Concrete Products

FEB 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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Page 58 of 77 February 2019 • 55 TECHNICAL TALK 2019 TRB MEETING • The use of nanosilica coating as bonding agents to improve bond per- formance of connections in PBEs would result in a slight cost increase with respect to the control. "The use of nanosilica coatings as bonding agents shows great promise, mainly because of their relative low cost, improvement of bond strength, and potential durability enhancement of the bonded region (i.e., interface)," the authors state. "The benefits would not be limited to precast bridge element connections applications, but also to any existing cold joint in an infrastructure." FINITE ELEMENT ANALYSIS GIVES CLUES TO PRECAST PAVEMENT PERFORMANCE The change in performance-related environmental responses for precast/prestressed concrete pavement (PPCP) systems due to dif- ferent conditions can be accurately forecast using finite element analysis (FEA), say Kukjoo Kim, Republic of Korea-U.S. Army Com- bined Division; and Sanghyun Chun, Bongsuk Park, Sangyoung Han, Engineering School of Sustainable Infrastructure and Environment, University of Florida-Gainesville, in their technical paper, Analytical Approach to Predict Environmental Behavior of Precast Prestressed Concrete Pavement System. PPCP systems have become more popular in recent years due to their ability to improve pavement performance, their cost efficien- cies, and abilities to reduce construction time for early opening to traffic. "The peculiar characteristics of PPCP systems include the application of precast concrete slabs [that are] post-tensioned and compressed concurrently with longitudinal and transverse post-ten- sioning of steel strands," the authors write. Increased prestressing force helps induce compressive stresses in the slab, so the concrete panel behaves as a thicker pavement, they say. "Also, the prestressing forces provide additional capability to overcome any inconsistencies in the subgrade underneath the PPCP, and to control crack width by confinement effect," they add. "Previous research has widely reported that the PPCP system is able to improve durability and constructability, as well as to minimize traffic disruption to the public." In this study, the 3-D FE model was developed to evaluate the environmental response characteristics of PPCP system under typ- ical severe temperature gradient conditions, say Kim, et al.. "The FE model was calibrated by matching the analytical FWD deflection basins with the measured FWD deflection basins obtained from PPCP test road," authors observe. "The model developed was then utilized to perform a numerical analysis for determination of the curling deflections and curling stresses by changing the important pavement parameters (i.e. prestress forces, concrete property, and subgrade stiffness) known to control its performance." The main findings are: • The 3-D FE model developed for PPCP system was capable of providing a reliable prediction in terms of the change in environmental behavior of PPCP due to different conditions. • Curling stresses in PPCP system were greatly influenced by the change in prestress forces. The maximum tensile stresses in PPCP system occur at the edge of the slab along the transverse centerline where the region was diminutively affected by the prestressing force. • Thermal stress predicted in the concrete slab increased significantly as the concrete modulus increased. This indicates that the higher concrete modulus will increase the curling stresses in the concrete that may result in increased potential for cracking of the PPCP panels. • The maximum curling stress decreased with increase in subgrade stiff- ness. However, the effect of the subgrade stiffness on change in curling stresses appears to be relatively negligible. Continued on page 54

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