STABILISATION OF TROPICAL BLACK CLAY USING CALCIUM CARBIDE RESIDUE AND COCONUT SHELL ASH AS ADMIXTURE

ABSTRACT

A Tropical Black Clay (TBC), obtained by method of disturbed sampling, at a depth of between 0.5m to 1.5m, at Gwako village, Abuja, Nigeria, was treated with 0, 2, 4, 6, 8, and 10% each of Calcium Carbide Residue (CCR) and Coconut Shell Ash (CSA). Effect of the additives  was  investigated  with  respect  to  compaction  characteristics  (Maximum  Dry Density-MDD and Optimum Moisture Content-OMC) and Unconfined Compressive Strength (UCS) cured at 1, 7, 14, 28, 60 and 90 days. Results of index properties of the soil indicated that it is classified under CH and A-7-5, according to Unified Soil Classification System (USCS)   and   American   Association   of   State   Highway   and   Transportation   Officials (AASHTO) respectively. There was a general decrease in MDD of the treated soil with increase in dosage of the additives from 1.784 g/cm3at 0% CSA and 0% CCR to a minimum value of 1.666 g/cm3at 8% CSA and 4% CCR, while the OMC increased with increase in dosage of the additives from 18.0% at 0% CSA and 0% CCR to a maximum value of 23.7% at 4% CSA and 8% CCR. UCS of the treated soil showed general increase with increase in dosage of the both additives and curing period from 19.196 kN/m2 at 0% CSA and 0% CCR to a maximum value of 1194.972 kN/m2 at 0% CSA and 10% CCR after 90 days curing. It was therefore, concluded that, although the treated soil did not meet the 1710 kN/m2 UCS value require for base materials, the requirement of 687-1373 kN/m2  for sub-base materials was achieved within the composition considered and therefore could be used as sub-base materials for lightly trafficked roads.

CHAPTER ONE

1.0      INTRODUCTION

1.1       Background of the Study

Soil is the fundamental and most economical of construction materials. It bears the loads of structures and pavements transmitted through foundations and sub-bases, respectively. Researchers have shown that the suitability of a soil as a construction material is a function of its geotechnical properties (Bowels, 1984; Venkatramaiah, 2012). The use of the existing soil at a construction site for engineering purpose may be hindered by poor engineering properties including poor bearing capacity, higher compressibility, and alternate shrink and swell behavior. Soils whose use is limited as a result of their engineering properties are referred to as deficient soils (Alhassan and Mustapha, 2015).

Deficient soils are regarded as soils which do not meet some or all the criteria required for their satisfactory performance as geotechnical structures. These could either be for base courses  for  road,  embankment  for  dam,  subsoil  base,  clay  liners  for  containment  of leachates and backfill for retaining walls (Alhassan and Mustapha, 2015). In the tropical region, these soils could be lateritic soils, tropical black clay, collapsible soils or any other tropical soils.

Expansive soils are fine grained soil or decomposed rocks that show huge volume change when exposed to fluctuations of moisture content (Hesham, 2013).Typical example of an expansive soil is the “Tropical black clay” found in North-East Nigeria and other parts of the world such as India and USA. They are so named because of their colour and suitability for growing cotton. Tropical black clay have colours ranging from light grey to dark grey and black (Oriola and Moses, 2011).

Tropical black clay is confined to semi-arid regions of tropical and temperate climatic zones and is abundant where the annual evaporation exceeds the precipitation (Chen, 1988; Warren and Kirby; 2004). They are vastly available in North Eastern Nigeria lying within the Chad basin and the upper Benue trough (Adesunloye, 1987).

Tropical black clay occurs in continuous stretches as superficial deposits and is typical of flat terrains with poor drainage. The absence of quartz in the clay mineralogy enhances formation of fine-grained soil material, which is impermeable and waterlogged (Balogun, 1991). The mineralogy of this soil is dominated by the presence of this montmorillonite, which is highly responsible for the attendant shrink-swell behavior of the soil depending on the amount of available moisture in the soil and is the main cause of the many problems associated with these soils. Shrinkage during the dry season often lead to surface cracks that could open up to 50mm or more and several millimeters deep (Osinubi et al., 2011).

Tropical black clay presents various challenges to engineers all over the world due to their characteristic of severe loss of strength and swelling with respect to changes in moisture regime. As a result, structures, roads and highways constructed on them are subject to severe deformations and frequent repairs, leading to high cost of maintenance. Various efforts have been made to stabilize tropical black clay with cement, lime, admixtures and waste products to make them meet requirements for construction works (Osinubi et al., 2009; Ola, 1983; Balogun 1991).

