Paulo Monteiro - Profile on Academia.edu (original) (raw)
Papers by Paulo Monteiro
Calcium Sulfoaluminate Sodalite (Ca4Al6O12SO4) Crystal Structure Evaluation and Bulk Modulus Determination
Journal of the American Ceramic Society, 2013
The predominant phase of calcium sulfoaluminate cement, Ca4(Al6O12)SO4, was investigated using hi... more The predominant phase of calcium sulfoaluminate cement, Ca4(Al6O12)SO4, was investigated using high‐pressure synchrotron X‐ray diffraction from ambient pressure to 4.75 GPa. A critical review of the crystal structure of Ca4(Al6O12)SO4 is presented. Rietveld refinements showed the orthorhombic crystal structure to best match the observed peak intensities and positions for pure Ca4(Al6O12)SO4. The compressibility of Ca4(Al6O12)SO4 was studied using cubic, orthorhombic, and tetragonal crystal structures due to the lack of consensus on the actual space group, and all three models provided similar results of 69(6) GPa. With its divalent cage ions, the bulk modulus of Ca4(Al6O12)SO4 is higher than other sodalites with monovalent cage ions, such as Na8(AlSiO4)6Cl2 or Na8(AlSiO4)6(OH)2·H2O. Likewise, comparing this study to previous ones shows the lattice compressibility of aluminate sodalites decreases with increasing size of the caged ions. Ca4(Al6O12)SO4 is more compressible than other c...
Cement & Concrete Composites, Feb 1, 2021
Efforts are currently underway to improve the performance of small electric antennas and resonato... more Efforts are currently underway to improve the performance of small electric antennas and resonator-based antennas embedded in the civil infrastructure. One of the main limitations of these small antennas is that they have narrow bandwidths which limit their use when embedded in concrete. The present work shows that by changing the amount of iron (III) oxide microparticles in a cementitious matrix, not only does the impedance matching of the embedded array improve by as much as 20 dB, it also produces a lesser shift in resonant frequency (RF) than the original cementitious matrix alone. Further analysis of antenna transmission coefficient S21 values shows that adding 4% iron (III) oxide into cement paste improves the RF power transmission into the material compared to the control by as much as 10 dB. Given that iron (III) oxide microparticles are easily available as admixture pigments for coloring mortar or concrete, it is possible to fasttrack implementation of this application in new construction.
Physical Mesomechanics, 2019
Acta Crystallographica Section A, Aug 8, 1996
Scientific Reports, Nov 9, 2017
Small resonator antennas, such as metaresonator antennas, have narrow bandwidths, which limits th... more Small resonator antennas, such as metaresonator antennas, have narrow bandwidths, which limits their effective range of frequencies. When they are used as embedded antennas in building materials, their performance is affected more than other types of antennas, as typical building materials have a shielding effectiveness (SE) of 80 dB to 100 dB. Adding magnetic and/or metallic particles to cement mixes changes the properties of the concrete, which can improve the performance of antennas. Specifically, enhancing a cement paste with iron-based magnetic particles improves the bandwidth and S 11 of embedded antennas. This report investigates the impact of two different iron-based magnetic particle sizes (micro-and nanosized particles) to determine the effects that they have on the S 11 and S 21 characteristics of the metaresonator antenna array embedded in enhanced cement pastes. Results show that compared to cement paste only sample, cement paste with micro-sized iron-based magnetic particles had the greatest improvement of performance of a metaresonator antenna array in terms of a small shift in the resonance frequency and an increase of bandwidth. Particularly for a cement paste enhanced with micro-sized iron (III) oxide particles, the S 21 curve was improved over the cement paste only sample by as much as 10 dB.
