Abstract
The ASTM C1550 round panel test is used to assess the post-crack performance of fiber reinforced concrete (FRC) and fiber reinforced shotcrete (FRS) and has become firmly established as the most repeatable means of post-crack performance assessment available for these materials. When the test method was first published, two methods of test machine control were permitted: displacement control, in which the displacement of the loading actuator is used as the control parameter in the test, and strain control, in which the central deflection of the specimen is used as the controlling parameter. Both these methods of control, however, require expensive testing machines, with the result that some operators have used cheaper open-loop machines to test ASTM C1550 round panels. Doubts have arisen among specifiers of FRC and FRS in tunneling and mining projects as to whether specimens tested using open-loop machines result in the same apparent performance as would be expected using displacement- or strain-controlled testing machines. This investigation has established that under certain circumstances, an open-loop testing machine can produce results for ASTM C1550 panels that are similar to results obtained using a strain- or displacement-controlled testing machine. It was also found that the measurement of specimen deflection on the underside of the panel is problematic at large deformations and can lead to substantial variations in apparent performance.
