Abstract
This case study investigates the influence of the mineralogical composition of ultramafic rocks derived from two ophiolite complexes from Greece (Veria-Naousa and Gerania) on their mechanical, physical and physicochemical properties. The investigated lithologies include lherzolite, harzburgite, dunite and olivine-orthopyroxenite with variable degrees of alteration. The ratio of secondary minerals to primary minerals (SEC/PR) of the studied ultramafic rocks shows good correlations with their physical, physicochemical and mechanical properties, suggesting that alteration has a negative effect on the engineering performance of the ultramafic rocks. Among the secondary minerals, serpentine plays the most critical role in determining the moisture content, the total porosity and hence the soundness of the host rocks, due to its phyllosilicate structure, which allows more water/solutions to be captured. The high percentage of serpentine creates surfaces of weakness, and as a result, it decreases the rock strength. The low microtopography of highly serpentinized rocks results in their reduced mechanical performance.
Highlights
Ophiolitic rocks are remnants of the Earth’s oceanic crust and upper mantle, derived from mid-ocean ridges or marginal basins [1]
Eighteenblock blocksamples samples of of ultramafic ultramafic rocks standard to evaluate their suitability as aggregates for construction applications, and they have standard to evaluate their suitability as aggregates for construction applications, and they have been been petrographically observed a combination of petrographic methods
The mineralogical and and textural characteristics of the samples were studied in 60 polished-thin sections (42 of them were prepared from regular hand specimens and 18 were prepared from the block samples) in a polarizing optical microscope (Leitz Ortholux II POL-BK Ltd., Midland, ON, Canada), according to the EN-932-3 [44] standard for the petrographic description of aggregates, and a scanning electron microscope (SEM)
Summary
Ophiolitic rocks are remnants of the Earth’s oceanic crust and upper mantle, derived from mid-ocean ridges or marginal basins [1]. A complete ophiolite suite consists of ultramafic, mafic, hypabyssal and extrusive rocks. Research of the properties of ophiolitic rocks for industrial and constructive purposes shows an increasing interest. Ophiolitic rocks are used extensively as engineering materials, including aggregates for road construction, concrete and railway ballast [2,3,4,5]. The engineering properties of rocks mainly depend on their mineralogical composition, textural characteristics, degree of chemical alteration, weathering and deformation [2,4,5,6,7,8,9,10]. Strong to very strong interrelationships among engineering properties of ultramafic rocks have been documented and studied by Petrounias et al [4] and Giannakopoulou et al [10].
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