Journal of the American Ceramic Society, Dec 7, 2020
The reviewer raises a valid point, so we included XRD measurements to show that the sample did no... more The reviewer raises a valid point, so we included XRD measurements to show that the sample did not have portlandite nor showed evidence of carbonation. The following addition was done on page 7, line 31: "The solid phase for both Ca/Si ratio was analyzed by XRD and only C-S-H was present. There was no evidence of the presence of portlandite nor of carbonation. The XRD results are shown in Figure ." 2. The schematic of C-S-H (tobermorite 14A) shown in Figure is in atomic-scale which is much smaller scale relative to this study. The authors seem to measure pores between C-S-H globules or clusters in nanoscale. Please specify the special resolutions for TEM tomography since it is directly related to 'the scale' in this study. Refer to page 11, line 8, we added "The voxel size of both models is 1.14 nm". 3. Page 6, Line 21: What do you mean by 'characterization mechanisms of hydration' ? Here we refer to reference no. 30 about hydration mechanisms which is not the focus of this study. We have clarified it by removing ", and characterization mechanisms of hydration" on page 6, Line 21. 4. In 2.1, please specify the w/b for each mixture since w/b is also a critical factor affecting the porosity of C-S-H. Indeed, the w/b can have a significant influence on the C-S-H" morphology so we added the following information: Refer to page 7, line 11, we added "The water to solid ratio of both samples was equal to 45" 5. Page 11, Line 19, what is the reason of selecting 5 particles (I do not think it is 'particle', it seems to be 'ROI' or 'area' in C-S-H)? selected randomly? We agree with the reviewer, so we changed the term "particle" to "region of interest (ROI)". We selected ROIs that look like a fiber along the original projection direction, but when we rotated, it turned out that they are foil-like. 5 ROIs we selected are not randomly. They are representative
Materials, Aug 31, 2016
This paper shows the microstructural differences and phase characterization of pure phases and hy... more This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C 3 A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C 3 A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C 3 A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C 3 A/gypsum systems were identified through the changes in the L III edge fine structure for Calcium. The results also show greater Ca L II binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C 3 A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments.
IET Microwaves, Antennas & Propagation
In an urban built city environment, the performance of electromagnetic (EM) wave propagation thro... more In an urban built city environment, the performance of electromagnetic (EM) wave propagation through building materials poses a new set of challenges to radio frequency engineers in the prediction of the 5G-network coverage planning. We propose the prospects on the use of composite building materials enhanced with different volumetric fractions of iron (III) oxide (Fe 2 O 3) inclusions as a reddish-brown colouring admixture in modern-day concrete. Using a non-destructive microwave measurement technique, a two-factor 6 � 10 factorial experiment and a randomized controlled statistical study from 3.40 to 3.60 GHz is conducted on 15-cm thick building material prototypes enhanced with 2-wt% to 10-wt% micro-sized Fe 2 O 3 inclusions to evaluate their efficacy on EM wave propagation. Transmission coefficients (S 21) data are analysed statistically between treatment and control groups, yielding up to 2.28 dB mean S 21 improvement in performance and a fractional bandwidth of 100% by the 2-wt% Fe 2 O 3 treatment group. Electromagnetic characterisations of the fabricated mortar samples with different Fe 2 O 3 inclusions are performed using Nicholson-Ross-Weir model followed by the evaluation of dielectric and propagation losses. Our findings support the use of 2-wt% Fe 2 O 3 as the optimal volumetric fraction which improves the microwave transparency, thus creating potential EM benefits for the fifth-generation (5G) wireless communication systems. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Cement and Concrete Research, 2021
Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the... more Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the creep is largely controlled by the binding phase calcium-(aluminum-)silicate-hydrate, or C-(A-)S-H. This phase has a lamellar structure and under deviatoric stress aligns its c-axis with the principal stress. However, the limiting resistance to this reorientation is unknown at the nanocrystalline level. Small-angle X-ray scattering shows that the lamellae thickness decreases under 100's MPa deviatoric stress. Deviatoric stress Raman spectroscopy shows that there are two ways that this break-up can occur. If the material's silicate chains are cross-linked, then strain in Si-O bonds does not increase above certain stresses, indicating a relaxation adjacent to the Si-O bond. If the chains are not cross-linked, then the silicate chains are broken up by rastering against each other, introducing defects. These results show that the plastic deformation of C-(A-)S-H is relevant for Portland cement creep. Table of contents image Material strain Si-O-Ca bond strain Calciumsilicate hydrate Raman laser Turbostratic slip observed! Deviatoric-stress Raman spectroscopy shows how the structure of cement hydrates affects the way they plastically deform.
