Sustainable Use of Leonardite Biopolymers as a Green Alternative in Soil Improvement Methods

Leonardite’s ability to stabilise marl, a challenging construction material, was confirmed through mechanical tests, including unconfined compressive strength, unconsolidated undrained triaxial tests, and chemical and microstructural analyses. Results confirmed that the strength improvement factor, cohesion improvement factor, and internal friction improvement factor significantly increased due to both the addition of Leonardite and the curing times. The addition of 15% Leonardite, along with curing periods of 7 to 14 days, resulted in considerable improvement factors ranging between 2 and 5, depending on the parameters investigated. Microstructural analysis confirmed that Leonardite could act as a filler, filling soil voids and reducing peaks associated with calcite content, which is responsible for the unfavorable behavior of marls. The formation of various functional groups and strong bands, such as carboxyl, hydroxyl, and carbonyl, as evidenced by FTIR analysis, was found to be responsible for improving the mechanical strength of samples containing Leonardite.