Abstract
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.
Highlights
In recent years, special geotechnical works have undergone a great development, becoming essential tools thatallow solving engineering problems, mainly related to interaction between the structures and terrain
For samples immersed in sodium sulphate solution, it has been observed an initial increasing tendency of this parameter, it decreased at greater ages
The increasing tendency of resistances R1 and R2 in the short-term for the grouts exposed to sodium sulphate solution could be due to the abovementioned progressive microstructure refinement produced by the new solids formation, as consequence of the clinker and slag hydration, and the pozzolanic reactions of fly ash
Summary
Special geotechnical works have undergone a great development, becoming essential tools thatallow solving engineering problems, mainly related to interaction between the structures and terrain. One of the most used special geotechnical works are micropiles They have many advantages, such as adaptability to all kind of terrains [1,2]. For this reason, micropiles are used for underpinning existing foundations, supporting the crown of tunnels and stabilizing slopes and excavations, among other applications [1,2]. Micropiles are small-diameter piles with diameters under mm, drilled and grouted with cement grout or mortar, reinforced with steel tubing and sometimes strengthened with one or several ribbed bars [1]. The micropiles standards [3,4] do not specify the cement type to use, provided that it reaches a certain compressive strength
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