Investigation of the First Sorption Cycle of White Portland Cement by 1H NMR

This work is focused on the effects of drying/re-saturation cycles on the structure and components of White Portland Cement (WPC) samples. In particular, WPC of 0.5 water-to-cement ratio was studied by 1H Nuclear Magnetic Resonance (NMR) Relaxometry. A number of NMR sequences and different data processing methods were applied. Short (14 days of re-saturation) and long (6 months for the whole cycle) sorption cycles were investigated, using two drying methods: oven drying and drying under controlled relative humidity. The evolution during drying/re-saturation processes of interlayer space, gel pores, and bigger pores was followed by both the transverse relaxation times and the intensities of the nuclear magnetization. As a result of drying, reversible and irreversible changes in the pore structure, especially concerning the smaller porosity (interlayer and gel pores), were seen. Likewise, 1H signals in the crystalline phases of the cement were investigated by the standard Quadrature Echo method and by a more informative analysis based and a proper acquisition and processing of the longitudinal relaxation data. This analysis allowed the signal separation of 1H nuclei with higher and lower mobility (“solid” components). The NMR signal from this last component was analyzed on the basis of the Pake-Doublet theory in the time domain and two components were clearly detected, and assigned to 1H nuclei of crystalline water in Ettringite and OH groups in Portlandite. Reversible changes of the solid components of the cement samples were observed. This is a new method to deeply investigate the changes of solid components during sorption cycles.