Freeze–thaw damage gradients in concrete: Insights into water uptake and microstructural evolution by single-sided ¹H NMR

Reliable prediction of the service life of concrete structures requires models capable of describing not only the temporal evolution but also the spatial distribution of damage. Freeze–thaw deterioration typically initiates at the exposed surface and propagates into the concrete, leading to pronounced depth-dependent damage gradients. However, commonly applied test methods predominantly rely on global damage indicators and do not resolve the internal damage distribution. In this study, freeze–thaw damage in concretes with different cement types and water-to-cement ratios was investigated using the CIF test in combination with single-sided proton nuclear magnetic resonance (¹H NMR) relaxometry. Freeze–thaw-induced water uptake and microstructural alterations were monitored non-destructively as a function of depth. Signal intensity profiles were used to quantify the rate and penetration depth of moisture ingress caused by freeze-thaw pumping and compare it to pure capillary suction. Furthermore, analysis of the transverse relaxation times enabled the identification of the range of microstructure most affected by frost attack. While the combination of CIF test and single-sided ¹H NMR enables a spatially and temporally resolved characterization of freeze–thaw damage propagation, the study identifies clear methodological challenges. These arise from scatter due to the inhomogeneous magnetic field, the heterogeneous concrete microstructure, and cement-specific paramagnetic effects, highlighting the need for further methodological refinement. Nevertheless, the approach provides a promising experimental basis for the development of depth-dependent damage models relevant for practical service life prediction of freeze–thaw exposed concrete. • Single-sided 1 H NMR enables the determination of depth dependent damage gradients. • The signal intensities of 1 H NMR correlate well with global damage criteria. • Freeze-thaw attack mostly effects microstructure in the range of small capillaries.