Safaa Elgamal - Academia.edu (original) (raw)
Papers by Safaa Elgamal
Silicates Industriels, 2005
Superplasticized blended Portland cement pastes containing silica fume were made by using water/c... more Superplasticized blended Portland cement pastes containing silica fume were made by using water/cement weight ratios of standard water of consistency with various additions of acrylate-PEG superplasticizer. Pastes were hydrated for various time intervals. The physico-chemical characteristics of the hardened cement pastes were studied and related to the pore system of the hardened pastes. The optimum addition of this superplasticizer suitable for the improvement of hydraulic properties of blended cement pastes containing 5% condensed silica fume is 1%, meanwhile its optimum addition is 0.25% for blended cement pastes containing 7.5% condensed silica fume.
Journal of Material Cycles and Waste Management
This work was focused on evaluating the suitability of replacing Portland cement (PC) by 5, 10 an... more This work was focused on evaluating the suitability of replacing Portland cement (PC) by 5, 10 and 15 mass % of activated alum sludge waste (AAS) as a pozzolanic material. Exploitation of low-cost nanocomposite for bolstering the physical, mechanical, and stability against firing of PC–AAS-hardened composites was inspected. CuFe2O4 spinel nanoparticle with average particle size (~ 50 nm) was prepared. Inclusion of CuFe2O4 spinel in different PC–AAS-hardened composites bolsters their physicomechanical features at almost normal curing ages as well as their stability against firing. The positive impact of synthesized CuFe2O4 spinel was affirmed via TGA/DTG and XRD techniques, which indicated the presence of diverse hydration yields such as CSHs, CASHs, CFSH, and CuSH that enhance the overall physicomechanical characteristics and thermal stability of various PC–AAS-hardened composites. The composite containing (90 PC–10 AAS waste–2 CuFe2O4) offers many benefits from the economic and env...
Journal of Thermal Analysis, 1993
The hydration of two calcium hydroxide - silica fume mixtures was studied at 25~ these are Mix I ... more The hydration of two calcium hydroxide - silica fume mixtures was studied at 25~ these are Mix I and Mix II with molar lime/silica ratios of 1 and 1.7, respectively. The free lime, free silica and chemically combined water contents were determined at various time of hydration from ...
Journal of the Korean Ceramic Society, 2020
Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventio... more Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventional sintering technique using commercial monoclinic zirconia, Yttrium oxide and waste-derived magnesia-rich spinel (MMA) powder mixtures. In this study, effect of MMA content and sintering temperature on stabilization and densification properties of zirconia has been duly considered. The obtained results showed that m-ZrO 2 in MMA-free Z0 reference specimen is partially stabilized upon temperature rising into tetragonal phase by Y 3+ ions diffusion inside zirconia structure. MMA-free Z0 reference specimen sintered at 1600 ºC showed m-and t-ZrO 2 dual-phase structure with a relative density of 80.2%. Unlike, upon rising the sintering temperature, Z10-Z50 composites containing 10-50 wt% MMA demonstrated higher relative density of more than 99% and showed variant behavior, where their m-ZrO 2 is transformed and stabilized into cubic form by diffusion of Y 3+ , Mg 2+ and Al 3+ ions inside zirconia lattice structure. The outcomes indicate that MMA has significantly improved both the densification and stabilization behavior of m-ZrO 2 through facilitating Y 3+ diffusion inside zirconia lattice structure.
