Olugbenga O. Amu et al. / International Journal of Engineering and Technology Vol.3 (2), 2011, 87-94 Potentials of Coconut Shell and Husk Ash on the Geotechnical Properties of Lateritic Soil for Road Works Olugbenga O. Amu *1 , Opeyemi S. Owokade 2 , Olakanmi I. Shitan 3 1 Senior Lecturer / Civil Engineering Dept., Obafemi Awolowo University, Ile-Ife, Nigeria 2,3 Research Student / Civil Engineering Dept., Obafemi Awolowo University, Ile-Ife, Nigeria * Corresponding Author *E-mail: olugbengaamu@yahoo.com, Tel. No: +234-803-5188-646 Submitted: December 31st 2010. Abstract– This paper examined the geotechnical properties of lateritic soils modified with coconut shell and husk ash with a view to obtaining a cheaper and effective road stabilizer. After collecting samples A, B and C from three borrow pits meant for road construction works, we performed preliminary tests on them for identification and classification purposes, followed by the consistency limit tests. We also performed engineering property tests (compaction, California bearing ratio (CBR) and triaxial) both at the stabilized and unstabilized states with the addition of 2, 4, 6, 8 and 10% coconut shell and husk ash (CSHA) contents. The results showed that the soil samples were well graded sand with good to excellent rating as subgrade material for pavement construction. However, the engineering properties of the samples were further improved with the addition of 4% CSHA contents. This caused reductions in the PI of samples A and C from 20.43 to 16.74% and 29.51 to 15.67% respectively and reduction at 2% of CSHA in sample B. We obtained optimum values of maximum dry densities (MDD) and shear strengths at 4% CSHA stabilization. The addition of CSHA increased the values of shear strengths to 136.32, 146.91 and 127.96 kN/m 2 whereas MDD increased to 1939.00, 1749.86 and 2080.25kg/m 3 respectively in samples A, B and C. We therefore concluded that coconut shell and husk ash has a good potential for improving the geotechnical properties of lateritic soils. Index Terms- Coconut shell ash, geotechnical property, road stabilization, soil improvement I. INTRODUCTION Pavement engineers have long recognized the long term benefits of improving the strength and durability of pavement soil by mixing in a cementitious binder during reconstruction or new construction. Millions of Naira can be saved by soil stabilization in comparison to cutting and replacing the unstable soil material. When included in pavement design, stabilizing the subgrade can reduce the thickness of other pavement layers [1-2]. Laterite which is good for road construction occurs in large quantity in the tropical areas which includes Nigeria. This laterite may contain some amount of clay minerals such that its strength and durability cannot be determined under load, especially in the presence of moisture. Since this type of soil is common in Nigeria, it will be economically wise to improve it to meet the desired properties [1-2]. Over the years, cement and lime have been used to stabilize subgrade materials. These materials have rapidly increased in price due to the sharp increase in the cost of energy since 1970s [3]. This has recently motivated researchers aimed at sourcing possible alternative soil stabilizing materials, especially those that are locally available and less costly. Many local materials which have been used by different researchers include: rice husk ash, sawdust ash, sugarcane ash, all of which are easily obtainable since the parent materials are usually regarded as waste. This study is therefore aimed at investigating the potentials of the coconut shell and husk ash as stabilizer in lateritic soil for road works. A. Lateritic Soil The soil name "laterite" was coined from a Latin word "later" meaning brick. Soils under this classification are characterized by forming hard, impenetrable and often irreversible pans when dried. However there is confusion in the use of the term, because a variety of materials with many types of compositions and various origins have been called laterites, ranging from iron cappings found on the plateaux of Southern India to the zonal soils of the humid tropics and from the whole weathered profile beneath a laterite of Buchanan's meaning to the iron-rich breccias and slope wash accumulations. Because of this confusion, most workers now prefer to use the definitions based on hardening, such as "ferric" for iron-rich cemented crusts, "alcrete" or bauxite for ISSN : 0975-4024 April - May 2011 87