Stabilization of A‟a Lava Gravel as Base Course Material Using Pozzolana/ Volcanic Ash

Abstract

Stability of a road base layer is depends on the quality of material and particle size distribution. And in order to construct stable pavement with in proposed construction period and cost, using locally available materials plays a significant role. However, these materials are not always suitable and cannot be found in areas close to the construction site, stabilizing locally available material would be a good alternative to achieve the desired pavement construction work. A’a lava gravels occur extensively in Boset and Fentale woredas of Oromia regional state. But in the past it never have been used in road construction due to its absence of fine material, light weight, rough surfaces and high porosity even though it would substantially reduce road construction costs in many instances. Therefore in this study Natural Pozzolana material were collected from Adama Area in order to stabilize the gravel by blend the two materials. Pozzolanicity test was conducted using unconfined compression test conducted on two specimens of the volcanic ash /Pumicite, the average UCS value for 3days to 7days of curing which increases from 86.5 to 151Kpa. And also the characteristics of A’a lava gravel using Gradation, Los Angeles Abrasion, Aggregate Crushing Value, Absorption and Specific gravity tests were conducted in the laboratory. Then finaly to check the performance of mechanically stabilized A’a lava gravels to be used as road base material in order to achieve the Ethiopia Road Authority manual specification, it was blended with some trail proportion of 5, 10, 15, 20, and 25 % of pozzolana material/pumicite by mass and different tests including compaction, CBR, grain size distribution and atterberg limit are conducted in the laboratory. Based on the laboratory test results it is shown that, from both Modified proctor and CBR test for different percent of pumicite, it has been observed that the optimum amount of pumice in order to improve A’a lava gravel properties is 20 % by mass proportion. CBR laboratory test results compared with similar researches and it shows that stabilized A’a lava gravel performed well when it comes to load carrying capacity. The cost comparison, on the other hand, indicated that based on the current market price during the study period, stabilized A’a lava gravel with pumice has cost benefit against using the crushed aggregates for the road base construction