THOMAS TESHOME AND SAMUEL TADESSE
In road construction using locally available materials plays a significant role in cost and time saving of road construction projects. Cinder gravel is abundantly available in different parts of Ethiopia. However, its use has been for too limited purposes due to its light weight, rough surfaces and high porosity. In this study two types of Natural Pozzolanas were collected from Ziway Area in order to stabilize cinder gravel for road base. One was Pumice (coarser) and the other was volcanic ash (Pumicite). Pozzollanicity test was conducted on both samples using strength activity index test. For the Pumice the strength activity index value was 89.17% while for the volcanic ash (Pumicite) it was 76.43%. Since the volcanic ash (Pumicite) satisfies the minimum requirement for Pozzollanicity and is finer, it was used as a stabilizer. From the unconfined compression test conducted on two specimens of the volcanic ash (Pumicite), the average UCS value increases from 84.65KPa to 266.63KPa for 3 and 7 curing days, respectively. The cinder gravel was blended with 0, 4, 8, 12, 16, 20 and 24% by mass of volcanic ash (Pumicite). Compaction, California Bearing Ratio, Gradation, Atterberg limit, Los Angeles Abrasion, Aggregate Crushing Value, Ten Percent Fines Value, Absorption and Specific gravity tests were conducted in the laboratory. From the laboratory test results of moisture content vs. density relationship, it has been observed that the optimum amount of natural pozzollana (volcanic ash) is 20% by mass proportion at a dencity of 1.76g/cc. For the optimum blending proportion; the range of soaked CBR increases from 98% to 245% whereas for the unsoaked condition the CBR increases from 118% to 307%, for 0 to 28 days curing.