Engineering geological characterization of volcanic rocks of ethiopian and sardinian highlands to be used as construction materials

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.