الفهرس 
Introduction and Object of investigationOnly 14 pages are availabe for public view
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Abstract
Manufacturing of Ordinary Portland cement (OPC) induces many crises environmentally and economically. Owing to its high energy consumption and greenhouse gas emissions as CO2 resulted during its production. Various techniques have been introduced to reduce the carbon footprint in the OPC industry such as replacing OPC with waste materials, especially those that are by-products of industrial processes that can be either pozzolanic material such as silica fume (SF) and fly ash (FA) or non-pozzolanic materials as the marble dust (MD). SF is a finely divided by-product material resulting during the smelting process of silicon or ferrosilicon alloys and composed mainly of amorphous silica particles while FA is the coal combustion residue from the thermal power stations and composed mainly of silica and alumina. MD is a waste product formed during the production of marble and composed mainly of calcium carbonate.
Although blended cement has its merits, it suffers from some limitations in many characteristics, therefore, researchers have been looking into using nanomaterials in the construction field to scale down these limitations and to develop additional properties in the cement paste. Nanomaterials have been used widely in many potentials as their inclusion to cement materials create new types of nanocomposites that possess high performance, such as developed mechanical characteristics, stability against fire, self-cleaning, and shielding against radiations. Two types of synthesized nanoparticles were used in this study namely nano zirconia (nano ZrO2, Zr) and nano hematite (α-Fe2O3, Fe).
In this investigation, different blended OPC pastes were prepared by replacing OPC with different quantities of SF, FA, and MD and admixed with 0, 0.25, 0.5, and 1% of each of nano ZrO2 and nano Fe2O3. The compressive strength values of the prepared pastes were evaluated after 1, 3, 7, 28, and 90 days of curing at normal curing conditions as well as for the hardened specimens (cured for 28 days) after being fired at 250, 550, and 850℃ and cooled by two ways (slow and rapid). The bulk density (B.D) and total porosity (T.P%) of hardened pastes were evaluated after 3 and 28 days of curing. Besides, the shielding efficiency against gamma-ray radiation produced from two different gamma-ray sources (60Co of high intensity and 137Cs of low intensity) was evaluated for some selected hardened specimens. Also, the antimicrobial activity for selected hardened composites (after 28 days of curing) was investigated against different microorganisms, particularly two bacteria (Bacillus Subtilis-ATCC 6633, Klebsiella pneumoniae-ATCC 13883) and two fungi strains (Aspergillus niger and Aspergillus fumigatus) using agar diffusion method. Additionally, the formed phases and morphological features of some selected composites were characterized using X-ray diffraction (XRD), differential thermogravimetric analysis (DTGA/TG), and scanning electron microscope with energy dispersive X-ray (SEM/EDX).
The findings of this investigation are summarized in the following sections:
Part A: Physicochemical, hydration kinetics, and mechanical properties of OPC paste blended with SF, MD, and different nanoparticles
In this part, the effect of replacing OPC with 5 and 10% of each of MD and SF on the physicochemical, mechanical characteristics, kinetics of hydration, microstructure of the hardened specimens, stability against firing, gamma radiation shielding, and their biological activity was investigated. Besides, utilization of small doses (0.25, 0.5, and 1 mass%) of nano ZrO2 (Zr), and nano Fe2O3 (Fe) for promoting the durability of OPC replaced with 10% silica fume +10%marble dust blend was studied.
Based on the obtained results, the following conclusions could be derived:
Specimens made from OPC replaced with 5%SF +5% MD (mix S) showed comparable compressive strength (CS) values compared to neat OPC, while increasing the replacement to 20% (SF+MD), mix S1 induces lower CS values due to the high dilution effect for the mineralogical phases.
Specimens made from mixes S or S1 showed lower B.D values compared to that of neat OPC. This result is assigned to the lower specific gravity of MD and SF compared to OPC particles, as well as the formation of lower quantities of hydration products.
The free lime content for mixes S and S1 increases up to 7 days, followed by a sharp decrease up to 90 days which can be ascribed to the consumption of the free portlandite via the pozzolanic reaction of SF particles.
XRD and DTGA/TG techniques indicated the formation of lower quantities of various hydration products (CH, CSH, and CASH) in the case of specimens made of mix S1 days compared to that made of neat OPC at the same time.
Specimens made from mixes S or S1 presented higher thermal stability compared to neat OPC when exposed to different elevated temperatures (250, 550, and 850℃), whether they cooled slowly or suddenly. mix S1 exhibits the best thermal stability. Scanning electron microscope (SEM) images revealed that specimens of mix S1 possess highly dense structure, compared to that of control (OPC) when fired at 250℃, due to the formation of an extra amount of hydration products such as CSH and CASH via the internal autoclaving reaction.
All specimens made from mix S1 blended with different % of nano zirconia presented higher CS values compared to that made from mix S1 itself, owing to the vital role of nano zirconia particles in activation of the hydration reaction as well as their filling effect.
