Mechanical Properties of Soil-RAP-Geopolymer for the Stabilization of Road Base/Subbas

There can be environmental problems associated with using cement to stabilize soils. Thus, a substitute for cement in the stabilization of road base/subbase is desirable. A Geopolymer can be a good alternative for cement stabilization, as geopolymer produces fewer greenhouse gasses compared to cement. Soil-RAP-Geopolymer as road base and subbase material have been investigated in this research. The standard method of soil stabilization in Louisiana is soil-cement, hence 5% and 10% soil-cement was selected for the comparison. In addition to the physical and mechanical tests, the durability test was also conducted to evaluate the long-term performance of Soil-RAP-Geopolymer mixtures developed in this study.;Two different types of soils with medium and high plasticity indices from Louisiana were used. Water content was substituted with alkali at an OMC level to compact the Soil-RAP-Geopolymer at a maximum dry density. An experimental design matrix was established for developing statistical based regression models for the UCS and to optimize the mixture design. Higher FA and RAP content produced mixtures with higher strength, and hence 25% FA and 25% RAP provided the better performance in terms of mechanical properties. Optimum sodium silicate content however depended on the type of soil, and the percentage of FA and RAP in the mixture. UCS, resilient modulus, dynamic modulus and elastic modulus of the optimum mixture were found to be better than 5% and 10% of soil-cement mixtures. The optimum Soil-RAP-Geopolymer mixtures successfully passed the minimum strength criteria of CSD and CTD as used by Louisiana Department of Transportation and Development (DOTD). The durability characteristics also confirmed that the developed Soil-RAP-Geopolymer mixture could be used in the field of soil stabilization. The microstructure and morphology analysis on optimum mixtures confirmed that geopolymer was formed with FA, RAP, and soil in the presence of alkali.