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

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.