10th Asian Regional Conference of IAEG (2015)

The Suitable Utilization of Extractive Tuff as Building Materials Based on Mineral
Composition and Rock Strength
Ade TRIYUNITA (1), Prasma Feby RAHMADHANI (1) and Raden Irvan SOPHIAN (2)(1) Faculty of Geological Engineering, Undergraduate Program, University of Padjadjaran
Jl. Raya Bandung – Sumedang KM.21, Jatinangor, 45363
E-mail:triyunitaade@gmail.com(2) Laboratory of Engineering Geology, Faculty of Geological Engineering, University of Padjadjaran
Jl. Raya Bandung – Sumedang KM.21, Jatinangor, 45363
Abstract
Rocks that exist in this world can be used for various things such as building foundations,building material mixture, Industry, and others. Rock samples are taken from the village Ciawitali,
Sumedang regency, West Java. Examined rocks which are pyroclastic rock in the form of lithic tuff
and crystal tuff is quaternary volcanic sediment. Rock samples were petrographic analyzed todetermine the mineral composition and point load strength tested to determine the strength of therock. Lithic tuff dominated by the rock fragments with igneous rock types as much as 63.75% andhas a compressive strength of 0.441 MPa. Crystal tuff dominated by plagioclase and chlorite
minerals with a total of 85% and amounted to 0.6119 MPa compressive strength. Rock strength isinfluenced by mineral composition, grain density and the existing cavity. This study wasconducted to look at the suitability of the use of extractive tuff and inform the general public about
it.
Keywords: Sumedang, tuff, petrographic, point load test
1.

Introduction

1.1 BackgroundIn the research area, there are many sites ofexcavation, whether conducted by the community
using traditional tools or using heavy equipment suchas excavators. Many rocks mined in the area of
research is the result of volcanic products.
Most of the mined rock used for building
materials, either for material mix or for building
foundations.
The rocks of volcanic products usually have a

Research Area lies in the area Ciawitali,
Sumedang, West Java, Indonesia located at latitude
6o40 '18 "- 6o34'55" S and longitude 107o 51' 51 "107o 57 '17" E. This area is located in the westernpart of Java Island. Rock samples in the form of lithic
tuff and tuff crystals derived from quaternary
volcanic sediment. Residents in the Ciawitali area
often take the rock to be used as building materials.

Fig. 1 Location of Research Area110th Asian Regional Conference of IAEG (2015)

epoch, Bogor Basin lifted into the mainland andbecome a magmatic track volcanic activity, and it
creates
depositsofQuaternary
Volcanoes(Martodjodjo, 1984). Van Bemmelen (1949), named
this morphology as strong antiklinorium accompanied
by faulting.
Pyroclastic rocks composed of fragments ofexplosive volcanic eruptions (Williams, Turner,Gilbert, 1954). These rocks consist of pyroclastic
material in the form of glass fragments, crystal, andlithic / volcanic rocks. Pyroclastic rocks are classified
by its grain size.

loose characteristic, because it has not compacted
optimally and have a lot of cavities.
Point load strength test performed on tuff
samples that exist in the research area to determine
the strength of the rock. In addition, texture andmineral composition which compose this tuff also
have an important role in determining the usability ofthis tuff.

1.2 Problems
Society in the research area often used the tuff
material as a building material. However, tuff is a
result material of a volcanic explosive eruption thatusually composed of fragments, lithic, glass,Table 1 Schmidt Classification of Pyroclastic Rocks Grain Sizeand crystal. This rock is easily separated
and unconsolidated. If the utilization of thetuff material for building material is, it willcause crumbly and collapsed buildings
when there is a disaster.
This study is intended to determine the mostappropriate use of tuff as a building material and to
2.2 Keywords Explanation
inform the general public about the most suitable
Tuff is included in pyroclastic rock types.
utilization of tuff as a building material.
Pyroclastic rocks is a rocks that consist of reworked
material that is erupted from an explosive volcanic,
1.3 Objectives
transported by air as well as cloud incandescent Determining the mineral composition and texture
material, then deposited on the ground in dry
tuff in the research area
conditions or in the body of water. (Fisher, 1961 & Determine the strength of tuff by compressive
Vide Carozi, 1975).
strength test point load
Based on lithological variations, Schmidt (1981) Determine the usefulness of tuff as extractive to
distinguishes
tuff into three types: vitric tuff, lithic
be utilized as a building material.
tuff and crystal tuff. In the research area, there are To provide knowledge to the general public
two types of tuff that are lithic tuff and crystal tuff.
about the suitable utilization of tuff as an
Lithic tuff is a pyroclastic rock which is dominatedextractive.
by rock fragments. Rock fragments which usually
2. Literature Review
become tuff constituent are andesite, porphyry,
diorite and others. This fragment that determines how2.1 Geology of Research Area
well the quality of this tuff as a building material
In physiographic, research areas included in thebecause each type of fragment has a predominance ofBasin Bogor, on Zone Bogor (Martodjojo, 1984).
different mineral composition.
Bogor zone is a zone that extends east-west trending,
Crystal tuff is a pyroclastic rock that is
has a maximum width of 40 km with intensive
dominated by crystal fragments. Fragments of crystal
folding and reverse fault to the north. Constituent
in the form of minerals such as of plagioclase,rocks consist of Tertiary sedimentary rocks andpyroxene, amphibole, biotite and others. The
igneous rock either intrusive or extrusive.
dominance of this crystal will also affect how wellThis zone has the morphological that shows hilly
the rock quality based on existing mineralappearance indicating that this zone has been foldedcharacteristics. Vitric tuff is dominated by glassstrong. Morphology of steep hills was formed byfragments.
intrusive igneous rock. In the Pliocene-Pleistocene210th Asian Regional Conference of IAEG (2015)

