Limits...
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.


Ball-stick figures of representative crystals to illustrate the structures of each group of CSH and CS crystals: (a.2) Alite; (b.1) Afwillite; (c.2) Suolunite; (c.3) Kilchoanite; (d.2) Anomalous T11 Å; (d.7) Foshagite.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4256593&req=5

f1: Ball-stick figures of representative crystals to illustrate the structures of each group of CSH and CS crystals: (a.2) Alite; (b.1) Afwillite; (c.2) Suolunite; (c.3) Kilchoanite; (d.2) Anomalous T11 Å; (d.7) Foshagite.

Mentions: Table 1 lists 20 crystal phases with well-documented atomic positions used in this study placed into four groups: a, Clinker and hydroxide phase; b, nesosubsilicates; c, sorosilicates; and d, ionosilicates. Each group in Table 1 is arranged in ascending order of calcium to silicon (C/S) ratio. The clinker phases (a.1 and a.2) and the Portlandite (a.3) are placed in groupa. Portlandite is included in this group since it forms the basis for hydration of cement. The remaining crystals are grouped according to the Strunz scheme. In this scheme, the silicate units at each polymerization step are indicated by Qn, where the Si tetrahedron is connected to n other silicate tetrahedra. For example, an isolated silicate tetrahedron not connected to any other is denoted by Q0. The nesosubsilicates with isolated [SiO4]−4 groups are placed in group b. These CSH phases possess the lowest degree of polymerization. The sorosilicates with [Si2O7]−6 groups in the next polymerization step are placed under group c. For these phases, the [Si2O7]−6 is connected to two isolated tetrahedra via one bridging-O to form the so-called pyrogroups. Thus, all silicon tetrahedra are Q1. These silicon tetrahedra are linked via non-bridging O, to six-, seven- or even eight fold-coordinated Ca atoms. A special case of sorosilicate structures are those with mixtures of isolated tetrahedra (Q0) and finite triple chains (Q2), in which the silicon tetrahedra are connected to 6 and 8-fold coordinated Ca atoms. The group d contains the inosilicates. These comprise structures with infinitely long chains with a wide variety of C/S ratios, ranging from 0.50 in Nekoite (d.1) to 1.5 in Jennite (d.8). According to the degree of polymerization, the phases in this group could be subdivided into inosilicates with single chains (all tetrahedra are Q2), and double chains (2/3 Q2 and 1/3 Q3). The representative crystals from each group are illustrated in Figure 1. They are Alite (a.2) for group a; Afwillite (b.1) for group b; Suolunite (c.2), Kilichoanite (c.3) for group c; and Anomalous T11 A (d.2), forshgite (d.7) for group d. Similar images of all 20 crystals are displayed in the supporting information (SI) as Figure S1.


Quantum mechanical metric for internal cohesion in cement crystals.

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

Ball-stick figures of representative crystals to illustrate the structures of each group of CSH and CS crystals: (a.2) Alite; (b.1) Afwillite; (c.2) Suolunite; (c.3) Kilchoanite; (d.2) Anomalous T11 Å; (d.7) Foshagite.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Ball-stick figures of representative crystals to illustrate the structures of each group of CSH and CS crystals: (a.2) Alite; (b.1) Afwillite; (c.2) Suolunite; (c.3) Kilchoanite; (d.2) Anomalous T11 Å; (d.7) Foshagite.
Mentions: Table 1 lists 20 crystal phases with well-documented atomic positions used in this study placed into four groups: a, Clinker and hydroxide phase; b, nesosubsilicates; c, sorosilicates; and d, ionosilicates. Each group in Table 1 is arranged in ascending order of calcium to silicon (C/S) ratio. The clinker phases (a.1 and a.2) and the Portlandite (a.3) are placed in groupa. Portlandite is included in this group since it forms the basis for hydration of cement. The remaining crystals are grouped according to the Strunz scheme. In this scheme, the silicate units at each polymerization step are indicated by Qn, where the Si tetrahedron is connected to n other silicate tetrahedra. For example, an isolated silicate tetrahedron not connected to any other is denoted by Q0. The nesosubsilicates with isolated [SiO4]−4 groups are placed in group b. These CSH phases possess the lowest degree of polymerization. The sorosilicates with [Si2O7]−6 groups in the next polymerization step are placed under group c. For these phases, the [Si2O7]−6 is connected to two isolated tetrahedra via one bridging-O to form the so-called pyrogroups. Thus, all silicon tetrahedra are Q1. These silicon tetrahedra are linked via non-bridging O, to six-, seven- or even eight fold-coordinated Ca atoms. A special case of sorosilicate structures are those with mixtures of isolated tetrahedra (Q0) and finite triple chains (Q2), in which the silicon tetrahedra are connected to 6 and 8-fold coordinated Ca atoms. The group d contains the inosilicates. These comprise structures with infinitely long chains with a wide variety of C/S ratios, ranging from 0.50 in Nekoite (d.1) to 1.5 in Jennite (d.8). According to the degree of polymerization, the phases in this group could be subdivided into inosilicates with single chains (all tetrahedra are Q2), and double chains (2/3 Q2 and 1/3 Q3). The representative crystals from each group are illustrated in Figure 1. They are Alite (a.2) for group a; Afwillite (b.1) for group b; Suolunite (c.2), Kilichoanite (c.3) for group c; and Anomalous T11 A (d.2), forshgite (d.7) for group d. Similar images of all 20 crystals are displayed in the supporting information (SI) as Figure S1.

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.