Experimental and theoretical study on the physico-mechanical characteristics and radiation shielding capability of hardened alumina sludge waste-cement pastes containing MnFe2O4-nanoparticles

Abstract

This research investigates the impact of incorporating low-cost MnFe₂O₄ spinel nanoparticles (MF-NPs) at varying concentrations (0.5, 1, and 2 mass%) on the mechanical and physical properties of blended cement pastes. These pastes were produced by replacing different proportions (5, 10, and 15 mass%) of ordinary Portland cement (OPC) with activated alumina sludge waste (AAS), to promote sustainability. Also, the research examined the gamma radiation shielding effectiveness of certain hardened composites against a ¹³⁷Cs gamma radiation source with an energy of 661.64 keV using a NaI (Tl) detector (Oxford Model) with 3″ × 3″, amplifier and 16 k multi-channel analyzer. The linear attenuation coefficient (LAC) of all the studded samples were calculated theoretically using a Monte Carlo code MCNP-5 code. The gamma radiation shielding properties were analyzed in depth using a Monte Carlo code MCNP-5 simulation model. The theoretical and experimental results for LAC were found to be in complete agreement. Phy-X/PSD software was applied to estimate the mass attenuation coefficient (MAC) for gamma radiation at various energies, as well as the effective atomic number (Zeff), mean free path (MFP), half-value layer (HVL), and tenth-value layer (TVL). The findings demonstrated that the addition of 0.5% MnFe2O4 nanoparticles (MF-NPs) to blended cement pastes exhibited the best physical and mechanical characteristics, as well as the most effective gamma radiation shielding.

Highlights

Use of thermally activated alumina sludge (AAS) for achieving sustainability in green buildings.

Inclusion of MnFe2O4 spinel nanoparticles up to 0.5 mass % boosts the physico-mechanical characteristics of OPC-AAS hardened composites.

Hardened nanocomposite pastes have an exceptional ability toward nuclear radiation shielding for use in nuclear protection applications and in medical fields.

Introduction

In recent times, the use of industrial and agricultural waste as supplementary cementitious materials has emerged as a promising solution in tackling global warming, reducing natural resource depletion, and achieving sustainable development goals [1]. Over the last few decades, researchers have explored the integration of solid industrial waste into construction materials, including the granulated blast furnace slag (GBFS) [2, 3], recycled brick powder (RBP) [4, 5], cement kiln dust (CKD) [6, 7], drinking water treatment sludge (DWTS) [8, 9], and glass wastes (GW) [10, 11].

Drinking water treatment plants generate a significant amount of alumina sludge (AS), which has become a major environmental challenge as a hazardous waste. AS is currently utilized as a supplementary cementitious material (SCM) in construction applications due to its high alumina and silica content. This approach offers the dual benefits of reusing AS and curtailment of the application of cement, which contributes to global warming and poses several environmental hazards [12–16]. Thermal activation of alumina sludge at temperatures ranging from 475 °C to 1100 °C produces a highly reactive transition phase where crystalline alumina is converted to amorphous alumina, and silica remains in an amorphous state. This phase is likely to form calcium silicate hydrate, CSH, and calcium aluminosilicate hydrate, CASH, within the cement matrix [17–20]. The pozzolanic activity and microstructure of calcined alumina sludge are significantly affected by the calcination conditions. Calcined alumina sludge reactivity was found to improve at temperatures of 400 °C to 600 °C without substantial changes in the crystalline structure, and the main hydration product was CSH. However, for improved pozzolanic activity at the expense of extra-energy consumption, alumina sludge calcined at 800 °C exhibited the highest effectiveness due to the presence of γ-aluminum. At temperatures above 1000 °C, gamma-aluminum transformed into alpha-aluminum and combined with amorphous quartz to produce mullite as a filler in blended cement pastes [21]. The partial replacement ratio for calcined alumina sludge ranged from 5 to 30% cement by mass [18, 22, 23].

In recent years, nanoparticles have been utilized to improve the performance of building materials by embedding them in the cement matrix [24]. Previous studies have shown that nanomaterials such as nano-cerium (NC), carbon nanotube (CN), and others have a significant impact on enhancing the hydration, thermal, mechanical, electrical, rheological, microstructural and durability features of cementitious systems [25–27]. Spinel ferrite-nanoparticles, including NiFe₂O₄, CoFe₂O₄, ZnFe₂O₄, CuFe₂O₄, and Fe₃O₄, have been investigated in OPC and blended-OPC hardened pastes [28–30]. Even though nuclear technology is used in numerous important applications, such as industry, agriculture, and medicine, it is critical to develop materials with high protective properties against nuclear radiation emissions, as this kind of radiation can be ionizing the media and emitting secondary- charged particles by very complicated mechanisms that can harm human health and the environment [31–34]. Therefore, in recent times, the interface between radiation and materials has become a significant consideration for physicists and researchers to avoid the negative impacts of these radiations on humans. Effective protection depends on the principle of “As Low As Reasonably Achievable” (ALARA), which involves optimizing thickness, time, and distance [35]. Concrete, polymers, and nanomaterials can be used in the radiation shielding field [36, 37]. Currently, there is a growing focus on nanomaterials that are used for shielding applications due to their promising features such as cost-effectiveness, its structural, and also its mechanical, and thermal stability for nuclear radiation protection [38–48]. For radiation shielding applications, spinel ferrite-NPs have been employed as dosimetric substances, which generate trap states for energetic electrons, exhibiting high absorption capacity for harmful radiations [31, 32].

