A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C₃A and Their Hydration Products in the Presence of Gypsum.

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 (C₃A), 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. C₃A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C₃A 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 C₃A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C₃A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution

Monosulfoaluminate (Ca4Al2(SO4)(OH)(12)center dot 6H(2)O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO42- and OH-) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formed ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel's salt or Friedel's salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed.ope

Unlocking the Secrets of Al-tobermorite in Roman Seawater Concrete

Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al3+ substitution for Si4+ in Q2 (1Al), Q3 (1Al), and Q3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na+ and K+ partially balance Al3+ substitution for Si4+. Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans

Identification of dendritic cell precursor from the CD11c+ cells expressing high levels of MHC class II molecules in the culture of bone marrow with FLT3 ligand

Dendritic cells (DCs) are readily generated from the culture of mouse bone marrow (BM) treated with either granulocyte macrophage-colony stimulating factor (GM-CSF) or FMS-like tyrosine kinase 3 ligand (FLT3L). CD11c+MHCII+ or CD11c+MHCIIhi cells are routinely isolated from those BM cultures and generally used as in vitro-generated DCs for a variety of experiments and therapies. Here, we examined CD11c+ cells in the BM culture with GM-CSF or FLT3L by staining with a monoclonal antibody 2A1 that is known to recognize mature or activated DCs. Most of the cells within the CD11c+MHCIIhi DC gate were 2A1+ in the BM culture with GM-CSF (GM-BM culture). In the BM culture with FLT3L (FL-BM culture), almost of all the CD11c+MHCIIhi cells were within the classical DC2 (cDC2) gate. The analysis of FL-BM culture revealed that a majority of cDC2-gated CD11c+MHCIIhi cells exhibited a 2A1-CD83-CD115+CX3CR1+ phenotype, and the others consisted of 2A1+CD83+CD115-CX3CR1- and 2A1-CD83-CD115-CX3CR1- cells. According to the antigen uptake and presentation, morphologies, and gene expression profiles, 2A1-CD83-CD115-CX3CR1- cells were immature cDC2s and 2A1+CD83+CD115-CX3CR1- cells were mature cDC2s. Unexpectedly, however, 2A1-CD83-CD115+CX3CR1+ cells, the most abundant cDC2-gated MHCIIhi cell subset in FL-BM culture, were non-DCs. Adoptive cell transfer experiments in the FL-BM culture confirmed that the cDC2-gated MHCIIhi non-DCs were precursors to cDC2s, i.e., MHCIIhi pre-cDC2s. MHCIIhi pre-cDC2s also expressed the higher level of DC-specific transcription factor Zbtb46 as similarly as immature cDC2s. Besides, MHCIIhi pre-cDC2s were generated only from pre-cDCs and common DC progenitor (CDP) cells but not from monocytes and common monocyte progenitor (cMoP) cells, verifying that MHCIIhi pre-cDC2s are close lineage to cDCs. All in all, our study identified and characterized a new cDC precursor, exhibiting a CD11c+MHCIIhiCD115+CX3CR1+ phenotype, in FL-BM culture

Multi-Scale High-Resolution X-ray Synchrotron Characterization of Air Voids in Concrete

