Water Redistribution within the Microstructure of Cementitious Materials due to Temperature Changes Studied with ¹H NMR

Abstract

Changes of water state within the pore structure of cement paste due to temperature changes are followed by means of 1H-proton nuclear magnetic resonance (NMR) relaxation analysis. The study shows that with increasing temperature, the signal due to water contained in the smallest C-S-H interlayer spaces decreases while that from the larger gel pores, and to a lesser extent from the capillary pores, increases. On cooling, the opposite behavior is observed with complete reversibility. The observed changes in water populations appear to be instantaneous compared to the rate of temperature change in the samples. These changes are postulated to be responsible for macroscopically observed changes of relative humidity in pores during heating/cooling and are therefore key in understanding thermal deformations of cement based materials. It is evident that the previous hypothesis of microstructural delayed water transport being responsible for macrostructural delayed thermal deformations can be rejected. Different microstructural mechanisms are discussed that could explain the redistribution in water signals, namely water migration and pore rearrangement mechanisms

Autogenous Healing in Cementitious Materials with Superabsorbent Polymers Quantified by Means of NMR

“…One way to study water transport and binding non-destructively in a hardening sample is the use of NMR. Some studies used NMR to study the hydration of cement [13][14][15] , the internal curing by superabsorbent polymers [16][17][18] , or drying and heating [19][20][21][22][23] . One study used a solid-state NMR to study the reactivity of sodium silicate based systems 24 .…”

Temperature Dependency of Short-Term Length-Change and Desorption Isotherms of Matured Hardened Cement

“…Consequently, the larger gel-pore water [(C) of Fig. 8] is created from this densification at elevated temperature in a manner similar to an instantaneous reaction caused by a temperature change (Wyrzykowski et al 2017). This occurred prior to the measurements taken in this study.…”

“…A portion of the evaporable water found at 5% RH at different temperature conditions may probably not contribute to the shrinkage strain. This can be explained by the hypothesis that the calcium-silicate-hydrate (C-S-H) meso-scale agglomeration as well as molecular-scale structures change at elevated temperatures, as suggested by Proton Nuclear Magnetic Resonance ( 1 H-NMR ) Relaxometry data (Wyrzykowski et al 2017).…”

Application-oriented fundamental research on concrete and reinforced concrete structures: selected findings from an Austro-Chinese research project

“…The solid constituents shrink according to their coefficients of thermal expansion and the solid hydrates take up water, the Kelvin radius decreases, the internal relative humidity decreases, the average effective pore underpressures increase, and this manifests itself macroscopically as an additional poromechanical contribution to the macroscopic shrinkage of the cement paste. As regards the experimental validation of the described phenomena, the water uptake/release characteristics of the hydrates were observed recently based on proton nuclear magnetic resonance relaxometry tests of cement paste subjected to temperature changes [21].…”