U.S Crops of Engineers Gyratory Testing Machine on Rainhart Co.

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	U.S Crops of Engineers Gyratory Testing Machine
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	larger image		The GTM is combination compaction and simple-shear testing machine, suited to use with cylindrical specimens of soils and base course materials as well as bituminous mixes, Desired vertical loading (anticipated maximum tire contact pressure for bituminous surface course) and degree of shear strain (gyratory angle) are selected. Then sample material is placed in the mold, the mold is clamped in the chuck, and the machine is started. Upper and lower rollers travel around the chuck flange to transmit a gyrating kneading motion to the specimen based on a user preset gyratory angle from 0° to 3° between the rollers. While this machine induced angle is fixed, the angle developed by the floating mold chuck varies depending on quality of the sample mix. The magnitude of the floating angle is due to dilation of material during the shearing process and represents shear strain. The weaker the material, the higher the floating angle. At the same time, the measured GTM roller pressure decreases as an indicator of reduced shear strength. when voids become over-filled due to excessive densification or excessive voids filling medium (Water in soils or bitumen in pavement mixes), the floating angle increases (excess plasticity) and roller pressure decreases (reduced shear strength). Upper limit of bitumen content at a selected design stress (vertical pressure) is determined as that mix content when the floating angle begins to increase. Determines Gyratory Stability Index (GSI), a measure of plasticity (loss of stability) during densification. Optimum bitumen content is identified independently of voids criteria via floating angle measurements. Establishes unit mass (compaction) requirements by compacting to equilibrium under design vertical stress. This eliminates need for empirical correlations of number of loading cycles to duplicate ultimate field density. Determines Gyratory Strength factor (GSF), a measure of ability to withstand simple shear. Determines Gyratory Static Shear and compressions moduli. Determines Gyratory Compactability Index (GCI), a measure of ease of compaction of a mix. Determines Gyratory Elastic-plastic Index (GEPI) on aggregate alone or on bituminous mix. This index of internal friction is an indicator of aggregate quality. Determines resilient moduli for soil send base course specimens and bituminous pavement specimens at controlled elevated temperatures of 100°F+(24°C+). Desired machine model is selected according to diameters of specimen to be tested as set by maximum aggregate size in the test mixes. The GHM-604 comes with two 4inch (102 mm) dia. molds. GHM-606C also includes two 6 inch (152 mm) dia. molds Largest GHM-608 GTM has two 8 inch (203 mm) dia. molds in addition. All machines include loading plates, carrying trays, and standard spacers for use with molds supplied. Precision ground molds are heat treated to 1500° F (816° C), quenched in oil at 400° F (204° C), and tested to Rockwell C50-55 hardness. All machines include a 1/3 hp hydraulic loading system with adjustable automatic vertical pressure control, an angle-adjustable gearmotor-powered gyrating mechanism (3/4 hp for GHM-604C, 2 hp for others) with roller carriage, adjustable lower roller and interchangeable oil-filled and air-filled upper rollers, mold chuck with thermostatically controlled heating elements, bearing-mounted upper head, and wall friction apparatus. Also included are transducers for measuring gyratory floating angle, specimen height, vertical pressure, roller pressure, and revolutions. A laptop computer with printer, and GTM software is provided along with operating/maintenance manuals. GTM's have resilient modulus capabilities for cyclic as well as constant vertical load, a reduced friction ball-spline shaft for accurate vertical load transmission. and controlled variable speed on the gyrating gearmotor. All machines are caster-mounted for lab mobility. Computer hardware and software for making calculations associated with GTM testing are provided with all GTM models. The integral computer based data acquisition system measures displays and prints out density, shear strength, and shear strain Screen prompts guide the operator during test up. Compaction is automatically terminated at operator-specified conditions. Test options including compaction to equilibrium, to user-specified density, or to user-specified number of revolutions. Calculations are preformed for all GTM parameters including density and stress-strain properties. Results may be printed or stored on disk. Software sections are included for testing subgrade and base coarse materials, and for system calibration