Effectiveness of Sludge Ash of Wood and Paper Mill as Nontraditional Additive for Clayey Soil Treatment

Abstract

This study evaluated the effectiveness of sludge ash of wood and paper (SAWP) mills for improving the physical and mechanical properties of three different clayey soils. The influence of SAWP was assessed through compaction, Atterberg limits, soaked and unsoaked unconfined compressive strength (UCS), and pulse velocity of compression waves (Vp) tests. In addition, changes in the mineralogical and microstructural features of the SAWP-treated samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. Finally, toxicity characteristic leaching procedure (TCLP) tests were conducted on the SAWP-treated samples to determine the leachability of heavy metals. Experimental results revealed that SAWP treatment improved physical and mechanical characteristics of all three types of clayey soils. The improvements indicated a considerable decrease in plasticity index and a significant increase in UCS and Vp values. The results of XRD and SEM analyses showed significant changes in the mineralogy and microstructural of the SAWP-treated samples. The changes were attributed to the formation of new cementitious compounds that not only strengthen the bond of particles but also fill the pores resulting in a denser matrix in the SAWP-treated samples. Concentration of leached heavy metals in SAWP-treated samples was less than the permissible values determined by the relevant organizations. The results of this study corroborate the effectiveness of SAWP as a nontraditional additive for soil treatment.