Urgent!!!　About Hammer Test

Hammer Test 我諗你係想講 Schmidt Hammer.

The Schmidt hammer method (Schmidt, 1951) is today routinely used to test the strength and the quality of rock and hardened concrete. For the latter there are standardised methods for obtaining the compressive strength of hardened concrete in Svensk Standard SS 13 72 37, SS 13 72 50 and SS 13 72 52. The second one uses only the rebound number (see below) and the third one uses both the rebound number and the P-wave velocity of the hardened concrete to determine the strength of the concrete.

The device consists of a spring loaded steel mass that is automatically released against a plunger when the hammer is pressed against a concrete or a rock surface. A small sliding pointer indicates the rebound of the hammer on a graduated scale (see Figure 2.7).

The principle of the test is based on the absorption of part of the stored elastic energy of the spring through plastic deformation of the rock surface and mechanical waves propagating through the stone while the remaining elastic energy causes the actual rebound of the hammer. The distance travelled by the mass, expressed as a percentage of the initial extension of the spring, is called the Rebound number, (Kolaiti et al, 1993). There are two types of hammers: L-type for rocks and N-type for concrete.

The quantity measured is the rebound number (the height of the rebounded hammer). The equipment needed is a comerially available Schmidt hammer.

As used today the method has some limitations; a) very fractured and closely jointed rocks are difficult to test. b) The method is not applicable to extremely weak rocks. c) Non-homogenous rocks are difficult to test.

The damages detected by the method must be confined to the surface of the stone. The Schmidt hammer method is well established in civil engineering for testing concrete and rock with the above mentioned limitations.

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2006-12-25 01:47:46 補充：
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