# 6506-11 - GYRTORY TESTING MACHINE (GTM) developed by John...

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GYRTORY TESTING MACHINE (GTM) developed by John L. McRae Schematic Section of the GTM OIL AND AIR UPPER ROLLER The GTM compacts a sample through a gyrating action. The gyrating action of the GTM simulates the traffic compaction on the asphalt mixture The shear stresses experienced by the pavement as a vehicle goes over it are similar to the shear stresses experienced by the specimen during gyratory compaction. COMPACTION VARIABLES IN THE GTM 1. Ram pressure - the vertical pressure applied to the specimen. Usually a ram pressure equal to the maximum expected tire pressure is used (e.g. 120 psi) 2. Gyratory angle - initial angle of 1 to 3° is typically used. (Compactive effort increases with higher angle) 3. Type of roller Fixed, Oil or Air roller 4. Number of revolutions - typically 60 to 200 revolutions are used to simulate ultimate compaction condition. The GTM as a Testing Machine The following properties are measured during the compaction of the test samples: (1) Gyrograph – a recording of the shear strain experienced by the sample during compaction. From the gyrograph, the following property can be calculated: Gyratory Stability Index (GSI) = θ max / θ I where θ max = maximum gyratory angle θ I = initial gyratory angle A stable mixture will have a GSI of 1or close to 1. A GSI of greater than 1 indicates instability of the mix. Gyrograph

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## This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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6506-11 - GYRTORY TESTING MACHINE (GTM) developed by John...

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