Compressive strength analysis aims to determine
the strength of rock samples. The tools used for thistest is a press machine equipped with a pressuregauge. Before using the tool, specify a point load ofrock samples and then calculate the geometry
according to ISRM suggested methods fordetermining point load strength. If the conditions are
not fulfilled, then the rock will not split perfectly
when the point load test performed.
After conducting such analyzes will be known
suitability utilization of tuff on Ciawitali area as abuilding material.

Fig. 2 Schmidt Classification ofPetrography is petrology that focuses on detailed
descriptions of rocks. It relies heavily on observations
made with the petrographic microscope. A
petrographic description of a rock first involves
identification of the minerals and, where possible,
determination of their compositions. The mineralcontent and the textural relationships within the rockare described in detail. Petrographic descriptions startwith the field notes at the outcrop and include
megascopic description of hand specimens. The
detailed analysis of minerals by optical mineralogy inthin section and the micro-texture and structure are
critical to understanding the origin of the rock.
The point load test is intended as an index test forthe strength classification of rock materials. It may
also be used to predict other strength parameters withwhich it is correlated

4.

Result and Discussion

4.1 Petrography Analysis
Crystal tuff with sample code A has thesefollowing characteristics: color without analyzers iscolorless, color with analyzers is black, and texture isvery smooth, angular grain shape, close fabric, andwell sorted. These rocks are dominated by crystalline
in the form of plagioclase 40%, chlorite 25%, 15%
glass, and other minerals as much as 20%. There are
not too many voids.

3.

Methodology
The object of this research is the lithic andcrystal tuff in the area Ciawitali, Sumedang, WestJava, Indonesia. In the area there are two types oflithic tuff, which is coarse grained lithic tuff withcode sample C, fine grained lithic tuff with code
sample B, and code samples A for crystal tuff.
The research methods used are petrographic
analysis and point load strength test on rock samples.
In petrographic analysis, samples of rocks made ofthin slice thickness 0,03 mm and then analyzed undera refraction polarizing microscope. Petrographic
analysis aims to determine the mineral content andthe textural relationships within the rock aredescribed in detail. The detailed analysis of minerals
by optical mineralogy in thin section and themicro-texture and structure are critical tounderstanding the origin of the rock.

Fig.3a Megascopic Appearance ofCrystal Tuff Sample Code A

Fig.3b Microscopic Appearance ofCrystal Tuff Sample Code A310th Asian Regional Conference of IAEG (2015)

There are 21.25% crystal fragments which is ofplagioclase, alkali feldspar, quartz, opaque minerals,
pyroxene, amphibole, and oxides minerals, as well as
fragments of glass are 13.75%.

Fine grained lithic tuff with sample code B has
these following characteristics: color without
analyzers is colorless, the color after using analyzers
is blackish gray, fine texture, sub angular - angulargrains shape, closed fabric, and moderately-wellsorted. The composition of these rocks is dominatedby lithic fragments as much as 55.5%. The lithic
fragments are volcanic rocks that dominated byplagioclase and have sub angular shape. There arealso crystal fragments as much as 32% in the form ofplagioclase, alkali feldspar, quartz, pyroxene, biotite,and opaque minerals and also contained fragments ofglass as much as 12.5%. In these rocks there are not
too many voids.