Specimens made from mix S1 Zr 0.5 showed the highest B.D, CS values, and lowest T.P% among the other nanocomposites. While the further increase in the nano zirconia percentage to 1% induces lower CS values, which is attributed to the agglomeration of the nanoparticles.
The XRD and DTGA/TG techniques for S1 Zr 0.5 specimens confirmed the acceleration of nano ZrO2 for pozzolanic consumption of CH by SF particles, as well as the formation of extra hydration products, which affirms the higher mechanical properties of these composites.
All nano zirconia incorporated composites showed higher thermal stability at 250, 550, and 850℃ with both cooling regimes than mix S1.
Specimens made from S1 Zr 1 composite presented the highest thermal stability among all tested nanocomposites at the three firing temperatures in both cooling regimes. This result assigned to the positive impact of nano zirconia on the mechanical behavior of the hardened composite as well as the high thermal stability of nano zirconia particles.
All specimens made from mix S1 blended with different % of nano Fe2O3 presented higher CS, higher B.D, and lower T.P% values compared to that made from mix S1, which confirms the positive impact of nano hematite particles via its physical role (activation the hydration process and pore filling effect), besides, its chemical role by their pozzolanic reaction forming CFH and CFSH that offer additional binding phases.
Specimens made from S1 Fe 1 composite presented the highest mechanical properties (Highest CS values, highest B.D, and lowest T.P%).
XRD analysis for S1 Fe 1 mix indicated the formation of additional peaks characteristic for the CFSH (ilvaite) phase, with a notable decrease in the intensity of CH peak at both ages compared to those of mix S1.
DTGA/TG thermograms of S1 Fe 1 affirm the XRD results and affirm the activation effect of nano Fe2O3 as well as its pozzolanic activity.
All nano ferric incorporated composites showed higher thermal stability at 250, 550, and 850℃ with both cooling regimes than mix S1. Mix S1 Fe 1 exhibited the highest CS values after firing compared to the other nanocomposites.
SEM micrograph affirmed the denser microstructure of mix S1 Fe 1 among mix S1 under the same conditions.
Specimens made from S1 Fe 1 and S1 Zr1 composites exhibited high linear attenuation coefficient values at low gamma-ray intensity than that at high gamma-ray intensity, and higher than that of the S1 mix at both gamma-ray intensities.
The biological activity of nano-incorporated specimens showed an inhibitory effect for the microbial and fungal growth which in turn shows their self-cleaning performance against Bacillus Subtilis, K. pneumoniae, Aspergillus niger, and Aspergillus fumigatus strains.
Part B: Physicochemical, hydration kinetics, and mechanical properties of OPC pastes blended with FA, MD, and different nanoparticles
In this part, the effect of replacing OPC with 5 and 10% of each of FA and MD on the physicochemical, mechanical characteristics, kinetics of hydration, microstructure of the hardened pastes, thermal stability, shielding for gamma radiation, and their biological activity was studied. Additionally, utilization of small doses (0.25, 0.5, and 1 mass%) of nano ZrO2 (Zr), and nano Fe2O3 (Fe) for boosting the durability of OPC replaced with 10% FA +10% MD composite was investigated.
Based on the obtained results, the following conclusions could be derived:
Specimens made from OPC replaced with 10% (FA + MD) mix F, and 20% (FA+MD) mix F1 induce a continuous decline in CS values owing to the reduction of the mineralogical phases that are responsible for the formation of binding phases.
Specimens made from mixes F or F1 showed lower B.D and higher T.P% values compared to those of neat OPC. This result is assigned to the lower specific gravity of MD and FA compared to OPC particles, as well as the formation of lower quantities of hydration products.
The free lime content for mixes F and F1 increases up to 7 days, followed by a continuous decrease up to 90 days which can be ascribed to the consumption of the free portlandite via the pozzolanic reaction with FA particles.
XRD and DTGA/TG techniques for specimens of mix F1 indicated the presence of the peak characteristic for SiO2 (Quartz) which indicates the presence of unreacted silica as well as the formation of lower quantities of various hydration products (CH, CSH, and CASH) compared to that made of OPC) at the same curing time. These results agreed with the low CS values obtained for both composites
Specimens made from mixes F or F1 indicated higher thermal stability compared to neat OPC when exposed to different firing temperatures, whether it cooled slowly or suddenly. Mix F1 showed the best thermal stability.
SEM micrographs of mix F1 after firing at 250℃ and gradually cooled displayed the presence of a compact matrix composed of highly stacked plates of CASH intermixed with fibrous CSH.
All specimens made from mix F1 blended with different % of nano ZrO2 presented higher CS, higher B.D, and lower T.P% values compared to that made from mix F1; owing to the vital role of both nanoparticles in activation of the hydration reaction as well as their pore filling effect.
Specimens made from mix F1 Zr 0.5 showed the highest B.D, CS values, and lowest T.P% among the other nanocomposites.
