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Rock Unconfined Compressive Strength (UCS) using Equotip Hardness Tester

Equotip 550 Application 01 smallRock strength can be measured using a variety of method. Generally, the UCS (Unconfined Compressive Strength) is the most common form of assessment.  Direct measurement is undertaken similarly to concrete cylinders i.e. a core of rock must be extracted from the rock mass you wish to assess. Extractig a rock core requires specialised coring equipment. The UCS can be significantly affected by defects in the rock giving erroneous "low" results. It is a relatively expensive method with requires a number of resources.

Non-destructive methods offer several advantages:

  1. They can be completed in the field on the rock wthout a sample
  2. When used on a rock core the core can be used for other testing (ie UPV)
  3. The tests can be correllated with other factors (eg comminution factors)

Equotip for Rock UCS

1The Equotip provides the user with a highly portable, accurate tool to test rock hardness. The instantaneous results can be stored and saved on the indicating device. Whilst designed and used to determine the hardness of metal a new application in determining the compressive strength rock (UCS) and logging rock core sample has been researched. This allows the Equotip to be used as a rock strength testing machine without destroying sample (ie non-destructively)

Equipment

The Equotip instrument consists on the Impact device and the control/logging box. Seen below the impact device consists of a 3mm dia. Spherical shaped tungsten carbide test tip which is spring mounted in an impact body. The test tip impacts on the test surface under spring force from which it rebounds.

3The velocity that the impact body is impelled and rebounds with is measured by the passing of a permanent magnet through a coil of wire. This induces a voltage proportional to the devices velocity.

The LEEB hardness value is the quotient of the impelled velocity over the rebound velocity multiplied by 1000. Harder materials will rebound the impact device giving higher LEEB hardness values.

2There are a number of options when purchasing the Equotip. The Equotip 550 offers the user a range of Impacter types, whilst the Equotip 540 can only be used with the D type impacter. Similarly the Equotip Live is only capable of measuring the Leeb D scale, however it has a number of features such as Cloud syncing of data and a log of information about the data set.

Ring Supports

Support ringsAccurate testing using the Equotip relies on the test specimen being immobilized. This can be achieved using a simple test jig firmly connected to a heavy vibration resistant base. Furthermore the Support Ring (part 6) is designed to give a firm connection between the Impact Device and the core. The standard support ring I ideal for cores with radius greater than 60mm and flat surfaces. The Z14.5 to 30 support ring allows testing of cores between 29 and 60mm dia.

Impact Device Type S

The S type impact device uses highly durable material in the test tip in the impact body of the standard D type Impact Device. This improved durability is ideal for core logging because it prolongs the usage of the Impact Device between servicing. It is only used with the Equotip 550.

RockSchmidt for Rock UCS

Schmidt hammers are used internationally for testing of rocks as well as concrete/cementitious material.  ASTM D5873 (Rock) has been developed as a standard for this form of testing. Generally an L Type Test Hammers is used.  Conversion to rock strength (UCS) also rely on the mineralogy of the rock in question.  Many conversion curves exist and can be loaded into the RockSchmidt for UCS conversion on site. Schmidt Hammers lend themselves to grading rock core in the lab and testing rocks in the field.

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