RSC Adv., 2017
Calcium (alumino)silicate hydrate (C–(A–)S–H) is the critical binding phase in modern Portland ce... more Calcium (alumino)silicate hydrate (C–(A–)S–H) is the critical binding phase in modern Portland cement-based concrete, yet the relationship between its structure and stoichiometry is not completely understood.
Composites Part B: Engineering, 2018
This paper presents an experimental study that investigates the influence of the low fiber conten... more This paper presents an experimental study that investigates the influence of the low fiber content of polypropylene and hooked-end steel fibers on the properties of high-strength concrete. The study variables include fiber types and fiber contents. The effect of combining both fibers with a total fiber content of 1.0% was also studied in some mixtures. Silica fume, as a supplementary cementitious material, was used at 10% of the cement weight in all fiber-reinforced concrete mixtures. Compressive strength, modulus of elasticity, longitudinal resonant frequency, rapid chloride migration and free drying shrinkage tests were performed for different curing ages. The results show that replacement of the cement weight with 10% silica fume improved all of the characteristics of the concrete evaluated in this research study. It was observed that the inclusion of fibers, particularly steel fibers, enhanced the mechanical properties of concrete. It was found that the incorporation of polypropylene fibers resulted in a reduction of chloride diffusivity, while introducing steel fibers significantly increased the chloride diffusivity of concrete. Finally, the results showed that hybridization of two types of fibers was an effective way to improve the properties of concrete and specifically reduce the drying shrinkage compared with that of the plain concrete.
ACS applied materials & interfaces, Jan 27, 2017
Properties of organic/inorganic composites can be highly dependent on the interfacial connections... more Properties of organic/inorganic composites can be highly dependent on the interfacial connections. In this work, molecular dynamics, using pair potential based force fields, was employed to investigate the structure, dynamics and stability of interfacial connections between calcium silicate hydrates (C-S-H) and organic functional groups of three different polymer species. The calculation results suggest that the affinity between C-S-H and polymers is influenced by the polarity of the functional groups, the diffusivity and aggregation tendency of polymers. In the interfaces, the calcium counter-ions from C-S-H act as the coordination atoms in bridging the double-bonded oxygen atoms in the carboxyl groups (-COOH), and the Ca-O connection plays a dominant role in binding poly acrylic acid (PAA) due to the strong bond strength defined by time correlated function. The defective calcium silicate chains provide significant number of non-bridging oxygen sites to accept H-bonds from -COOH gr...
American Mineralogist, 2017
Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoal... more Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoaluminate hydrate (abbreviated as kuzelite) are the major minerals in the hydration reaction of tricalcium aluminate in the presence of gypsum and have critical impacts on the kinetics and thermodynamics of early-age cement hydration mechanisms. Here, spectroscopic analysis of these minerals is conducted using scanning transmission X-ray microscopy (STXM). Their Ca L 2,3-edge near edge X-ray absorption fine structure (NEXAFS) spectra are measured and correlated to the known Ca coordination environments. The results indicate that these minerals have unique Ca environments that can be differentiated from one another based on the intensities and positions of the absorption peaks at 346.5-348.5 and 350.5-351.5 eV. It is concluded that Ca in tricalcium aluminate (cubic and orthorhombic polymorphs) and katoite is in cubic-like coordination with negative 10Dq, whereas Ca is in an octahedral-like coordination with positive 10Dq in ettringite, gypsum, and kuzelite. For tricalcium aluminate, the Ca atoms in both polymorphs are in similar chemical environments with slightly more distortion in the orthorhombic polymorph. As a common issue in STXM experiments, absorption saturation of NEXAFS spectra is also investigated. It is demonstrated that the optical density difference between pre-and post-edge absorption levels provides a reliable indication of the sample thickness in the systems studied. The present work provides a reference for the STXM study of the calcium (sulfo)aluminate reactions in cement hydration and natural aqueous environments, and in the former case, provides a more complete understanding of a system that may serve as a low-C alternative to Portland cement.
