Application of 1H NMR to hydration and porosity studies of lime–pozzolan mixtures

1H nuclear magnetic resonance (NMR) relaxation is applied to lime–pozzolan mixtures to monitor in real-time the hydration and porosity evolution during setting. The hydrated products formed during the setting of these mixtures are similar to those formed in hydraulic binders (e.g. cement and natural hydraulic limes). In this work, we demonstrate that by using a portable, low field (0.29 T) Halbach magnet it is possible to study in detail, the evolution of the pore structure, modified through the formation of C–S–H and C–A–H, by means of the 1H NMR technique. Contrary to the standard porosimetry methods, which require drying procedures before analysis, NMR is a non-invasive straightforward technique, allowing the study of the hydration kinetics in real-time, during the setting and hardening of the lime–pozzolan binding system. Thus, by measuring the 1H NMR spin–lattice relaxation T1 of two lime–pozzolan mixtures, it was possible to distinguish between different pore populations within the system (at different setting periods), and to study the growth of the hydrated phases. The interpretation of the results proved that, similarly to mercury intrusion porosimetry (MIP) and nitrogen adsorption, 1H NMR probes the development of the pore structure within the lime–pozzolanmortar matrix, indicating key changes of pore size populations.

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► Real time hydration monitoring of lime–pozzolan mortars by NMR.
► Correlation of T1 relaxometry to mercury and nitrogen porosimetries.
► Non-invasive determination of different pore populations in conservation mortars.
► The effect of pozzolan amount to the pore structure evolution of lime-based mortars.
► Calibration of NMR signal for field estimation of hydration in conservation mortars.