![]() | Only 14 pages are availabe for public view |
Abstract In this work, all the data of field observation, geochemical, geological, petrographical, mechanical, physical data and concentrated laboratory works have been collected and create to extract the following conclusions: 1- characterization of the engineering properties of metavolcanics rocks can provide a base for a more rational approach to use these rocks in civil engineering works. 2- characterization of the physical and mechanical properties can be helpful both for early selection for building stone. The selected areas in the Central Eastern Desert embraces Ambagi and Sid areas and in Southern Eastern Desert are Shadli and Idfu Marsa Alam area are made up of porphyritic metabasalt, olivine metabasalts, basaltic meta-andesite , meta-andesite, metadacite and metarhyolite. Chemical analysis (XRF) was carried out to define the mineral composition and to know the nature and degree of alterations of the various rock units from the selected area. Geochemically, the different types of metavolcanics from four location represent tholeiitic characterization. Slightly down of K2O and enrichment of Na2O occurred in the mafic units. The mafic rocks are also medium in MgO (<9.5%) and P2O5 and TiO2 which might signify highly developed magma from deep mantle sources. Related to plate tectonic theory, the different types of metavolcanics located in island arc with tholeiitic characterization The physical and mechanical properties (porosity, density, uniaxial compressive strength, water absorption, flakiness and elongated index and specific gravity) of the metabasaltic rocks indicated these rocks could be used as cobblestone, masonry stone and slabs for sidewalks. There is also a direct relation between the compressive strength and density of rock aggregates. On the other hand, the relation between the porosity, water absorption and compressive strength is indirect relationship. Metabasalt rocks have low porosity with high compressive strength compared to metarhyolite, metadacite and meta-andesite. The relationship between the compressive strength and normative mafic minerals contents is direct relation. The Ambagi metabasalts are also excellent building stones as much as physical and mechanical properties are concerned. Relating to aggregate properties, every rock unit has its specific properties subject upon its petrological and textural characteristics. Flakiness and Elongation indices are generally measured to be a characteristic property of the rock itself depending mainly upon its petrological, texture and structure; and partly on the crushing methodology/techniques. The Flakiness index ranges from 15% to 44% while the elongation index ranges from 15% to 32%. However, most metabasalt samples fall in the range from 15% to 29% which meet the ASTM D4791 specifications as concrete aggregates. The highest compressive strength values, are measured from the Ambagi and the lowest one measured from metarhyolite in Shadli area so, the Ambagi basalt is the main source of aggregates to be utilized in concrete in the area of study and can be used as crushed aggregate for concrete mix in large sized buildings, bridges and roads. After mixing aggregates with cement and water for concrete, The compressive strength of different metavolcanics aggregate type effect on the compressive strength, flexural tensile strength were investigated using constant mixture proportions. Five different aggregate types (metabasalt, basaltic meta-andesite, meta-andesite, metadacite and metarhyolite) were used in the concrete mixtures. The results of the investigation showed that aggregate strength and texture influenced the compressive strength, flexural tensile strength of concrete. A relationship was existed between aggregate compressive strength of concrete and compressive strength of aggregates with correlation coefficients R² = 0.44. A good relationship was existed between aggregate compressive strength and flexural tensile strength with correlation coefficients R² = 0.541. There is a good relationship was existed between concrete strength and Bulk density of concrete, with correlation coefficients o R²=0.926. A relationship was existed between concrete strength and porosity, with correlation coefficients R² = - 0.795. A strong relationship existed between tensile strength for concrete and bulk density for concrete with correlation coefficients R²= 0.7134 .Ultrasonic waves are a very effective tool for quantifying mechanical changes in concrete. Sonic tests (P-wave velocity and the shear wave velocity) on metavolcanic concrete pastes gave a quantitative valuation of the degree of development achieved through the cement addition in terms of strength gain. There is a good relationship was existed between uniaxial compressive strength for concrete (UCS) and shear modulus for concrete by ultrasonic with correlation coefficients R²=0.6378. A good relationship was also existed between ultrasonic p waves and the dynamic elastic modulus with correlation coefficients R²= 0.9981 SEM and EDX were approved for qualitative understanding the strength minerals formed during stabilization. The formation of the cementitious compounds containing calcium hydroxide CaOH2 and calcium silicate hydrated (CSH). These remarks show that a good mixing between metavolcanics aggregates and cement additives might have resulted. The procedure for formation the cementing materials may be formed by the reaction of the silica and alumina from the metavolcanics aggregates and the calcium hydroxide from cement. This process increases the strength by formation additional cementitious materials, which increase the interparticle bonding. Recommendations for future work So far, the Ambagi, Sid, and El Sukkari metabasalts and Shadli metabasalt have been used as building material. For selection of aggregate in concrete production without any physical and mechanical characterization, this leads to failure of the engineering structures before the design life. The present study identified important physical, chemical and mechanical properties of the selected areas in general. However, the following recommendations are given for future consideration: 1- There is an incorrect thought that accepts all basaltic rocks are considered as very good source of aggregates for concrete and asphalt mix; however this is totally wrong, instead attention should be attentive on the mineral constituents of the rocks to identify deleterious components 2- Aggregate identification, quarrying, storage and handling should be done professionally. |