2026-09-22T10:16:58Zhttps://iris.unica.it/oai/requestoai:iris.unica.it:11584/2664562022-10-20T08:57:41Zcom_11584_207615com_11584_111066col_11584_265854
Engineering geological characterization of volcanic rocks of ethiopian and sardinian highlands to be used as construction materials
ENGIDASEW, TESFAYE ASRESAHAGNE
Abbasanta-Borore
(Sardinia)
Debrebirhan (Ethiopia)
Dimension stone
chemical properties
crushed aggregate
mechanical properties
mineralogical composition
physical properties
Settore GEO/05 - Geologia Applicata
This thesis presents the results of the study conducted on the “Geoengineering characterization
of volcanic rocks from Ethiopian and Sardinian highlands to be used as construction
materials”. Though, the two project areas are geographically far apart, both are partly
covered with volcanic rocks mainly consisting of basic and subordinate felsic rocks.
The research was conducted in two countries; part I, the Ethiopian Project area located on the
northwestern central Highlands of the Amhara regional state. It is characterized by rugged
topography being situated on the western margin of the Main Ethiopian Rift, while, Part II, the
Sardinian Project area, is located in the northwestern central part of the Island stretched from
Abbasanta-Borore on the Altopiano di Abbasanta.
The major objectives of the study in both project areas include; a) engineering geological
characterization of the volcanic rocks of Sardinian (Abbasanta-Borore area) and Ethiopian
highland (Tarmaber formation) to be used as construction materials b)assessing the volcanic
rocks for their suitability to be used as building stone and coarse aggregates/construction
materials with regard to the various time honoured standards and specifications like American
Society for Testing and Materials(ASTM), British Standards(BS), American Association of
State Highway and Transportation Officials (AASHTO), Ente Nazionale Italiano di
Unificazione (UNIEN) c) presenting a conceptual framework which puts forward a vision for
future crushed aggregate characterization of the Tarmaber formation, d)evaluation and
comparison of the physical and mechanical properties of the Sardinian highland Plio-
Quaternary basalt with that of Ethiopian Tarmaber formation(basalt).
The field work in the Ethiopian study area was accomplished in two phases, the first field work
was conducted during the months of February and July, 2011 and the second was in February
and September, 2012, while the Sardinian project field work was carried out during May and
June, 2012. In all these field work periods geological traverses, field documentations and
adequate samples were collected for the various laboratory tests in both project areas.
Laboratory testing of chemical, physical and mechanical properties were carried out to
characterize the volcanic rocks from both study areas to ascertain the suitability of the rocks
as construction materials.
iv
Geologically, the Ethiopian study area is part of the Miocene Shield volcanic terrain that
covered the western and north western central plateaux of Ethiopia forming a conspicuous
land feature in East Africa. The studied area is specifically covered with the Tarmaber
formation (Megezez subdivision) consisting of aphyric basalt, phyric basalt, trachybasalt,
ignimbrite/rhyolite, tuff and minor trachyte.
Thorough literature review has been conducted on volcanic rocks as construction materials
and from the compiled information a laboratory testing program was envisaged and conducted
on the samples collected from the studied areas. Selection of the tests was based upon the tests’
precision, efficiency, and predictive capabilities and relevancy for the specific geographic
location and geologic formation. In the laboratory testing phase of this project, the proposed
tests were used to evaluate the full range of the project area crushed aggregate resources.
Moreover, a conceptual laboratory test flow diagram is developed for future aggregate
characterization of the Ethiopian project area. Furthermore, a geological map is prepared
outlining the various lithotypes which could help to predict the geo-engineering properties of
the rocks by identifying the rock types.
The Ethiopian project area is the major source and future potential of crushed coarse
aggregates by both private and public sectors. This study has identified recent advances in the
understanding and testing of crushed aggregates to be produced from the Tarmaber formation
(Megezez subdivision).
The geo-engineering properties depend on the mineral composition, texture and overall fabrics
of the rock. Each of the rock type crushed aggregate demonstrates rather well defined ranges
of geo-engineering properties and mineralogical characteristics. The laboratory work included
Uniaxial Compressive Strength, Abrasion resistance, Ultrasonic pulse velocity, Bulk density,
Water absorption, Specific gravity, Porosity, Petrographic examination, Aggregate Impact
Value (AIV), Aggregate Crushing Value (ACV), Los Angeles Abrasion Value (LAAV), Sodium
Sulphate Soundness Value (SSSV), X-ray Diffraction(XRD) and Alkali-Silica Reactivity(ASR),
Water soluble Sulphate and Chloride tests.
