Stabilization Of Weak Sub Grade Soil Using Maize Cob Ash Mixed With Cement (Case Study On Jimma Town)

Abstract

Clayey soils present in its natural state at construction site sometimes may not have the suitable strength. Due to moisture fluctuations, it may have swell and shrinkage distinctiveness and causes volumetric changes and weaken the subgrade by inducing cracking which meets out significant damage to the overlying pavement structures. Those problems are extensively occurring in Ethiopia. The total coverage of expansive soils in Ethiopia is estimated to be 24.7 million acres. However, utilization of such soil in the construction of road is limited due to their substandard qualities. Especially in urban areas, selected materials are not easily available which has to be hauled from Long distance. Since most soil which is found in Jimma town are plastic clay soils, to utilize such expansive soils, conventional stabilizing agents commonly used and replacement of the inferior subgrade soils by borrow materials are fairly expensive and also, the production of those stabilizing agents released into the atmosphere, among those about 7% of Co2 released into the atmosphere is normally through the process of cement production, which is responsible for global warming. The general objective of this research was to assess the stabilization of weak subgrade soil using maize cob ash (MCA) mixed with cement to improve engineering properties of substandard soils to be used as sub-grade materials. In this study Moisture Content, Atterberg Limits Testing, Particle Size Distribution, Classification, Free Swell Index, Specific gravity, Compaction (Maximum Dry Density, Optimum Moisture Content) and CBR were determined. The research design followed the experimental type of study area which began by collecting samples. Two expansive soil samples were taken for the study by observation and free swell index tests at a depth of 1.5m-2m to remove organic matters. The data processing and analyzing were conducted by using both descriptive and analytical methods. Laboratory tests carried out on chemical analysis of maize cob ash and this shows that the total content of main oxides (SiO2+Al2O3+Fe2O3) was 73.75% and specific gravity was 2.29. The chemical properties were fulfilling the requirements according to ASTM C-618. The Hermata Mentina soil sample has plastic index 57.11 %, free swell index 83 % and CBR value 2.62%. In addition, the Mandera Kochi soil sample has plastic index 63.82 %, free swell index 81% and CBR value 2.17%. Since both the given soil sample before any stabilizers are added was very high expansive according to their plasticity index and CBR value as comparing with standards and specifications stabilization was made by (0, 1.5C+6MCA, 3C+4.5MCA, 4.5C+3MCA, 6C+1.5MCA, 7.5C and 7.5MCA). As the amount of cement ratio increases LL, PI, OMC, FSI, CBR swell decreased whereas PL, MDD, CBR are increased, rather than maize cob ash. But amount of cement decreasing with increasing maize cob ash beyond 1.5% the results was decreased as perspectives of tests. For this study (1.5MCA + 6C) is an optimum ratio which achieves by most of geotechnical parameters in the study. The laboratory result was compared with ERA, ASTM, specifications. More investigation shall be performed on different parts of the country by conducting tests with different percentages of MCA alone and by mixing with other stabilizers such as lime. Additional parameter like unconfined compressive strength and mineralogical tests should also be performed to have more realistic test results.