Surface relaxation and chemical exchange in hydrating cement pastes: A two-dimensional NMR relaxation study

Abstract

We report the first nuclear magnetic resonance ͑NMR͒ two-dimensional correlation T 1 -T 2 and T 2 -T 2 measurements of hydrating cement pastes. A small but distinct cross peak in the two-dimensional relaxation spectrum provides the first direct evidence of chemical exchange of water between gel and capillary pores occurring over the first 14 days of hydration. A correlation of features along the line T 1 =4T 2 provides strong supportive evidence for the surface diffusion model of 1 H nuclear spin relaxation in cements and for a multimodal discrete pore size distribution. Differences in detail of the results are reported for white cement paste and white cement paste with added silica fume. Both the method and the theory presented can be applied more widely to other high surface area materials with other reactive surface areas.

Use of bench-top NMR to measure the density, composition and desorption isotherm of C–S–H in cement paste

“…NMR of cement directly probes water in different environments [8,9,10,11] but to date there has been disagreement on the assignment of signals so limiting the interpretation of results. We provide clarification by cross-referencing NMR results to thermogravimetric (TGA), X-ray diffraction (XRD) and thermodynamic modelling analyses of the same samples.…”

NMR observation of water transfer between a cement paste and a porous medium

“…On the other hand 1 H NMR (Nuclear Magnetic Resonance) relaxometry provides the distribution of (NMR) relaxation times of hydrogen-bearing fluid molecules embedded in a sample volume that are known to depend on pore size, surface chemistry and saturation state. So far, this technique has mainly been used to study the pore characteristics of cement [21], plaster [22] or model porous systems [23][24] or more globally the structure evolution of cement or lime pastes [25][26][27].…”

Magnetic resonance in porous media: Recent progress

“…2D NMR correlation experiments ͑T 1 − T 2 and T 2 − T 2 ͒ have been performed on hydrating cement pastes. 71,72 A cross peak in the two-dimensional relaxation spectrum was observed and was interpreted as evidence of exchange of water between gel and capillary pores. The exchange rate was found to be on the order of 5 ms −1 .…”