Concrete is a versatile, cost-effective, and exceptional shielding material, which is widely used due to its presumed water content and relatively high density. It comprises a mixture of light and heavy elements that can attenuate photons and neutrons, with high atomic number elements commonly employed in high-density concrete [38, 49–52]. The composition of concrete can be enhanced to achieve a high efficiency for shielding properties, which is one of its most significant advantages. Concrete is considered a composite-substance, consisting of a mixture of collective particles such as gravel, sand, stone, and filler with cement or a binder, providing a chance to improve its elemental composition via mixing it with other elements to have a high shielding properties [53]. However, using of concrete as a shielding material encounters obstacles due to the transportation of radioactive chemicals, emphasizing the importance of developing a new type of concrete to overcome these challenges [50–52].

To the best of our knowledge, MnFe₂O₄ spinel nanoparticles have not been previously used in cementitious matrices to investigate their radiation shielding effect while enhancing the mechanical properties of hardened Portland cement-alumina sludge waste pastes. Thus, the primary objective of our study is to recycle large quantities of industrial waste (alumina sludge AS), which has become a major environmental challenge as a hazardous waste to produce environmentally-friendly building materials with specific characteristics to achieve sustainability, utilizing small doses of easily prepared and inexpensive MnFe₂O₄-nanomaterials (MF-NPs), and compare the gamma radiation protection efficiency of these nanoparticles using experimental and theoretical methods. To study the shielding capability of hardened nanocomposite pastes against gamma-rays, five samples were prepared: one sample of plain OPC (C0), whereas the other four samples contained cement with 0.5 mass% MF-NPs (C0MN0.5), cement with 0.5 mass% MF-NPs and 5 mass% of AAS (CS1MN0.5), 0.5 mass% MF-NPs and 10 mass% of AAS (CS2MN0.5), and 0.5 mass% MF-NPs and 15 mass% of AAS (CS3MN0.5). The samples were used to measure the gamma radiation from a ¹³⁷Cs source at an energy of 661.64 keV. LAC and MAC were calculated, and the experimental results were compared with the MCNP-5 model and Phy-X/PSD software. Additionally, HVL, TVL, Z_eff, and RPE% were calculated.

Materials and methods

Materials

Cement

The El-Sewedy cement company in Egypt provided Ordinary Portland cement (OPC) with a Blaine area of 349.5 m²/kg.

Alumina sludge

The Beni-Suef Company for Drinking Water and Wastewater provided the water treatment plant sludge (WTPS), which was oven-dried at 105 °C for one day. The dried WTPS was thermally activated by burning for 120 min in an electric oven at 500 °C with a heating rate of 5 °C/minute, followed by gradual cooling. With the use of X-ray fluorescence (XRF: Xios, style PW-1400), the chemical composition of the Ordinary Portland cement (OPC) and thermally activated alumina sludge (AAS) are given in Table 1. Using Philips' Xpert-2000 model of X-ray diffraction (XRD), the AAS XRD patterns are displayed in Fig. 1.

Table 1. The oxide chemical composition of OPC and recycled alum sludge (mass %)

Oxides	OPC	AAS
Al2O3	4.90	14.66
SiO2	19.41	62.64
Fe2O3	3.60	4.98
CaO	62.01	6.70
MgO	2.54	1.41
Cl −	0.09	0.19
SO3	2.80	0.64
K2O	0.63	0.66
Na2O	0.41	0.48
L.O.I	3.63	7.90

Fig. 1 [Images not available. See PDF.]

XRD pattern of AAS; Q = Quartz; Mu = Muscovite; A = Albite; AL = Albite low; AH = Albite high; C = Calcite

Superplasticizer

For this investigation, a modified polycarboxylate-based superplasticizer (Sika-Viscocrete 5230 L) was sourced from Sika Company in Egypt. Due of its high water reduction, good slump retention, and molecular designability, polycarboxylate superplasticizer is becoming a popular additive in concrete manufacturing [54]. The superplasticizer (SP) was employed to achieve the desired workability and as a dispersing agent for MF-NPs [24]. The SP exhibited the following characteristics: a yellow–brown liquid color, pH of 7.51–7.53, a specific gravity of 1.08 g/mL, and a solid residue content of 39.9%.

MF-NPs nanoparticles

MnFe₂O₄ spinel nanoparticles (MF-NPs) were synthesized according to Ref. [28], the particles size of MF-NPs $\approx$ 13–40 nm with a surface area of 30.73 m²g⁻¹. The physical features of the MF-NPs nanoparticles were analyzed through various techniques, including N₂-adsorption/desorption, SEM, HR-TEM, and XRD, which are depicted in Figs. 2, 3, 4, and 5, respectively.

Fig. 2 [Images not available. See PDF.]

N_2-adsorption–desorption isotherms of MF-NPs-nanograins

Fig. 3 [Images not available. See PDF.]

SEM of MF-NPs-nanograins

Fig. 4 [Images not available. See PDF.]

