Nowadays, the use of micropiles has undergone a great development. In general, they are made with cement grout, reinforced with steel tubing. In Spain, these grouts are prepared using OPC, although the standards do not forbid the use of other cements, like sustainable ones. Micropiles are in contact with soils and groundwater, in which the presence of sulphates is common. Their deleterious effects firstly affect to the microstructure. Then, the aim of this research is to study the effects of sulphate attack in the microstructure of micropiles grouts, prepared with OPC, fly ash and slag commercial cements, compared to their behaviour when they are exposed to an optimum hardening condition. The microstructure evolution has been studied with the non-destructive impedance spectroscopy technique, which has never been used for detecting the effects of sulphate attack when slag and fly ash cements are used. Its results have been contrasted with mercury intrusion porosimetry and “Wenner” resistivity ones. The 28-day compressive strength of grouts has been also determined. The results of microstructure characterization techniques are in agreement, although impedance spectroscopy is the most sensitive for following the changes in the porous network of grouts. The results showed that micropiles made using fly ash and slag cements could have a good performance in contact with aggressive sodium sulphate media, even better than OPC ones.

Una técnica de refuerzo de vigas y forjados consiste en la disposición de perfiles metálicos bajo los elementos a reforzar y retacados a ellos. En general, este refuerzo se concibe como pasivo: los perfiles no entran en carga en tanto no se incrementan las acciones sobre el elemento reforzado.  La alternativa que se plantea en este trabajo es un planteamiento activo: introducir fuerzas (por ejemplo, mediante gatos, barras roscadas, etc.) entre el perfil y el elemento a reforzar, y retacando posteriormente el perfil a la pieza en los puntos de introducción de las fuerzas, manteniendo la predeformación obtenida en el perfil mediante mortero, calzos metálicos, etc.  El presente expone los aspectos técnicos básicos a considerar en este tipo de refuerzos, tanto en el diseño como en su posterior ejecución y control. En relación con este último, la fiabilidad del cálculo de flechas en perfiles metálicos permite un control exhaustivo de las fuerzas introducidas, tanto al reforzar como a lo largo de la vida de la estructura, mediante la auscultación de las flechas en el perfil durante el proceso y la posterior etapa de servicio.  Se muestran en este trabajo algunos ejemplos de refuerzo desarrollados recientemente con esta técnica.

One technique for strengthening flexural members in general, and reinforced concrete beams and slabs in particular, entails caulking the underside of these members with steel shapes. This sort of strengthening is often designed from a passive approach; i.e., until the load is increased, the shapes are either not loaded or are only slightly loaded to some unquantified extent by caulking with steel shims.