Experimental investigation of deep mixing column behavior with blast furnace slag additive

Within the scope of this study; The effects of blast furnace slag (BFS) on the performance of deep mixing columns formed by replacing cement in certain ratios were investigated experimentally. In this study, low plasticity clayey soil (CL), normal portland cement (CEM I 42.5 R) and blast furnace slag were used. In the thesis, firstly, different ratios of CEM I 42.5 R cement were determined from rheological property tests for BFS substitutes; sedimentation and Marsh cone experiments were performed. According to rheological test results, water / binder (W / C) ratio was chosen as the water content of the soil is 27%, which is between the plastic limit-liquid limit values. In order to investigate the effects of BFS on deep mixing columns, the cement ratio was chosen at 15% and 20% of dry weight of clay.Furthermore, small scale deep mixing columns were produced with BFS substitution in 5 different ratios (0%, 10%, 20%, 35%, 50%) of dry weight percentage of cement in both ratios. Unconfined compressive strength, splitting tensile strength, permeability tests were carried out on soilcrete samples after 7, 28 and 56 days curing time respectively. As a result of the common evaluation of the experimental results applied to the small-scale deep mixing columns, A total of 4 large scale Deep Mixing Columns at a cement ratio 20% of dry weight of clay were manufactured by replacing 0%, 20%, 35%, 50% of cement with blast furnace slag and they were cured for 28 days. XRD analysis and SEM image analysis were performed to determine the binding components formed in the chemical structure from core samples. After 7 days curing time, the small-scale samples of deep mixing column that content BFS as a replacement material with cement show a decrease in unconfined compressive strength compared to samples without BFS (0% BFS). However, as the curing time increased, it has been observed that the increment in BFS as a replacement ratio increase the strength of the samples. The least permeable sample is 20% cement and 50% BFS replacement sample. As a result of XRD analysis, kaolinite mineral was found in pure clay. In addition, C-H, etrenite and C-S-H structures were determined. However, the strength of large-scale DMC samples is smaller than that of small-scale samples. The strength of large scale DMC samples ranges from 60% to 85% of small scale DMC samples. Keywords: Deep mixing column, clayey soil, SEM analysis, Unconfined compressive strength test, Blast furnace slag