HR-TEM and micrographs of MF-NPs-nanograins

Fig. 5 [Images not available. See PDF.]

X-ray diffraction patterns of MF-NPs-nanograins

Methods

Preparation of the hardened cement pastes

In this study, a range of OPC-AAS dry mixes were generated utilizing a porcelain ball mill for approximately 6 h to achieve complete homogenization, as shown in Table 2. These mixes were subsequently blended with water in a ratio of 0.27 (water/cement) to create nanocomposite pastes. For the preparation of these pastes, various ratios of MF-NPs-nanograins (0.5, 1, and 2% by mass of cement) were added individually to OPC and various series of OPC-AAS. The dispersion of MF-NPs was achieved by ultra-sonication using an Ultrasonic homogenizer (LUHS0A12, 220 V/50HZ, 650 W) along with a superplasticizer (0.35% by mass of the solid) for a duration of 45 min at 25 °C.

Table 2. Composition of the different mixes and their notations

Mix	W/C, ratio	Mix proportions, mass%
		OPC	Sludge	(MF-NPs)	SP
C0	0.27	100	–	–	0.30
C0MN0.5	0.27	100	–	0.5	0.30
C0MN1	0.27	100	–	1.0	0.30
C0MN2	0.27	100	–	2.0	0.30
CS1	0.27	95	5	–	0.30
CS1MN0.5	0.27	95	5	0.5	0.30
CS1MN1	0.27	95	5	1.0	0.30
CS1MN2	0.27	95	5	2.0	0.30
CS2	0.27	90	10	–	0.30
CS2MN0.5	0.27	90	10	0.5	0.30
CS2MN1	0.27	90	10	1.0	0.30
CS2MN2	0.27	90	10	2.0	0.30
CS3	0.27	85	15	–	0.30
CS3MN0.5	0.27	85	15	0.5	0.30
CS3MN1	0.27	85	15	1.0	0.30
CS3MN2	0.27	85	15	2.0	0.30

To evaluate the mechanical properties, freshly prepared pastes were poured into 25 mm cubic molds and maintained at approximately 98 ± 2% relative humidity at room temperature overnight. Subsequently, the cubic samples were demolded and immersed in tap water at 25 °C until the testing intervals (3, 7, 14, and 28 days) were reached.

Test methods and characterizations

Various hydration characteristics, including the chemically combined water content (Wn %), free portlandite contents (CaO %), and gel/space ratio (X), were measured at different curing ages. The determination of Wn %, CaO %, and (X values) was carried out using the methods detailed in previous publication [55].

For the strength tests, a Ton-industry machine (West Germany) with a maximum load capacity of 60 tons was employed at different curing intervals (3, 7, 14, and 28 days).

To qualitatively identify the hydrates/gels formed and the unreacted phases at different treatment times (3 and 28 days), X-ray diffraction (XRD) analysis was conducted using a Xpert-2000 instrument from Philips.

Shielding parameters calculations

To determine the experimental linear attenuation coefficient (LAC), a gamma-ray spectrometer system was utilized. This system comprised of a NaI (TI) Scintillation detector with a dimension of 3″ × 3″, along with an amplifier and 16K multi-channel analyser. The cement samples’ attenuation was assessed by the use of a thin beam gamma-ray transmission geometry. The lead container that contained the radiation source had a 0.5 cm face hole. The cement samples were positioned 5 cm from the source on a sample holder, while the source and detector maintained a distance of 10 cm. To mitigate an impact of scattered radiations on a detector, it was shielded by lead and placed away from the walls of the room to prevent secondary radiation (background, bremsstrahlung and fluorescence). The spectra were recorded and analyzed using Genie2000 software. To ensure an arithmetic mistake of less than 1%, the detector was set to 600 s for every measurement. The counts for background were also registered at the same duration 600 s and used to modify the measurements. LAC experimental value was determined by computing the arithmetic average of five observed LAC values. Figure 6. illustrates the experimental setup geometry of the gamma-ray spectrometer system [33].

Fig. 6 [Images not available. See PDF.]

Experimental setup for linear attenuation coefficient determination

The Nuclear and Radiological Safety Research Center used gamma-rays from radioactive point sources ¹³⁷Cs with an activity of 5 µCi and energy of 661.64 keV to calculate the LAC (cm⁻¹) of all cement samples. To minimize measurement errors [56, 57], three analysis times were completed. The MCNP-5 model and the Phy-X/PSD program were used to calculate the theoretical LAC of the paste shields that investigated in the energy scale of 0.015–15 MeV [58]. Cement paste shields were chemical blends made up of diverse compounds and elements. MAC for all hardened cement pastes samples was evaluated experimentally using the Beer–Lambert equation [36, 59].

1

$$\text{MAC}=\frac{\text{ln}\left(\frac{{\text{I}}_{\text{O}}}{\text{I}}\right)}{\text{x}}/\rho \left(\frac{{\text{cm}}^2}{\text{g}}\right)$$

According to [59], the intensity of gamma-rays transmitted through a cement sample with thickness (x) can be represented by I, whereas I_o denotes the initial intensity of gamma-rays, and ρ indicates the density of the cement sample.

