ALKALI ACTIVATED FLY ASH BASED CONCRETE: EVALUATION OF CURING PROCESS USING NON-LINEAR ULTRASONIC APPROACH

This paper investigates the applicability of nondestructive testing and evaluation (NDT&E) method using ultrasonic signals to monitor the curing of alkali activated fly ash based concrete (AAFC). The evaluation was carried out on AAFC specimens with two different water/binder (W/B) ratios of 0.3 and 0.5 and after curing at 60 °C for 7, 14 and 28 days, respectively. The signals are recorded and analyzed using linear and non-linear ultrasonic techniques. The results show that the non-linear ultrasonic technique has a clear advantage over the linear ultrasonic technique when monitoring the curing of AAFC specimens with the lower W/B ratio. However, the specimens with the higher W/B ratio do not undergo proper curing and therefore do not show clear distinctions between the curing times measured from the two ultrasonic techniques. The unconfined compressive strength (UCS) of the AAFC specimens at different W/B ratios and curing times is also measured. The UCS results showed a good correlation with the ultrasonic results.

Evaluation of concrete columns with the ultrasonic technique

El ultrasonido ha sido usado desde hace aproximadamente medio siglo para la evaluación de estructuras de concreto, y es a la fecha la técnica no destructiva más utilizada en el mundo. Consiste en la medición del tiempo en la que un pulso de sonido de alta frecuencia atraviesa la masa del material; conociendo la distancia recorrida se puede obtener la velocidad. Esta técnica se utiliza principalmente para la detección de grietas y la estimación de la resistencia del concreto. El objetivo del presente estudio fue observar el efecto de las barras de acero de refuerzo en la velocidad, así como la variabilidad de la velocidad medida en columnas de tres edificios. Se midió la velocidad en veinticinco columnas utilizando transductores de onda longitudinal colocados en arreglo directo. En los tres edificios se obtuvo un rango de velocidades medias de 3.491 a 3.653 m/s en un contexto en el que se utilizaron los mismos materiales y se tuvieron similares niveles de esfuerzo en cada columna; de acuerdo con las velocidades medidas, únicamente un edificio cumplió con la resistencia de diseño.

Estimation via Laser Ultrasonics of the Ultrasonic Attenuation in a Polycrystalline Aluminum Thin Plate Using Complex Wavenumber Recovery in the Vicinity of a Zero-Group-Velocity Lamb Mode

In this paper, we present a method to recover the complex wavenumber dispersion relations using spatial Laplace transform from experimental spatiotemporal signals measured by laser ultrasonic technique. The proposed method was applied on zero-group-velocity Lamb modes in order to extract the ultrasonic attenuation in a polycrystalline aluminum plate of about 70 μm thickness. The difference between the experimental and theoretical Laplace Fourier transforms was minimized in the least square sense to extract the complex amplitudes and complex wavenumbers of the modes at about 40 MHz. The experimental results were compared to values reported in the literature that were measured by other means and those estimated by using the quality factor extracted from a single temporal signal.