Influence of Petrogenesis on the Engineering Properties of Ultramafic Aggregates and on Their Suitability in Concrete  
[PERSON]  
1 Section of Earth Materials, Department of Geology, University of Patras, 265 04 Patras, Greece; [EMAIL_ADDRESS] (P.P.G. ); krogkala@uptras. aggregates to be binded [2; 5; 6]. The aggregates act as an inert filler, accounting for up to 80 vol% of the concrete. Rocks of variable lithological types (quarries or pits) and from distinct geological formations, being mechanically crushed, serve as aggregates provided from natural sources [7]. The capillary porosity appearing in aggregates is considered important to produce cohesive concrete, of high quality. Magmatic rocks exhibit a wide range of capillary pore types compared to most of the metamorphic rocks, and those having been developed after sedimentary processes [8]. Structural internal characteristics that include microroughness, the mineral phases and their chemistry, as well as compressive strength and structures are amongst factors regarded as important to determine the final concrete's strength and overall quality [9; 10; 11]. The mineral chemistry participating in the aggregate material and also the extent of alteration are directly linked with their mechanical properties and behaviour [12; 13; 14; 15; 16]. High modal participation of secondary mineral phases (e.g., serpentine, chlorite, bastite and talc) have a profound effect upon the mechanical behaviour of the compositionally ultrabasic aggregate material due to their hydrous nature, their internal layering, and often their fibrous texture and cleavage [17; 18; 19]. The study of the physico-mechanical and physicochemical behaviour of ophiolites requires careful research, since these formations encompass distinct lithologies of variable chemistry and textures; determining these properties is of high importance to evaluating aggregates used for concretes. The soundness testing of aggregates (magnesium sulphate heptahydrate) is most commonly applied to aggregates of coarse grain size to determine their durability. This testing, complied with additional testing, such as uniaxial compressive strength (UCS) and the Los Angeles abrasion test (LA), can provide critical information regarding the durability properties of the aggregates [20]. The engineering properties of rocks are strongly correlated with their mineralogical (mainly alteration degree), textural and morphological characteristics [12; 21; 22; 23; 24; 25]. Even within a single ophiolitic ultramafic suite it can be observed that distinct lithotypes types of variable chemistry, mineralogy and fabric texture properties and textural features can coexist, resulting in different mechanical behaviour. Variations in the aforementioned features can affect their physico-mechanical behaviour and their properties, which become poor in cases when alteration and even deformation are of high degree. A number of researchers have examined the effects of the participating minerals and their type related to their mechanical properties [12; 14; 15; 16; 26]. The increased percentage of soft minerals has a negative effect upon the ultramafic aggregate's mechanical properties [17; 18; 19]. Petrography is considered as an important tool to unravel the internal properties of the aggregates and thus to provide insights regarding their quality [27]; particularly their strength, as well as their durability, are highly associated with their micropetrographic properties which unravel the effects of alteration [16; 28; 29; 30]. Amongst all of the alteration procedures, the most common is serpentinization, which can occur either in oceanic shallow conditions or in depth (e.g., subduction zones and exhumation) [31; 32; 33; 34]. In this case, olivine is the first mineral to be affected and become serpentine, whereas orthopyroxene tends to resist more before also turning into serpentine (bastatite formation--pseudomorphic preservation of phenocrysts) [35; 36].