| Abstract
| - Quantitative analysis of inelastic neutron scattering spectra from cement paste specimens that had undergone various degrees of decalcification indicates that ∼23% of the Ca in C−S−H gel with Ca/Si = 1.7 is charge-balanced by OH groups. This substantial concentration of Ca−OH bonds supports the hypothesis that C−S−H gel has a local structure resembling a disordered form of the mineral jennite.
- Inelastic neutron spectroscopy (INS) was used to determine the content of Ca−OH bondsin a series of mature tricalcium silicate (3CaO·SiO2) and white portland cement (WPC) pastesthat were decalcified to calcium/silicon molar ratios (Ca/Si) as low as 1. These measurementsindicate that the band in the INS data at 41 meV, which originates from lattice modesinvolving the translational oscillations of OH groups attached to Ca, has intensitycontributions from both Ca(OH)2 and C−S−H gel, the main hydration product of cementpaste. Quantitative analysis of the INS spectra show that ∼23% of the Ca in C−S−H gelwith Ca/Si = 1.7 is charge-balanced by OH groups, with the remainder charge-balanced bysilicate groups. This substantial concentration of Ca−OH bonds supports the hypothesisthat C−S−H gel has a local structure resembling a disordered form of the mineral jennite.On decalcification, the concentration of Ca−OH bonds in C−S−H gel decreases and iseliminated at Ca/Si ratios slightly above 1. The observed trend is shown to be consistentwith charge balance calculations and interpretations of recent phase equilibrium findings.
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