or dowel corrosion may cause more restrain to joint opening and closing than dowel rotational misalignment of typical levels. 4.2 Suggested Research Although the findings of this project were based on a sig- nificant amount of field and laboratory measurement and finite element analysis, additional studies would help improve these findings and the recommended guidelines. Such studies may include the following: 1. Evaluation of in-service pavement sections with high mis- alignment levels after they have been exposed to traffic to determine the effect of these misalignments on the long- term pavement performance and further evaluate the equiv- alent dowel diameter concept. 2. Laboratory investigations of the influence of concrete mixtures, curing procedures, and other construction factors on misalignment. 3. Investigation of approaches and concepts for improving dowel placement. 4. Investigation of the mechanisms associated with joint lockup and the premature cracking and spalling in the proximity of transverse joints.
