In some countries, low cost roads have an important role in the road network as they provide a faster way to travel between villages and can improve the access to basic services.In this paper, a geopolymer synthetized from low calcium fly ash and an alkaline solution made from sodium silicate and sodium hydroxide was used to stabilize a silty sand from Colombia, in order to evaluate its suitability for unpaved roads.Results show that strength and stiffness are significantly increased by this treatment as measured by unconfined compression strength tests and seismic wave measurements performed on several mixtures. Some existing specifications for soil-cement were also applied in this new stabilized soil and the results revealed a similar behaviour to soil-cement mixtures in terms of resistance to wetting and drying cycles, resistance at early ages and resistance to immersion.