The physical and mechanical properties like Water absorption, Flakiness and Elongation
indices, and Specific gravity, strength and durability parameters have been determined and
examined critically with reference to suitability and stability, taking into consideration the
various specifications and time honoured standards. Hence, based on the geo-engineering and
petrographic properties, optimal end uses of the different rock types have also been discussed
even though the current study is mainly geared towards crushed aggregate sources for cement
and asphalt concrete mix.
The field and laboratory works were compiled and compared together to reveal the
engineering performance of the basaltic rocks in terms of crushed coarse aggregates
suitability. The basaltic rocks show a variety of textural and mineralogical characteristics,
which may affect their physical and mechanical properties as well as their use as construction
materials. The Uniaxial compressive strength of the basaltic rock ranges from 130MPa to
350MPa, Ultrasonic pulse velocity from 4000m/s to7000m/s, Open porosity from 0.95% to
3.08%, Bulk density from 2.8g/cm3 to 3.03g/cm3, Point load index from 4.83 to15.29MPa,
Water absorption from 0.33% to 1.08%, Dynamic Elastic Modulus from 64GPa to 120GPa,
Abrasion Resistance(Capon wheel) from 15.5mm to 25.2mm, Specific gravity from 2.51 to
3.00, SSSV from 1% to 10%, ACV from 15% to 30%, AIV from 20% to 36%, TPFV from 110kN
to 200kN, Los Angeles Abrasion Value from 12% to 30%, Flakiness index from 15% to 37%,
and Elongation index from 15% to 38%. The Alkali-Silica Reactivity test was carried out using
‘Mielenz quick chemical’ test (ASTM C289) and few basaltic flow layers were found to be
potentially Alkali-Silica Reactive. The petrographic examination and XRD analysis also
confirmed the presence of reactive quartz and harmful zeolite group minerals.
In this study, the different rock types has been investigated as sources of individual rock type
crushed aggregate for specific end use rather than aggregates comprised of various rock types.
In this respect, the aphyric basalts are found to be the most suitable crushed aggregate source
for ordinary Portland cement and asphalt concrete, sub base and base course. The porphyritic
basalt and glassy rhyolite should be used in unbound pavements only. The minor amounts of
zeolite bearing uppermost layer of phyric columnar basalt also should be avoided from
concrete making for safe stability of structures due to risk of potential Alkali silica reactivity.
Geochemically the Tarmaber formation represents alkaline-subalkaline bimodal mafic-felsic
volcanic series. The mafic volcanic suite is more abundant and characterized by alkaline
basalts and minor silica undersaturated rocks (basanites) and the felsic suite is relatively less
abundant and represented by strongly welded ignimbrite/rhyolite, tuff and minor lava flows of
trachyte. Furthermore, the mafic suite is characterized by sodic affinity on conventional K2O
versus Na2O diagram. The Fe2O3 content is high for all the samples (11.53-15.79%) and high
Na2O + K2O content (~4.04-6.2%) is typical of alkaline basalts of Tarmaber formation. The
MgO is low (3.45-7%), while 0.3-1.3%P2O5 and 2.8-4.5%TiO2 are relatively high. Loss On
Ignition (LOI) varies between 0.5% and 1.5% indicating the unaltered nature of the sampled
rocks.
The geo-engineering properties of the Tarmaber formation (the basalts and
pyroclastics/ignimbrite) indicated that the pyroclastics (ignimbrite) are found to be good
building materials with regard to their high uniaxial compressive strength, abrasion resistance
and weathering index. However, their relatively higher water absorption and porosity limit
them not to be used in public walkways, horizontal pavements, public car parks and flooring in
supermarkets in an open environment as intensive use while some flow layers of the basalts are
mainly suitable for production of coarse aggregates for cement concrete mix.
The Sardinian project area is part of the Plio-Quaternary volcanic rocks that covered the north
western central plateaux of the island forming flat topped land feature. The studied area is
specifically covered with the ‘Basalti di Plateau” consisting of porphyritic basalt, vesicular
basalt, andesitic basalt and trachybasalt. The physical and mechanical tests conducted on
these rocks proved the high potential of the studied rocks to be used in the construction
industry. The Uniaxial compressive strength ranges from 35 to 177MPa, Ultrasonic P-wave
velocity from 4143m/s to 6066m/s, Water absorption from 1.51 to 3.11%, Porosity from 0.64 to
10.33%, Specific gravity from 2.26 to 2.71, Bulk density from 2.2 to 2.69g/cm3, Abrasion
Resistance(Capon wheel) from 19.4 to 23.6mm, Point Load index from 1.98 to 7.05MPa, ACV
from 19 to 46%, LAAV from 17 to 33%, Dynamic Young’s Modulus from 33GPa to 92GPa to
mention a few test results. Furthermore, Alkali Silica Reactivity test, X-ray diffraction analysis
and detail petrographic studies were conducted on the collected Sardinian samples. According
to the Alkali Silica Reactivity test, a sample is found to be deleterious (highly reactive) and
later XRD analysis and petrographic study also confirmed the Alkali Silica Reactivity test
result.