Electrical Engineering, 2021
The effect of zirconium oxide nanoparticles (NZ) addition on the electrical and physical properti... more The effect of zirconium oxide nanoparticles (NZ) addition on the electrical and physical properties of porcelain insulators over high different sintering temperatures was investigated. Different amount of zirconia nanoparticles (0–8 wt%) was added to porcelain sample that obtained from local raw materials found in large quantities and excellent quality in the Sinai and Aswan (Egypt). Samples were produced by powder technology with compositions of 50% kaolin, 25% feldspar and 25% quartz. The prepared samples admixed with different amounts of zirconia were sintered at different temperatures (1100, 1200, 1300 and 1400 °C) for 2 h. The microstructures of some selected samples were characterized by scanning electron microscopy (SEM). Phase composition of some nanocomposites samples was identified using X-ray diffraction (XRD), to evaluate the thermal, structural and microstructural changes by increasing the concentration of zirconia. The electrical properties of different samples were evaluated by measuring the AC breakdown strength, the relative permittivity ( ε r ) and dielectric loss (tan δ ) at different frequencies at room temperature. A finite element method (FEM) axisymmetrical model of the samples is used to evaluate their breakdown strength. The results obtained revealed that, samples sintered at 1300 °C give the best electrical and physical properties. Also, nanocomposite porcelain sample admixed with 4 wt% zirconia nanoparticles and sintered at 1300 °C present the maximum density (3.678 g/cm 3 ), minimum water absorption (0.031%) and minimum porosity (0.049%) values as well as good insulating characteristics and confirm the electro technical porcelain production feasibility.
Journal of Materials Science: Materials in Electronics, 2020
The high-voltage electrical porcelain insulator plays an important role in the electrical power i... more The high-voltage electrical porcelain insulator plays an important role in the electrical power industry. The effect of silica nanoparticles (NS) addition on the electrical and physical properties of porcelain insulators sintered at different temperatures was investigated in the present study. Kaolin, feldspar, and quartz (in the form of silica sand) were used as economical raw materials to prepare porcelain insulator samples. Different additions of silica nanoparticles (0–15 wt%) were used. The porcelain specimens were compressed under 50 MPa pressure and treated at different sintering temperature (from 1100 to 1400 °C). The morphology and microstructure of the raw materials and some selected specimens were investigated using scanning electron microscope. Phase composition of some selected samples was identified using X-ray diffraction, to evaluate the thermal, structural, and microstructural changes by increasing the concentration of silica (0–15 wt%). The dielectric properties were evaluated by measuring the AC breakdown strength, the relative permittivity ( ε r ) and dielectric loss (tan δ ) at different frequencies at room temperature. A finite element method axi-symmetrical model of the samples with the help of FEMM 4.2 package is used to evaluate their breakdown strength. The results revealed that the physical and dielectric properties of porcelain samples enhanced by increasing the sintering temperature. The porcelain samples admixed with 10 wt% silica nanoparticles and sintered at 1300 °C present the maximal density (3.57 g/cm 3 ), minimal water absorption (0.0173%) and minimal porosity values (0.043%) as well as a good insulating characteristic.
Journal of Taibah University for Science, 2020
The performance of oil well cement (OWC) incorporating pozzolana under diverse hydrothermal curin... more The performance of oil well cement (OWC) incorporating pozzolana under diverse hydrothermal curing circumstances was inspected. OWC was partially replaced by 5 weight% of silica fume (SF) or fly ash (FA). The prepared composites were cured under different hydrothermal circumstances (60°C/0.02 MPa, 100°C/0.1 MPa and 150°C/0.48 MPa) for 7 days. The outcomes established that increasing curing temperature and pressure brought about a decline in the compressive strength magnitudes of various neat OWC pastes. This finding is correlated to the metamorphosis of CSH to the greatly crystalline phase of α-dicalcium silicate hydrate (α-C2SH). Such transformation motivates the destruction of the pore structure and promotes compressive strength decline. Admixing OWC with 5 wt.% SF or FA displayed enrichment in the mechanical aspects accompanied by the progression of highly compact microstructures. Additionally, the presence of SF or FA motivates the advancement of stable and desirable hydration products. DTG/TG, XRD and SEM analyses affirm these results.
Journal of Taibah University for Science, 2018
The immobilization effect of 1 and 3 mass % of Ni 2+ or Co 2+ ions on the hydration reaction of o... more The immobilization effect of 1 and 3 mass % of Ni 2+ or Co 2+ ions on the hydration reaction of ordinary Portland cement (OPC) and ordinary Portland cement blended with 5 and 15 mass % pumice was investigated. This was done by studying the bulk density, total porosity, compressive strength as well as identifying the phase composition of the formed hydrates using X-ray diffraction (XRD) technique. In addition, leaching behaviour of Ni 2+ and Co 2+ ions was examined up to 90 days using static leaching technique. The results indicated that the incorporation of these ions causes a notable retardation for the early hydration of the OPC. This effect is more noticeable in presence cobalt ions. Besides, the retarding effect was increased by increasing the percentage of heavy metal ions incorporated in the hydrated matrix. However, for OPC-pumice blended cement pastes, the existence of Ni 2+ or Co 2+ ions resulted in an enhancement in the compressive strength values during the hydration period from 3-28 days to be comparable with the values of neat OPC pastes. This enhancement is attributed to the interaction of these ions with pumice which increases the heavy metal fixation.
