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Calcium silicate compounds belong to a complicated class of silicates. Among their many industrial applications, calcium silicates are heavily used as a building material as they constitute the main ingredient in today’s cement clinker. We report here an extensive surface analysis of synthetic calcium silicate phases (tricalcium silicate, C3S, and dicalcium silicate, C2S) using first-principles computational methods. We calculate surface energies (γ) for all lower-index orientations and determine the most stable surfaces as well as the equilibrium Wulff structures. We analyze the variation of γ with surface coordination number and find an interesting and unexpected trend where loss of coordination of ionic Ca and O atoms can lower γ. The stability of surface orientations is examined as a function of oxygen partial pressure. Finally, we compute the energy required to remove Ca from different surfaces and find that it is inversely proportional to γ, supporting the energetic preference of extracting atoms from higher energy surfaces. Knowledge of the atomic structure and properties of calcium silicate surfaces is important for understanding and controlling the hydration of such systems.

Ettringite is a rare mineral with high-water content, more than half of its weight, and a relevant secondary product in Portland cement. Using density functional theory, we simulate the crystal structure and properties of ettringite under pressure. Our calculations predict a change in slope for all the lattice parameters versus pressure at about 2.5 GPa. Above such pressure, the elastic properties show a drastic increase of nearly 80% in the bulk modulus. This finding is explained in terms of a concurrent amorphization and densification of the hydrogen bond network. At low pressures, ettringite can be compressed substantially without significant repulsion in the hydrogen bond network. At high pressures, the hydrogen bonds become stiff, and their contribution to the total repulsion is then important. These changes are also supported by the evolution on the electronic density of ettringite with pressure.

Calcium silicate hydrated (C–S–H) gel is the principal binding phase of the cement paste and responsible for its strength. It is basically composed of silicate chains held together with CaO layers, where different guest ions can enter its structure. In particular, the substitution of Al in the silicate chains is expected to play a decisive role for the resulting properties of the cementitious materials. This work explores by means of molecular dynamics simulation the incorporation of aluminium into C–S–H gel. For that purpose we simulate the polymerisation of C–S–H gel in presence of Al atoms and analyse both the connectivity of the (alumino)silicate chains and the position of the aluminium atoms within the structure of C–S–H gel. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This work explores from a theoretical viewpoint the mechanical properties of the most important hydration product present in cementitious environments, the so called C-S-H (calcium-silicate-hydrate) gel. The dependence of the bulk (K), shear (G) and Young's (E) modulus for the C-S-H crystals respect to its composition and the length of its silicate chains is analysed by lattice dynamic simulations with parameterised two-body and three-body potentials. Our simulations reveal that the mechanical properties of C-S-H crystals show a strong dependence on their composition. Nevertheless our calculated numbers systematically overestimate the experimental values for C-S-H gels. Only when the finite length of the silicate chains is taken into account this discrepancy disappears. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ruminants produce more methane (CH4) than any other livestock animal. Consequently, focus has been placed on developing mitigation strategies for ruminants in both the dairy and the beef industries. The objective of this study was to determine the effect of addition of fat or cellulose to fiber from dried distillers' grains and solubles (DDGS) on ruminal CH4production. Three representative samples of DDGS were obtained from different commercial biorefineries and NDF residue was isolated. The purified NDF residue was fermented 1) alone (control), 2) with feed-grade corn oil, or 3) with microcrystalline cellulose powder using the in vitro gas production technique. Both cellulose and corn oil were added along with NDF residue at a 4:1 ratio (DM basis). Inoculum was obtained by collecting a mixture of rumen fluid from two steers (BW = 543.3 ± 20.6 kg) consuming a diet containing 30% concentrate and 70% roughage. For each treatment within each run, gas production was measured in real time over a 48-h period. Using a paired but separate bottle, the concentration of CH4gas produced was measured using a gas chromatograph at 0, 4, 8, 18, 24, and 48 h. The volume of methane produced at each time point was calculated by multiplying total gas produced by the concentration of CH4. Three separate runs (n= 3) were conducted and data were analyzed as a randomized complete block in which run and source of DDGS were considered random effects and treatment was considered a fixed effect. Compared with the control (74.0 ± 6.06 mL/g), addition of corn oil tended (P= 0.11) to reduce total gas production (58.0 ± 6.04 mL/g) whereas addition of cellulose increased (P= 0.02) gas production (85.7 ± 6.06 mL/g). Similarly, compared with the control (0.075 ± 0.0125 mL/g), the addition of corn oil tended (P= 0.12) to reduce CH4production (0.043 ± 0.0125 mL/g) whereas the addition of cellulose increased (P= 0.02) CH4production (0.099 ± 0.0125 mL/g). In an in vitro setting, the addition of oil or cellulose to NDF resulted in the decrease or increase of methane production, which suggests that dietary components can be used to mitigate methane in ruminant livestock.

This study utilized 16S rRNA gene amplicon sequencing to describe the rumen bacterial community composition in Holstein and Jersey cows fed an identical diet by sampling the rumen microbiota via the rumen cannula or esophageal tubing. Five ruminally cannulated Holstein cows and 4 Jersey cows (not cannulated) were fed a diet composed of 51% forage and 49% concentrate during 4 wk. On the 28th day, rumen samples were collected from both Holstein and Jersey cows using the esophageal tubing, and an additional rumen sample was collected from Holstein cows via the cannula. After collection of the rumen sample via esophageal tubing, particles attached to the metal strainer were added to the sample to better represent whole rumen content and to include particle associated bacteria. Total rumen DNA was extracted using the PowerMagt™ Soil DNA Isolation Kit, and the V3 region of the bacterial 16S rRNA was amplified and then sequenced using the Ion Torrent™ Personal Genome Machine. The resulting sequences were quality filtered and operational taxonomic units (OTUs) were generated at 97% similarity. Taxonomy assignment was performed using the Greengenes database. The 2 main phyla identified regardless of breed or sampling method, were Firmicutesand Bacteroidetes, which accounted for 44.3 and 42.9% of the sequences. Alpha diversity metrics, observed OTUs and Chao1 estimates, displayed higher (P< 0.01) bacterial richness in Holstein compared to Jersey cows. However, between the samples collected via the cannula and stomach tubing in Holstein cows, no difference in species richness was detected (P> 0.40). Principal coordinate analysis using the unweighted UniFrac displayed clustering by breed suggesting that Holstein and Jersey cows may harbor distinct rumen bacterial communities. Non-parametric multivariate analysis of variance supported the significant effect of breed (P= 0.01). No significant difference in bacterial community structure was detected by sampling method (P= 0.18). Linear discriminant analysis of effect size was used to identify OTUs that differ between breeds. Family level classification of most abundant differential OTUs identified OTUs from the bacterial families Lachnospiraceae, Veillonellaceae, Ruminococcaceae, and Fibrobacteraceaeto be more predominant in Holstein compared to Jersey cows whereas an OTU from the family Prevotellaceaewas more predominant in Jersey compared to Holstein cows. Overall, results suggest that the bacterial community between Holstein and Jersey cows differ and that esophageal tubing with collection of feed particles associated with the strainer provides an adequate sampling method for rumen bacterial community studies.