The shielding parameters including HVL, TVL, MFP, and Z_eff were computed with various energy scales using theoretical LAC values obtained from the Phy-X/PSD program. HVL and TVL are parameters that can be applied to calibrate the thickness of a shield (cm) required to reduce the original gamma-ray intensity to half and one-tenth of its value, respectively. Three parameters can be computed numerically using these equations [60–62].

2

$$\text{HVL}=\frac{\text{ln}2}{\text{LAC}}$$

3

$$\text{TVL}=\frac{\text{ln}10}{\text{LAC}}$$

4

$$\text{MFP}=\frac{1}{\text{LAC}}$$

According to [59], the Z_eff parameter plays a crucial role in predicting the interactions between photons and a compound [37]. The calculation of the Z_eff value for the total photon reactions was done as follows:

5

$${\text{Z}}_{\text{eff}}=\frac{\text{MAC}}{{\text{N}}_{\text{A}}{\sum }_{\text{i}}\frac{{\text{w}}_{\text{i}}}{{\text{A}}_{\text{i}}}}/\frac{1}{{\text{N}}_{\text{A}}}\sum {\text{f}}_{\text{i}}\frac{{\text{A}}_{\text{i}}}{{\text{Z}}_{\text{i}}}{\left(\text{MAC}\right)}_{\text{i}}$$where $N_A$ is Avogadro’s number, $A_i$ is the atomic weight of an $i$ th element, $f_i$ indicate the fractional abundance of the element $i$ for the number of atoms, and $Z_i$ is the atomic number of the $i$_th element.

According to [38], Transmission% of shield substance for γ-rays with energy (E) through thickness (x) was computed through Eq. (6).

6

$$Tansmission\%=\frac{I(E,x)}{I(E,0)}\times 100$$where I (E, x), or I is a γ-ray’s intensity for shielding substance with thickness x and I(E,0) or I₀ is a γ-ray’s intensity in the absent of shield substance [37].

The RPE% coefficient was calculated from the transmitted and fallen photon intensities (I₀ and I) to assay the performance of studied samples in γ- attenuation [59].

7

$$\text{RPE \%}=\left(1,-,\frac{\text{I}}{{\text{I}}_0}\right)$$

Monte Carlo simulation cede

Monte Carlo Code (MCNP-5) was used as the main tool for the implementation of this work. A source was defined in the MCNP-5 data card with commands energy (ERG), types of particles (PAR), position (POS), and direction (DIR), respectively. The ¹³⁷Cs radioactive point source with energy 661.64 keV and activity of 5 μCi was placed 10 cm from the detector, and a nanocomposite shield was placed between the detector and the radioactive source at a distance of 5 cm from the source. Standard cement C0 was chosen as a primary shield and four nanocomposite samples as CS1MN0.5, CS2MN0.5, CS3MN0.5 and C0 MN0.5 in different thicknesses from 5 to 12.5 cm and all the samples were uniformly cubic- shaped. The linear attenuation coefficients had been determined by computing the transmission of γ-rays through those five different nanocomposites samples individually. The point detector tally F5 for the MCNP-5 had been used to calculate photon intensity and gamma dose rate. The simulations were performed with 10⁸ histories. All simulated results were reported with < 0.1 error.

Results and discussion

Chemically combined water contents (Wn %)

The chemically combined water content results (Wn %) for hardened composite pastes hydrated up to 28 days are presented in Fig. 7A–E. An increase in Wn values was observed for all tested samples, with a continuous and gradual rise noted until the 28 days hydration mark. This can be attributed to the continuous hydration process of all hardened composite pastes, which results in the liberation of free portlandite [63].

Fig. 7 [Images not available. See PDF.]

Chemically combined water contents (Wn %) of hardened composites pastes at different hydration ages

In hardened blended pastes, the Wn contents increased slightly with the addition of activated alumina sludge (AAS) up to10 mass % in mixes CS1 and CS2, respectively, as compared to the control mix (C0) at all curing ages. This can be explained by the high pozzolanic activity of AAS [64]. However, a significant decline in Wn contents was observed in mix CS3, which contained 15 mass % AAS. This is due to the reduction of clinker mineralogical phases within the composite as a result of substitution with high proportions of AAS, leading to a decrease in major hydration products such as (calcium aluminate hydrates CAH, calcium aluminosilicate hydrate CASH, and calcium silicate hydrate CSH), in addition to a reduction in the quantity of portlandite required for the pozzolanic reaction [65]. Notably, mix CS3 with the highest AAS content (15% of AAS) exhibited the highest combined water contents at all hydration ages.

The impact of MF-NPs addition on the Wn% values of various hardened composites during the hydration period is presented in Fig. 7B–E. The inclusion of 0.5% and 1% MF-NPs-nanograins in different blends (mixes C0MNP0.5, C0MNP1, CS1NMFs0.5, CS1MNP1, CS2MNP0.5, CS2MNP1, CS3MNP0.5, and CS3MNP1) significantly improved the Wn % values at all curing times when compared to the blank sample (mix C0). This can be attributed to the presence of MF-NPs-nanograins, which serve as nucleation centers for the hydration process, thereby accelerating the process of cement granule hydration [28].

Increasing the MF-NPs content to 2% resulted in a slight reduction in the Wn values, but the values still remained higher than those of the reference samples (mixes CS1-CS3) due to the ferromagnetic nature of MF-NPs-nanograins, which led to their agglomeration [66].

