Use of sewage sludge ash for soil improvement

This study presents the application of incinerated sewage sludge ash (SSA) as a soil stabilizing agent. The ash used in this study was obtained from Gaziantep wastewater treatment plant, and had fine particles passing through 0.425 mm sieve. The SSA was mixed with a clay at different percentages (0%, 5%, 10%, 15%, 20%, and %30), and an extensive laboratory study was employed including Atterberg's limits, standard Proctor, unconfined compressive strength (UCS), California bearing ratio (CBR), vane shear, consolidation, fall cone, falling head permeability, and plate load tests. The testing results showed about 30% increment in liquid limit and plasticity index of clay as the SSA percentage increased. A decrease about 2% in maximum dry unit weight for the clay was observed by increasing SSA content up to 30%. An increment about 40% in optimum water content for clay was observed by increasing the SSA percentages up to 30%. The CBR performance of the unsoaked samples was found to be increased up to 6 times greater than the untreated clay, while those of the soaked samples was found to be increased up to 4 times greater than the clean clay. Curing periods have a varying effect on the UCS as well as the CBR testing results. The UCS values was observed to be increased up to 3 times higher than the clean clay samples. In the plate loading tests, the SSA addition increased bearing capacity of clay up to about 75%. The oedometer characteristics of SSA-clay mixtures were controlled mainly by the SSA content. A reinforced circular model box, which has a diameter of 2.0 m and a depth of 1.50 m and a 40 t loading capacity frame, was also constructed to perform plate loading tests in order to investigate bearing capacity of the samples. The results of the plate loading tests showed that the SSA addition increased the bearing capacity, and that the mixtures with SSA had a less settlement than the untreated clay. The laboratory testing results reported in this research showed that the SSA can be used as an alternative soil stabilizing agent. Keywords: Sewage sludge ash, clay, geotechnical properties