The Potential Use of Cinder material blended with Fine grained Soil as a Sub base (The Case Study of Adama Awash Road)

Abstract

Cinder is a highly porous pyroclastic material, which is vitric in nature, and does not meet the conventional road base and sub base specification. The cinder gravel and fine-grained soil was collected from Adama-Awash Road Area. The objective of this study was to evaluate the performance such as functional and structural conditions which influenced by factors like traffic, environment, economic and stress distribution factors of cinder and fine-grained blended soil as a sub base material. In order to have satisfactory data, samples from cinder source and fine grained soil source collected and laboratory tests like grain size distribution, Atterberg Limit, compaction, California bearing ratio, Los angeles abrasion, absorption and linear Shrinkage was conducted in accordance with American association of State Highway and Transportation Officials (AASHTO) and Ethiopian Road Authority (ERA) manual standard specification requirement. The cinder gravel was blended with some trail proportion of 0, 7, 14, 21 and 28% of fine-grained soil by mass and tests aforementioned above conducted in the laboratory. From the particle distribution the blending shows coarser at the start of the blending and tends to be much finer at the highest blending proportion especially the grading of the after compaction. The grading of the after compaction at 0.075 mm sieve shows 4.7% pass at cinder only blending, 7.9% pass at 7% blending, 11.1% pass at 14% blending, 14.8% pass at 21% blending and 21% pass at 28% blending. The test result showed that the California bearing ratio values of all trial proportions were more than 30% (48.5%,51.8%,63%,71% and 53.5% at 0%,7%,14%,21% and 28% blending proportion respectively) which is above the requirement of the ERA specification for sub base. However, the value decreases at 28% blending proportion, since at this trial proportion the intermediate particles were replaced by the finer particles which this trend tends to decrease the California bearing ratio value. Based on the laboratory test results it is shown that, from both maximum dry density- percent of fine-grained soil curve and California bearing ratio -percent of fine-grained soil curve, the optimum amount of fine-grained soil required in order to improve its properties is 21 % by mass proportion which improves the maximum dry density of the cinder 1.686% to 1.751% at 21% blending proportion and California bearing ratio of the cinder 48.5% to 71%.