Cement and Concrete Composites, 2017
Cenosphere particles are hollow, but due to their hard shells, they can be used in cementitious c... more Cenosphere particles are hollow, but due to their hard shells, they can be used in cementitious composites to produce ultra-lightweight cement composites (ULCC) with high strength and low thermal conductivity. This study integrates thermal conductivity with mechanical experimental research, microscopic investigation, and numerical simulations to provide new insights into the behavior of these advanced composites. The microstructure of ULCC samples was characterized using synchrotron high-resolution microtomography, transmission electron microscopy and scanning electron microscopy. Composite models were used to predict the thermal conductivity of the cenospheres based on the experimental results of ULCC thermal conductivity and the porosity of the samples.
Cement and Concrete Research, 2016
This paper reports an investigation of the recycled concrete (RC) microstructure using synchrotro... more This paper reports an investigation of the recycled concrete (RC) microstructure using synchrotron microtomography (μCT) at the Advanced Light Source combined with Scanning Electron Microscopy analysis. The study evaluated the influence of 50% of recycled concrete aggregate (RCA) and its water absorption compensation on the RC microstructure. The following variables were studied: a) the compressive strength of the original concrete used to obtain the RCA (40 and 80MPa) and b) the initial moisture condition of the RCA (Saturated Surface Dry and Oven Dry). The microtomographic images showed the mixtures cast with RCA in the dry condition developed an evident macropore network surrounding the RCA particle that was not observed in the mixtures using RCA in the SSD condition. SEM images confirmed the initial findings from CT and showed that the thickness of the interfacial transition zone in RC is in the same order of magnitude as the reference concrete.
Preferred orientation of ettringite in concrete fractures
Journal of Applied Crystallography, 2009
Sulfate attack and the accompanying crystallization of fibrous ettringite [Ca6Al2(OH)12(SO4)3·26H... more Sulfate attack and the accompanying crystallization of fibrous ettringite [Ca6Al2(OH)12(SO4)3·26H2O] cause cracking and loss of strength in concrete structures. Hard synchrotron X-ray microdiffraction is used to quantify the orientation distribution of ettringite crystals. Diffraction images are analyzed using the Rietveld method to obtain information on textures. The analysis reveals that thecaxes of the trigonal crystallites are preferentially oriented perpendicular to the fracture surfaces. By averaging single-crystal elastic properties over the orientation distribution, it is possible to estimate the elastic anisotropy of ettringite aggregates.
Effect of polycarboxylate ether on the expansion of ye'elimite hydration in the presence of anhydrite
Cement and Concrete Research, 2021
Abstract Polycarboxylate ether (PCE), a commonly used superplasticizer, is known to influence the... more Abstract Polycarboxylate ether (PCE), a commonly used superplasticizer, is known to influence the morphology of ettringite during the early hydration of C3A- and ye'elimite-containing cements. According to existing theories, such morphological changes may be crucial to the expansive behavior of these cements. This paper studied the expansion of ye'elimite-anhydrite pastes and found the use of PCE to reduce expansion after 4 days of curing. Hydration studies were conducted by calorimetry, X-ray diffractometry, scanning electron microscopy, mercury intrusion porosimetry, inductively coupled plasma–optical emission spectrometry, and X-ray microtomography. The results show that the influences of PCE on the morphology of ettringite and the hydration of ye'elimite were quite small after 2 days. Based on the crystal growth theory, the range of pores in which ettringite can grow was calculated to explain the observed expansive behaviors. The presence of ettringite nano-crystals in aluminum hydroxide was also revealed and considered as a possible expansion mechanism.
A hydration study of various calcium sulfoaluminate cements
Cement and Concrete Composites, 2014
ABSTRACT The present work studies the hydration process and microstructural features of five calc... more ABSTRACT The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.
