Evolution of a short-T2 liquid-like 1H signal during the hydration of White Portland Cement

Abstract

The kinetics of cement hydration has been studied by 1H-NMR, through the analysis of the Free Induction Decay (FID) combined with quasi-continuous T1 relaxation time distributions analysis, operating a sort of 2D T1–T2 correlation analysis on a somewhat more physical than mathematical basis. The analysis allowed us to distinguish two solid components, SS (Solid-Short) with T1 of a few milliseconds and SL (Solid-Long) with T1 of the order of a second, ascribable to 1H of anisotropically bound groups in the C–S–H gel, and to 1H nuclei of the Portlandite crystals and possibly to crystal water in Ettringite crystals, respectively. A liquid-like component LS (Liquid-Short) with very short T2 (∼80μs) and T1 a few milliseconds, both quite stable during hydration, was isolated and interpreted as water confined in the inter-layer spaces of the gel. Amounts of LS and SS increase together steadily during hydration, and these, divided by LL (Liquid-Long, the signal from the water in the pores), are proportional to 1/T1 for LL, confirming a surface relaxation effect for LL.