Characterization of gravel borrow pits materials for construction of low volume roads in Dodoma Tanzania

The study was conducted to investigate suitability of gravel materials from borrow pits which are used for low volume roads construction in Dodoma region Tanzania. Characterization of four borrow pits gravel materials from Dinda, Mahomanyika, Nkulabi and Ntyuka were conducted. Blending process of the borrow pits materials with sand from Ihumwa and clay from Michese in order to improve missed engineering properties were conducted. The GC, SP and PI were 25.4 units, 391.3 units and 16% for Dinda, 32.3 units, 56.0 units and 10% for Mahomanyika, 33.7 units, 148.1 units and 14% for Nkulabi and 32.8 units, 111.2 units and 13% for Ntyuka borrow pit materials respectively. Results of CBR for source materials were 14%, 16%, 29%, and 30% for Dinda, Nkulabi, Mahomanyika, Ntyuka borrow pits materials respectively. The results indicated that all source gravel materials did not comply with requirements as gravel materials for low volume roads. This is because Mahomanyika borrow pit materials has low SP values which required blending with clay materials and Dinda, Nkulabi and Ntyuka have high PI values which required blending with sand. Results of GC, SP and PI for the blended materials were 20.1 units, 259.9 units and 12% for 75Dind25San, 31.3 units, 126.7 units and 11.9% for 85Mah15Cla, 31.0 units, 120.0 units and 11.2% for 80Nku20San and 30.3 units, 104.2 units and 10.4% for 80Nty20San respectively. CBR values of blended materials were 19%, 32%, 16% and 26%, for 75Din25San, 85Mah15Cla, 80Nku20San and 80Nty20San respectively. It has been investigated that all blended materials are suitable for construction of low volume roads in Dodoma region since they have satisfied GC, SP, PI and CBR requirements as surfacing materials for construction of low volume roads. It is important to characterized source materials before use in order to investigate engineering properties. In case source materials lack some engineering properties it is necessary to blend with other materials in order to improve missing engineering properties before use. Keywords: Gravel Materials, Low Volume Roads, Characterization, CBR, Blending.