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

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.

Nondestructive inspection of metal specimen using tone-burst vibro-acoustography.

Even though the pulse-echo ultrasonic technique is commonly used for the assessment of metal structures, it has some inherent limitations. Vibro-acoustography (VA) is a relatively new ultrasonic technique which has demonstrated a great potential in revealing defects in objects, however it is traditionally used to analyze the integrity of specimens made of low-stiffness materials. This work presents the evaluation of the performance of VA technique for the inspection of a steel structure, which was manufactured with defects of known geometry on its inner surface. All the inspection process was done automatically, from the data acquisition to the image processing for characterizing the defects. Experimental results show that VA was able to identify and characterize even the smallest defects in the structure, with a diameter of 2 mm. In addition, the results show that VA was able to characterize the artificial defects in the steel structure with almost the same errors as the traditional pulse-echo method, which indicates a potential use of VA in the inspection of materials with high mechanical stiffness.

Contribución a la restauración y el mantenimiento de obras de importancia histórica, cultural y social de la ciudad de La Habana / Contribution to the restoration and maintenance of works of historical, cultural and social importance of the city of Havana

RESUMEN Entre las aplicaciones de la Ciencia e Ingeniería de Materiales que realiza el Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear CEADEN está el apoyo mediante varias técnicas físicas a la restauración y el mantenimiento de estructuras y objetos de la ciudad de La Habana que poseen interés histórico, cultural y social . En el presente trabajo es abordado el campo de la Defectoscopía, en lo cual los Ensayos no destructivos aplicados tributaron a la restauración del patrimonio cultural, a la mejora de instalaciones deportivas de la capital y, en mayor medida, a la seguridad de instalaciones de interés social como son los parques de diversión. En ese sentido se presentan la inspección de estructuras en el marco de la restauración de la Sala Cabildo del Museo de la Ciudad de La Habana en el Palacio de los Capitanes Generales en La Habana Vieja; el diagnóstico de uniones soldadas durante la restauración de la iluminación y la instalación de la pantalla gigante del Estadio Latinoamericano del Cerro y la Inspección realizada sistemáticamente en mantenimiento a elementos críticos de equipos de los parques de diversión.

ABSTRACT Among the applications of Materials Science and Engineering carried out by the Center for Technological Applications and Nuclear Development (CEADEN) / Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear CEADEN is the use of various physical techniques to support the restoration and maintenance of buildings and other work objects of historical, cultural and social interest in Havana city. The field of Defectoscopy is addressed in this paper, where the applied Nondestructive testings also contributed to restore the cultural heritage, to upgrade the structural conditions at an important sport facility in Havana, and in a greater extent, to the safety of facilities of social significance, such as amusement parks. In this regard, three examples are presented: the inspection of structures during the restoration of the City Hall in the Museum of the Havana City at the Palace of Captains General; the welded joints testing during the restoration of the lighting system and the installation of the digital screen at the Latin American Stadium in Cerro municipality; and finally, the inspection systematically performed at maintenance works to critical elements and related devices at amusement parks.

Linear Versus Nonlinear Acoustic Probing of Plasticity in Metals: A Quantitative Assessment.

The relative dislocation density of aluminum and copper samples is quantitatively measured using linear Resonant Ultrasound Spectroscopy (RUS). For each metallic group, four samples were prepared with different thermomechanical treatments in order to induce changes in their dislocation densities. The RUS results are compared with Nonlinear Resonant Ultrasound Spectroscopy (NRUS) as well as Second Harmonic Generation (SHG) measurements. NRUS has a higher sensitivity by a factor of two to six and SHG by 14⁻62%. The latter technique is, however, faster and simpler. As a main result, we obtain a quantitative relation between the changes in the nonlinear parameters and the dislocation density variations, which in a first approximation is a linear relation between these differences. We also present a simple theoretical expression that explains the better sensitivity to dislocation content of the nonlinear parameters with respect to the linear ones. X-Ray diffraction measurements, although intrusive and less accurate, support the acoustics results.

Sparse Ultrasound Imaging via Manifold Low-Rank Approximation and Non-Convex Greedy Pursuit.

Model-based image reconstruction has improved contrast and spatial resolution in imaging applications such as magnetic resonance imaging and emission computed tomography. However, these methods have not succeeded in pulse-echo applications like ultrasound imaging due to the typical assumption of a finite grid of possible scatterer locations in a medium⁻an assumption that does not reflect the continuous nature of real world objects and creates a problem known as off-grid deviation. To cope with this problem, we present a method of dictionary expansion and constrained reconstruction that approximates the continuous manifold of all possible scatterer locations within a region of interest. The expanded dictionary is created using a highly coherent sampling of the region of interest, followed by a rank reduction procedure. We develop a greedy algorithm, based on the Orthogonal Matching Pursuit, that uses a correlation-based non-convex constraint set that allows for the division of the region of interest into cells of any size. To evaluate the performance of the method, we present results of two-dimensional ultrasound imaging with simulated data in a nondestructive testing application. Our method succeeds in the reconstructions of sparse images from noisy measurements, providing higher accuracy than previous approaches based on regular discrete models.

Corrosion Assessment of Steel Bars Used in Reinforced Concrete Structures by Means of Eddy Current Testing.

This paper presents a theoretical and experimental study on the use of Eddy Current Testing (ECT) to evaluate corrosion processes in steel bars used in reinforced concrete structures. The paper presents the mathematical basis of the ECT sensor built by the authors; followed by a finite element analysis. The results obtained in the simulations are compared with those obtained in experimental tests performed by the authors. Effective resistances and inductances; voltage drops and phase angles of wound coil are calculated using both; simulated and experimental data; and demonstrate a strong correlation. The production of samples of corroded steel bars; by using an impressed current technique is also presented. The authors performed experimental tests in the laboratory using handmade sensors; and the corroded samples. In the tests four gauges; with five levels of loss-of-mass references for each one were used. The results are analyzed in the light of the loss-of-mass and show a strong linear behavior for the analyzed parameters. The conclusions emphasize the feasibility of the proposed technique and highlight opportunities for future works.