# The Influence of Solid Content Distribution on the Low-Field Nuclear Magnetic Resonance Characterization of Ferric-Containing Alkali-Activated Materials

## TL;DR

This paper shows how solid content distribution affects low-field NMR analysis of materials with iron, and proposes a method to ensure sample homogeneity for reliable results.

## Contribution

A screening method is proposed to ensure sample homogeneity for reliable LF-NMR analysis of ferric-containing alkali-activated materials.

## Key findings

- Paramagnetic or ferrimagnetic particles and excess water distort LF-NMR analysis.
- Layered analysis reveals settling creates vertical signal gradients.
- Slurries with higher water content and CaO-deficient materials show pronounced stratification.

## Abstract

What are the main findings?
Paramagnetic or ferrimagnetic particles and excess water distort LF-NMR analysis.Layered analysis reveals settling creates vertical signal gradients.A screening method is proposed to ensure sample homogeneity.

Paramagnetic or ferrimagnetic particles and excess water distort LF-NMR analysis.

Layered analysis reveals settling creates vertical signal gradients.

A screening method is proposed to ensure sample homogeneity.

What are the implications of the main findings?
Settled slurry top layer has higher free water and fewer paramagnetic substances.Preventing slurry settling ensures reliable LF-NMR interpretation; BFS stable, FA stratified.Slurry must be vertically homogeneous in water for reliable LF-NMR testing.

Settled slurry top layer has higher free water and fewer paramagnetic substances.

Preventing slurry settling ensures reliable LF-NMR interpretation; BFS stable, FA stratified.

Slurry must be vertically homogeneous in water for reliable LF-NMR testing.

Recent applications of low-field NMR in alkali-activated materials (AAMs) often adopt interpretation models developed for Portland cement systems, overlooking the distinct influences of paramagnetic/ferrimagnetic components and free-water redistribution. This study investigates how paramagnetic or ferrimagnetic component and free water distribution influence low-field nuclear magnetic resonance (LF-NMR) and proton density magnetic resonance imaging (PD-MRI) characterization of alkali-activated materials (AAMs). Blast furnace slag, fly ash, and steel slag were activated with NaOH solution at liquid-to-solid ratios of 0.45 and 0.5, and analyzed across top, middle, and bottom layers. Slurries prepared with less mixing water and CaO-rich raw materials exhibited negligible settling and uniform relaxation behavior, whereas those with higher water content and CaO-deficient raw materials showed pronounced stratification, resulting in distinct gradients in signal intensity. The results indicate that the LF-NMR data interpretation of relatively dilute system may be unreliable as the relaxation time of protons will be extended after they transfer from bottom to the top of the slurry. A preliminary method for assessing slurry suitability for LF-NMR characterization is proposed for future validation.