Journal of Astm International, 2009
Corrosion of steel reinforcing bars (rebar) is the most prevalent mechanism of deterioration of r... more Corrosion of steel reinforcing bars (rebar) is the most prevalent mechanism of deterioration of reinforced concrete structures. Microcomposite low carbon, chromium steels (ASTM A1035) have been recently developed and used as a more corrosionresistant alternative to conventional low-carbon steel rebar (ASTM A615). These steels (typical composition in wt%: C 0.08, Cr 9.0, Mn 0.6, bal. Fe) are produced with a
Calcium Sulfoaluminate Sodalite (Ca4Al6O12SO4) Crystal Structure Evaluation and Bulk Modulus Determination
Journal of the American Ceramic Society, 2013
The predominant phase of calcium sulfoaluminate cement, Ca4(Al6O12)SO4, was investigated using hi... more The predominant phase of calcium sulfoaluminate cement, Ca4(Al6O12)SO4, was investigated using high‐pressure synchrotron X‐ray diffraction from ambient pressure to 4.75 GPa. A critical review of the crystal structure of Ca4(Al6O12)SO4 is presented. Rietveld refinements showed the orthorhombic crystal structure to best match the observed peak intensities and positions for pure Ca4(Al6O12)SO4. The compressibility of Ca4(Al6O12)SO4 was studied using cubic, orthorhombic, and tetragonal crystal structures due to the lack of consensus on the actual space group, and all three models provided similar results of 69(6) GPa. With its divalent cage ions, the bulk modulus of Ca4(Al6O12)SO4 is higher than other sodalites with monovalent cage ions, such as Na8(AlSiO4)6Cl2 or Na8(AlSiO4)6(OH)2·H2O. Likewise, comparing this study to previous ones shows the lattice compressibility of aluminate sodalites decreases with increasing size of the caged ions. Ca4(Al6O12)SO4 is more compressible than other c...
Cement & Concrete Composites, Feb 1, 2021
Efforts are currently underway to improve the performance of small electric antennas and resonato... more Efforts are currently underway to improve the performance of small electric antennas and resonator-based antennas embedded in the civil infrastructure. One of the main limitations of these small antennas is that they have narrow bandwidths which limit their use when embedded in concrete. The present work shows that by changing the amount of iron (III) oxide microparticles in a cementitious matrix, not only does the impedance matching of the embedded array improve by as much as 20 dB, it also produces a lesser shift in resonant frequency (RF) than the original cementitious matrix alone. Further analysis of antenna transmission coefficient S21 values shows that adding 4% iron (III) oxide into cement paste improves the RF power transmission into the material compared to the control by as much as 10 dB. Given that iron (III) oxide microparticles are easily available as admixture pigments for coloring mortar or concrete, it is possible to fasttrack implementation of this application in new construction.
Physical Mesomechanics, 2019
Acta Crystallographica Section A, Aug 8, 1996
Scientific Reports, Nov 9, 2017
Small resonator antennas, such as metaresonator antennas, have narrow bandwidths, which limits th... more Small resonator antennas, such as metaresonator antennas, have narrow bandwidths, which limits their effective range of frequencies. When they are used as embedded antennas in building materials, their performance is affected more than other types of antennas, as typical building materials have a shielding effectiveness (SE) of 80 dB to 100 dB. Adding magnetic and/or metallic particles to cement mixes changes the properties of the concrete, which can improve the performance of antennas. Specifically, enhancing a cement paste with iron-based magnetic particles improves the bandwidth and S 11 of embedded antennas. This report investigates the impact of two different iron-based magnetic particle sizes (micro-and nanosized particles) to determine the effects that they have on the S 11 and S 21 characteristics of the metaresonator antenna array embedded in enhanced cement pastes. Results show that compared to cement paste only sample, cement paste with micro-sized iron-based magnetic particles had the greatest improvement of performance of a metaresonator antenna array in terms of a small shift in the resonance frequency and an increase of bandwidth. Particularly for a cement paste enhanced with micro-sized iron (III) oxide particles, the S 21 curve was improved over the cement paste only sample by as much as 10 dB.
