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 62 of 77 February 2019 • 59 TECHNICAL TALK 2019 TRB MEETING PREFABRICATED ULTRA HIGH PERFORMANCE CONCRETE BRIDGE UNITS DOUBLE AS STAY-IN-PLACE FORMWORK A study shows the feasibility of using a prefabricated ultra high performance concrete (UHPC) shell as stay-in-place formwork, say Atorod Azizinamini, Ph.D., P.E., director, Accelerated Bridge Construc- tion, University Transportation Center, and Shahryar Reheat and Amir Sadeghnejad, all of Florida International University, Miami, in their technical paper, Enhancing Resiliency and Delivery of Bridge Elements Using Ultra High Performance Concrete as Formwork. "The core concept of this idea is prefabrication of UHPC shell, which acts as a stay-in-place formwork," the authors say. "In the proposed approach, after transporting the UHPC shell to site, the con- struction of structural element is completed by placing a reinforcing cage inside the UHPC shell and post-pouring with normal concrete." The superior properties of UHPC provides an excellent means to enhance the service life of bridge elements and make them resilient against weather, while eliminating the need for placement or removal of formwork, Azizinamini, Rehmat, Sadeghnejad write. As a proof of concept, combination of experimental and numerical study was conducted. Prior to conducting experimental work, numeri- cal study in the form of a finite element (FE) analysis was carried out to investigate performance of the UHPC shell during placement of the normal concrete. To provide a base line comparison between UHPC shell formwork and conventional methods, two large scale specimens were constructed and tested under three-point load setup. "The shell test specimen demonstrated flexural strength, 14 per- cent greater than companion normal strength concrete specimen," Azizinamini, Rehmat, Sadeghnejad write. The UHPC shell test spec- imen did fail as debonding of the shell at the interface took place, with development of a large crack in the shell. "The shell test specimen exhibited improved levels of ductility before failure," the authors observe, adding the proof-of-concept tests demonstrated that the idea is feasible and useful for Accelerated Bridge Construction applications. Based on the study, they conclude: • Compared to control beam made by conventional methods, the UHPC shell beam demonstrated an increase in flexure capacity by 14 percent, and ductility by 30 percent. • The ribs set inside the formwork shell did not provide sufficient bond for composite action. Improvement to shear transfer mechanism through use of shear studs or closely spaced ribs needs to be considered. • The strain behavior during load tests exhibited a gradual increase in difference of strain for surface and embedded vibrating wire gauges. This difference is attributed to gradual debonding of shell formwork from normal concrete (NC). • The shrinkage monitoring indicated that NC inside the UHPC shell experienced shrinkage, resulting in tensile stress in NC. Because of the system being in equilibrium, the tensile stress in the NC is balanced by compressive stress in UHPC shell. • The thickness of formwork shell was based on preliminary FE analysis. However, the actual thickness provided in the experimental study was conservative. Based on experimental results, the FE will be calibrated and a parametric analysis carried out to optimize the proportions for economy. • From a construction stand-point, self-consolidating properties and flow- ability allowed shaping UHPC into a shell configuration. The fibers in the UHPC were uniformly distributed over the depth of the shell. Shrinkage cracks were not observed in either UHPC or the post-poured NC. Construction stages for a UHPC beam: a) casting of UHPC; b) re- moval of Styrofoam; c) placing rebar cage within; and d) casting of normal concrete. PHOTOS: Azizinamini, Rehmat, Sadeghnejad Construction stages for UHPC shell formwork. SCHEMATIC: Azizinamini, Rehmat, Sadeghnejad BOOTH #860 © 2019 Cresset Chemical / Folio 7008-0219 C R E S S E T . C O M GREEN T E C H A M E R I C A' S M O S T P R E F E R R E D C O N C R E T E R E L E A S E A G E N T S Want concrete results like this? Use Cresset release agents.

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