A new approach of quantitatively analyzing water states by neutron scattering in hardened cement paste

The three-component model is typically used to analyze the quasi-elastic neutron scattering data and study the water dynamics of hydrating cementitious system. Its application to the hardened cement paste is hindered due to the inaccuracy in evaluating free water at normal ambient temperature. This paper presents a novel approach to quantifying the amount of free water through conducting neutron scattering under freeze-thaw cycling. Disk-like cement paste samples were prepared and applied with four freeze-thaw cycles by varying temperatures in the range of 240 K to 300 K. Quasi-elastic neutron scattering data collected before and after the freeze-thaw cycles and elastic neutron scattering data was collected during each cycle. The signal intensity associated with the free water was obtained by combining QENS and ENS data analysis and a mathematical deduction. We introduced the index of the total immobile water to quantitatively demonstrate water content. The fractional change of the immobile water after freeze-thaw cycle was also studied. The significance of this method is that it is not limited to be applied to cement paste system but also compatible with other systems where the amount of free water cannot be accurately quantified by the standard QENS analysis.