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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.


(a) Total bond order density vs. C/S ratio in 19 crystals. (Portlandite (a.3) was excluded since it has no Si atoms.); (b) TBOD distribution map vs. the composition of Ca:Si:H. The color bar labels the values for the TBOD. The dot-dash lines indicate specific C/S ratios.
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f3: (a) Total bond order density vs. C/S ratio in 19 crystals. (Portlandite (a.3) was excluded since it has no Si atoms.); (b) TBOD distribution map vs. the composition of Ca:Si:H. The color bar labels the values for the TBOD. The dot-dash lines indicate specific C/S ratios.

Mentions: Figure 3(a) shows the plot of TBOD vs the C/S ratio showing an approximate inverse relationship. It is apparent that crystals with the same C/S ratio can have very different TBOD. Since TBOD is more sensitive to the bonding and relevant to cohesion, its use for classifying CSH crystals is most appropriate. This plot also shows that the four groups discussed above do not cluster together in relation to the TBOD. Group c has a wide range of C/S as well as TBOD. However, group d, believed to be closest to hydrated cement, has a narrow distribution in C/S but a wider TBOD range. Roughly speaking, we can divide the 20 crystals into to 3 groups according to their TBOD – high, medium and low. Crystals a.1, b.4 and c.5 belong to the low TBOD group mainly because of the high C/S ratio. On the opposite end, b.1 from group b, c.1 and c.2 from group c and d.1, d2 and d4 from group d belong to the high TBOD group. The rest of 10 crystals belong to the medium TBOD group which mostly from group d crystals. The mixing of groups based upon Strunz classification and a weak correlation of TBOD with C/S ratio signifies the complex interplay and tradeoffs between the covalent bonds and HBs in these CSH structures. Although, Qn chains in group d crystals tend to reduce C/S ratio, interlayer hydroxyl, water and HBs drastically alter the TBOD by increasing the effective volume without modification to C/S ratio. For example, crystal T14 (d.3) has a low C/S ratio but still has medium TBOD. The reason is that there are two types of silicate. Both d.2 and d.4 structures have double silicate chains whereas d.3 has only single silicate chains, which affects the TBOD considerably.


Quantum mechanical metric for internal cohesion in cement crystals.

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

(a) Total bond order density vs. C/S ratio in 19 crystals. (Portlandite (a.3) was excluded since it has no Si atoms.); (b) TBOD distribution map vs. the composition of Ca:Si:H. The color bar labels the values for the TBOD. The dot-dash lines indicate specific C/S ratios.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: (a) Total bond order density vs. C/S ratio in 19 crystals. (Portlandite (a.3) was excluded since it has no Si atoms.); (b) TBOD distribution map vs. the composition of Ca:Si:H. The color bar labels the values for the TBOD. The dot-dash lines indicate specific C/S ratios.
Mentions: Figure 3(a) shows the plot of TBOD vs the C/S ratio showing an approximate inverse relationship. It is apparent that crystals with the same C/S ratio can have very different TBOD. Since TBOD is more sensitive to the bonding and relevant to cohesion, its use for classifying CSH crystals is most appropriate. This plot also shows that the four groups discussed above do not cluster together in relation to the TBOD. Group c has a wide range of C/S as well as TBOD. However, group d, believed to be closest to hydrated cement, has a narrow distribution in C/S but a wider TBOD range. Roughly speaking, we can divide the 20 crystals into to 3 groups according to their TBOD – high, medium and low. Crystals a.1, b.4 and c.5 belong to the low TBOD group mainly because of the high C/S ratio. On the opposite end, b.1 from group b, c.1 and c.2 from group c and d.1, d2 and d4 from group d belong to the high TBOD group. The rest of 10 crystals belong to the medium TBOD group which mostly from group d crystals. The mixing of groups based upon Strunz classification and a weak correlation of TBOD with C/S ratio signifies the complex interplay and tradeoffs between the covalent bonds and HBs in these CSH structures. Although, Qn chains in group d crystals tend to reduce C/S ratio, interlayer hydroxyl, water and HBs drastically alter the TBOD by increasing the effective volume without modification to C/S ratio. For example, crystal T14 (d.3) has a low C/S ratio but still has medium TBOD. The reason is that there are two types of silicate. Both d.2 and d.4 structures have double silicate chains whereas d.3 has only single silicate chains, which affects the TBOD considerably.

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.