Journal of Thermal Analysis and Calorimetry, 2017
This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cos... more This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cost nanooxides additions for improving the mechanical properties and thermal resistance of hardened ordinary Portland cement (OPC) pastes. NS was synthesized from rice husk ash in the absence of any surfactant, while NA was synthesized from AlCl 3 in the presence of CTAB as a surfactant. The average particle sizes of synthesized NS and NA were 30 and 40 nm, respectively. Nano-silica or nano-alumina was added to OPC as a single phase with different ratios of 0.5, 1, 2 and 3 by mass % of OPC. The physico-chemical characteristics of different OPC-NS and OPC-NA hardened pastes were studied after 1, 3, 7, 14, 28 and 90 days of hydration. The resistance of the hardened composites for firing was evaluated for specimens cured for 28 days under tap water and then fired at 300, 600 and 800°C for 3 h. The fired specimens were cooled by two methods: gradual cooling and rapid cooling. The compressive strength test was performed for all mixes at each firing temperature. The compressive strength results revealed that the optimum addition of NS is 1, whereas the optimum addition of NA is 0.5 by mass % of OPC. XRD, TG/DTG and SEM results indicated that illcrystalline and nearly amorphous C-S-H, C-AS -H and C-A-H were the main hydration products.
Journal of Thermal Analysis, 1996
The hydration of two calcium hydroxide-silica fume mixtures was studied at 25~ The mixtures were ... more The hydration of two calcium hydroxide-silica fume mixtures was studied at 25~ The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiOz and H20/SiO2 molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis, The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO2 and H20/SiO2 in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.
Journal of Thermal Analysis and Calorimetry, 2012
Journal of Thermal Analysis and Calorimetry, 2011
The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V... more The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V) and expanded vermiculite (EV) exposed to high temperatures were studied. Different mixtures were prepared using 2.5, 5, and 10 wt% of both types of V. Each mixture, after 28 days of hydration, was heated at 300, 600, and 800°C for 3 h. Two modes of cooling were used; gradual cooling in air and rapid cooling in cold water. The percentage of residual strength, chemically combined water content, change in phase composition, and the thermal stability of the heated specimens were studied. The specimens cooled in water showed greater loss in strength than the air-cooled specimens. The presence of V improved the heat resistance of ordinary type I Portland cement (OPC) pastes. 5 wt% replacement revealed the best performance at all heating temperatures. The EV showed better thermal resistance than the nonexpanded one. Addition of silica fume (SF) with V in OPC pastes lead to superior performance. This can be explained as result of the combined effects of insulation properties of V and pozzolanic reactivity of SF which accounts for the notable increase in the residual strength for these mixes.
Journal of Thermal Analysis and Calorimetry, 2012
ABSTRACT In this investigation the effect of addition of magnetite nanoparticles on the hydration... more ABSTRACT In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe3O4 nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe3O4 nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character.
Hydration of ordinary Portland cement in the presence of two different types of superplasticizers... more Hydration of ordinary Portland cement in the presence of two different types of superplasticizers namely sodium lignosulfonate (LS) and naphthalene sulfonate-formaldehyde condensate (NSF) was studied using different experimental techniques. Superplasticized ordinary Portland cement pastes were prepared using the values of standard water of consistency with different additions of each types of superplasticizers used. Pastes were hydrated for different time intervals under normal curing conditions. The results reveal that both of superplasticizers increase the workability and reduce the standard water of consistency. This results in an improvement in the mechanical properties of superplasticized cement pastes at all ages of the hydration-hardening process. Naphthalene sulfonate-formaldehyde condensate was found to has the higher efficiency in improving the mechanical properties of the hardened pastes than that of sodium lignosulfonate superplasticizer.
