Soil stabilization using geopolymers obtained from wastes

Soil stabilization is a technique based on the use of a binder, which is able to improve the bonding of soil particles, increasing the mechanical properties and durability. The binders usually used are lime, portland cement,... [ view full abstract ]

Soil stabilization is a technique based on the use of a binder, which is able to improve the bonding of soil particles, increasing the mechanical properties and durability. The binders usually used are lime, portland cement, and lime-pozzolan mixtures. All these binders, primarily portland cement, have a high carbon footprint. It is estimated that the production of one ton of portland cement generates approximately one ton of carbon dioxide. Research is currently being carried out into the development of binders whose production generates fewer greenhouse gases. This research it´s oriented towards the achievement of the Sustainable Development Goals, and would be fundamentally focused on the 11 goal (sustainable cities and communities), and the 13 goal (climate action). These binders are called alkali-activated cements, or geopolymers. These new binders consist of a precursor, which is a silicon-aluminous material and an activator, which is a high alkaline material. The binding of precursor and activator favours the development of a series of chemical reactions whose products have cementing properties. More recently, research in the field of alkali-activated cements has focused on the use of waste materials in the composition of precursors and / or activators. This would mean an even greater reduction in the production of greenhouse gases. In the research carried out, has been used as a precursor the spent catalytic cracking catalyst (FCC), which is a residue of the petroleum industry.  Different residues such as rice husk ash (RHA), rice straw ash (RSA) and brew filtration material (BFW) have also been used in the composition of the alkali activator. Stabilized soil samples of 4cmx4cmx4cm were prepared and cured for 7 and 90 days at a temperature of 22ºC and relative humidity of 50%. The results of compressive strength showed the good mechanical behaviour of the stabilized soil. In none of the tested specimens were obtained mechanical strengths below 10 MPa. In the experiments in which FCC was used as a precursor, the highest compressive strengths were obtained using the composition of the activator RHA and BFW, where they exceeded 20 MPa. In these latter two cases, the mechanical strengths obtained were higher than the control specimens in which portland cement had been used as a binder. FCC-CSW mixtures were also used as a precursor to obtain sufficient mechanical strength for construction applications. The results obtained allow us to hope for the use of geopolymers obtained from waste as a viable and more sustainable environmental option for soil stabilization.