Fig.5a Megascopic Appearance ofCoarse Grained Lithic Tuff Sample

Fig.4a Megascopic Appearance ofFine Grained Lithic Tuff Sample

Fig.5b Microscopic Appearance ofCoarse Grained Lithic Tuff Sample
4.2 Point Load Test- Tuff with sample code A that will be tested has
geometric size as follows: W (width) 4.5 cm; D(thickness) of 4.2 cm; L (length) of 5.6 cm.
Based on the geometric correction we obtained
value of compressive strength is 0.6119 MPa.
- Tuff with sample code B has geometric size asfollows: W 5.925 cm; D 5.5 cm; L 7.6 cm. Basedon the geometric correction we obtained value ofcompressive strength is 0.3604 MPa.
- Tuff with sample code C has geometric size asfollows: W 6.175 cm; D 4.25 cm; L 6.8 cm. And
based on the geometric correction, we obtained
value of compressive strength is 0.441 MPa.

Fig.4b Microscopic Appearance ofFine Grained Lithic Tuff Sample
Coarse grained lithic tuff with sample code C has
no color when not using analyzers and black withanalyzers, the texture is coarse, moderately sortedwith open – closed fabric, and the shape of grains are
sub angular - angular. This rock composed by 63.75%
lithic fragments which are volcanic rocks that
dominated by plagioclase and have sub angular shape.

410th Asian Regional Conference of IAEG (2015)

this structure will not change because it has astructure that forms the skeleton.
However, when viewed from the compressive
strength of the rock, it is included in extremely low
strength (ISRM, 1978). This is happen because tuff
itself is not consolidated and compacted.

4.3 Discussion
Judging from the rock’s characteristic by
microscopic it can be seen that the crystalline form
dominated by angular shape but has a fine grain size
which indicates that this tuff transported through themedium of air and not too far from the source of theeruption.
From the mineral composition of the rock, it canbe seen that the rocks dominantly composed ofplagioclase and alkali feldspar. Plagioclase and alkali
feldspar is included in the subclass of tectosilicate.
Minerals that have tectosilicate structure tend to bestronger than the other structures.
Tectosilicate subclass is often called the"framework silicates" because its structure iscomposed of interconnected tetrahedrons goingoutward in all directions, forming an intricate
framework analogous to the framework of large
building. In addition, when exposed to the pressure of

Table 2 Classification of the Uniaxial CompressiveStrength of Rocks (ISRM,1978)

Table 3 Standard of natural rocks for building materials SNI.
Rock UsabilityNo.

Characteristics

Building Foundation

Prop andPavements

Ornamental Stone

500

600200~~~~~~~~~~~~~~

~

27

4050~

~

~

with Bauschinger, mm/min~

~

~

~

0,16~

5Maximum water absorption

558556

Permanent form with Na2SO4

12

34Heavy

MediumLight

Curbstone

1500

1000

800

Rudellof Broken Tenacity~~

a.Minimum Index (%)~b.Maximum piercing 2 mm (%)

Minimum average of compressive
strength (kg/cm2)

Los Angeles Shear Resistance,
maximum piercing 1,7 mm (%)
Maximum Aus Friction Resistancea.

121212b.Crack, Rupture, Defect12125*

12**

12No crack and defect

From the compressive strength values obtained,
if seen from the table of natural rock quality
standards for building materials, the strength of tuff
in the research area is very far from the standards as afoundation of the building. So this tuff is moresuitable for use as an adhesive material or a mixtureof building materials than used as a building
foundation.

5. Conclusions
The results obtained from the research that has
been conducted are the characteristics of rocks,
mineral composition and compressive strength whichindicates that these rocks are not suitable used as abuilding foundation as it is more appropriately used

510th Asian Regional Conference of IAEG (2015)as material mixture or adhesive mixture. Then thesociety in research area will understand more about
the usability of tuff as extractive.
References
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materials, quality and test methods. National
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03-2825-2008.
Fachrudin, A.Arif. (2010): Mineralogy Dictates.
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International Society of Rock Mechanics. (1985):
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Martodjodjo, Soejono. (2003): The Evolution ofBogor Basin West Java. ITB Publisher. Bandung.
Philpotts, Anthony R. (1989) : Petrography of
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R.W., Van Bemmelen. (1949): The Geology ofIndonesia, Volume I A. Netherland: The Hague
Martinus Nijhoff.
Silitonga, P.H..(1973): Geological Map of The
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Syafri, Ildrem. (2002): Petrologi. Geology Educationand Training Center. Bandung.

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