This research studied the use of alkaline activation of fly ash, as a silica and alumina amorphous source, to improve soft soils. A laboratory programme -including tests to study strength and deformability development, alternative curing methods, the effect of the different components of the grout, effect of raising initial temperature and comparison with a cement grout -was carried out. Laboratory tests revealed that the use of fly ash and alkaline activator resulted in a soil strength improvement up to 11 . 4, 16 . 7 and 43 . 4 MPa, at 28, 90 and 365 days curing, respectively. The most effective combinations obtained in the laboratory were chosen for the field application with jet grouting. The grout performed adequately to pass standard engineering specifications for soil mixing, achieving up to 26 . 4 MPa at 90 days curing. The main conclusion is the potential of alkaline activation for soil improvement, and therefore this research has created a basis for further studies.

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Alkaline activation involves a reaction between aluminium silicates and compounds with alkalis or alkaline-earth elements in a caustic environment and under certain thermal and pressure conditions. It has been used in the production of non-structural building materials and in so-called ‘green’ concrete, as products display high mechanical strength, low chemical reactivity and high resistance to fire. Green concrete could be an eco-efficient alternative to concrete made using ordinary Portland cement (OPC), reducing CO2 emissions substantially. The main goal of this work is to test common clays, glass cullet and other industrial wastes as an alternative to the commonly used binders (metakaolin or fly ash) in geopolymers. Optimized formulations show interesting mechanical strength (approaching 20 MPa) after just 48 h of curing. The addition of F-sand as aggregate minimizes the shrinkage upon curing and the amount of activator required, and increases the density/degree of compaction of the bodies, thus improving their mechanical resistance within certain limits. Curing in ambient conditions also has a beneficial affect on the mechanical strength.

La geopolimerización es una manera viable para procesar y agregar valor a los residuos industriales de alumino-silicato dando lugar a materiales con elevadas resistencias mecánmicas, alta inercia química y que permiten encapsular otros residuos, incluso peligrosos.