The crystallization of ice in porous materials can lead to a significant decrease in durability. This is particularly important for reinforced concrete structures where ice formation can compromise the civil infrastructure. Much progress has been made in how to reduce the damage, but to develop new improvements, it is necessary to characterize the multi-scale dimensional structure of air-entrained concrete exposed to low temperatures. Synchrotron radiation laboratories supply their equipment with high flux high brightness light, offering phenomenal and varied exploration for fine-tuned and precise characterization techniques that are unafforded, in comparison, by standard stand-alone laboratory equipment with significantly limited source illumination. The use of synchrotron radiation has opened exciting new lines of research, and this dissertation uses cutting-edge techniques to image, for the first time, the in-situ ice formation inside a hydrated air-entrained cement paste using hard x-ray synchrotron microtomography (µCT). The results provide clear evidence of the importance of air-entrainment to mitigate freezing damage, and the ability to observe undisrupted internal paste ice formation opens the possibility to non-destructively observe and evaluate air entrainment variables in action. This novel technique opens new lines of research on the in-situ quantification of ice crystallization, a critical information for the micromechanical modeling, including cryo-suction of porous materials exposed to freezing conditions. Using a custom-made loading device mounted on the loading stage of the µCT, it was possible to record, for the first time, the in-situ formation and propagation of microcracks in entrained air void mortar pastes subjected to compression and tension. It is well-known that the presence of distributed small air voids in paste protects the matrix against ice expansion, but the enhanced durability comes at a cost of reduced mechanical strength. However, the mechanism of the reduction of strength has not been studied. The in-situ mechanical tests clearly show how the cracks form near or at the air void and develop a complex cracking pattern connecting the voids. The studies provide physical evidence for improvement of topology of the air void system in the cementitious matrix. Even though the use of surfactants has been used to successfully entrain air in concrete, the understanding of their mechanism is far from complete. This lack of understanding prevents the development of optimized surfactants. For this reason, this dissertation presents a sub-micron scale chemical speciation of the shell structure formed around entrained air voids in hardened entrained cement paste using scanning transmission x-ray microscope (STXM). Some detailed location specific information is revealed in this study, such as the state of carbonation, the identification and composition of the hydration products, and the level of hydration at and near the air void shell. It is found that the air void shell is made mostly of calcium silicate hydrate (C-S-H) with higher Ca/Si ratio in composition than the C-S-H that exists in the matrix, which contradicts previous studies performed using a scanning electron microscope energy dispersive spectroscopy (SEM-EDX). The study of ancient Roman concrete has been receiving attention because of its long durability. One of the open questions is how the Roman concrete survived frost action. For this reason, ancient concrete samples collected both from marine and land structures were collected and subjected up to 20 cycles of freeze-thaw. Their varied resistance to freeze damage was documented using µCT and while some patterns were identified, it was not possible to establish a universal law to predict the frost resistance of Roman concrete

Incorporating carbon sequestration materials in civil infrastructure: A micro and nano-structural analysis

The Calera method for carbon sequestration promotes carbon mineralization through aqueous precipitation. This work reports a comprehensive analysis on a carbonate obtained by the Calera process to evaluate its suitability as a cement replacement for concrete applications. This work focuses on the analysis of two hydrated cement pastes made with a blend of Portland cement and Calera carbonates by various advanced analytical techniques. Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was used to observe microstructures and determine elemental compositions. The synchrotron X-ray diffraction technique combined with Rietveld analysis were applied to identify constituent phases and refine crystal structures, crystallite sizes as well as relative phase abundances. Calcite and vaterite are observed in all samples while CSH II and portlandite are dominant in the cement pastes. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectrometry and Scanning Transmission X-ray Microscopy (STXM) experiments were conducted to investigate chemical speciation and morphological information of carbonate minerals with different absorption energies. STXM results confirmed heterogeneity of the samples, and also provided a nano-scale phase map across multiple particles. Differential Thermogravimetric (DTG) was used to observe heat transfer through structures and changes in mass upon heating. A compressive strength tests were performed on materials and shown comparable strength to Portland cement. © 2013 Elsevier Ltd. All rights reserved

A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C3A and Their Hydration Products in the Presence of Gypsum

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 (C3A), 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. C3A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C3A 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 C3A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C3A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments

Incorporating carbon sequestration materials in civil infrastructure: A micro and nano-structural analysis

The Calera method for carbon sequestration promotes carbon mineralization through aqueous precipitation. This work reports a comprehensive analysis on a carbonate obtained by the Calera process to evaluate its suitability as a cement replacement for concrete applications. This work focuses on the analysis of two hydrated cement pastes made with a blend of Portland cement and Calera carbonates by various advanced analytical techniques. Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was used to observe microstructures and determine elemental compositions. The synchrotron X-ray diffraction technique combined with Rietveld analysis were applied to identify constituent phases and refine crystal structures, crystallite sizes as well as relative phase abundances. Calcite and vaterite are observed in all samples while CSH II and portlandite are dominant in the cement pastes. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectrometry and Scanning Transmission X-ray Microscopy (STXM) experiments were conducted to investigate chemical speciation and morphological information of carbonate minerals with different absorption energies. STXM results confirmed heterogeneity of the samples, and also provided a nano-scale phase map across multiple particles. Differential Thermogravimetric (DTG) was used to observe heat transfer through structures and changes in mass upon heating. A compressive strength tests were performed on materials and shown comparable strength to Portland cement. © 2013 Elsevier Ltd. All rights reserved

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution.

Monosulfoaluminate (Ca₄Al₂(SO₄)(OH)12∙6H₂O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO₄2- and OH-) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formed ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel's salt or Friedel's salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed

A scanning transmission X-ray microscopy study of cubic and orthorhombic tricalcium aluminate and their hydration products in the presence of gypsum

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 (C3A), 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. C3A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C3A 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 C3A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C3A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments