Investigation of structural and radiological shielding properties of pozzolana-portland cement
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Date
2015-11-03
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Abstract
The physical properties of the ordinary Portland cement (OPC) are enhanced when
the matrix of the OPC is partially replaced by admixtures such as Pozzolana. This
research investigated the radiological shielding properties and the structural strength
of Pozzolana-Portland Concrete (PPC) at different ratios of 0% (S0), 10% (S1), 20%
(S2), 30% (S3), 40% (S4), 50% (S5), 60% (S6), 70% (S7) and 80% (S8) of Pozzolana.
Radiological shielding property of a material is its ability to shield or absorb ionizing
particles/rays; thus preventing it from being released into the environment when a
source thereof is housed in containment. Ionizing radiations are found in nuclear
reactors, γ-rays and x-rays equipment used in energy and health sectors. They are also
found in sources used in quality assurance industries. Compression test was
performed using CONTROL electronic type compressiontesting machine. Test
samples were made of concrete (mixture of Portland and Pozzolana cement) cubes
and cylinders. The experiments were conducted at a temperature of 27 ± 2
o
C at the
following days of aging; 2, 7, 14 and 28. The compression test results showed that
concrete of Portland-Pozzolana cement (PPC) at 20% Pozzolana has more
compressive strength than that of the ordinary Portland cement at 28 days of curing.
Flexural and ultrasonic tests were conducted to confirm the results. Neutron
activation analysis (NAA) was also carried out to determine the elemental
compositions of Pozzolana and ordinary Portland cement. The neutron activation
analysis results showed that Europium, Hafnium, Copper, Calcium, Iron, Cobalt and
Aluminum, all of which have significant macroscopiccross sections (shielding
properties) dominating more in Pozzolana cement than in the ordinary Portland
cement. X-ray shielding analysis was carried out toascertain the veracity of the NAA
results. Linear attenuation coefficient (µ l ) of each sample at photon energy of 0.15
iv
MeV was determined with the 50% PPC showing highestvalue. Further, X-ray
Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were
performed to identify the phases contributing to the highest strength at 20% PPC (33
MPa) and highest shielding, µ lat 50% PPC (1.533 cm
-1
). The results in all showed
that Pozzolana positively affects structural and radiological shielding properties of the
ordinary Portland cement (OPC), since the OPC (Control) concrete had a
compressive strength of 28.44 MPa at day 28 and a linear attenuation coefficient (µ l )
of 0.140 cm
-1
. The XRD results showed that Calcite (CaCO3), which is a carbonate
mineral and the most stable polymorph of calcium carbonate (CaCO3) accounts for
the very high strength in the 20% PPC while Iron (Fe), Copper (Cu), Manganese
(Mn) and Aluminum Hydroxide (AlHO2) account for the very high shielding ability
of the 50% PPC.
Description
A Thesis submitted to the Department of Materials Engineering, College of Engineering, in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Materials Science and Engineering,