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Evaluation of the Effect of Moisture, Fines Content and Plasticity in the Fill Materials (G3) used for Roadwork in Tanzania Study Area Pwani Region

Joseph Stephen Gimonge, Siya Rimoy

Tanzania roadwork construction activities must adhere established guidelines of standard specification and pavement and materials design manual established by the ministry of work. The construction of fill layer requires the materials which constitute CBR equal or more than 3%, having minimum compaction of 90% and with maximum Swelling Index of 2%. Tests of gradations and plasticity properties are disregarded during the classification. This situation has resulted into the use of soil with high water susceptibility during the construction due to lack of control on the plasticity and the percentage of fines content. Tanzania comprises three climatic zones of dry, moderate and wet; the established guidelines had omitted the division of climatic zone during classification the fill material requirement. The study to evaluate the effect of fines content, plasticity and moisture change in the fill materials has been undertaken. The investigation test conducted comprised soil specimen having fines content to the proportional of 5%, 10%, 45%, 60% and 80% sampled from Pwani region. Each sample were investigated at three climatic zones whereas dry, moderate and wet with 75% of OMC, 100% of OMC and 125% of OMC respectively. The effects were investigated through resilient modulus (Mr) and strength (CBR) parameters. The laboratory results and analysis revealed that fines content and plasticity are detrimental to the performance of fill layer. CBR is inversely proportional to the fines content and PI. The Mr values are increased when the fines content increases up to optimal content of fines, and the soil structure with most fined grains has poor performance when exposed to the wet condition. The findings might have a great implication in the roadwork construction industry in Tanzania and other countries with similar characteristics. For instance, the ministry of work might utilize the findings by adding the fine content and plasticity limit. Roadwork construction specification urged to include the limit of fines content and plasticity. Also, the classification must be separated based on climatic zone. The minimum compaction effort must be improved from 90% to 93% together with CBR value from 3% to 5%.