Abstract:
A wide range of granular materials resulting from the weathering of rocks can be
used as road base materials. In Ethiopia, there are many Kilometers of unpaved roads in
federal and regional road networks, as well as access roads to mining sites and other natural
resources. Dust is generated on unpaved road networks that pollute the environment, and the
loss of fines associated with road dust contributes to increased gravel loss and the need for
frequent maintenance. Hence, this research aims to evaluate the performance of natural gravel
mixed with calcium chloride (CaCl2) as a stabilizer for unpaved road surfacing. For this
research, Natural Gravel samples were collected from an open borrow pit and an Anhydrous
CaCl2 stabilizer was obtained from the market. In this research experimental laboratory work
was employed. The engineering properties of natural gravel were investigated in the laboratory.
Different percentages of CaCl2 in increasing percentages as 2%, 4%, 6%, 8%, and 10% were
added to the specimen by the dry weight of natural gravel in order to evaluate its performance.
For performance evaluation, tests carried out include grain size analysis, specific gravity,
moisture absorption, Atterberg limits, linear shrinkage, compaction test, UCS, and CBR
according to AASHTO, ASTM, and other relevant standards.
The natural gravel was classified A-2-7 (0) as per the AASHTO soil classification system and
GC (Clayey Gravel) as per USCS. The hygroscopicity or moisture absorption capacity of the
fine grained part of the natural gravel is increased from 1.2 to 9.45% with increased amount of
CaCl2 up to 10%. The test results indicated that the plastic index decreased from 17 to 4% and
similarly linear shrinkage decreased from 9.2 to 2.7% with an increased ratio of CaCl2 up to
10%. It was noted that with increased content of up to 10% of CaCl2 in the mixture, the value of
MDD is increased from 1.640 to 1.795g/ and that of OMC is decreased from 13.7 to 10.1%.
Also, the CBR value is increased from 26 to 48% and the CBR swell is decreased from 1.21 to
0.20% with an increased amount of CaCl2 in the mixture up to 10%. The UCS value increased
from 210.37 to 286.34KN/ with increased amount up to 4% CaCl2 and decreased with a
further increase of CaCl2 content.
It was found that 4% CaCl2 is an optimum amount that is recommended to be used for effective
stabilization of natural clayey gravel material, which could improve both its plasticity and
strength requirements for unpaved road surfacing construction.
