T1-T2 relaxation correlation measurements

[Display omitted] •T1-T2* measurement permits speciation of different spin populations when a T1-T2 measurement is impossible.•Tracking the T1-T2* coordinate, and associated intensity may reveal structural changes.•The T1-T2* measurement permits a simple assignment of T1 to different T2* populations.•The T1-T2* measurement will permit discrimination solid-like species in mixtures. The majority of low field Magnetic Resonance (MR) analyses rely on T2 lifetime measurements. Modification of the T2 measurement to include a T1 dimension has made the T1-T2 measurement a very powerful analytical technique. The T1-T2 measurement is uniquely well suited to characterization of different spin populations in porous materials, such as fluid bearing reservoir rocks, and in soft biopolymer materials, for example foods. However, the T1-T2 measurement is challenging or impossible if the T2 relaxation lifetime, or a component lifetime, is short-lived and the signal unobservable in an echo measurement. This occurs in many important classes of materials. A short lifetime T2 will not however, in general, preclude observation of a free induction decay with signal decay governed by T2*. As outlined in this paper a T1-T2* measurement is a useful analog to the T1-T2 experiment. T1-T2* measurement enables one to differentiate species as a function of T2* in one dimension and T1 in the other dimension. Monitoring changes of the T1-T2* coordinate, and associated signal intensity changes, has the potential to reveal structural changes in materials evolving in time. These methods may also be employed to discriminate and identify solid-like species present in static samples. The T1-T2* measurement is very general in application, but in this paper we focus on cement-based mortars to develop and illustrate the essential ideas. T1-T2* results show a multi-modal behaviour of the MR signal lifetimes, T1 and T2*, in mortar samples under study, indicating at least two different water populations. The short T2* lifetime was assigned to interlayer water (water between C–S–H layers) where the associated T1 is also short lived. The longer T2* lifetime was assigned to water in the pore space, where T1 is also longer lived. In addition to mortar samples we also show application of the method to a crystalline organic species, o-phenylenediamine, which features Sinc Gaussian and exponential decays of transverse magnetization.