Determination of structure-activity relationships between organic components and alkali-activated binders in ground improvement

• Applicant: Professor Dr.-Ing. Frank Rackwitz
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569497222

Organic soils are often classified as having low bearing capacity due to their material behaviour, which is characterised by low undrained shear strength and high compressibility. As a result, they do not meet the requirements for use in conventional geotechnical structures. As a result, ground improvement, i.e. improving the deformation and strength properties of the native soil, is increasingly being used and is less costly and environmentally damaging than measures such as soil replacement or deep foundations. Ground improvement with hydraulic binders typically uses Portland cements, which harden by reacting with water, resulting in increased strength of the soil-binder matrix. However, Portland cements are only partially suitable for stabilising organic soils. With hydraulic binders such as Portland cement, strength development occurs mainly through the formation of calcium silicate hydrates (C-S-H). In the presence of organic components, a reaction can occur between the soluble humic substances of the organic matter and the calcium ions of the cement, limiting the availability of calcium for the formation of C-S-H phases and thus inhibiting the hydration process. Alkali-activated binders offer a promising alternative. They are based on the reaction of aluminosilicate materials, such as blast-furnace slag or fly ash, with alkaline solutions, resulting in a stable aluminosilicate network. The aim of the research project is to investigate the chemical and physical interactions between organic components and alkali-activated binders in order to develop sustainable solutions for ground improvement in organic soils. The research project includes an extensive laboratory programme divided into five work packages. First, the organic soils will be chemically and physically characterised to analyse their composition and variability. Reactivity studies will then be carried out to evaluate the effect of different binders, activators and mixing ratios. Mechanical properties will be investigated using soil mechanical element tests and ultrasonic pulse measurements, while microstructural investigations using scanning electron microscopy and energy dispersive X-ray spectroscopy will analyse the underlying stabilisation mechanisms. Finally, all results will be combined to derive well-founded structure-effect relationships.

• DFG Programme: Research Grants