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...

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One of the most important problems of reinforced steel concrete in marine environments is the corrosion of the reinforcing bars. Most of the times, this corrosion is a consequence of the local destruction of the passive layer formed on the surface of the embedded steel, due to the arrival of chlorides present in the environment. Many efforts have been made to determine the chloride diffusion coefficient in concrete structures, both using natural diffusion methods, and accelerated migration methods. This coefficient determines the velocity of ingress of chlorides, and as a consequence the life time of the structures. In this work it is presented the possibility of using the technique of impedance spectroscopy, that is, very simple to use and requires no chemical or conductivity measurement, to determine the value of the non-steady-state diffusion coefficient. This technique, together with the equivalent circuits proposed for the interpretation of the measurements, allows the determination of the chloride saturation of a concrete or mortar sample. Pores of the material that are initially filled with water have high resistivity, and as the chlorides penetrate into the sample the value of the resistivity decreases. This diminution can be determined in situ, and permits the calculation of the diffusion coefficient saving experimental time and efforts. The results have been obtained both with concrete and mortar samples, and using different cement types.

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5An empirical model based on constant flux is presented for chloride transport through

Storms can alter the beach shape, relocating large volumes of sediments and generating drastic changes in the coastline. In the last 60years, beaches shoreline behaviour has been different even though the energy of the waves was similar. Therefore, it is necessary to understand the factors that affect the sandy coasts for better future management. In this research, two beaches, with different erosion rate, located in the southeast of Spain (separated by only 40km of distance) have been studied. The beaches: i) have similar orientations, ii) are open to waves with similar sand lengths of 9.8km and 6.6km, and iii) have similar median sediment size (D). For its study, shoreline evolution has been analysed from 1956 to 2017. From the results obtained, it can be seen that: i) Between 1992 and 2017, San Juan just lost 3% of its surface, while in the previous period (1956-1990) it was 50%, and ii) Guardamar surface lost in 1992-2017 was 18%, and in the previous period it was 14%. For the analysis of the agents involved in both beaches, cross-shore profiles (volume), marine climate, biocenosis and sedimentology studies were carried out. The results showed that the energy on both beaches was very similar. The biocenosis had not changed and, however, the morphology of Guardamar seabed had increased to 1m deep in some places, which had caused part of the beach berm erosion. Furthermore, important differences were found from the sedimentological study, concluding that the content of calcites and the degree of homogeneity of the particles are the real factors that caused these two beaches to behave differently against erosion.

One of the main problems of coastlines around the world is their erosion. There are many studies that have tried to link coastal erosion with different parameters such as: maritime climate, sediment transport, sea level rise etc. However, it is unclear to what extent these factors influence coastal erosion. For example, the Intergovernmental Panel on Climate Change (IPCC) has predicted an increase in sea level at a much faster rate than that experienced in the first part of this century, reaching 1 m of elevation in some areas. Another factor to consider is the lack of sediment supply, since currently the contribution of new sediments from rivers or ravines is interrupted by anthropic activities carried out in their basins (dams, channelling, etc.). The big storms, increasingly frequent due to climate change, also should be considered, since they produce an offshore sediments transport, so that these cross the depth of closure, causing nonreturn of the sediment to the beach. Also, the sediment undergoes a process of wear due to various reasons such as the dissolution of the carbonate fraction and/or breakage and separation of the components of the particles. All these elements, to a greater or lesser extent, lead to the retreat of the coastline. Therefore, the aim of this study is to analyse the different factors causing the retreat of the coastline, in order to determine the degree of involvement of each of them and, therefore, be able to pose different proposals to reduce the consequences of coastal erosion.