Crack assessment in cement-based materials using Ultrasound and T₂ NMR relaxation time

A. Villarreal, S.E. Solis-Najera, L. Medina

The elastic properties and durability of concrete based structures, directlydepend on the microstructure of the hydrated cement paste. The microstructurevaries with time due to several chemical reactions and mechanical loads,leading to micro fractures, among other effects. For this reason, it is necessaryto develop techniques to locate and measure fractures. Ultrasound hasproven to be a reliable diagnostic tool, so the primary objective of this paperis to propose a composite nondestructive methodology based on NMR relaxometryand through-transmission ultrasound for crack assessment in cementpaste specimens. While the Hilbert-Huang transform of ultrasonic signals areable to locate the defects, the T2 transverse relaxation time gives the watercontent in the crack. The results show, that the Hilbert-Huang transformenhanced the ultrasonic echoes coming from the fracture allowing to detectand locate fractures with an error of 15%, and the crack size is given by thedecay parameter of the relaxation time T2, based by exponential fitted theFID signal.