Relations Between the Printability Descriptors of Mortar and NMR Relaxometry Data.

Area of Science:

• Materials Science
• Construction Engineering
• Chemical Engineering

Background:

• Concrete printing is crucial for modern construction, but lacks standardized characterization tools.
• Printability of cementitious materials is influenced by rheology and early-stage hydration.
• Nuclear Magnetic Resonance (NMR) relaxometry offers non-destructive insights into material properties.

Purpose of the Study:

• To establish correlations between concrete printability descriptors and low-field NMR relaxometry data.
• To investigate the combined effects of acrylic superplasticizers and calcium nitrate accelerators on mortar properties.
• To explore the potential of NMR for characterizing the structural buildup in printed concrete.

Main Methods:

• Mortars with fixed ratios of white Portland cement, fine aggregates, and silica fume were prepared.
• Printability was assessed using extrusion tests and visual inspection of filaments to determine the printing window.
• Low-field NMR relaxometry was employed to measure transverse (T2) and longitudinal (T1) relaxation times.

Main Results:

• Both superplasticizer and accelerator enhanced the mortar's printing window.
• Calcium nitrate accelerator accelerated the increase in specific surface area of capillary pores (S/V) after 30-60 minutes of hydration.
• Correlations were identified between the printing window and the linear increase range of transverse relaxation rates (1/T2) and S/V.

Conclusions:

• Low-field NMR relaxometry shows promise for characterizing the structural buildup in cementitious materials during printing.
• NMR data can be linked to key printability descriptors, facilitating the development of standards for concrete printing.
• The study highlights the potential of NMR as a tool for quality control and process optimization in additive manufacturing of concrete.