Silicates Industriels, 2005
Superplasticized blended Portland cement pastes containing silica fume were made by using water/c... more Superplasticized blended Portland cement pastes containing silica fume were made by using water/cement weight ratios of standard water of consistency with various additions of acrylate-PEG superplasticizer. Pastes were hydrated for various time intervals. The physico-chemical characteristics of the hardened cement pastes were studied and related to the pore system of the hardened pastes. The optimum addition of this superplasticizer suitable for the improvement of hydraulic properties of blended cement pastes containing 5% condensed silica fume is 1%, meanwhile its optimum addition is 0.25% for blended cement pastes containing 7.5% condensed silica fume.
Journal of Material Cycles and Waste Management
This work was focused on evaluating the suitability of replacing Portland cement (PC) by 5, 10 an... more This work was focused on evaluating the suitability of replacing Portland cement (PC) by 5, 10 and 15 mass % of activated alum sludge waste (AAS) as a pozzolanic material. Exploitation of low-cost nanocomposite for bolstering the physical, mechanical, and stability against firing of PC–AAS-hardened composites was inspected. CuFe2O4 spinel nanoparticle with average particle size (~ 50 nm) was prepared. Inclusion of CuFe2O4 spinel in different PC–AAS-hardened composites bolsters their physicomechanical features at almost normal curing ages as well as their stability against firing. The positive impact of synthesized CuFe2O4 spinel was affirmed via TGA/DTG and XRD techniques, which indicated the presence of diverse hydration yields such as CSHs, CASHs, CFSH, and CuSH that enhance the overall physicomechanical characteristics and thermal stability of various PC–AAS-hardened composites. The composite containing (90 PC–10 AAS waste–2 CuFe2O4) offers many benefits from the economic and env...
Journal of Thermal Analysis, 1993
The hydration of two calcium hydroxide - silica fume mixtures was studied at 25~ these are Mix I ... more The hydration of two calcium hydroxide - silica fume mixtures was studied at 25~ these are Mix I and Mix II with molar lime/silica ratios of 1 and 1.7, respectively. The free lime, free silica and chemically combined water contents were determined at various time of hydration from ...
Journal of the Korean Ceramic Society, 2020
Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventio... more Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventional sintering technique using commercial monoclinic zirconia, Yttrium oxide and waste-derived magnesia-rich spinel (MMA) powder mixtures. In this study, effect of MMA content and sintering temperature on stabilization and densification properties of zirconia has been duly considered. The obtained results showed that m-ZrO 2 in MMA-free Z0 reference specimen is partially stabilized upon temperature rising into tetragonal phase by Y 3+ ions diffusion inside zirconia structure. MMA-free Z0 reference specimen sintered at 1600 ºC showed m-and t-ZrO 2 dual-phase structure with a relative density of 80.2%. Unlike, upon rising the sintering temperature, Z10-Z50 composites containing 10-50 wt% MMA demonstrated higher relative density of more than 99% and showed variant behavior, where their m-ZrO 2 is transformed and stabilized into cubic form by diffusion of Y 3+ , Mg 2+ and Al 3+ ions inside zirconia lattice structure. The outcomes indicate that MMA has significantly improved both the densification and stabilization behavior of m-ZrO 2 through facilitating Y 3+ diffusion inside zirconia lattice structure.
Electrical Engineering, 2021
The effect of zirconium oxide nanoparticles (NZ) addition on the electrical and physical properti... more The effect of zirconium oxide nanoparticles (NZ) addition on the electrical and physical properties of porcelain insulators over high different sintering temperatures was investigated. Different amount of zirconia nanoparticles (0–8 wt%) was added to porcelain sample that obtained from local raw materials found in large quantities and excellent quality in the Sinai and Aswan (Egypt). Samples were produced by powder technology with compositions of 50% kaolin, 25% feldspar and 25% quartz. The prepared samples admixed with different amounts of zirconia were sintered at different temperatures (1100, 1200, 1300 and 1400 °C) for 2 h. The microstructures of some selected samples were characterized by scanning electron microscopy (SEM). Phase composition of some nanocomposites samples was identified using X-ray diffraction (XRD), to evaluate the thermal, structural and microstructural changes by increasing the concentration of zirconia. The electrical properties of different samples were evaluated by measuring the AC breakdown strength, the relative permittivity ( ε r ) and dielectric loss (tan δ ) at different frequencies at room temperature. A finite element method (FEM) axisymmetrical model of the samples is used to evaluate their breakdown strength. The results obtained revealed that, samples sintered at 1300 °C give the best electrical and physical properties. Also, nanocomposite porcelain sample admixed with 4 wt% zirconia nanoparticles and sintered at 1300 °C present the maximum density (3.678 g/cm 3 ), minimum water absorption (0.031%) and minimum porosity (0.049%) values as well as good insulating characteristics and confirm the electro technical porcelain production feasibility.
