Concrete Products

MAR 2016

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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52 • March 2016 www.concreteproducts.com During the second week of January, the epicenter of the transpor- tation world was Washington, D.C. and the 95th annual meeting of the Transportation Research Board. Over 12,000 transportation pro- fessionals from around the world came to see more than 5,000 presen- tations in nearly 800 sessions and workshops. Concrete Products was there. Here are summaries of some of the most pertinent peer-reviewed technical papers in precast/prestressed concrete presented at TRB. Next issue we will look at new research in ready-mixed concrete and cast-in-place structures. For more infor- mation about the 2017 meeting, or to obtain the full 2016 meeting papers, visit www.trb.org. TTI TESTS SHOW NEW-DESIGN BARRIER MEETS AASHTO SPECS A new-design, modular precast concrete traffic barrier with support- ing wall units has potential for use in transportation infrastructure, based on test results presented at TRB. Testing showed the Gravix TL-4 barrier met all the strength and safety performance criteria of AASHTO's Manual for Assessing Safety Hardware (MASH) TL-4 specs, say William F. Williams, P.E., associate research engineer, Texas Trans- portation Institute (TTI), and Thomas Rainey, P.E., president, Earth Wall Products, Marietta, Ga., in their paper, Design & Full Scale Testing of Gravix Modular Barrier and Retaining Wall System. This product presents potential savings in construction, as it relies on on-site backfill, rather than material trucked in. "Gravix is an earth retaining wall system that was created to meet the need for a retaining wall system that makes use of on-site backfill, vs. bringing in select or off site select fill for backfill behind retaining walls," the authors note. The units vary in stem depth dependent upon the wall height as well as surcharge, and a typical wall section has the longest units at the bottom, getting shorter as they are stacked vertically. "The units incorporate a triangular section in the stem that allows the weight of the backfill to bear on the units below, transferring downward pressure, which results in a stabilizing effect of the wall units," note Williams and Rainey. "In combination, the units will create a coherent gravity mass designed to resist overturning, sliding and bearing failure." For this project, TTI crash-tested a barier unit consisting of a 36-in. high single slope traffic barrier. The modular units were 8 ft. long and 7 ft. high. In anticipation of the test, extensive analysis was performed to design the steel reinforcement and concrete geometry required to resist the anticipated impact load. "The units are precast concrete, a good sustainability material, providing one of the longest design lives for buried structures," Wil- liams and Rainey say. During tests, the Gravix TL-4 barrier met all the strength and safe- ty performance criteria. "The vehicle did not override or penetrate through the barrier, and therefore met all the performance require- ments for MAST TL-4 Specifications," the authors conclude. Further improvements were made to the barrier system by improving the strength and the gap tolerance of the tongue and groove connection. The tongue thickness was increased by 1/2-in., which will further reduce the permanent deformation that was observed (3/4-inch) in the crash test. Continued on page 54 TECHNICAL TALK BY TOM KUENNEN Precast barriers, double tee girders get look at TRB 2016 Installation of Gravix barrier prior to testing Isometric view of precast Gravix barrier unit IMAGE, PHOTOS: Williams and Rainey

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