Free portlandite contents (CaO %)

Figure 8A–E displays the results of free portlandite content for hardened composite pastes at different hydration ages. All tested mixes showed a gradual and continuous increase in (CaO %) content until reaching 28 days of hydration age. This can be attributed to the ongoing hydration process of all hardened composite pastes, resulting in the formation of more hydrated products such as CSH and Ca(OH)₂ phase with increasing ages of hydration.

Fig. 8 [Images not available. See PDF.]

Free portlandite content for hardened composite pastes at different hydration ages

In the case of hardened blended pastes, the free portlandite content (CaO %) values slightly decreased with increasing AAS content in hardened blended pastes upto 10% of AAS (mass %) in mixes CS1 and CS2, respectively, compared to the control mix (mix C0). This is due to the higher pozzolanic activity of activated alumina sludge, which reacts with Ca(OH)₂ released during the hydration process, causing the consumption of CaO to develop secondary CSH gel and resulting in a decline in the (CaO %) content [67]. Additionally, the mix containing 15% of AAS (mix CS3) exhibited a relatively low value in the rate of free lime content, which can be attributed to the dilution of the proportion of cement in the sample (mix CS3) [65].

As shown in Fig. 8B–E, the free portlandite contents of MF-NPs-hardened composite pastes exhibited decreasing orientation behavior. This is due to the interaction of MF-NPs-nanograins with the released Ca(OH)₂ during the hydration process, accelerating the hydration rate and generating extra-amounts of yields such as CFH, CFSH, and MnCSH [28]. Furthermore, the values of (CaO %) contents obtained for all different series of OPC-AAS-MF-NPs hardened composite pastes were lower than those of the reference samples (mixes CS1-CS3).

Gel/space ratio (X)

The (X) ratio for all different series of OPC, OPC-AAS, and OPC-AAS-MF-NPs hardened composite pastes showed an increase with hydration age, as illustrated in Fig. 9A–E. This is due to the accumulation of additional amounts of CSH, CFSH, and CFH [68]. The (X) values for the different mixes containing MF-NPs-nanograins exhibited a higher increase compared to all other composite pastes. This can be attributed to the higher pozzolanic power of MF-NPs-nanograins, which accelerates the hydration rate and leads to the formation of more hydration products [25].

Fig.9 [Images not available. See PDF.]

Gel/space ratio (X) for hardened composite pastes at different hydration ages

The inclusion of 0.5 mass% of MF-NPs-nanograins in mix CS2MNP0.5 showed higher values of (X) ratio compared to the control paste, with values of 10.34%, 55.00%, 70.33%, and 61.56% for the samples hydrated for 3, 7, 14, and 28 days, respectively.

Compressive strength (CS)

Compressive strength

Figure 10A–E presents the compressive strength results of OPC, OPC-AAS, and OPC-AAS- MF-NPs hardened composite pastes. It can be observed that the CS values improved with increasing hydration age for all samples. This is due to the ongoing hydration process of all hardened composite pastes and the formation of excessive amounts of hydration yields such as calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH), which accumulate within the voids and gradually create a compact cementitious matrix [69].

Fig. 10 [Images not available. See PDF.]

Compressive strength of hardened composite pastes at different hydration ages

The obtained data indicated that the CS magnitudes of the OPC-AAS blends increased with increasing AAS content upto 10% of AAS (mass %) compared to the blank sample (mix C0), followed by a decline in CS magnitudes at 15% AAS. The increase in CS magnitudes at 10% of AAS can be attributed to the higher pozzolanic activity of AAS, causing the formation of further hydrated products. In contrast, the decline in CS magnitudes at 15% AAS may be related to the dilution effect of OPC content inside the composite due to its substitution by high proportions of activated alumina sludge (AAS), which reduces the major hydration products like (CAH and CSH) and further reduces the quantity of Ca(OH)₂ required for the pozzolanic reaction [70].

Furthermore, the CS magnitudes were enhanced for all composite pastes containing 0.5% and 1% MF-NPs compared to the blank sample (mix C0). This can be attributed to the higher pozzolanic power of MF-NPs-nanoparticles, which improved the rate of hydration and formed an excess of hydration products such as CSH and CAH, in addition to producing new phases such as MnCSH, CFSH, and CFH. The introduction of 2% of MF-NPs caused a slight decrease in the CS magnitudes compared to their references (mixes C0-CS3) due to their poor dispersion resulting from the agglomeration of MF-NPs-nanoparticles [71]. These findings are in good agreement with the values of chemically combined water and will be confirmed later by XRD and SEM tests.

X-ray diffraction analysis

The X-ray diffraction lines of hardened composite pastes of various mixes, including C0, CS2, C0MN0.5, and CS2MN0.5, hydrated at 3 and 28 days are displayed in Fig. 11A, B. The XRD diffraction lines for these mixes revealed peaks corresponding to main hydration products such as CSH and Ca(OH)₂ phases, as well as peaks for belite (β-2CaO.SiO₂), alite (3CaO.SiO₂), calcium carbonate (C $\overline{\text{C}}$) at 2θ of ~ 29.32°, and unreacted quartz. The Ca(OH)₂ peaks were more intense in the plain cement paste (mix C0), and the CSH peak intensity increased as the hydration process continued. Nanocomposites containing 0.5 MF-NPs exhibited the formation of new phases of hydration products at 28 days of hydration, including CFH, MnCSH located at 2θ 12.84, 18.36, and 29.6°, Glaucochroite [(Ca,Mn)₂SiO₄] located at 2θ 16.9°, and ilvaite (CFSH) located at 2θ 51° [28, 72]. These findings are consistent with the compressive strength test results and the hydration kinetics results.

