# Low-Field NMR for Carbon-Modified Cements: Dispersion and Hydration Studies

## TL;DR

This study uses low-field NMR to explore how carbon black and superplasticizers affect cement hydration and microstructure, offering non-contact insights for developing carbon-integrated cement composites.

## Contribution

The study introduces a non-contact NMR method to assess carbon dispersion and hydration in cement, enabling lower material consumption and better understanding of microstructural evolution.

## Key findings

- An acrylic-based superplasticizer improves colloidal stability of carbon black in water at SP/CB ratios between 0.1 and 2.
- Higher superplasticizer dosage leads to more refined pore networks in hardened cement, as shown by narrower NMR relaxation time distributions.
- NMR can distinguish carbon ink signals from cement paste, enabling non-destructive evaluation of dispersion in fresh pastes.

## Abstract

What are the main findings?
Improved colloidal stability of carbon black into water is revealed in the presence of an acrylic-based superplasticizer at SP/CB weight ratios between 0.1 and 2.During the in situ NMR mixing of carbon ink with cement, the peak ascribed to the carbon ink decreases with water content and paste mixing time.In fresh cement pastes, an increase in superplasticizer dosage induced smaller initial transverse relaxation times and slower evolutions in the relaxation rate, indicating improved dispersion of cement particles and slower structural build-up.In hardened cements, the increase in superplasticizer dosage induced more narrow relaxation time distributions and shorter relaxation times, indicators of a more refined pore network.

Improved colloidal stability of carbon black into water is revealed in the presence of an acrylic-based superplasticizer at SP/CB weight ratios between 0.1 and 2.

During the in situ NMR mixing of carbon ink with cement, the peak ascribed to the carbon ink decreases with water content and paste mixing time.

In fresh cement pastes, an increase in superplasticizer dosage induced smaller initial transverse relaxation times and slower evolutions in the relaxation rate, indicating improved dispersion of cement particles and slower structural build-up.

In hardened cements, the increase in superplasticizer dosage induced more narrow relaxation time distributions and shorter relaxation times, indicators of a more refined pore network.

What are the implications of the main findings?
They open new approaches in the characterization of carbon-containing cementitious composites that are non-contact and compatible with hydrated and hardened paste samples and allow a lower consumption of carbon materials during research stages.They further clarify the impact of the carbon black-dispersant role over cement hydration and microstructure.They contribute to the developing research interface between fundamental studies on cement, multifunctional carbon-integrated composites, and fields including smart buildings and additive manufacturing.

They open new approaches in the characterization of carbon-containing cementitious composites that are non-contact and compatible with hydrated and hardened paste samples and allow a lower consumption of carbon materials during research stages.

They further clarify the impact of the carbon black-dispersant role over cement hydration and microstructure.

They contribute to the developing research interface between fundamental studies on cement, multifunctional carbon-integrated composites, and fields including smart buildings and additive manufacturing.

This study investigates the interface between cement hydration, low-field NMR relaxometry, and the incorporation of carbon-based fillers into cementitious materials. The objective is to provide NMR-based insights into how carbon black (CB) and an acrylic superplasticizer (SP) influence cement hydration and the resulting microstructural evolution. CB was integrated into white Portland cement (WPC) using both wet and dry mixing approaches, with water content and SP dosage varied independently. First, water-based “inks” containing different SP/CB weight ratios were prepared and evaluated through dynamic light scattering (DLS) and ζ-potential measurements to assess colloidal stability and dispersibility. For the wet-mixing route, an in situ NMR experiment was performed to monitor the progressive incorporation of carbon ink into cement pastes while increasing the water content. The ability to distinguish ink-related signals from those originating from the cement paste represents a promising step toward non-destructive assessments of carbon dispersion in fresh pastes. Separately, ex situ NMR measurements were performed on samples extracted from dry-mixed pastes with various SP dosages. These experiments mark the SP-induced delay in hydration and the refinement of the pore network that is also associated with improved particle dispersion. Complementary optical microscopy (OM) and ultrasonic pulse velocity (UPV) measurements on hardened samples corroborate the NMR findings.