The XRD and DTGA/TG results for F1Zr 0.5 composite manifested the acceleration of nano ZrO2 for pozzolanic consumption of CH by FA particles, as well as the formation of extra hydration products, which agreed with the higher mechanical properties of this composite.
All nano zirconia incorporated composites showed higher thermal stability at 250, 550, and 850℃ with both cooling regimes compared to that of F1 specimens. F1 Zr 1 composite presented the highest thermal stability at all testing temperatures ad at both cooling modes.
Admixing F1 composite with 0.25, 0.5, and 1% of nano Fe2O3 augment its CS values at different ages, because of their nucleation and pore-filling effect, as well as their pozzolanic activity which forms new binding phases as CFH and ilvaite that in turns boosts its CS values with an optimal dose 1% nano ferric oxide.
Mix F1 Fe 1 possesses the highest B.D, CS values, and the lowest T.P.% among the other studied specimens at both studied ages.
XRD analysis for F1 Fe 1 mix indicated the formation of additional peaks characteristic for the CFSH (ilvaite) phase, with a notable decrease in the intensity of CH peak at both ages compared to those of mix F1.
DTGA/TG thermograms of F1 Fe 1 affirm the XRD results and affirm the activation effect of nano Fe2O3 as well as its pozzolanic activity.
All nano hematite incorporated composites showed higher thermal stability at 250, 550, and 850℃ with both cooling regimes than that of mix F1. Specimens of F1 Fe 1 composite exhibited the highest CS values after firing compared to the other nanocomposites.
SEM image of F1 Fe 1 composite affirms the presence of highly dense microstructure after firing at 250℃ and gradual cooling. This accounts for the high thermal stability of this composite.
Specimens made from F1 Fe 1 and F1 Zr 1 composites exhibited high linear attenuation coefficient values at low gamma-ray intensity than that at high gamma-ray intensity and higher than that of the F1 mix at both gamma-ray intensities.
The biological activity of nano-incorporated specimens showed an efficient inhibition effect for the microbial and fungal growth which in turn shows their self-cleaning performance against Bacillus Subtilis, K. pneumoniae, Aspergillus niger, and Aspergillus fumigatus strains.
Part C: Physicochemical and mechanical properties of OPC pastes admixed with different nanoparticles
In this part, the effect of admixing of OPC with 0.25, 0.5, and 1 mass% of nano ZrO2 and nano Fe2O3 on the physicochemical, mechanical characteristics, stability against firing, gamma radiation shielding, and biological activity of the hardened specimens were investigated.
Based on the obtained results, the following conclusions could be derived:
All OPC specimens admixed with different doses of nano ZrO2 or nano Fe2O3 indicated high CS values compared to neat OPC at all ages of hydration.
C Zr 0.5 and C Fe 1 composites presented the highest CS, B.D values, and lowest T.P % among the other tested composites.
XRD patterns of mix C Zr 0.5 reveal the presence of some characteristic peaks as control at the same age, which confirms the physical role only of nano zirconia particles. While in the case of C Fe 1 composite, a new peak characteristic for ilvaite was distinguished, affirming that nano Fe2O3 has both physical and chemical roles.
The stability of the hardened specimens against firing at a temperature range from 250 to 850℃ indicated that all C-Zr composites and C-Fe composites have high thermal resistance compared to control under the two cooling conditions. C Zr 1 and C Fe 1 hardened specimens exhibited the best enhanced thermal stability.
SEM micrographs for C Zr 1 and C Fe 1 specimens after firing at 250℃ and cooled slowly reveal the formation of high dense matrix containing excessive quantities of CASH and CSH compared to that of neat OPC
DTGA/TG analysis confirms the formation of large quantities of various hydration products in the case of C Zr 1 and C Fe 1 specimens after 7 and 28 days of hydration compared to control at the same age.
Admixing OPC with 1% nano zirconia (C Zr 1) or 1% nano hematite (C Fe 1) positively affected its gamma radiation shielding ability against different intensities of gamma rays. C Fe 1 composite showed higher μ values compared to C Zr 1.
Inclusion of different doses of nano zirconia or nano hematite increases the antimicrobial inhibition activity for various bacterial and fungal growth (Bacillus Subtilis, K. pneumonia, Aspergillus niger, and Aspergillus fumigatus).
Part D: Overall conclusion from this study
The stability against firing for all nano zirconia composites is higher than that obtained with nano ferric oxide due to the higher thermal stability of nano zirconia.
Mix S1 Zr 1 possesses the highest thermal stability specimen among all studied composites
All nano ferric oxide composites showed higher radiation shielding ability than nano zirconia composites owing to the chemical and physical role of nano hematite that develops the microstructure of the specimens.
Mix S1 Fe 1 showed the highest linear attenuation coefficient values among all other studied composites at both intensities.
All nanocomposites containing nano zirconia or nano hematite possess good antimicrobial inhibition efficiency and self-cleaning performance. Depending on the field of application, the suitable nanomaterial and the suitable dose will be chosen.