Journal of the American Ceramic Society, Dec 7, 2020
The reviewer raises a valid point, so we included XRD measurements to show that the sample did no... more The reviewer raises a valid point, so we included XRD measurements to show that the sample did not have portlandite nor showed evidence of carbonation. The following addition was done on page 7, line 31: "The solid phase for both Ca/Si ratio was analyzed by XRD and only C-S-H was present. There was no evidence of the presence of portlandite nor of carbonation. The XRD results are shown in Figure ." 2. The schematic of C-S-H (tobermorite 14A) shown in Figure is in atomic-scale which is much smaller scale relative to this study. The authors seem to measure pores between C-S-H globules or clusters in nanoscale. Please specify the special resolutions for TEM tomography since it is directly related to 'the scale' in this study. Refer to page 11, line 8, we added "The voxel size of both models is 1.14 nm". 3. Page 6, Line 21: What do you mean by 'characterization mechanisms of hydration' ? Here we refer to reference no. 30 about hydration mechanisms which is not the focus of this study. We have clarified it by removing ", and characterization mechanisms of hydration" on page 6, Line 21. 4. In 2.1, please specify the w/b for each mixture since w/b is also a critical factor affecting the porosity of C-S-H. Indeed, the w/b can have a significant influence on the C-S-H" morphology so we added the following information: Refer to page 7, line 11, we added "The water to solid ratio of both samples was equal to 45" 5. Page 11, Line 19, what is the reason of selecting 5 particles (I do not think it is 'particle', it seems to be 'ROI' or 'area' in C-S-H)? selected randomly? We agree with the reviewer, so we changed the term "particle" to "region of interest (ROI)". We selected ROIs that look like a fiber along the original projection direction, but when we rotated, it turned out that they are foil-like. 5 ROIs we selected are not randomly. They are representative
Materials, Aug 31, 2016
This paper shows the microstructural differences and phase characterization of pure phases and hy... more This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C 3 A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C 3 A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C 3 A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C 3 A/gypsum systems were identified through the changes in the L III edge fine structure for Calcium. The results also show greater Ca L II binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C 3 A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments.
IET Microwaves, Antennas & Propagation
In an urban built city environment, the performance of electromagnetic (EM) wave propagation thro... more In an urban built city environment, the performance of electromagnetic (EM) wave propagation through building materials poses a new set of challenges to radio frequency engineers in the prediction of the 5G-network coverage planning. We propose the prospects on the use of composite building materials enhanced with different volumetric fractions of iron (III) oxide (Fe 2 O 3) inclusions as a reddish-brown colouring admixture in modern-day concrete. Using a non-destructive microwave measurement technique, a two-factor 6 � 10 factorial experiment and a randomized controlled statistical study from 3.40 to 3.60 GHz is conducted on 15-cm thick building material prototypes enhanced with 2-wt% to 10-wt% micro-sized Fe 2 O 3 inclusions to evaluate their efficacy on EM wave propagation. Transmission coefficients (S 21) data are analysed statistically between treatment and control groups, yielding up to 2.28 dB mean S 21 improvement in performance and a fractional bandwidth of 100% by the 2-wt% Fe 2 O 3 treatment group. Electromagnetic characterisations of the fabricated mortar samples with different Fe 2 O 3 inclusions are performed using Nicholson-Ross-Weir model followed by the evaluation of dielectric and propagation losses. Our findings support the use of 2-wt% Fe 2 O 3 as the optimal volumetric fraction which improves the microwave transparency, thus creating potential EM benefits for the fifth-generation (5G) wireless communication systems. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Cement and Concrete Research, 2021
Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the... more Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the creep is largely controlled by the binding phase calcium-(aluminum-)silicate-hydrate, or C-(A-)S-H. This phase has a lamellar structure and under deviatoric stress aligns its c-axis with the principal stress. However, the limiting resistance to this reorientation is unknown at the nanocrystalline level. Small-angle X-ray scattering shows that the lamellae thickness decreases under 100's MPa deviatoric stress. Deviatoric stress Raman spectroscopy shows that there are two ways that this break-up can occur. If the material's silicate chains are cross-linked, then strain in Si-O bonds does not increase above certain stresses, indicating a relaxation adjacent to the Si-O bond. If the chains are not cross-linked, then the silicate chains are broken up by rastering against each other, introducing defects. These results show that the plastic deformation of C-(A-)S-H is relevant for Portland cement creep. Table of contents image Material strain Si-O-Ca bond strain Calciumsilicate hydrate Raman laser Turbostratic slip observed! Deviatoric-stress Raman spectroscopy shows how the structure of cement hydrates affects the way they plastically deform.
