Evaluating the Potential of Coconut Shell Charcoal Dust on Compaction Properties of Granular Soil for Road Works

Soil stabilization improves soil strength, durability, and stiffness while reducing plasticity, swelling, and shrinkage. However, coconut shells are commonly discarded as waste materials, causing environmental pollution in many coastal areas. This study aimed to evaluate the potential of coconut shell charcoal dust (CSCD) in stabilizing granular soils for road works. The coconut shells were burned in a furnace at 700 °C, cooled, ground, and sieved to obtain fine charcoal dust. Two granular soil samples were collected from boreholes drilled to a depth of 2 m along Boko Magerezani Road in Dar es Salaam, Tanzania. Standard laboratory compaction tests were then conducted to determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of soils mixed with different percentages of CSCD. The CSCD was added to the granular soil samples at 1%, 2%, 3%, and 4% by dry weight. Grain-size analysis indicated that less than 27.33% of the soil passed through a 0.75-mm sieve before compaction. The compaction results showed that CSCD increased the Maximum Dry Density (MDD) by 5.7% and the Optimum Moisture Content (OMC) by 7% in both soil samples. These findings demonstrate the potential of CSCD as an environmentally sustainable stabilizing material for granular soils in road construction, while also reducing pollution caused by coconut shell waste.