Nuclear Techniques ›› 2019, Vol. 42 ›› Issue (6): 60502-060502.

• NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH •

Analysis of the dynamics of water confined in cement based on the quasi-elastic neutron scattering spectra

Xiaohui LIU,Peina DENG,Hua LI()

1. Department of Physics, Jinan University, Guangzhou 510632, China
• Received:2018-02-03 Revised:2018-11-09 Online:2019-06-10 Published:2019-06-18
• Contact: Hua LI E-mail:tlihua@jnu.edu.cn
• About author:LIU Xiaohui, female, born in 1992, graduated from Jinan University in 2015, master student, focusing on data analysis of QENS spectra

Abstract: Background

Cement is a widely used construction material. Calcium-silicate-hydrate (C-S-H) is the main component of aged Portland cement concrete. In order to reduce the CO2 emissions in the manufacturing CaO-based cements, the cement of magnesium-silicate-hydrate (M-S-H) was developed. The quality and durability of concrete depended heavily on the dynamical characteristic of water contained in cement. Quasi-elastic neutron scattering (QENS) is a suitable method to study dynamics of water contained in cement.

Purpose

This study aims to analyze dynamics of confined water at low temperature based on M-S-H paste, compare different models to fit the M-S-H samples and compare the hydrodynamic behavior of M-S-H and C-S-H samples in the same temperature range.

Methods

First of all, jump-diffusion and rotation-diffusion model (JRM) was used to fit the QENS spectra of M-S-H and C-S-H paste samples at temperatures from 280 K to 210 K for the whole scattering vectors Q between 3 nm?1 and 19 nm?1. Five extracting parameters of JRM describing the dynamics of water confined in these cementitious systems are obtained: Debye-Waller factor A, the index of immobile water C, the self-diffusion coefficient D t, the average residence time between two jumps τ 0 and the rotational diffusion constant D r.

Results

The fitted results show that the QENS spectra is fitted very well for both M-S-H and C-S-H samples. The fitting parameters and their combined parameters can effectively describe the water dynamics of cement samples. The parameter AC obtained by multiplying C is an important parameter that provides information for the transition of the dynamics of water confined in the cement paste samples and the structure of these samples. When Q < 10 nm?1, the values of AC varying with the temperature presents that the dynamics of water confined in cement samples changes from 220 K to 230 K. When Q = 7 nm?1, the composed parameter D t τ 0/T increases distinctly at T < 240 K, indicating the crossover phenomena for the dynamics of water confined in cement samples. Furthermore, for Q = 7 nm?1, the fitted average residence time τ 0 exhibits a super-Arrhenius behavior at T ≥ 230 K and an Arrhenius behavior at T ≤ 230 K, implying dynamic crossover of the confined water and the crossover temperature 227 K.

Conclusions

All these results illustrate that there is a crossover phenomenon of confined water at 220~230 K. The crossover temperature is 227 K. Key words Dynamics of confined water, Quasi-elastic neutron scattering spectra, Jump-diffusion and rotation-diffusion model, Cement paste sample

CLC Number:

• TL411+.3，O571.56