title: Translational and rotational dynamics of water contained in aged Portland cement pastes studied by quasi-elastic neutron scattering.
abstract: Cement is a widely used construction material in the world. The quality and durability of aged cement pastes have a strong relationship with the water contained in it. The translational and rotational dynamics of water in ordinary Portland cement (OPC) pastes cured for 7, 14 and 30days were studied by analyzing Quasi-elastic Neutron Scattering (QENS) data. The effect of a new super-plasticizer (SP) additive was also studied by comparing the samples with and without the additive. By fitting the QENS spectra with the Jump-diffusion and Rotation-diffusion Model (JRM), six important parameters including the bound water index (BWI), the self-diffusion coefficient, D(t), the average residence time, τ0, the rotational diffusion constant, D(r), the rotational residence time, τ(r), and the mean squared displacement (MSD), 〈u(2)〉, were obtained. From these parameters, we can quantitatively follow the evolution of the bound water fraction (BWI). We can clearly see the different time ranges for the translational and rotational dynamics of water contained in the OPC pastes by τ0 and τ(r). From the MSD values compared with those of molecular dynamics simulation, we can distinguish between immobile water (mainly bound water) and mobile water, which includes confined water and ultraconfined water. Furthermore, by the fitted parameters' values and their change of slopes with increasing setting time for cement pastes with and without additive SP, it becomes clear that the effect of additive SP is to make the mobile water more confined and induce a more uniform the aging process during the evolution of the OPC pastes.
authors.affiliation: Department of Physics, Jinan University, Guangzhou 510632, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Physics, Jinan University, Guangzhou 510632, China.
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Zhang
authors.affiliation: Department of Physics, Jinan University, Guangzhou 510632, China.
authors.forename: Zhou
authors.initials: Z
authors.lastname: Yi
authors.affiliation: Department of Chemistry Ugo Schiff and CSGI, University of Florence, via della Lastruccia 3-Sesto Fiorentino, I-50019 Florence, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Fratini
authors.affiliation: Department of Chemistry Ugo Schiff and CSGI, University of Florence, via della Lastruccia 3-Sesto Fiorentino, I-50019 Florence, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Baglioni
authors.affiliation: Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Sow-Hsin
authors.initials: SH
authors.lastname: Chen
keywords: Jump-diffusion and rotation-diffusion model; Portland cement pastes; Quasi-elastic neutron scattering; Water dynamics