Microstructure and durability of fly ash cement grouts for micropiles

Abstract

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...

Effects of Environment in the Microstructure and Properties of Sustainable Mortars with Fly Ash and Slag after a 5-Year Exposure Period

“…Generally, the migration coefficients showed by mortars with additions were lower for all studied conditions in comparison with those noted for CEM I mortars. This would agree with several studies [12,15,23,24], which have pointed out that using slag and fly ash cements brings a noticeable improvement in chloride ingress resistance. Firstly, this could be explained in relation to the higher refinement of pore network provided by fly ash and slag in comparison with pure clinker [7][8][9]14,15].…”

“…This would agree with several studies [12,15,23,24], which have pointed out that using slag and fly ash cements brings a noticeable improvement in chloride ingress resistance. Firstly, this could be explained in relation to the higher refinement of pore network provided by fly ash and slag in comparison with pure clinker [7][8][9]14,15]. On the other hand, this good resistance of fly ash and slag mortars to chloride ingress since very early ages and its maintenance when the hardening was produced under non-optimum environments, which produced a lower microstructure refinement in the long-term compared to an optimum condition, could also be justified as a consequence of the higher chloride binding capacity of slag and fly ash cements, compared to OPC.…”

“…On the other hand, the fly ash has pozzolanic activity, which means that it reacts with portlandite produced along the clinker hydration, giving rise to the formation of additional hydrated products, thus increasing the refinement of the pore network of mortars and concretes [9][10][11]. The abovementioned pore refinement produced by both additions improves the performance of cementitious materials, for example their chloride ingress resistance [12][13][14][15][16][17] and their permeability [18].…”

The Utilization of Waste Water from a Concrete Plant in the Production of Cement Composites

“…At the same time, there are new sustainable technologies being developed for the purpose of the recycling of fresh concrete waste [7], where even fresh concrete waste with a high content of calcium silicate was classified as a cement paste and used as a medium capturing CO 2 [8], similar to the use of sludge from waste water treatment plants [9]. The use of some types of waste waters and industrial waste materials in the concrete production sector has already been proven in the past [10][11][12][13][14][15][16][17].…”

Development and Prospect of Root Piles in Tunnel Foundation Reinforcement

“…The specific surface area of colloidal particles generated from cement hydrate is 1,000 times that of original cement particles, thus generating great surface energy. Grouting is used not only to seal the voids in the soil mass but to close weathered cracks as well, improving the strength of cement soil at the macro level [30][31][32].…”