Study of the porous structure of hardened gypsum by pulsed nuclear magnetic resonance

The porous structure of hardened gypsum prepared by hydration of CaSO₄·0.5H₂O and CaSO₄ was studied by nuclear magnetic resonance. The combined analysis of the melting curves of water confined in pores, the shapes of diffusional echo attenuations and dependencies of apparent self-diffusion coefficients of water and olygomer confined in pores on diffusion time, shows that the porous geometry of the hardened gypsum prepared from calcium hemihydrate and anhydrite can be represented by a model of randomly oriented layers. In the case of hemihydrate, most of the pores are arranged in the macropores range. In the case of pure anhydrite, the fraction of macropores is about 90% and diminishes to 30% as a result of modification. The rest of the pores (10%–30%) are arranged in the mesopores range. This has been established for the first time for the hardened gypsum. The length of pores along the layer was also estimated. In the case of hemihydrate, this value was more than 2.5×10^–5 m, and in the case of anhydrite it was about 0.5×10^–6 m. It is found that the use of modifiers results in a decrease in the layer thickness and permeability of the hardened gypsum.