This paper deals with the study of damage produced during freeze-thaw (F-T) cycles using two non-destructive measurement approaches—the first approach devoted to continuous monitoring using embedded sensors during the cycles, and the second one, performing ultrasonic imaging before and after the cycles. Both methodologies have been tested in two different types of concrete specimens, with and without air-entraining agents. Using the first measurement approach, the size and distribution of pores were estimated using a thermoporometrical model and continuous measurements of temperature and ultrasonic velocity along cycles. These estimates have been compared with the results obtained using mercury porosimetry testing. In the second approach, the damage due to F-T cycles has been evaluated by automated ultrasonic transmission and pulse-echo inspections made before and after the cycles. With these inspections the variations in the dimensions, velocity and attenuation caused by the accelerated F-T cycles were determined.

ABSTRACT:The current standards that regulate use of structural concrete have highlighted the durability of concrete. However, how the fracture energy of concrete evolves under the action of freeze-thaw cycles is not well known. The fracture energy of two types of concrete, one with an air-entraining additive and the other with silica fume addition, is studied after four, 14 and 28 freeze-thaw cycles. The results obtained show that the concrete with an air-entraining additive was undamaged and that fracture energy grew slightly. In addition to this, they also showed that the concrete with silica fume addition suffered severe surface scaling and its fracture energy changed due to the greater fracture areas generated. KEYWORDS: RESUMEN: Evolución de la energía de fractura de dos hormigones resistentes a la acción de ciclos hielo-deshielo.La actual normativa que rige el empleo de hormigón estructural ha puesto enfásis en la durabilidad del hormigón. Sin embargo, no se conoce cómo evoluciona la energía de fractura del hormigón sometido a ciclos hielodeshielo, lo cual es de vital importancia para asegurar la durabilidad y el correcto comportamiento mecánico de las estructuras de hormigón en entornos con heladas durante su vida útil. Se ha estudiado la evolución de la energía de fractura de un hormigón con aireante y de un hormigón con humo de sílice después de 4, 14 y 28 ciclos hielo-deshielo realizando ensayos de fractura. Los resultados muestran cómo el hormigón con aireante no sufre daño por los ciclos hielo-deshielo y cómo la energía de fractura del mismo aumenta ligeramente. El hormigón con humo de sílice se daña por los ciclos hielo-deshielo y reduce su energía de fractura al aumentar el area fracturada. PALABRAS CLAVE:

Most of the standards that evaluate the resistance of concrete against freeze-thaw cycles (FTC) are based on the loss of weight due to scaling. Such procedures are useful but do not provide information about the microstructural deterioration of the concrete. The test procedure needs to be stopped after several FTCs for weighing the loss of material by scaling. This paper proposes the use of mercury-intrusion-porosimetry and thermogravimetric analysis for assessing the microstructural damage of concrete during FTCs. Continuous strain measurement can be performed without stopping the FTCs. The combination of the above techniques with the freeze-thaw resistance standards provides better and more precise information about concrete damage. The proposed procedure is applied to an ordinary concrete, a concrete with silica fume addition and one with an air-entraining agent. The test results showed that the three techniques used are suitable and useful to be employed as complementary to the standards. RESUMEN: Resistencia del hormigón frente a ciclos hielo deshielo medida con técnicas complementarias.Las normas para evaluar la resistencia del hormigón a los ciclos hielo-deshielo (CHD) se basan habitualmente en la pérdida de peso por descascarillamiento. Son útiles, pero no proporcionan información sobre el deterioro microestructural del hormigón. Además, exigen detener el ensayo para pesar el material desprendido. Se propone el uso complementario de la porosimetría por intrusión de mercurio y el análisis termogravimétrico para evaluar el daño microestructural del hormigón durante los CHDs. La medida continua de las deformaciones puede hacerse sin detener los CHDs. La combinación de las técnicas enumeradas con las normas de ensayo proporciona información más completa sobre el daño del hormigón. El procedimiento propuesto se aplica a un hormigón convencional, a un hormigón con adición de humo de sílice y a otro con aireante. Los resultados de los ensayos mostraron que las tres técnicas usadas son útiles y adecuadas como complemento a las establecidas en las normas.