Effects of wood and groundnut shell ashes on the geotechnical properties of lateritic soil

This research seeks to explore the possible application of wood ash (WA) and groundnut shell ash (GSA) for improving the geotechnical properties of lateritic soil for road subgrade. The materials were heated at 600 °C for a duration of 120 min; then used solely with the mixture and were applied at replacement levels of 0%, 2.5%, 5%, 7.5% and 10% by dry weight of soil. The laboratory tests were carried out which are standard proctor compaction test, unconfined compressive strength (UCS) test, California bearing ratio (CBR) test, and SEM with EDX. According to AASHTO classification, the untreated soil was found to be classifiable as A-7-6 unsuitable subgrade with 19.7% optimum moisture content, 1853 kg/m³ maximum dry density, 236 kPa UCS and 6% soaked CBR. After stabilization, the 10% replacement of GSA + WA gave the best results as UCS reached 287.9 kPa, which was an improvement of almost 22% over untreated soil. Soaked CBR also reached from 6% to 15% (around 150% improvement). The MDD increased to 1920 kg/m³ which indicates packing. Microstructural analysis confirmed a large quantity of pozzolanic reactions in all samples. The calcium content increased dramatically from 0.17% to 30.71% atomic concentration. Moreover, C-S-H and C-A-H were detected in all samples. The results show a better performance of using combined GSA + WA treatment as compared to individual treatments especially at higher level of replacement. It must be noted that the 10% replacement only if optimum in the range studied (0-10%); higher dosages and long-term durability need further research. The study results indicate that blended agro-waste ashes can replace conventional stabilizers for the improvement of lateritic soil.