The Sardinian samples have shown acceptable abrasion resistance values and uniform
physical and mechanical properties which guarantee to be used as dimension stone/cut stone.
The Abbasanta-Borore Plio-Quaternary basalt resource is huge; however, some clays in some
samples were indicated by the XRD analysis and these clays might have deleterious effect when
using these basalts as aggregate; therefore, the clay fraction should be determined with
quantitative XRD analysis for curiosity, otherwise, almost all the conducted aggregate tests
indicated relatively good quality aggregate resource except the vesicular basalt. The vesicular
basalt showed poor aggregate test values, like LAAV and Water absorption, ACV and
Uncompacted bulk density. However, for its aesthetic value, the vesicular basalt could be used
for indoor and sheltered cladding purposes as the case may be.
One of the purposes of this research was to compare some of the engineering properties of
basaltic rocks to determine whether there are similarities and differences between each of the
different source countries, Ethiopia and Sardinia. This is particularly interesting given the
distance between the two countries and the different processes that have occurred since the
formation of these basaltic rocks. The Ethiopian volcanic successions lack rocks of
intermediate composition (bulk rock chemistry: SiO2, 52-63%), defining strong silica gap as
observed in other volcanic areas, suggesting the bimodal volcanism nature of the Ethiopian
volcanic suite in non subduction tectonic setting and implying anorogenic magmatism
probably connected to plume/hot spot source.
Geochemically, the Sardinian Plio-Quaternary volcanic rocks lack significant ultrabasic
compositions (i.e., bulk rock silica SiO2 composition <45% are rare, Lustrino et al., 2007)
while the Ethiopian Tarmaber formation bulk rock silica composition reaches as low as 42%
and not greater than 51% while the Sardinian rocks reaches as high as 63% (andesitic).
Intermediate rocks are totally absent in the Ethiopian Tarmaber formation. The physical and
mechanical properties of the Tarmaber basalt are found to be higher than the Sardinian Plio-
Quaternary basalts. Although grouped under the engineering term “basaltic”, there are
distinct differences within the specific types present in each of the countries considered in this
study, i.e. mainly basaltic andesite in Sardinia and basalt in Ethiopia.
Evaluation of the physical and mechanical data indicates that the Ethiopian basalts are
typically of higher density and resistance to static crushing than the Sardinian Plio-Quaternary
basalt. The difference in engineering properties of aggregates from Sardinia on one hand and
Ethiopia on the other hand is explained partly by the chemical composition of the material, but
also by geological age, geological history and climate.
In both countries the geological history of the basalts might have influenced the aggregate
properties. Furthermore and more importantly, regional conditions (such as hydrothermal
activity) might have influenced the rock properties and alteration products. The physical and
mechanical properties of the Ethiopian basalts have shown better compliance with the various
specifications than the Sardinian basaltic samples especially the aggregate test results.
viii
Comparison of the results is revealing that different physical and mechanical trends are
observed from rocks that are similar in basic mineralogical composition. This suggests that the
relationships between physical and mechanical properties are often specific to rock type and
occurrence.
Aggregate quarrying provides necessary raw materials for infrastructure and civil
development; however, mining and/or quarrying operations have a non-zero environmental
impact. By the very nature of the requirements for the final products, dimension stone and
aggregate quarrying is a clean industry from a polluting point of view. Natural aggregates and
dimension stone are used in its natural state, and do not require concentration and extraction
from an ore; it is these latter two processes that result in significant environmental impacts.
However, the visual impacts are often significant, given that many deposits are situated in
topographically high areas. The environmental impacts of dimension stone and aggregate
quarrying are mainly of temporary duration, and can be effectively managed via revegetation,
landscaping, rock shading, if appropriate planning and consideration is followed from the
exploration stage through to quarry closure. Hence, quarrying and post-quarrying activities
should always target the mitigation of potential environmental and/or social impacts.
2014-04-15
info:eu-repo/semantics/doctoralThesis
http://hdl.handle.net/11584/266456
eng
numberofpages:348
info:eu-repo/semantics/openAccess
Università degli Studi di Cagliari
license:Non specificato