Effect of fly ash stabilization on strength and durability properties of clayey soils

Stabilizing engineering properties of weak soils with some methods such as physical, chemical and hydraulic is called as soil stabilization. Chemical stabilization is one of the most widely used methods among them. In this study, two soils (S and B) having different plasticity were chosen as a research material. Lime and F type fly ash are used as chemical additives. Soils are mixed with various amount (% 5, % 10, % 15, % 20 and% 30) of fly ash. Afterwards, lime was added to these soils with varying proportion (% 3, %5 and % 7) in order to evaluate the effect of it on same soils. Furthermore, lime was mixed with same proportions while % 30 of fly ash remains constant to interpret the effect of both fly ash and lime on soils. First, index tests (specific gravity, hydrometer, consistency limit and standard compaction) were performed on untreated and treated clays. Then, samples prepared with optimum water content were exposed to strength tests (unconfined compression, indirect tensile strength, immediate bearing index, moisture condition value, California bearing ratio, linear swelling and freezing-thawing). Curing time were selected as 0, 7 days and 28 days for unconfined compression strength and indirect tensile strength tests. California bearing ratio and linear swelling test samples were cured only for 28 days. Samples cured for 28 day curing were exposed to 2, 4, 6, 8 and 12 cycles of freezing-thawing. Freezing thawing test and microlevel analysis are performed only specified mixtures (S, S30FA, S30FA5L, S5L, B, B30FA, B30FA5L ve B5L). According to obtained results, engineering performances of S and B soils containing only fly ash additives are far away to satisfy the conditions stated in the standards. Although, strength of mixtures having only lime additives are better then fly ash treated mixtures for all tests, strength results of some mixtures (S3L and B3L) were not good enough according to expectation for CBR test. Strength increase obtained from all mixtures containing both fly ash and lime are very huge when compared with lime only treated mixtures. The maximum strength values were obtained for the mixtures of S30FA5L, S30FA7L, B30FA5L and B30FA7L. It has been concluded that S30FA5L and B30FA5L mixtures are optimum mixtures since these mixtures are economical and also meet the requirements specified by the standards.