Journal of Materials Science: Materials in Electronics, 2020
The high-voltage electrical porcelain insulator plays an important role in the electrical power i... more The high-voltage electrical porcelain insulator plays an important role in the electrical power industry. The effect of silica nanoparticles (NS) addition on the electrical and physical properties of porcelain insulators sintered at different temperatures was investigated in the present study. Kaolin, feldspar, and quartz (in the form of silica sand) were used as economical raw materials to prepare porcelain insulator samples. Different additions of silica nanoparticles (0–15 wt%) were used. The porcelain specimens were compressed under 50 MPa pressure and treated at different sintering temperature (from 1100 to 1400 °C). The morphology and microstructure of the raw materials and some selected specimens were investigated using scanning electron microscope. Phase composition of some selected samples was identified using X-ray diffraction, to evaluate the thermal, structural, and microstructural changes by increasing the concentration of silica (0–15 wt%). The dielectric properties were evaluated by measuring the AC breakdown strength, the relative permittivity ( ε r ) and dielectric loss (tan δ ) at different frequencies at room temperature. A finite element method axi-symmetrical model of the samples with the help of FEMM 4.2 package is used to evaluate their breakdown strength. The results revealed that the physical and dielectric properties of porcelain samples enhanced by increasing the sintering temperature. The porcelain samples admixed with 10 wt% silica nanoparticles and sintered at 1300 °C present the maximal density (3.57 g/cm 3 ), minimal water absorption (0.0173%) and minimal porosity values (0.043%) as well as a good insulating characteristic.
Journal of Taibah University for Science, 2020
The performance of oil well cement (OWC) incorporating pozzolana under diverse hydrothermal curin... more The performance of oil well cement (OWC) incorporating pozzolana under diverse hydrothermal curing circumstances was inspected. OWC was partially replaced by 5 weight% of silica fume (SF) or fly ash (FA). The prepared composites were cured under different hydrothermal circumstances (60°C/0.02 MPa, 100°C/0.1 MPa and 150°C/0.48 MPa) for 7 days. The outcomes established that increasing curing temperature and pressure brought about a decline in the compressive strength magnitudes of various neat OWC pastes. This finding is correlated to the metamorphosis of CSH to the greatly crystalline phase of α-dicalcium silicate hydrate (α-C2SH). Such transformation motivates the destruction of the pore structure and promotes compressive strength decline. Admixing OWC with 5 wt.% SF or FA displayed enrichment in the mechanical aspects accompanied by the progression of highly compact microstructures. Additionally, the presence of SF or FA motivates the advancement of stable and desirable hydration products. DTG/TG, XRD and SEM analyses affirm these results.
Journal of Taibah University for Science, 2018
The immobilization effect of 1 and 3 mass % of Ni 2+ or Co 2+ ions on the hydration reaction of o... more The immobilization effect of 1 and 3 mass % of Ni 2+ or Co 2+ ions on the hydration reaction of ordinary Portland cement (OPC) and ordinary Portland cement blended with 5 and 15 mass % pumice was investigated. This was done by studying the bulk density, total porosity, compressive strength as well as identifying the phase composition of the formed hydrates using X-ray diffraction (XRD) technique. In addition, leaching behaviour of Ni 2+ and Co 2+ ions was examined up to 90 days using static leaching technique. The results indicated that the incorporation of these ions causes a notable retardation for the early hydration of the OPC. This effect is more noticeable in presence cobalt ions. Besides, the retarding effect was increased by increasing the percentage of heavy metal ions incorporated in the hydrated matrix. However, for OPC-pumice blended cement pastes, the existence of Ni 2+ or Co 2+ ions resulted in an enhancement in the compressive strength values during the hydration period from 3-28 days to be comparable with the values of neat OPC pastes. This enhancement is attributed to the interaction of these ions with pumice which increases the heavy metal fixation.
