Microstructure and durability of fly ash cement grouts for micropiles

• Durability of micropiles increases when using cement containing fly ash.
• The refinement of the pore network may be the origin of that improvement.
• The impedance spectroscopy can be used to study the microsctructural evolution.
• The only limiting factor for the use of fly ash cement is the maximum w:c ratio used.
• Under the studied conditions the use of fly ash cements can be recommended for grouting micropiles.

This paper presents a study on the possibility of using fly ash cement as grouts for micropiles. This type of special geotechnical work is commonly used for many applications. Generally, micropiles grouts are prepared using Portland cement, although the standards do not restrict the cement type to use, as long as they achieve a strength requirement. In this research, fly ash cement grouts made with w:c ratios 0.40, 0.45, 0.50 and 0.55 were studied from 2 up to 90 days of age. Their microstructure was characterized using the non-destructive impedance spectroscopy technique, electrical resistivity, and mercury intrusion porosimetry. Their durability properties have been studied by determining the water penetration under pressure, and the chloride diffusion coefficient. The compressive strength was also measured and determined, and a maximum water:cement ratio, different for each cement type was obtained. All the results were compared to those obtained for Portland cement grouts. The results obtained confirm that the performance of micropiles made using fly ash cement grouts is adequate, and as it is well know the cements with mineral admixtures provide environmental benefits, so the use of cement including fly ash will contribute to the sustainability, with similar properties to those given by OPC.