Fig. 11 [Images not available. See PDF.]

XRD for mixes C0, CS2, C0MN0.5 and CS2MN0.5; (A) 3 days of hydration; (B) 28 days of hydration; CH = 1; CSH = 2; CC = 3; β-C₂S = 4; C₃S = 5; C₄AF = 6; MnCSH = 7; Quartz = 8; CASH = 9; CFSH = 0; CFH = 10

Radiation shielding parameters

Table 3 shows the LAC values for all studded samples under investigation, which were evaluated using a γ- ray spectrometer technique at a photon energy of 661.64 (keV) and also calculated theoretically using the MCNP-5 code at the same photon energy. It is evident from the Table 3 that all the investigated samples exhibit a higher LAC value than mix C0, with CS2MN0.5 demonstrating the highest value. The slight discrepancies observed between the values of LAC obtained through theoretical and experimental methods can be attributed to variations in geometry and other factors specific to each method. The relative difference between the two methods for all samples increased from ~ 4.402% to 12.598%, indicating good agreement between the two methods. The radiation shielding parameters of the prepared cement samples were also computed using PhysX/PSD software. Furthermore, The MAC of all samples was calculated by dividing the experimental LAC over their density (ρ) (g/cm³). LAC magnitudes of the five nanocomposite samples at different energies were illustrated at Fig. 12. It is noteworthy that LAC is inversely proportional to the fallen photon energy and straightway proportional to the shield's density. Thus, the CS2MN0.5 sample exhibits the maximum LAC value, indicating its superior ability to shield against radiation.

Table 3. The experimental and theoretical LAC (cm⁻¹) for studied samples at energy 661.64 keV

Samples	Linear attenuation coefficient LAC (cm−1)
	LAC (Exp.)	LAC(Theo.) MCNP-5	RD%	MAC (cm2/g)	Density (g/cm3)
C0	0.1501	0.1621	4.402	0.0752	1.996
CS2MN0.5	0.1613	0.1789	9.837	0.0784	2.057
CS1MN0.5	0.1554	0.1778	12.598	0.0755	2.056
C0 MN0.5	0.1513	0.1659	8.801	0.0756	2.002
CS3MN0.5	0.1510	0.1631	7.418	0.0712	2.138

Fig. 12 [Images not available. See PDF.]

The variance of LAC for samples studied at various γ-ray energies

.

In Fig. 13., the MAC results for all the samples under investigation are presented for energies ranging from 0.015 to 15 MeV. As shown in the Fig. 13, all the investigated samples have a higher MAC value than C0, with CS2MN0.5 exhibiting the highest value, indicating its superior ability for radiation shielding. It can be concluded that increasing the amount of AAS enhances the MAC value and the efficiency of gamma shields, while increasing photon energy reduces the MAC value due to variations in the interaction mechanisms of photons with matter at different energies. Specifically, the probability of the photoelectric effect (PE) decreases with increasing photon energy, while intermediate-energy Compton scattering (CS) becomes more favourable. The cross section falls off with increasing photon energy, with the pair production process (PP) dominating in the higher energy field (beyond 12 MeV) [73]. According to the high concentration of Fe and Mn, CS2MN0.5 demonstrates the highest values of MAC at all energies compared to the other studied samples for the same energy, wherever attenuation is dependent on the density and concentration of the elements in the matrix, and energy of the fallen photons.

Fig.13 [Images not available. See PDF.]

The simulated γ-mass attenuation coefficients (MAC) for paste shields at an energy scale from 0.015 to 15 MeV

Table 4 presents the HVL and TVL values, which were calculated using the Phy-X/PSD software, for all the studied samples to estimate the degree of attenuation. These parameters help in determining the sample thickness required to shield half and tenth of the initial photon intensity. It is generally assumed that the superior shielding substances have thinner coats of TVL and HVL [74].

Table 4. TVL and HVL magnitudes for all studied specimens in the energy scale (0.015–15 MeV)

