Analysis of complex 1H nuclear magnetic resonance relaxation measurements in developing porous structures: A study in hydrating cement

Abstract

¹H nuclear magnetic resonance (NMR) is widely used for the study of water kinetics into various porous systems like sandstones, zeolites, clays, and various cementitious materials. In the case of hydrating cement pastes the evolution of the cement structure ultimately leads to a broad pore size distribution, and consequently to a multiexponential magnetization recovery represented in many cases by a Kohlraush–Williams–Watts ‘‘stretched exponential’’ curve. However, it has been proven an extremely difficult task to fully clarify and exploit the information contained in the multiexponential magnetization recovery of cementitious materials. This difficulty is due to the fact that spin‐lattice relaxation times T₁ exhibit broad multimodal distributions, which sometimes extend over more than two orders of magnitude. In this work, a numerical routine using a combination of Monte Carlo and Simplex iterations (MCS) is examined which appears to estimate faithfully broad and complex spin‐lattice relaxation time distributions. First, the reliability of the routine has been tested on simulated data and then the algorithm has been applied to the analysis of ¹H NMR time domain measurements performed on different kinds of cement paste. The development of the pore structure is directly reflected in the time evolution of the T₁ distribution function.