RSC Adv., 2017
Calcium (alumino)silicate hydrate (C–(A–)S–H) is the critical binding phase in modern Portland ce... more Calcium (alumino)silicate hydrate (C–(A–)S–H) is the critical binding phase in modern Portland cement-based concrete, yet the relationship between its structure and stoichiometry is not completely understood.
Composites Part B: Engineering, 2018
This paper presents an experimental study that investigates the influence of the low fiber conten... more This paper presents an experimental study that investigates the influence of the low fiber content of polypropylene and hooked-end steel fibers on the properties of high-strength concrete. The study variables include fiber types and fiber contents. The effect of combining both fibers with a total fiber content of 1.0% was also studied in some mixtures. Silica fume, as a supplementary cementitious material, was used at 10% of the cement weight in all fiber-reinforced concrete mixtures. Compressive strength, modulus of elasticity, longitudinal resonant frequency, rapid chloride migration and free drying shrinkage tests were performed for different curing ages. The results show that replacement of the cement weight with 10% silica fume improved all of the characteristics of the concrete evaluated in this research study. It was observed that the inclusion of fibers, particularly steel fibers, enhanced the mechanical properties of concrete. It was found that the incorporation of polypropylene fibers resulted in a reduction of chloride diffusivity, while introducing steel fibers significantly increased the chloride diffusivity of concrete. Finally, the results showed that hybridization of two types of fibers was an effective way to improve the properties of concrete and specifically reduce the drying shrinkage compared with that of the plain concrete.
ACS applied materials & interfaces, Jan 27, 2017
Properties of organic/inorganic composites can be highly dependent on the interfacial connections... more Properties of organic/inorganic composites can be highly dependent on the interfacial connections. In this work, molecular dynamics, using pair potential based force fields, was employed to investigate the structure, dynamics and stability of interfacial connections between calcium silicate hydrates (C-S-H) and organic functional groups of three different polymer species. The calculation results suggest that the affinity between C-S-H and polymers is influenced by the polarity of the functional groups, the diffusivity and aggregation tendency of polymers. In the interfaces, the calcium counter-ions from C-S-H act as the coordination atoms in bridging the double-bonded oxygen atoms in the carboxyl groups (-COOH), and the Ca-O connection plays a dominant role in binding poly acrylic acid (PAA) due to the strong bond strength defined by time correlated function. The defective calcium silicate chains provide significant number of non-bridging oxygen sites to accept H-bonds from -COOH gr...
American Mineralogist, 2017
Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoal... more Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoaluminate hydrate (abbreviated as kuzelite) are the major minerals in the hydration reaction of tricalcium aluminate in the presence of gypsum and have critical impacts on the kinetics and thermodynamics of early-age cement hydration mechanisms. Here, spectroscopic analysis of these minerals is conducted using scanning transmission X-ray microscopy (STXM). Their Ca L 2,3-edge near edge X-ray absorption fine structure (NEXAFS) spectra are measured and correlated to the known Ca coordination environments. The results indicate that these minerals have unique Ca environments that can be differentiated from one another based on the intensities and positions of the absorption peaks at 346.5-348.5 and 350.5-351.5 eV. It is concluded that Ca in tricalcium aluminate (cubic and orthorhombic polymorphs) and katoite is in cubic-like coordination with negative 10Dq, whereas Ca is in an octahedral-like coordination with positive 10Dq in ettringite, gypsum, and kuzelite. For tricalcium aluminate, the Ca atoms in both polymorphs are in similar chemical environments with slightly more distortion in the orthorhombic polymorph. As a common issue in STXM experiments, absorption saturation of NEXAFS spectra is also investigated. It is demonstrated that the optical density difference between pre-and post-edge absorption levels provides a reliable indication of the sample thickness in the systems studied. The present work provides a reference for the STXM study of the calcium (sulfo)aluminate reactions in cement hydration and natural aqueous environments, and in the former case, provides a more complete understanding of a system that may serve as a low-C alternative to Portland cement.
