Atomic-Level and Surface Structure of Calcium Silicate Hydrate Nanofoils

Abstract

Deciphering the calcium silicate hydrate (C-S-H) surface is crucial for unraveling the mechanisms of cement hydration and property development. Experimental observations of C-S-H in cement systems suggest a surface termination which is fundamentally different from the silicate-terminated surface assumed in many atomistic level studies. Here, a new multiparameter approach to describing the (001) basal C-S-H surface is developed, which considers how the surface termination affects the overall properties (Ca/Si ratio, mean chain length, relative concentration of silanol and hydroxide groups). Contrary to current beliefs, it is concluded that the (001) C-S-H surface is dominantly calcium terminated. Finally, an adsorption mechanism for calcium and hydroxide ions is proposed, which is in agreement with the surface charge densities observed in previous studies.

Relevance of Specific Surface of Mixed Oxide Derived from Layered Double Hydroxides on the Rheological Properties and Porosity of Cement Pastes

“…The diffractograms (Figure (a)) showed the basal reflections typical of the lamellar structure, as evidenced by the (00 l ) peaks [(003), (006), and (009)], confirming formation of the Mg 0.66 Al 0.34 (OH) 2 (NO 3 ) 0.17 ·zH 2 O structure (JCPDS 14–0191) . The basal spacing determined using the Bragg equation (d 00 l =nλ/2sin(θ)) was 0.83–0.84 nm, confirming the intercalation of nitrate ions in the interlamellar galleries of the synthesized LDH. , Assuming 3R stacking of the layers, the average crystallite sizes determined using the Scherrer equation − for the samples aged for 0, 10, 20, and 30 h were 3.05, 3.24, 3.68, and 4.07 nm, respectively, for the c direction (003), and 7.34, 8.30, 9.09, and 9.30 nm, respectively, for the basal ab plane direction (110). As shown in Table , irrespective of the aging time, the average crystallite sizes were 2.3–2.6 times larger in the ab plane direction than in the c direction.…”

On the nanoscale interface, electronic structure, and optical properties of nanocarbon-reinforced calcium silicate hydrates

“…The energy requirement to isolate the Ca ions at the interface is 1.72 eV (PBE-D3), which is higher in magnitude compared to the energy requirement (0.29 eV) to separate Ca ions from the C-S-H surface to the bulk water (i.e., interlayer) computed using ReaxFF4 MD [56]. Recent work shows that the Ca-rich surface of C-S-H is probable, as concluded from this recent report [57]. It should be noted that these Ca ions tend to diffuse in the system, and the Ca/Si ratio is variable, ranging from 0.7-2.3 [8,56].…”

Sodium Sites and Hydration State in C–S–H Phases Synthesized under Alkaline Conditions from 1H and 23Na NMR Experiments

“…This holds for both the C–S–H samples with relative high (1.4) and low (0.8) Ca/Si ratios. The rather flexible exchange between Na­(b) and the interlayer Na­(a) and Na­(c) sites may reflect that the thickness of the C–S–H particles is rather low, e.g ., 3.5–4.0 nm, ,, implying a high ratio between surface sites and bulk (interlayer) sites.…”