|New Round-Panel Test Evaluates the Performance of Alternative Concrete Reinforcement Systems |
In September, ASTM Committee C09 on Concrete and Concrete Aggregates approved a significant new test for the concrete industry: C 1550, Standard Test Method for Flexural Toughness of Fiber Reinforced Concrete (Using Centrally Loaded Round Panel).
According to its developers, when the test method is used with performance-based specifications, engineers can specify the appropriate level of post-crack performance (toughness) required to maintain the integrity of joints in concrete slabs on grade, and verify the quality of fiber-reinforced shotcrete used for rock support in tunnels and mines.
The test involves the imposition of a point load to the center of a round concrete panel supported on three symmetric pivots and is primarily intended to assess the post-cracking performance of fiber-reinforced concrete and shotcrete, says its chief author, Dr. Stefan Bernard, TSE Pty. Ltd., Australia, who developed the standard with a C09 task group for quality control of fiber-reinforced shotcrete used in the construction of tunnel linings.
The test offers significant advantages over alternative methods of performance assessment because the within-batch Coefficient of Variation averages about 6-7 percent compared to between 15-18 percent for beams made of the same material, says Bernard. This is widely acknowledged as a very important advantage in QC testing.
Designers, testing consultants, fiber manufacturers, and academics created the new standard through voluntary consensus. Matt Miltenberger, senior project engineer, Master Builders, Inc., Cleveland, was on the task group. Testing the flexural toughness of fiber-reinforced concrete with the round panel method is important, he says, because it uses plate specimens that mimic the biaxial bending behavior of slabs and tunnel linings.
This new test method allows a direct comparison between fiber and conventional reinforcement because the plate specimens are large enough to incorporate standard welded wire fabric, Miltenberger continues. With this test, the engineering community can address the issue of equivalent performance between reinforcement systems, an issue that engineers have been struggling with for over a decade. The round panel shape is much easier to handle than square panels, which results in cost savings.
The elimination of saw-cutting reduces the cost of QC testing, Bernard explains. Many thousands of round-panel specimens have already been used for QC purposes in Australia where the test has been adopted as the principal performance assessment tool for fiber-reinforced shotcrete by the Roads and Traffic Authority of New South Wales.
FIber-reinforced concrete slabs on grade typically are used in highways, basements, and manufacturing facilities. The problem with conventional reinforcement is that the reinforcement needs to be located in the top third of the slab to perform effectively, Miltenberger says. However, the location of the reinforcement is controlled by the laborers working for the concrete-finishing contractor, and many times it is not located properly. One of the benefits of fiber reinforcement is that the fibers are distributed throughout the concrete. So, when the proper fiber and loading are specified for an application, the slabs performance is more reliable.
Direct technical questions to Dr. Stefan Bernard, TSE Pty. Ltd., Australia (phone: 61 418 407 892) or Matt Miltenberger, Master Builders, Inc., Cleveland, Ohio (phone: 216/839-7387). Committee C09 meets Dec. 8-11 in Miami Beach, Fla. For membership details, contact Jim Olshefsky, director, Committee Services, ASTM International (phone: 610/832-9714). //
Copyright 2002, ASTM