Investigation on the Utilisation of Coffee Husk Ashes to Stabilise Expansive Subgrade Soils for Road Construction in Tanzania

The use of expansive soils in civil engineering construction can damage the structure due to volumetric fluctuations when subjected to moisture variations as a result of seasonal climatic conditions. The objective of this study was to reduce the negative impact of expansive soils in civil engineering construction. The prepared coffee husk ash (CHA) was mixed with expansive soil in different proportions. Laboratory tests, including compaction, free swell, Atterberg limits, sieve analysis, and California bearing ratio (CBR), were used in this study to examine properties of the soil mixtures. Results indicate that the neat soil exhibited high to very high degrees of expansion, reaching a swell of around 1.66% and a plasticity index of 32.16%. The evaluated effect of CHA mixed with expansive soil using CHA contents of 5%, 10%, and 20% confirmed that as the CHA content increased to 20%, the properties of the neat expansive soil were modified due to reduced clay fraction, increased silt fraction, and a CBR value of 19.70%. The properties of neat soil were further modified due to decreased plasticity index and CBR values to 20.61% and 0.47%, respectively. Results from this study could help construction practitioners, including bidders, engineers, researchers, and academicians, to enhance performance and value for money in construction projects