Abstract
There was a greater need for granular materials for the construction of the subbase and base courses of pavement structures, for both low and high volume and high volume roads, due to increase in traffic volume. Several studies had explored using different technologies to enhance the performance of granular materials to increase the durability of pavements. Though most technologies involved the use of additives and other nonconventional construction materials. In this study, silica fume, an industrial waste produced from the smelting process of silicon metal and ferrosilicon alloy production, was used as an additive material for the soil stabilisation. Varying dosages of 3%, 5%, 7% and 10% of silica fume were used to modify natural gravel, G6 and G7 gravel materials. Series of Atterberg’s limits tests, standard proctor compaction tests, California bearing ratio (CBR) and unconfined compressive strength (UCS) tests were conducted on the G6 and G7 materials to evaluate their performance under traffic loads. The test results show that G6 material, when stabilised with 3% - 5% silica fume, cured for 7-14 days respectively could be used for subbase and base layer. Further, the results showed that G6 material compacted at 95-100% Mod AASHTO gave improved CBR values. In addition to that, 3% and 10% G7 material, when stabilised respectively at age 7 - 28 days showed a drastic failure when passed to the C4 class material. The test results further proved that the modified G7 material compacted at 95-100% Mod AASHTO gave unsatisfactory CBR values. However, a CBR value of 7 was obtained indicating that the material could only be used for the subgrade pavement layer, which requires a CBR value of between 3 and 15. Nonetheless, the test showed improved compressive strength and also reduced water permeability. Furthermore, the research results suggested that all the modified mixtures decreased the liquid limit and plasticity index, whilst increasing the plastic limit. The analysis indicated that silica fume as a stabilising agent for G6 soil material, modified with 3% and 5% concentrates, was suitable for base and subbase road courses. This also meant that the G6 material could be applied to the pavement layers mentioned above, only for low traffic roads.
M.Phil. (Civil Engineering Science)