الفهرس 
AbstractOnly 14 pages are availabe for public view
 |  | from | 145 |  |  |
| | | from | 145 | | |
Abstract
from the previous outcomes, the following conclusion can be addressed as follows:
Inspected serpentinite rocks, including antigorite serpentinite (AS), lizardite serpentinite (LS), and chrysotile serpentinite (CS) revealed variations in the mineralogical, geochemical, and morphological properties. More specifically, the AS sample is mainly composed of antigorite mineral with high SiO2 and Fe2O3%, while lizardite and chrysotile are the principal minerals of the LS and CS samples, respectively, with lower SiO2 and Fe2O3%. Magnetite and dolomite are the dominant associating minerals in these samples but in different magnitudes. As for the morphological features, AS sample had a sub-rectangular shape with a rough surface, while LS sample had a platy shape with rough morphology, and the CS sample possessed splintery and fibrous bundles with a smooth surface.
The physical, mineralogical, geochemical, and morphological properties of investigated rocks had significant implications for their radiation-shielding behaviour. This was evident in the deleterious impacts prompted by these properties on radiation shielding as follows: (a) in the CS sample, the higher water absorption and lower density, which are indicative of high porosity and lower specific gravity of this sample compared to the AS and LS samples (physical properties), (b) in the AS and CS samples, the higher proportion of lower density dolomite and chrysotile minerals, which are presented as veins in both CS and AS samples (mineralogy), (c) the higher LOI% of the Cs sample works as a false indication for crystalline H2O (geochemistry), (d) moreover, in the CS sample, the lower compactness of splintery and fibrous bundles with a smooth surface compared to the higher compactness of sub-rectangular and platy habits with rough surfaces in the AS and CS samples, respectively (morphology).
It was found that the radiation shielding behaviour followed the following order: LS > AS > CS, against both fast neutrons and γ-rays. This was correlated with the measured radiation attenuation parameters of fast neutrons and γ-rays, involving µ (cm−1), Σ (cm−1), MFP (cm), and HVL (cm).
Specifically, the radiation attenuation investigation of serpentinite rocks should be taken with caution. This can be assigned to the commonly associated dolomite mineral, which renders the LOI% misleading and illusive ratio for the crystalline H2O responsible for fast neutron attenuation. Therefore, LOI% cannot be directly indicative of the amount of crystalline H2O compared to other samples such as limonite and goethite.
The AS and LS samples are more convenient and competent for radiation shielding compared to the CS sample.
The serpentinite rocks are promising rocks as shields against fast neutrons and γ-rays in nuclear facilities considering their mineralogy and geochemistry.
With the same radiation measurement conditions (i.e., source type and geometry), the serpentinite rocks are more efficient as a radiation shield than some concrete mixes.
Unlike the mechanical properties (i.e., crushing and impact values), the physical properties (i.e., density and water absorption) of barite are more enhanced than those of hematite.
The densified structure of barite can be correlated to its orthorhombic-shaped grains, whereas the sub-spherical and botryoidal-shaped grains of hematite result in a decompressed structure.
The radiation attenuation of barite against fast neutrons and γ-rays surpassed that of hematite by 12.25 and 51%, orderly.
The high ratio of BaO (57.89%) and the densified structure of barite justify its higher radiation attenuation compared to hematite, which has a higher Fe2O3 % and a less compact structure.
A considerable agreement was obtained between the experimental and theoretical calculations (NXcom) of fast neutron attenuation for both barite and hematite samples, with reasonable deviations of 16 and 19.25%, respectively.
Compared to different concrete mixes, barite and hematite can be employed as a natural, sustainable, and cost-effective alternative to cement-consuming RSC.
The control concrete (CC) has reasonable shielding properties against thermal and fast neutrons, as well as γ-rays.
Compared to the CC sample, the barite additions have improved the physical properties of the prepared concrete mixtures (CB1 and CB2). More specifically, the density of the CB1 and CB2 samples increased by 19.5 and 26%, while their water absorption and porosity decreased by 1.2 and 14.6, as well as 1.3 and 6.6, respectively.
The barite additions caused ups and downs for the mechanical properties. More explicitly, the higher barite ratio (50%) induced an increase in the compressive and splitting tensile strength of the CB2 sample by about 91 and 111%, while the lower ratio (25%) caused a reduction in the compressive and splitting tensile strength of the CB1 sample by about 7.9 and 11%, respectively, at 90 days.
The barite additions improved the microstructural properties of chrysotile concrete in terms of the porosity of the cementitious matrix and ITZ. The high barite ratio, represented in the CB2 sample, decreased the porosity and the ITZ thickness.
Unlike the thermal neutrons, the barite additions have notably improved the radiation attenuation of concrete mixes against both fast neutrons and γ-rays. Compared to the CC sample, the fast neutron attenuation of the CB1 and CB2 sample was enhanced by 3.20 and 7.50%, respectively. While the γ-ray attenuation measured by PuBe for the CB1 and CB2 samples increased by 3 and 6%, and that measured by 60Co by 7 and 24% at 1173 keV, as well as 12 and 30% at 1332 keV, respectively.
There was a satisfactory correlation between the radiation attenuation measurements, as well as the NXcom and WinXCom programs and MCNP-5 code, confirming the validity of the experimental work.
The obtained γ-ray shielding parameters of single-valued Neff and Zeff, as well as ZPI,eff, ZPEA,eff, NPI,eff, and NPEA,eff also confirmed that the barite has promoted impact on the γ-ray attenuation.
CS is eligible to be employed as aggregates in eco-friendly RSC, respecting its physico-mechanical properties. Acceptable fast neutron attenuation (by scattering) and thermal neutron absorption, as well as γ-ray attenuation, were noticed for the control concrete (CC) with unfavorable physical and mechanical characteristics.
H3BO3 additions triggered very limited variations in the physical properties of prepared concrete mixtures, involving density, water absorption, and porosity.
H3BO3 additions diminished the splitting tensile and compressive strengths of the prepared concrete mixtures. More explicitly, the higher the H3BO3 ratio, the lesser the mechanical strength. At 90 days of curing, the compressive strength of CR1 and CR2 has been reduced by 10 and 64%, while the splitting tensile strength has been decreased by 16.7 and 55.5%, respectively, compared to the CC.
The microstructural properties of concrete have been deleteriously impacted by H3BO3 additions. The porosity of cement matrix increased gradually, while the interfacial transition zone (ITZ) became more porous and thicker with H3BO3 addition.
There was a satisfactory agreement between the radiation attenuation measurements, as well as the theoretical results obtained by NXcom and WinXCom programs and MCNP-5 simulation data, verifying the experimental work.
In contrast to the mechanical properties, the higher the H3BO3 addition, the more the fast neutron attenuation (by scattering) and thermal neutron absorption. In particular, the thermal neutron absorption and fast neutron attenuation (by scattering) have increased by 4 and 18, as well as 8 and 11% in CR1 and CR2, respectively, compared to the control. The γ-ray shielding parameters of single-valued Neff and Zeff, as well as, ZPEA,eff, ZPI,eff, NPEA,eff, and NPI,eff emphasize that the H3BO3 has a marginal impact on the γ-ray attenuation ability.
Due to the unpromising mechanical properties, the studied chrysotile concrete mixes are not preferred to be used as RSC. However, these concrete types can be employed in objectives that require insignificant mechanical strength such as wall-covering tiles for nuclear radiation sites or their surrounding construction.