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Quantum mechanical metric for internal cohesion in cement crystals.

Dharmawardhana CC, Misra A, Ching WY - Sci Rep (2014)

Bottom Line: We study electronic structure and bonding of a large subset of the known CSH minerals.Our results reveal a wide range of contributions from each type of bonding, especially hydrogen bonding, which should enable critical analysis of spectroscopic measurements and construction of realistic C-S-H models.A rarely known orthorhombic phase Suolunite is found to have higher cohesion (TBOD) in comparison to Jennite and Tobermorite, which are considered the backbone of hydrated Portland cement.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Missouri - Kansas City, 5110 Rockhill Road, Kansas City, MO 64110, USA.

ABSTRACT
Calcium silicate hydrate (CSH) is the main binding phase of Portland cement, the single most important structural material in use worldwide. Due to the complex structure and chemistry of CSH at various length scales, the focus has progressively turned towards its atomic level comprehension. We study electronic structure and bonding of a large subset of the known CSH minerals. Our results reveal a wide range of contributions from each type of bonding, especially hydrogen bonding, which should enable critical analysis of spectroscopic measurements and construction of realistic C-S-H models. We find the total bond order density (TBOD) as the ideal overall metric for assessing crystal cohesion of these complex materials and should replace conventional measures such as Ca:Si ratio. A rarely known orthorhombic phase Suolunite is found to have higher cohesion (TBOD) in comparison to Jennite and Tobermorite, which are considered the backbone of hydrated Portland cement.

No MeSH data available.


Distribution of bond order vs. bond length in four representative crystals.(a.2) Allite; (b.1) Alwillite; (c.2) Suolunite; and (d.8) Jennite. Symbols for different types of bonds are shown at the top, “-“ for covalent bond, “…” for hydrogen bond. The pie chart in the inset shows the percentage of different types of bonding: red, Ca-O; green, Si-O; violet covalent –(O-H); orange, other HB; blue, HB between H2O. Lower insets show different types of hydrogen bonds.
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f2: Distribution of bond order vs. bond length in four representative crystals.(a.2) Allite; (b.1) Alwillite; (c.2) Suolunite; and (d.8) Jennite. Symbols for different types of bonds are shown at the top, “-“ for covalent bond, “…” for hydrogen bond. The pie chart in the inset shows the percentage of different types of bonding: red, Ca-O; green, Si-O; violet covalent –(O-H); orange, other HB; blue, HB between H2O. Lower insets show different types of hydrogen bonds.

Mentions: The bond order (BO) between each pair of atoms represents the quantitative measure of the bond stiffness and strength22. They are important in revealing the origin of internal cohesion in the CSH crystals. We obtain the BO values between every pair of atoms in the crystal using the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method23 (see Method Section and Supplementary Information for details). Figure 2 shows the BO vs bond length (BL) distributions for four representative CSH crystals from each group (a: alite, b: afwillite, c: suolunite, and d: jennite). Different bond types in each crystals (Ca-O, Si-O, H-O-H, -(O-H), H2O···H2O and –(O···H)) are as indicated. As evident, there are two types of OH bonds. The strong covalently bonded ones and the weaker HBs. Further, there are two types of covalent O-H bonds: those within the water molecules (H-O-H) which do not contribute to internal cohesion, and those in the hydroxyl ions -(O-H), which attach to silicates (Si-OH) or Ca ions (Ca-OH). The HBs also have two categories: HBs between water molecules (H2O···H2O, shown as inset of Figure 2 for b.1), and all other types of HBs that are not exclusively between two isolated water molecules. For example, the HBs, such as Si-(O···H)O-Si and H2(O···H)O-Si, that are particularly significant are shown as inset of Figure 2 for c.2 and d.8, respectively. As an overall measure of the crystal cohesion, we define the total BO (TBO) to be the sum of individual BO values and the total bond order density (TBOD) as the TBO normalized by the crystal volume.


