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Introduction
Properties of stones are required for the exploitation of rock materials from the quarry and for marketing the stones for various applications. ASTM (American Society of Testing Materials), ISRM (International Society of Rock Mechanics) and BIS (Bureau of Indian Standards) has brought few standards on granite and dimensional stones. In this article the applicability of these standards to granite and dimensional stones is discussed.
Standards
Testing standards can be broadly classified into two groups.
1. To determine the input parameters for the optimum exploitation of the material from the quarry.
The following properties are usually required to decide about optimum blast design.
l Compressive strength
l Tensile strength
l Density
l P-wave velocity
These tests are carried out on cores drilled from blocks (12" x 12" x 7") obtained from a quarry. ASTM, ISRM and BIS codes are available to carryout these tests. Apart from the above properties, petrographic studies for the constituent minerals is very much essential before the extraction of the stone from the quarry.
2. Tests on stones for marketability
Here a large number of tests has been recommended and are listed below :
l Unconfined compressive strength
l Elastic constants Density/specific gravity
l Water absorption
l Porosity
l Hardness
l Thermal shock resistance
l Permeability
l Coefficient of linear expansion
l Abrasion resistance
l Impact strength
l Weather resistance
l Freeze resistance
l Knoop microhardness
All these properties are not required for each rock type but a few of the tests may be selected depending on the application stone. ISRM standards are useful for rock mechanics application and are not applicable for the marketability of stones. ASTM gives the standards for the following tests.
l Compressive strength
l Water absorption
l Specific gravity
l Abrasion resistance
l Flexural testing
l Modulus of rupture and modulus of elasticity
l Slake durability
l Coefficient of thermal expansion
Apart from the methodology of testing, ASTM also gives acceptance criteria for Granite, Marble, Sandstone and Slate building stones, and is given in the Table 1 for Granite and Marble.
BIS standards are more or less similar to ASTM standard, also gives the minimum property values for granite and is given in Table 2.
ASTM, ISAM and BIS have not recommended standards for the following tests.
Weather resistance
Freeze resistance
Thermal shock resistance
Accelerated aging
Apparently, the European Commission is bringing out various standards related to dimensional stones but the documents are yet to be published.
Facilities At National Institute Of Rock Mechanics (NIRM)
Modern laboratory facilities to determine various physical and mechanical properties of granites and other dimensional stones are available at NIRM. The laboratory is Hardness is determined using Schmidt hammer. The laboratory is equipped with abrasion tester to determine the abrasion resistance of stones subjected to foot traffic (C-241). Glossmeter measures the gloss at 20 degree, 60 degree and 80 degree.
Conclusions
Existing standards are insufficient for determination of properties required for the marketability of stones. Relevant standards for resistance to freezing, environmental tests, thermal shock resistance, accelerated aging tests, sawability of stones are equipped with latest sample preparation and testing machines and. all the tests are carried out as per ASTM, ISRM and other International standards. Presently, facilities are available to determine the following properties required. There is also a need of data base of properties of Indian rocks. NIRM is very keen to establish and develop the facilities as per international norms for testing granite and dimensional stones.
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Testing Standards for Granite and Dimens >>>