الفهرس 
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Abstract
This work deliberated the effect of geochemistry and mineralogy of some Egyptian serpentinite rocks on the feasibility of their exploiting as sources of fine and coarse aggregates for RSCs production. This was conducted by incorporating three different serpentinites with variable proportions of antigorite, lizardite, and chrysotile. The antigorite serpentinite was selected from G. Umm Khasila, Atud area, along Marsa Alam-Idfu road while the lizardite and chrysotile ones from Wadi Atalla, along Quseir-Qift road, Eastern Desert. These polymorphs are associated with different proportions of magnetite and dolomite. Three types of RSCs were prepared based on theses polymorphs aggregates, separately. Physico-mechanical tests including density, water absorption, and porosity, as well as compressive and splitting tensile strengths, were conducted for these concretes. While the attention properties against fast neutrons and γ-rays from a Pu-Be source and stilbene detector, respectively, were evaluated. Additionally, The NXcom program was applied to conduct the theoretical calculations for fast neutrons in correlation with the experimental data. On the other hand, the microstructural properties have been inspected, especially the interfacial transition zone (ITZ) between the aggregates and cementitious matrix.
The physical, mechanical, microstructural, and radiation shielding properties of serpentine-based concrete were negatively influenced by the serpentinization grade and the associated deformation processes. The lowest serpentinization grade product, antigorite serpentinite, revealed satisfactory metrics for RSCs production compared with the medium and high serpentinization products (lizardite and chrysotile, respectively). In addition to antigorite, the associating dolomite and magnetite of this aggregate contributed to a more comprehension of the radiation attenuation behavior of this type of concretes. Whereas the dolomite should be precisely considered for the determination of loss on ignition (LOI), otherwise, LOI will give a false indication of CBW of aggregate. This CBW is essential in the attenuation of fast neutrons. Moreover, the high magnetite content in antigorite aggregate, as known, enhanced the radiation attenuation of antigorite-based concrete against fast neutrons and γ-rays. Therefore, Mag and Dol concentrations, as well as the serpentine type should be considered when selecting the serpentine aggregates for producing RSCs. Thus, the antigorite-based concrete revealed better physical, mechanical, microstructural, and radiation shielding properties than those of lizardite- and chrysotile-based ones. Hence, the antigorite serpentinite is the most appropriate source of aggregates to be exploited in the production RSCs. Hereafter, the antigorite serpentinite was nominated for producing the control serpentine concrete to which the barite and hematite additives were applied. The impact of these additives on the physico-mechanical and radiation shielding properties of antigorite-based concrete was carefully studied. Whereas, the remarks of this aspect can be drawn as follow:
-The density of antigorite-based concrete increased with the gradual incorporation of barite and hematite with som privilege of the former. But, the only barite had a positive impact on water absorption and porosity.
-Concerning the radiation attenuation properties, both barite and hematite had a positive impact on the fast neutron attenuation properties of the serpentine-based concrete mixes, of which AB50 > AH50 > AB25 > AH25 > A. Whereas, the fast neutrons suffered from losing enormous energy by the inelastic collisions with heavy barite and hematite atoms. Thus, these moderated neutrons can be easily absorbed by hydrogen in the crystalline water of serpentine. The incorporation of barite was more desirable compared with hematite. This was attributed to the greater effectiveness of barite in moderating larger numbers of fast neutrons on account of its higher density. The higher density of barite raised the prospects of inelastic collisions with fast neutrons compared with hematite. Moreover, barite and hematite incorporations had a positive impact on the γ-ray attenuation properties of the RSCs, of which AB50 > AH50 > AB25 > AH25 > A. Thus, the high RSC compactness inherited from barite incorporation, slightly had contributed in greater γ-ray attenuation compared with the comparable ratios of hematite. Additionally, the high emission of secondary γ-rays generated from neutron capture in hematite also accounted for the lower attenuation efficiency of AH25, 50 for gamma rays. Attenuation coefficients ( and ) and parameters ( and HVL) were measured for the serpentine-barite/hematite concretes. Unlike and HVL, the values of and of the serpentine/barite concretes were higher than those of serpentine/hematite ones. The ratio of 50% barite was the best-improving ratio for fast neutron and γ-ray attenuation properties with magnitudes of 50 and 26 %, respectively. In brief, unlike the mechanical properties of serpentine concretes, each of barite and hematite had prospective properties in radiation attenuation favoring of the former.
-Besides its health-related issues, the chrysotile revealed inappropriate physico-mechanical and radiation shielding properties for RSCs production. Therefore, it is not recommended to be used as aggregates in RSCs.
Concisely, the Egyptian antigorite serpentinite is a promising source of aggregates for RSC production.