Abstract:
Highway development is one of the key actors to endore economic activities within a country.
Ethiopia is doing its best to expand this development radiating from Addis Ababa City towards
North to South and East to West directions. Hence, these developments resulted in greater
demands on commercial or processed construction materials that are used for every project
and it initiated the author to seek an alternative approach to find out pavement materials to
utilize where the road construction become very expensive due to the increase costs on crushed
stone aggregate. This was done through bleending naturally occurring river gravel with
crushed stone aggregate, it required to understand the characteristics of River aggregate
thoroughly in Ethiopia and specifically in kaffa context to enable their use in these engineering
applications.
This research focused on the experimental investigation on partial replacement of crushed base
course material using river gravel as unbound granular base course material for road
pavement construction. The methods used in this research involved experimental analysis using
laboratory tests. The samples used for physical and mechanical property tests selected
randomly composed of a sample size of one for Crushed aggregate from kaffa zone which is
around 60 Km from Bonga town while another samples for RG extracted from four River
sources at the same location to crushed stone aggregate.
From these samples physical and mechanical properties tested to determine the sieve analysis,
compaction, Atterberg's limit, Aggregate impact value, Aggregate crushing value, specific
gravity, water absorption, CBR, Loss angles abrasion, flakiness index. The crushed stone
aggregates tested on its initial state at 0% blending, while the following tests, blended with
River gravel aggregates of 10%,20% ,30% and 40% by weight respectively.
Results indicated that as the increasing blending ratio of River gravel aggregates (RG)
material, the CBR value increasese, which were similar to MDD. But, there were significantly
increased in Abrasion value, Specific gravity, Impact value, Crushing value, and water
absorption. Hence, it was found out that the optimum replacement by blending obtained at 30%
RG and satisfied the ERA Standard specifications. It is therefore recommended that river
gravel aggregates can be used as an unbound granular base course for road construction at
30% replacement of the crushed aggregates, specifically on project sites where there is the
scarcity of aggregates from quarry sites
