Hallo Pare Member.. ^_^
I am sorry for my late report, this report should be submitted before December. This report is actually the mini research I did in Geotechnical Measurement Engineering class under supervised by Prof. Satoru Kawasaki, Division of Sustainable Resource Engineering, Faculty of Engineering, Hokkaido University. The topic is about the physical properties measurement of rocks, especially hardness.
Rocks are made of one or more
minerals. Minerals are pure, solid,
inorganic (nonliving) materials found in Earth's crust. Rocks have chemical
compositions and physical properties related with their mineral properties. However,
rocks with the same mineral ingredients may be has different physical
properties due to variations in the amounts of minerals and the processes by
which they are formed such as being burned, doughy, or just right. Rock
material properties include rock type, color, particle size, texture, hardness,
and strength.
Hardness is one of the physical rock parameter. According to Chandler
(1999), hardness has a variety of meanings. To the metals industry, it may be
thought of as resistance to permanent deformation. To the metallurgist, it
means resistance to penetration. To the lubrication engineer, it means
resistance to wear. To the design engineer, it is a measure of flow stress and
to the mineralogist, it means resistance to scratching. Hardness may also be
referred to as mean contact pressure. In the other definition, hardness is the
subjective description of the resistance of an earth material to permanent
deformation, particularly by indentation (impact) or abrasion (scratching)
(ASTM D653 in USDA, 2012).
Hardness can be measured or tested by several classifications. The
necessity of all these different hardness classification is due to the need for
categorizing the great range of hardness from soft rubber to hard ceramics. Those
classifications are as follows (Private communication with Kawasaki, 2014).
1.
Abrasive hardness :
Deval, Los Angels, Taber
2.
Rebound hardness:
Shore, Duloscope, Equotip
3.
Indentation hardness:
Rockwell, Brinell, Vickers
4.
Scratch hardness:
Mohs, Martens
The
Equotip hardness tester is one of the useful testers developed so as to
understand elastic properties and strengths of metallic materials. It is picked
up as the characteristics of the Equotip hardness tester that a small sample is
needed for the test, sampling time is short, and the tester is convenient for
portable use (Kawasaki et al., 2001). The equotip devise is an electronic
battery-operated spring-based devise (see Figure
1). The piston moves through a coil and causes a current through the coil.
The voltage of the current which is proportional to the velocity of the piston,
before impact (V1) and after impact (V2) are measured
automatically and displayed as a ratio (V1/V2 × 1000)
which is denoted by the unit: L (Hack et al., 1993).
Table 1. Data of equotip hardness measurement on
rock samples
No. Measurement
|
Granite
|
Gravel Sand
|
Welded Tuff
|
Tuff
|
Fine Sand
|
1
|
891
|
865
|
577
|
575
|
715
|
2
|
881
|
841
|
556
|
492
|
679
|
3
|
888
|
849
|
569
|
656
|
691
|
4
|
894
|
847
|
252
|
603
|
632
|
5
|
904
|
856
|
472
|
618
|
697
|
AVERAGE
|
891.6
|
851.6
|
485.2
|
588.8
|
682.8
|
Standard Deviation
|
8.444
|
9.209
|
136.948
|
61.504
|
31.228
|
Figure 3. Graphic of average value of equotip hardness tester |
Based on Figure 3, the
highest value of average hardness is granite sample followed with gravel sand,
fine sand and tuff. While, the lowest value of hardness average data is welded
tuff. In the contrary, according to Figure
4 the most highest value of hardness
standard deviation data is welded tuff, and the lowest value of hardness
standard deviation data is granite.
Figure 4. Graphic of standard deviation value of equotip hardness tester |
The
correlation between average hardness and standardard hardness is invesely
proportional. According to Verwall and Mulder (1993), it is generally accepted
that surface rougness of the test specimen will affect result in rebound
testing. It influences standard deviation value. The texture and rougness of
each rock samples are presented in Figure
5.
Figure 5. Rock sample textures; 1. Granite, 2. Gravel sand, 3. Welded tuff,
4. Tuff, 5. Fine sand
|
The average
value of hardness measurement is influenced by the particle size and texture
of each rock samples. Particel size
refers to the size of the particles that make up a sedimentary or phyroclastic
rock, while texture refers to the crystallinity and granualarity of igneous and
crystalline metamorphic rocks. In the other hand, the standard deviation
value of hardness measurement is
influenced by the rougness of surface samples. Granite is common type of felsic
intrusive igneous rock which is granular and phaneritic in texture. This phaneritic
texture is proved by the size of the crystallinity which is can be seen by naked
eye. It forms by slow cooling of magma deep underground in the plutonic
environment. Gravel sand texture is also phaneritic. While fine sand and tuff
are aphanitic, which their component mineral crystals cannot detectable by the naked
eye. Welded tuff texture is porphyritic. It has a range of particles size, from
the largest agglomerates to very fine ashes.
Therefore it
can be concluded that the hardness value of rock properties is affected by
texture parameter. The biggest particle size and texture of the rock has the
highest hardness value.
Reference:
Hack, H. R. G. K., Hingira, J., Verwaal., W., 1993, Determination of Discontinuity Wall Strength by Equotip and Ball
Rebound Test, International Journal of Rock Mechanics Mineral Science &
Geomechanics, Pergamon Press Ltd.
Harry Chandler, 1999, Hardness
Testing, 2nd Edition, ASM International
Kawasaki, S., Yoshida, M., Tanimoto, C., Masuya, T., 2001, The Development of Property Evaluation
Method for Rock Materials based on the Simple Rebound Hardness Test:
Investigation on the Effects of Test Conditions and Fundamental Properties,
Rock Mechanics – a Challenge for Society, Sarkka & Eloranta (eds), Sweets
& Zeitlinger Lisse.
United States Department of Agriculture, 2012, National Engineering Handbook Part 631 Geology Chapter 4 Engineering
Classification of Rock Materials, (Amend. 55, January 2012), Washington, DC
Verwaal,
W., and Mulder, A., 1993, Technical Note
Estimating Rock Strength with the Equotip Hardness Tester, International
Journal of Rock Mechanics Mineral Science & Geomechanics, Pergamon Press
Ltd
Thanks for sharing this informative post. It's very helpful. Keep it up!
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