Journal of Thermal Analysis and Calorimetry, 2017
This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cos... more This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cost nanooxides additions for improving the mechanical properties and thermal resistance of hardened ordinary Portland cement (OPC) pastes. NS was synthesized from rice husk ash in the absence of any surfactant, while NA was synthesized from AlCl 3 in the presence of CTAB as a surfactant. The average particle sizes of synthesized NS and NA were 30 and 40 nm, respectively. Nano-silica or nano-alumina was added to OPC as a single phase with different ratios of 0.5, 1, 2 and 3 by mass % of OPC. The physico-chemical characteristics of different OPC-NS and OPC-NA hardened pastes were studied after 1, 3, 7, 14, 28 and 90 days of hydration. The resistance of the hardened composites for firing was evaluated for specimens cured for 28 days under tap water and then fired at 300, 600 and 800°C for 3 h. The fired specimens were cooled by two methods: gradual cooling and rapid cooling. The compressive strength test was performed for all mixes at each firing temperature. The compressive strength results revealed that the optimum addition of NS is 1, whereas the optimum addition of NA is 0.5 by mass % of OPC. XRD, TG/DTG and SEM results indicated that illcrystalline and nearly amorphous C-S-H, C-AS -H and C-A-H were the main hydration products.
Journal of Thermal Analysis, 1996
The hydration of two calcium hydroxide-silica fume mixtures was studied at 25~ The mixtures were ... more The hydration of two calcium hydroxide-silica fume mixtures was studied at 25~ The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiOz and H20/SiO2 molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis, The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO2 and H20/SiO2 in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.
Journal of Thermal Analysis and Calorimetry, 2012
Journal of Thermal Analysis and Calorimetry, 2011
The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V... more The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V) and expanded vermiculite (EV) exposed to high temperatures were studied. Different mixtures were prepared using 2.5, 5, and 10 wt% of both types of V. Each mixture, after 28 days of hydration, was heated at 300, 600, and 800°C for 3 h. Two modes of cooling were used; gradual cooling in air and rapid cooling in cold water. The percentage of residual strength, chemically combined water content, change in phase composition, and the thermal stability of the heated specimens were studied. The specimens cooled in water showed greater loss in strength than the air-cooled specimens. The presence of V improved the heat resistance of ordinary type I Portland cement (OPC) pastes. 5 wt% replacement revealed the best performance at all heating temperatures. The EV showed better thermal resistance than the nonexpanded one. Addition of silica fume (SF) with V in OPC pastes lead to superior performance. This can be explained as result of the combined effects of insulation properties of V and pozzolanic reactivity of SF which accounts for the notable increase in the residual strength for these mixes.
Journal of Thermal Analysis and Calorimetry, 2012
ABSTRACT In this investigation the effect of addition of magnetite nanoparticles on the hydration... more ABSTRACT In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe3O4 nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe3O4 nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character.
Hydration of ordinary Portland cement in the presence of two different types of superplasticizers... more Hydration of ordinary Portland cement in the presence of two different types of superplasticizers namely sodium lignosulfonate (LS) and naphthalene sulfonate-formaldehyde condensate (NSF) was studied using different experimental techniques. Superplasticized ordinary Portland cement pastes were prepared using the values of standard water of consistency with different additions of each types of superplasticizers used. Pastes were hydrated for different time intervals under normal curing conditions. The results reveal that both of superplasticizers increase the workability and reduce the standard water of consistency. This results in an improvement in the mechanical properties of superplasticized cement pastes at all ages of the hydration-hardening process. Naphthalene sulfonate-formaldehyde condensate was found to has the higher efficiency in improving the mechanical properties of the hardened pastes than that of sodium lignosulfonate superplasticizer.