The effect of sulphate on the bearing capacity of jet-grout columns constructed by using portland composite (Pozzuolana) cement and portland fly ash cement on sand soi̇ls with sulphate water content

Ground improvement methods are used to increase the required properties of the ground where engineering properties are not geotechnically favorable. Jet-grouting is one of the ground improvement methods that have been used effectively in recent years. With jet-grouting, high pressure cement injection breaks the existing floor forming concrete columns with ground content consisting of a mixture of ground grains and injection material. When the jet grout columns are formed on sulphate-containing grounds or in the presence of groundwater containing sulphate, the sulfate penetrates these columns and the columns are exposed to sulphate during their service life. Depending on the effect of the sulphate, deterioration and strength losses occur on the columns. Determining the damage to jet-grout columns is difficult and costly in land conditions. In this study, small-scale jet-grout columns have been formed by using Fly Ash Cement (FAC) and Composite Cement (CC) in sand ground environment prepared in certain laboratory conditions. As mixing water and curing water, normal tap water (NTW) and Sulfate containing groundwater (SCG) drawn from wells drilled in Konya Second Organized Industrial Zone was used. Core samples were taken from jet-grout columns at the end of first month, third months and sixth months. Unconfined compressive strength test was performed on core samples. At the same time, morphological structure analyses (SEM-EDS and XRD) have been conducted to determine the changes in the internal structure of the columns due to the effect of external sulfate. From the results of the unconfined compressive strength test, it was determined that the strength of the CC columns in the sulfated environment was higher than the strength of the FAC columns. At the end of 6 months, strength losses in the CC columns were found to be approximately 30%, and around 60% in the FAC columns based on the comparison of column strengths in NTW and SCG curing environments. Having evaluated the images obtained in SEM analysis, S/Ca and Al/Ca ratios obtained from EDS analysis and peak values obtained in XRD analysis, ettringite formation was observed in all columns due to the effect of sulfate. When all the experimental results were evaluated collectively, it was determined that there would be a time-dependent decrease in column strengths due to the effect of external sulfate. While using blended cement against the effect of sulphate, the sulfate cation type and concentration in the environment should be well assessed, and the blend type as well as the dosage to be used should be selected correctly.