Quantum mechanical metric for internal cohesion in cement crystals.

Dharmawardhana CC, Misra A, Ching WY - Sci Rep (2014)

Distribution of bond order vs. bond length in four representative crystals.(a.2) Allite; (b.1) Alwillite; (c.2) Suolunite; and (d.8) Jennite. Symbols for different types of bonds are shown at the top, “-“ for covalent bond, “…” for hydrogen bond. The pie chart in the inset shows the percentage of different types of bonding: red, Ca-O; green, Si-O; violet covalent –(O-H); orange, other HB; blue, HB between H2O. Lower insets show different types of hydrogen bonds.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256593&req=5

f2: Distribution of bond order vs. bond length in four representative crystals.(a.2) Allite; (b.1) Alwillite; (c.2) Suolunite; and (d.8) Jennite. Symbols for different types of bonds are shown at the top, “-“ for covalent bond, “…” for hydrogen bond. The pie chart in the inset shows the percentage of different types of bonding: red, Ca-O; green, Si-O; violet covalent –(O-H); orange, other HB; blue, HB between H2O. Lower insets show different types of hydrogen bonds.
Mentions: The bond order (BO) between each pair of atoms represents the quantitative measure of the bond stiffness and strength22. They are important in revealing the origin of internal cohesion in the CSH crystals. We obtain the BO values between every pair of atoms in the crystal using the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method23 (see Method Section and Supplementary Information for details). Figure 2 shows the BO vs bond length (BL) distributions for four representative CSH crystals from each group (a: alite, b: afwillite, c: suolunite, and d: jennite). Different bond types in each crystals (Ca-O, Si-O, H-O-H, -(O-H), H2O···H2O and –(O···H)) are as indicated. As evident, there are two types of OH bonds. The strong covalently bonded ones and the weaker HBs. Further, there are two types of covalent O-H bonds: those within the water molecules (H-O-H) which do not contribute to internal cohesion, and those in the hydroxyl ions -(O-H), which attach to silicates (Si-OH) or Ca ions (Ca-OH). The HBs also have two categories: HBs between water molecules (H2O···H2O, shown as inset of Figure 2 for b.1), and all other types of HBs that are not exclusively between two isolated water molecules. For example, the HBs, such as Si-(O···H)O-Si and H2(O···H)O-Si, that are particularly significant are shown as inset of Figure 2 for c.2 and d.8, respectively. As an overall measure of the crystal cohesion, we define the total BO (TBO) to be the sum of individual BO values and the total bond order density (TBOD) as the TBO normalized by the crystal volume.

Bottom Line: We study electronic structure and bonding of a large subset of the known CSH minerals.Our results reveal a wide range of contributions from each type of bonding, especially hydrogen bonding, which should enable critical analysis of spectroscopic measurements and construction of realistic C-S-H models.A rarely known orthorhombic phase Suolunite is found to have higher cohesion (TBOD) in comparison to Jennite and Tobermorite, which are considered the backbone of hydrated Portland cement.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Missouri - Kansas City, 5110 Rockhill Road, Kansas City, MO 64110, USA.

ABSTRACT
Calcium silicate hydrate (CSH) is the main binding phase of Portland cement, the single most important structural material in use worldwide. Due to the complex structure and chemistry of CSH at various length scales, the focus has progressively turned towards its atomic level comprehension. We study electronic structure and bonding of a large subset of the known CSH minerals. Our results reveal a wide range of contributions from each type of bonding, especially hydrogen bonding, which should enable critical analysis of spectroscopic measurements and construction of realistic C-S-H models. We find the total bond order density (TBOD) as the ideal overall metric for assessing crystal cohesion of these complex materials and should replace conventional measures such as Ca:Si ratio. A rarely known orthorhombic phase Suolunite is found to have higher cohesion (TBOD) in comparison to Jennite and Tobermorite, which are considered the backbone of hydrated Portland cement.

No MeSH data available.