Moisture Distribution during Water Absorption of Ordinary Portland Cement Mortars Obtained with Low-Field Unilateral Magnetic Resonance

Abstract

Moisture distribution in cement-based materials is important from the durability point of view. In the present study, a portable three-magnet array with an elliptical surface radio frequency coil was used to undertake magnetic resonance measurements of moisture content in ordinary Portland cement mortar and concrete samples. Measurements along the length of the samples during capillary water absorption produced moisture content profiles that were compared with reference profiles acquired using a magnetic resonance imaging instrument. Profiles obtained with the three-magnet array were similar in shape and in penetration depth to those acquired with magnetic resonance imaging. The correlation coefficient between the moisture content measured with both techniques was r2 = 0.97. Similar values of saturated permeability of the mortars with identical w/c ratio were computed with the Hydrus 1D software based on the moisture content profiles. Additionally, inverse Laplace transformation of the signal decays provided the water-filled pore size distribution in saturated and unsaturated regions of the samples. The three-magnet array was successfully used to acquire nuclear magnetic resonance signal from a concrete sample, which was not possible with the magnetic resonance imaging instrument using the single-point imaging technique.

Memorias del X Congreso Nacional de Alconpat México 2022

“…Otra aplicación del arreglo de tres magnetos ha sido en la determinación del contenido de agua en especímenes de mortero de cemento Portland durante absorción capilar (P. F. de J. Cano-Barrita & Díaz-Díaz, 2021). Debido al tiempo requerido para examinar un punto de la muestra, de aproximadamente una hora, la medición a tiempos menores a 1 día no es adecuada.…”

“…(P. F. de J. Cano-Barrita & Díaz-Díaz, 2021) Desde el punto de vista de durabilidad, otro núcleo de interés en el área de materiales base cemento es el 35 Cl debido al rol de los iones cloruro en la corrosión del acero de refuerzo. Aún cuando la imagenología por RMN ha demostrado su utilidad en la determinación de perfiles de distribución de iones cloruro (Cano et al, 2002;Pel et al, 2016), la baja sensibilidad del 35 Cl comparado con el 1 H (aproximadamente 10 veces menos sensible) ha requerido del uso de campos magnéticos mayores a 1.5 T. Una estimación del tiempo requerido para realizar una medición con el arreglo de tres magnetos (Figura 5), por ejemplo, indicó varios meses para una sola medición, lo cual es totalmente impráctico.…”