Thermal characteristics of lime- and phosphoric acid-stabilized montmorillonitic and kaolinitic soils

In this paper, thermal gravimetric (TG) method was used to study the time-dependent changes induced in thermal characteristics of lime- and phosphoric acid-stabilized soils comprised mainly of montmorillonite and kaolinite minerals. The technique was employed due to the “surface-associated” nature of soil-stabilizer reactions and the necessity of pore water presence for the formation of cementing compounds. The morphology of soils was also observed using field emission scanning electron microscopy (FESEM) prior and after treatment. From TG results, it was found that desorption of surface water was the main reason responsible for the mass losses in the lower-temperature regions. In addition, losses at around 300 °C in 8-month cured samples were evident. The latter was assigned to the evaporation of moisture encapsulated into the reaction products. This was confirmed via FESEM images which revealed the formations of white lumps on the surface of soil particles. From engineering point of view, the lime stabilization technique was most effective in increasing the compressive strength of montmorillonitic soils, whereas in laterite soils rich in iron oxides, the phosphoric acid treatment showed the highest degree of improvement.