Soil stabilisation is the alteration of one or more properties, by mechanical or chemical means, to create an improved material, possessing the desired engineering properties (Onyeloweand Okafor, 2012). Earlier, soil improvement has been in the qualitative sense only, but more recently, it has also become associated with quantitative values like compressive strength, shearing strength, load bearing quality, adsorption, softening and

reduction in strength and durability, which are related to soil performance (Amu et al., 2005). Soils may be stabilised to increase strength and durability or to prevent erosion and dust generation (Onyeloweand Okafor, 2012). Soil stabilisation deals with the physical and chemical methods to make the stabilised soil serve its purpose as pavement component material (Koteswara, 2011). Osinubi and Katte (1991) referred to soil stabilisation as the alteration or control of any soil property. It covers not only increase or decrease of any soil property, but also the variation of any property with changes in environmental condition, namely moisture or pressure. Stabilisation process could be mechanical or chemical, biological, electrokinetic and thermal.

Mechanical method includes replacement with non-expansive fill, compaction, soil reinforcement, addition of aggregates and mechanical remediation. Moreover, the most widespread mechanical stabilisation methods are rewetting, removal and replacement (Nelson and Miller, 1992). Chemical stabilisation enhances geotechnical properties of soils, by addition of some different materials such as fly ash, quick lime, Portland cement, bitumen, calcium chloride, chemical or bio-remediation, marble dust and scrap tire rubber (Arash et al., 2012). Some of these additives are industrial and agricultural wastes.

The ability to blend naturally occurring soil with some industrial and agricultural wastes to give better engineering properties in both strength and water proofing is very essential. Cost effective and locally available stabilisers such as Calcium Carbide Residue (CCR) and Coconut Shell Ash (CSA) are used for the stabilisation in this project.

1.2       Statement of the Research Problem

Tropical black clay belongs to the smectite group, which includes montmorillonite that are highly expansive and are the most troublesome clay minerals (Nelson and Miller, 1992). They are susceptible to seasonal volumetric changes, exhibit severe cracking when dry, swell and yield low bearing strengths when wet, ultimately resulting to heavy depressions and settlement (Seehra, 2008). These problems cause extensive damage to light structures and pavement resting on them (Jones and Holtz, 1993).

The  effort  made  by  researchers  (Mohammedbhai  and  Baguant,  1990;  Osinubi,  2000; Cokca, 2001; Medjo and Riskowski, 2004; Akinmade, 2008; Ochepo, 2008) to obtain cheaper additives which can be used to substitute the conventional soil improving additives (cement, lime and bitumen) led to the consideration of agricultural and industrial waste resources such as rice husk ash (RHA), bagasse ash (BA), locust bean waste ash (LBWA), Fly ash and Iron ore tailing. Thus, the use of cheap admixtures to replace or supplement cement or lime stabilised soils especially wastes from agricultural and industrial products will ultimately reduce the cost of construction works where expansive soils are found (Chesner et al., 2002; Phanikumar and Sharma 2004; Cokca 2001).

1.3       Aim and Objectives of the Research

The aim of this research is to investigate the effect of Calcium Carbide Residue (CCR) and Coconut Shell Ash (CSA) on Tropical Black Clay (TBC).

To achieve this aim, the objectives are to:-

i.      determine the chemical composition of Calcium Carbide Residue and Coconut Shell Ash.

ii.      determine the geotechnical properties of tropical black clay.

iii.       determine the effect of Calcium Carbide Residue and Coconut Shell Ash on the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of tropical black clay.

iv.      determine the effect of Calcium Carbide Residue and Coconut Shell Ash on the Unconfined Compressive Strength (UCS) of tropical black clay.

1.4       Scope of the Research

The scope of this research focused on the laboratory tests using tropical black clay. The following tests were conducted:

i.      Chemical composition of Calcium Carbide Residue (CCR) and Coconut Shell Ash (CSA).

ii.      Index properties test on the natural soil.

iii.       Compaction test on both the natural and stabilised soil with 0% CSA + (0, 2, 4, 6, 8 and 10)% CCR, 2% CSA + (0, 2, 4, 6, 8 and 10)% CCR , 4% CSA + (0, 2, 4, 6, 8 and 10)% CCR, 6% CSA + (0, 2, 4, 6, 8 and 10)% CCR, 8% CSA + (0, 2, 4, 6, 8 and 10)% CCR and 10% CSA + (0, 2, 4, 6, 8 and 10)% CCR.

iv.      Unconfined Compressive Strength (UCS) test on both the natural and stabilized soil cured at 1, 7, 14, 28, 60 and 90 days.

1.5       Justification of the Research

The rising cost of conventional soil stabilising additives such as cement and lime has motivated the search for cheaper and locally available materials for improving properties of deficient soils to meet geotechnical engineering requirements. Thus, the use of industrial and agricultural waste, such as calcium carbide residue and coconut shell ash which will considerably  reduce  the  cost  of  construction  and  as  well  reducing  the  environmental hazards the disposal of these waste causes.

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