Cement and Concrete Composites, 2017
Cenosphere particles are hollow, but due to their hard shells, they can be used in cementitious c... more Cenosphere particles are hollow, but due to their hard shells, they can be used in cementitious composites to produce ultra-lightweight cement composites (ULCC) with high strength and low thermal conductivity. This study integrates thermal conductivity with mechanical experimental research, microscopic investigation, and numerical simulations to provide new insights into the behavior of these advanced composites. The microstructure of ULCC samples was characterized using synchrotron high-resolution microtomography, transmission electron microscopy and scanning electron microscopy. Composite models were used to predict the thermal conductivity of the cenospheres based on the experimental results of ULCC thermal conductivity and the porosity of the samples.
Cement and Concrete Research, 2016
This paper reports an investigation of the recycled concrete (RC) microstructure using synchrotro... more This paper reports an investigation of the recycled concrete (RC) microstructure using synchrotron microtomography (μCT) at the Advanced Light Source combined with Scanning Electron Microscopy analysis. The study evaluated the influence of 50% of recycled concrete aggregate (RCA) and its water absorption compensation on the RC microstructure. The following variables were studied: a) the compressive strength of the original concrete used to obtain the RCA (40 and 80MPa) and b) the initial moisture condition of the RCA (Saturated Surface Dry and Oven Dry). The microtomographic images showed the mixtures cast with RCA in the dry condition developed an evident macropore network surrounding the RCA particle that was not observed in the mixtures using RCA in the SSD condition. SEM images confirmed the initial findings from CT and showed that the thickness of the interfacial transition zone in RC is in the same order of magnitude as the reference concrete.
Preferred orientation of ettringite in concrete fractures
Journal of Applied Crystallography, 2009
Sulfate attack and the accompanying crystallization of fibrous ettringite [Ca6Al2(OH)12(SO4)3·26H... more Sulfate attack and the accompanying crystallization of fibrous ettringite [Ca6Al2(OH)12(SO4)3·26H2O] cause cracking and loss of strength in concrete structures. Hard synchrotron X-ray microdiffraction is used to quantify the orientation distribution of ettringite crystals. Diffraction images are analyzed using the Rietveld method to obtain information on textures. The analysis reveals that thecaxes of the trigonal crystallites are preferentially oriented perpendicular to the fracture surfaces. By averaging single-crystal elastic properties over the orientation distribution, it is possible to estimate the elastic anisotropy of ettringite aggregates.
Effect of polycarboxylate ether on the expansion of ye'elimite hydration in the presence of anhydrite
Cement and Concrete Research, 2021
Abstract Polycarboxylate ether (PCE), a commonly used superplasticizer, is known to influence the... more Abstract Polycarboxylate ether (PCE), a commonly used superplasticizer, is known to influence the morphology of ettringite during the early hydration of C3A- and ye'elimite-containing cements. According to existing theories, such morphological changes may be crucial to the expansive behavior of these cements. This paper studied the expansion of ye'elimite-anhydrite pastes and found the use of PCE to reduce expansion after 4 days of curing. Hydration studies were conducted by calorimetry, X-ray diffractometry, scanning electron microscopy, mercury intrusion porosimetry, inductively coupled plasma–optical emission spectrometry, and X-ray microtomography. The results show that the influences of PCE on the morphology of ettringite and the hydration of ye'elimite were quite small after 2 days. Based on the crystal growth theory, the range of pores in which ettringite can grow was calculated to explain the observed expansive behaviors. The presence of ettringite nano-crystals in aluminum hydroxide was also revealed and considered as a possible expansion mechanism.
A hydration study of various calcium sulfoaluminate cements
Cement and Concrete Composites, 2014
ABSTRACT The present work studies the hydration process and microstructural features of five calc... more ABSTRACT The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.
Journal of Astm International, 2009
Corrosion of steel reinforcing bars (rebar) is the most prevalent mechanism of deterioration of r... more Corrosion of steel reinforcing bars (rebar) is the most prevalent mechanism of deterioration of reinforced concrete structures. Microcomposite low carbon, chromium steels (ASTM A1035) have been recently developed and used as a more corrosionresistant alternative to conventional low-carbon steel rebar (ASTM A615). These steels (typical composition in wt%: C 0.08, Cr 9.0, Mn 0.6, bal. Fe) are produced with a