This paper presents a study on the possibility of using fly ash cement as grouts for micropiles. 19 This type of special geotechnical work is commonly used for many applications. Generally, 20 micropiles grouts are prepared using Portland cement, although the standards do not restrict 21 the cement type to use, as long as they achieve a strength requirement. In this research, fly 22 ash cement grouts made with w:c ratios 0.40, 0.45, 0.50 and 0.55 were studied from 2 up to 23 90 days of age. Their microstructure was characterized using the non-destructive impedance 24 spectroscopy technique, electrical resistivity, and mercury intrusion porosimetry. Their 25 2 durability properties have been studied by determining the water penetration under pressure, 26 and the chloride diffusion coefficient. The compressive strength was also measured and 27 determined, and a maximum water:cement ratio, different for each cement type was obtained. 28All the results were compared to those obtained for Portland cement grouts. The results 29 obtained confirm that the performance of micropiles made using fly ash cement grouts is 30 adequate, and as it is well know the cements with mineral admixtures provide environmental 31 benefits, so the use of cement including fly ash will contribute to the sustainability, with 32 similar properties to those given by OPC. 33Keywords: micropiles, special geotechnical works, fly ash, durability, microstructure, 34 impedance spectroscopy, water:cement ratio. 35
1.-INTRODUCTION 36In the field of geological engineering, the use of special geotechnical works has become very 37 important. Some of the most commonly used special geotechnical works for civil engineering 38 structures and for building foundations are piles, micropiles, soil anchors and jet grouting 39injections. There are great differences between those types of works and one of these 40 differences is related to the material in which the steel reinforcement elements are embedded. 41In the case of the piles, concrete is usually used. However, for micropiles, soil anchors and jet 42 grouting injections, the reinforcement elements are embedded in cement grouts, although 43 mortars might also be used. This fact is very important, because the behaviour of the cement 44 grouts and mortars shows many differences compared to concrete. For example, in general 45 the porosity of hardened grouts is greater than the porosity of concretes [1], [2], and it could 46 influence the durability and mechanical properties of the elements of each particular special 47 geotechnical work. But on the other hand, a higher amount of cement might improve the 48 durability of this type of elements. So, a different performance could be expected if the 49 material used to protect the reinforcement steel elements is cement grout or concrete, as it is 50 3 usual for the majority of civil engineering structures. Furthermore, the uncertainties can 51 increase as a function of the cement type used, especially if it is used a sustainable cement, 52 which incorporates som...