Energy			HVL (cm)					TVL (cm)
(MeV)	C0	CS2MN0.5	CS1MN0.5	C0MN0.5	CS3MN0.5	C0	CS2MN0.5	CS1MN0.5	C0MN0.5	CS3MN0.5
0.02	0.02	0.01	0.01	0.03	0.02	0.07	0.04	0.04	0.05	0.07
0.02	0.05	0.03	0.03	0.04	0.05	0.17	0.10	0.10	0.12	0.16
0.03	0.16	0.09	0.09	0.11	0.15	0.54	0.31	0.31	0.37	0.50
0.04	0.35	0.21	0.21	0.25	0.33	1.17	0.70	0.70	0.83	1.09
0.05	0.61	0.38	0.38	0.45	0.57	2.01	1.27	1.27	1.48	1.89
0.06	0.89	0.60	0.60	0.68	0.84	2.95	1.98	1.99	2.25	2.80
0.08	1.42	1.08	1.09	1.16	1.37	4.72	3.56	3.57	3.86	4.55
0.10	1.83	1.51	1.52	1.57	1.78	6.07	5.02	5.03	5.22	5.92
0.15	2.43	2.21	2.25	2.26	2.41	8.07	7.35	7.45	7.46	7.99
0.20	2.78	2.58	2.67	2.68	2.77	9.24	8.57	8.87	8.88	9.20
0.30	3.29	3.08	3.22	3.23	3.28	10.90	10.21	10.68	10.69	10.88
0.40	3.69	3.46	3.63	3.65	3.68	12.23	11.49	12.06	12.07	12.22
0.50	4.04	3.80	4.00	4.01	4.04	13.42	12.62	13.26	13.28	13.41
0.60	4.38	4.12	4.33	4.34	4.37	14.52	13.66	14.36	14.37	14.52
0.66	4.57	4.30	4.52	4.53	4.57	15.16	14.26	14.99	15.00	15.15
0.80	4.98	4.69	4.93	4.95	4.98	16.54	15.56	16.37	16.38	16.53
1.00	5.54	5.22	5.49	5.50	5.54	18.40	17.31	18.22	18.23	18.39
1.02	5.60	5.27	5.55	5.56	5.60	18.59	17.50	18.41	18.42	18.59
1.25	6.20	5.83	6.14	6.15	6.20	20.56	19.35	20.36	20.37	20.56
1.50	6.80	6.39	6.72	6.73	6.80	22.55	21.21	22.31	22.32	22.55
2.00	7.85	7.37	7.74	7.75	7.86	26.06	24.46	25.70	25.71	26.07
2.04	7.94	7.45	7.83	7.84	7.94	26.35	24.72	25.97	25.98	26.36
3.00	9.55	8.90	9.31	9.32	9.56	31.68	29.52	30.89	30.91	31.71
4.00	10.82	10.01	10.42	10.43	10.84	35.92	33.20	34.58	34.61	35.98
5.00	11.80	10.82	11.22	11.23	11.83	39.15	35.89	37.23	37.26	39.25
6.00	12.54	11.41	11.78	11.79	12.58	41.61	37.87	39.10	39.13	41.75
7.00	13.11	11.84	12.19	12.20	13.16	43.52	39.30	40.45	40.48	43.68
8.00	13.55	12.16	12.47	12.48	13.61	44.96	40.35	41.39	41.42	45.16
9.00	13.88	12.39	12.67	12.68	13.95	46.07	41.11	42.03	42.06	46.31
10.00	14.14	12.55	12.80	12.81	14.22	46.94	41.63	42.46	42.51	47.20
11.00	14.34	12.66	12.88	12.90	14.43	47.60	42.02	42.75	42.80	47.89
12.00	14.49	12.74	12.94	12.95	14.59	48.09	42.29	42.93	42.97	48.41
13.00	14.61	12.79	12.96	12.98	14.71	48.48	42.45	43.02	43.07	48.82
14.00	14.70	12.82	12.97	12.98	14.80	48.76	42.54	43.03	43.08	49.12
15.00	14.75	12.83	12.95	12.97	14.86	48.95	42.57	43.90	43.93	49.33

The results indicated that TVL and HVL minimized with an increasing amount of AAS and escalated with growing photon energies, as photons with high energy lose their energy in a shorter distance than those with low energy. At 15 MeV, the HVL for all the studied samples varied between 12.8 and 14.8 cm for CS2MN0.5 and C0, respectively, while at 0.02 MeV, it varied between 0.01 and 0.02 cm for CS2MN0.5 and C0, respectively. The TVL ranged between 42.6 and 49.0 cm for CS2MN0.5 and C0, respectively, at 15 MeV, and is likely lowest for all the samples at 0.02 MeV, with the values of 0.04 cm and 0.07 cm for CS2MN0.5 and C0, respectively. Both TVL and HVL changed with fallen energy due to the photoelectric reaction, where the reaction cross section was particularly commensurate with the atomic number [75]. Also, they increased slowly with the increasing of the fallen energy due to the Compton effect. Based on our study, it can be concluded that sample CS2MN0.5 is the most effective shielding material. The HVL of CS2MN0.5 was found to be lower than that of the usual C0, making it the best gamma shield material.

The MFP is an important factor in determining the ability of shielding materials to reduce gamma-rays. It means the average dimension between the two subsequent interactions of fallen γ photons. Hence, materials with a lower MFP are better shields. Figure 14. illustrates that as the photon energy increases, the MFP of the samples also increases, with the values being very close at low energy but showing an increase at high energy. Moreover, as the amount of AAS increases, the MFP value decreases significantly. The MFP of the CS2MN0.5 sample appeared to be the smallest, indicating that it is the best sample due to the highest concentration of Fe and Mn compared to the other studied samples. The order of decreasing MFP is CS2MN0.5 < CS1MN0.5 < C0MN0.5 < CS3MN0.5 < C0.

Fig. 14 [Images not available. See PDF.]

