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This work was performed to investigate modernization of the equipment used for the physical testing of gypsum board that has not been basically changed over a period of many years and is not commercially available. A comprehensive study has been made using a commercially available machine for three strength tests, with the expectation that this type of equipment might be incorporated into ASTM methods and specifications in the future. Technical advances in the methods of evaluating gypsum board are desirable in a progressive industry.
The procedure used was to run the three major physical tests: flexural strength; core, end, and edge hardness; and nail pull resistance on a machine using constant strain rate loading and compare those results with those obtained on the commonly used ASTM specified machine that uses a constant stress rate. A TM 51008 tester made by Testing Machines, Inc. was used for the work reported in this paper. Comparative tests were made on equipment conforming to the specifications of ASTM Physical Testing of Gypsum Board Products, Gypsum Lath, Gypsum Partition Tile or Block, and Precast Reinforced Gypsum Slabs (C 473). Preliminary work was done in a research laboratory to develop the fixtures and procedures necessary to use the new equipment. The machine was then placed in a manufacturing plant and duplicate tests on all types of board products were run for a period of several months.
Data will be presented to show that the constant strain rate method of testing can give equally precise results with a very substantial saving in time and physical effort. For flexural strength, nail pull resistance, and core hardness there is a simple linear correlation between the results with the two machines. The constant strain rate machine can more accurately determine the maximum load causing failure than the constant stress rate machine. Correlation between the results of tests on either machine shows that the core hardness and nail pull resistance tests tend to duplicate information on core properties.
gypsum, physical tests, physical properties, gypsum board, constant stress, constant strain
Research associate, United States Gypsum Company, Graham J. Morgan Research Center, Libertyville, IL