Performance Evaluation of Natural Gravel mixed with Calcium Chloride for Unpaved Road Surfacing

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.