The variation of MFP with energy for all studied samples

Z_eff, which represents the effective number, is another crucial factor in determining the attenuation capability of OPC-AAS-MF-NPs-composite pastes. Figure 15. presents the Z_eff magnitudes for all samples studied in the photon energy scale 0.015–15 MeV. Obviously, Z_eff is affected by the photon energy and the changes in the concentration of activated alumina sludge (AAS) [76]. In the lowest energy region, the largest values were observed for all the samples, where the photoelectric effect predominates, and the values varied from 18.55, 19.55, 19.63, 21.03, and 21.04 for CS3MN0.5, C0, C0MN0.5, CS1MN0.5, and CS2MN0.5, respectively. Also, minimum magnitudes were noticed in the intermediate energy scale as a result of the influence of Compton scattering, with slight increments at intense energies as a result of the pair production phenomenon. The values varied from 13.41, 12.88, 16.13, 17.38, and 17.39, as shown in the figure. C0 and CS3MN0.5 showed the lowest values of Z_ef, whereas the CS2MN0.5 and CS1MN0.5 give the highest Z_eff magnitudes in the given photon energy scale. Therefore, the addition of activated alumina sludge (AAS) with the highest concentration of Fe and Mn significantly increased the Z_eff value.

Fig. 15 [Images not available. See PDF.]

Variety of efficient atomic number Z_eff with energy for all samples studied

Figure 16 presents the gamma transmission factors for the 0.015–15 MeV photon energy scale as a function of energy for all the studied samples. It is evident from the Fig. 16. that, at low energies, the transmission values were very close for all the studied samples and improved with increasing energy. Moreover, all the samples had lower transmission factors than C0. The transmission factor increased with the increasing concentration of the elemental composition. Therefore, the CS2MN0.5 and CS1MN0.5 shields with the highest density had the lowest γ-rays transmission magnitudes. Additionally, the addition of 5% and 10% of AAS and 0.5% of nanoparticle MnFe₂O₄ could reduce the transmission of gamma-rays by approximately 14%.

Fig. 16 [Images not available. See PDF.]

Transmission coefficient of all pastes shields for γ-ray at energies scale from 0.015 to 15 MeV

Figure 17. displays the radiation protection efficiency (RPE%) at the energy of 661.64 keV for the samples studied. The results indicate that all the samples had higher RPE% values than C0, with CS2MN0.5 having the highest RPE% value among all the samples.

Fig. 17 [Images not available. See PDF.]

Variation of radiation protection efficiency (RPE%) for all samples at energy 661.64keV

The RPE% magnitudes varied from 28% (for plane C0) and increased to 28.8% (CS3MN0.5), 30% (C0MN0.5), 32.9% (CS1MN0.5), and 35.2% (CS2MN0.5) at 661.64 keV. These findings suggest that the CS2MN0.5 and CS1MN0.5 samples were more effective against higher-energy photons. Therefore, the CS2MN0.5 sample, which had the highest AAS content (10% of AAS) and the highest Fe and Mn content, is the best choice for radiation shielding.

Conclusion

Based on the findings of this study, the following conclusions can be drawn:

• Incorporating activated alumina sludge (AAS) at levels of up to 10% (by mass) mixes CS1 and CS2 resulted in a slight increase in the Wn contents and a slight decrease in the free portlandite content compared to the control mix (C0) at all curing ages.

• The CS magnitudes were enhanced for all composite pastes containing 0.5% and 1% MF-NPs compared to the blank sample (mix C0).

• The inclusion of 2% MF-NPs resulted in a slight decrease in the CS magnitudes compared to their references (mixes C0-CS3) due to poor dispersion caused by the agglomeration of MF-NPs-nanoparticles.

• The gamma-ray shielding capacity of the prepared samples using experimental measurements and theoretical modeling techniques based on LAC, MAC, HVL, TVL, MFP, Z_eff, and (RPE%). Our results demonstrate that the prepared samples exhibited higher LAC, MAC, and Z_eff values compared to the plain OPC specimen (mix C0). Furthermore, the addition of 5%, 10% AAS, and 0.5% MnFe₂O₄-nanoparticles with a high concentration of Fe and Mn to OPC pastes improved their shielding capacity by reducing the HVL, TVL, and MFP values and increasing LAC and MAC. The CS2MN0.5 and CS1MN0.5 samples had the highest gamma-ray protection among all the samples. In addition to CS2MN0.5 mix exhibiting the highest value, indicating its superior ability for radiation shielding.

In summary, our findings suggest that composite pastes with AAS waste and MF-NPs-nanoparticles have excellent potential for nuclear radiation shielding in nuclear protection applications and in the medical field.

Acknowledgements

The authors are grateful to acknowledge all who have been instrumental in the creation of this review article.

Author contributions

1. Amal A. El-Sawy: conceptualization, writing—original draft preparation, investigation, software, writing—reviewing and editing, data curation, visualization. 2. Mohamed Heikal: supervision, data curation, visualization, validation, software investigation, writing—reviewing and editing. 3. Sahar Ibrahim: validation, writing—review & editing, investigation, visualization. 4. Ola A. Mohamed: conceptualization, writing—original draft, validation, methodology, visualization, software, investigation, writing—review & editing.

Funding

This research received no external funding.

Data availability

Some or all data, models, or codes that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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