Detection of Drying‐Induced Microcracking in Cementitious Materials with Space‐Resolved 1 H Nuclear Magnetic Resonance Relaxometry

Nuclear magnetic resonance (NMR) relaxation time mapping in partially dried mortar is presented. Relaxation times in concrete are typically multi‐exponential, and exhibit highly effective relaxation mechanisms ( T 1L ∼ 3 ms, Δν 1/2 ∼ 2500 Hz). One‐dimensional mapping of the spin–lattice relaxation time is used to study relative changes in the water‐occupied surface‐to‐volume ratio, as a function of mixture conditions, initial hydration period, and drying time. These results provide evidence for a penetrating microcracking phenomenon, due to local drying‐induced tensile stresses. This conclusion was further supported by a relaxation time study of samples which were preconditioned so as to be at equilibrium with various relative humidities.