The aim of this study was to characterise the technical and environmental implications of non-traditional treatments of a low-plasticity compacted silt (PI = 14) and to investigate their actions both at the micro-and macro-structural scales. Three non-traditional additives derived from industrial vegetal by-products were studied. These additives are classified as an acid solution (AS), an enzymatic solution (ES) and calcium lignosulfonate (LS). The first step was to characterise the effects of these treatments on Proctor compaction, bearing capacity, unconfined compressive strength and stiffness. The index properties of the treated samples were also measured to assess changes in the interaction between soil minerals and the additives. These experimental results showed that the 0.002% ES and 2.0% LS treatments were the most effective at improving the soil dry density and allowing the soil to reach optimum density using 3% less water or 25% less compaction energy. In a second step the mechanisms involved by the treatment were investigated. A microscopic study was conducted including scanning electronic microscopy (SEM) and mercury injection porosity (MIP) tests, measurements of the surface tension of non-traditional additives mixed with water completed the study and demonstrated that the ES treatment has the same surfactant properties as sodium dodecyl sulfate, a common surfactant. Compaction tests confirmed that the behaviours of the soil after ES and sodium dodecyl sulfate treatments were similar.