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European Journal of Applied Sciences – Vol. 10, No. 4
Publication Date: August 25, 2022
DOI:10.14738/aivp.104.12605. Zagalo, A. H., Hamid, A. H., Rochette, P., & Konate, M. (2022). Petrographic and Geotechnical Characterization of Granites from
Karay (Eastern Chad) for Their Use in Civil Engineering. European Journal of Applied Sciences, 10(4). 232-246.
Services for Science and Education – United Kingdom
Petrographic and Geotechnical Characterization of Granites from
Karay (Eastern Chad) for Their Use in Civil Engineering
Al-Hadj Hamid Zagalo
University of Science and Technology of Ati, Faculty of Life Sciences
Earth Sciences and Land Management, Ati, Chad
Adelkerim Hassan Hamid
Abdou Moumouni University of Niamey
Faculty of Science and Technology - Niamey, Niger
Pierre Rochette
University of Aix Marseille, CEREGE, Aix en Provence, France
Moussa Konaté
Abdou Moumouni University of Niamey
Faculty of Science and Technology - Niamey, Niger
ABSTRACT
Chad is in need of huge amount of aggregates, the most used materials, for its
building and road construction. It is necessary to evaluate the geotechnical
properties of the different types of rock outcropping in this country. This paper is
focused on the petrography and geotechnical characteristics of granites from Karay
(East Chad) for their use in civil engineering. The study area is located in the eastern
Chad at about 50 km south to the town of Oumhadjer. The rocks that outcrop there
form an isolated relief within a vast expanse of sand forming an inselberg. This
relief is made up of fine, medium to coarse grained monzogranite cropping out as
blocks and slabs, exposed to surface conditions (temperatures, waters and winds)
that sometime transformed the micas and feldspars into clay. Microscopic
description of thin sections of rock shows that they display a medium grained
texture and are composed of quartz (32.8%), alkali feldspar (24.7%), plagioclase
(21.4%), biotite (10.4%), muscovite (6.8 %) and opaques (3.7%). The geotechnical
data showed that aggregates from the above rocks display Los-Angeles coefficient
varying between 20.50 and 39.70% with an average of 29.60% and a Microdeval
coefficient of comprised between 6.9 and 12.6 % with an average of 9.4%. These
results indicate that the study materials can be used for civil engineering works.
The correlation between the petrographic and geotechnical results indicates that
the size of the grains, their arrangement (texture) and the mineralogical
composition of rocks influence the geotechnical behavior of the aggrgates.
Keywords: Karay granite - Petrography - Geotechnical characteristics - Aggregates – Chad
INTRODUCTION
Due to the importance of their use throughout the world, aggregates constitute after air and
water, the third substance used by man [1]. Their intrinsic quality in terms of resistance to
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Zagalo, A. H., Hamid, A. H., Rochette, P., & Konate, M. (2022). Petrographic and Geotechnical Characterization of Granites from Karay (Eastern
Chad) for Their Use in Civil Engineering. European Journal of Applied Sciences, 10(4). 232-246.
URL: http://dx.doi.org/10.14738/aivp.104.12605
fragmentation or wear, condition their use. It is thus frequent to find rocks of crystalline or
magmatic origin in the most mechanically stressed parts of structures because their
characteristics are often clearly superior to those of rocks from sedimentary origin [2]. Granitic
formations occupy the major part of the earth's crust. This is why their development is
becoming more and more important for researchers.
Chad has several granitic formations that can be exploited and valorized for various uses [3]
and [4]. Unfortunately, there is often a production of aggregates and also a lack of knowledge
of the physical-mechanical characteristics of the materials. These deficiencies constitute a
danger for the durability of the works and delay the development of infrastructure process.
The geotechnical characteristics of aggregates from the Karay massif (Fig 1) is not known up to
the present date. The present study aim is to determine the geotechnical properties of
aggregates from rocks of this massif for their valorization as construction materials.
Figure 1: Location map of the study area
METHODOLOGY
Location of the study site and sampling
The Karay massif is located at about 50 km south of the town of Oumhadjer, East Batha
Department. Seven (07) rocks samples were collected on the whole massif corresponding to
the different petrographic types encountered (Fig.2). These samples were used for the
preparation of thin sections and geotechnical tests. From a geological point of view, the Karay
Legend
Flooding area
Road
Study area
Outcrop contour
Path
Sampling station
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
massif is made up of plutonic rocks with fin to medium texture surrounded by sedimentary
terrain within which it constitutes an inselberg.
Figure 2: Sampling map
Experimentation
The preparation of the thin sections was carried out at the Laboratory of Geology of the
University of Niamey (Niger) and the geotechnical tests were carried out at the Civil
Engineering Laboratory of N'Djamena (Chad).
Preparation of thin section
Thin sections realization consists of four main steps: sawing the rock, gluing the sugar on the
glass slide, making the thin sections itself by reducing the rock thickness to 30 μm and it
polishing, and finally the observation and photography:
• Sawing of the rock
The samples are sawn with a circular diamond saw in order to obtain rock sugars of rectangular
parallelepiped shape of 3cm length, 1.5cm width and 1cm thickness.
• Gluing
One of the large rectangular sides of the rock sugar is polished with a diamond edge saw
equipped with a hydraulic device to cool the saw. The rock sugar is then washed and polished
again with silicon carbide to remove the saw marks. This is placed on a hot plate at 104.8°C for
15 minutes to dry after washing. After drying, the polished side of the sugar is glued on the slide
of 5cm length, 3cm width and 0.15cm thickness. The gluing is done using glue mixed with a
hardener. After gluing, it is necessary to make sure that the air bubbles are expelled to allow a
good adhesion. Then proceed to the pressure drying which consists in placing the whole
Sampling station
Massif’s contour
Path
Road
Localities
Legende