The W-M-255 Low Impact Manual Test Hammer is the instrument used for the non-destructive testing of hardened concrete for thin wall thicknesses. The unit is also used on rock cores, it’s low impact energy not damaging brittle specimens. This easy-to-use instrument provides a quick and simple test for obtaining an immediate indication of concrete strength in various parts of a structure. The minimum verifiable strength is 1400 PSI (10 MPa) to approximately 9000 PSI (62 MPa). All concrete test hammers measure the surface hardness of the material they are testing; this is then correlated to concrete compressive strength.
The Low Impact Test Hammer has a number of specialized applications. It is typically used for thin concrete specimens (between 50 mm (2″) and 100 mm (4″) thick) such as sidewalks, bridge decks and some driveways. The unit can be used on plaster and morar as well to verify consistency. The Test Hammer is also used on brittle rock cores where a larger impact will damage the specimen. These units are commonly used to classify rock cores and brittle rock specimens. Finally, it is also suitable for paper and film rolls where the larger impact energy of a standard hammer will damage the surface of the material being tested.
Paper and Film testing are a significant application for the Low Impact Manual Test hammer. Typically eight to ten readings are taken across the surface of the paper or film roll to determine if the edges are as tightly wound as the center, and that winding has been even through out. TAPPI specifies readings 25 mm – 75 mm (1″- 3″) from the edge and 150 mm ( 6″ ) down the length of the roll. Rolls too loosely wound, or to soft will go out of round during shipment and storage. This will cause unwind speeds to be slowed thereby lowering productivity. Rolls that are wound too tightly or hard can burst or tear during transport, and storage.
The manual concrete test hammer (aka. Rebound Hammer, Schmidt Hammer, Swiss Hammer, Sclerometer), is the most widely used non-destructive test instrument for determining compressive strength. However, it also typically has the largest coefficient of variation; therefore, its results should be verified with another non-destructive test, such as the V-Meter MK IV™.