STABILIZATION OF CLAYEY SOIL USING CEMENT AND VOLCANIC ASH FOR SUSTAINABLE ROAD CONSTRUCTION

ABSTRACT

A residual clay soil was collected at Bako village along Gwagwalada-Garki road in Federal Capital Territory of Nigeria using the method of disturbed sampling. The clay was characterized and microstructural tests including X-ray Diffraction (XRD) test, Scanning Electron Microscopy (SEM) test and Electron Dispersive Spectroscopy (EDS) tests were also conducted on the clay soil. The clay was then compacted at Standard Proctor energy level to obtain the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). Unconfined Compressive Strength (UCS) tests were then conducted on the natural clay and clay mixed with 0, 2, 4 and 6% cement which are in turn admixed with 0, 3, 6, 9, 12 and 15% Volcanic Ash (VA) each.  The clay also consists majorly of montmorillonite, ankerite, calcium silicide, anorthite, anothoclase and orthoclase minerals. The SEM test revealed flaky nature of the clay with pore spaces. The natural clay specimen compacted at standard proctor energy level mixed with varied composition of VA showed 2.5 times increase in UCS compared to the value of the natural clay. For clay made of 6% cement with varied percentage VA, the UCS increased by 80% compared with UCS of specimen containing 6% cement-0% VA. The optimal VA value for maximum UCS values lies between 6% and 9% VA.

CHAPTER ONE

1.0      INTRODUCTION

1.1      Background of the Study

Clay soils constitutes major problems in geotechnical engineering compared to other forms of soils. Their particles are normally surrounded by negative charges resulting from the ions around the particles. Soft clay soil has the characteristics of high deformation on application of small loads while stiff unsaturated clay soils have the tendency of large swelling with ingress of water. Therefore, the application of clay soils as foundation soil for structures either suffers excessive deformation on application of load or swells excessively with ingress of water. In most occasions, road pavement structures have been founded on clay soils or clay soil have been used as pavement material due to non-availability of quality pavement materials. In any of these cases, the clay soil will require stabilization to improve its strength and durability.

A lot of stabilization methods ranging from mechanical, chemical and biological forms have been used to stabilize clay soils. Mechanical stabilization entails mixture of two or more  soils  of  different  gradation  in  other  to  achieve  optimal  mixture  which  when compacted will result in to most dense state. Some of the mechanical stabilizations includes the work of Ibrahim (1983) who stabilized black cotton soil with sharp sand found as deposit below the superficial black cotton soil deposit. The mixture was used for the construction of Maiduguri-Gamburu road in north-eastern Nigeria. Another mechanical stabilization is the stabilization of clay soils using non-plastic silt (Alhaji and Sadiku,

2015). The Unconfined Compressive Strength (UCS) was observed to increase from 272

and 770 kN/m2 for British Standard Light (BSL) and British Standard Heavy (BSH) compaction energy levels at 0% replacement to 295 and 795 kN/m2  for BSL and BSH compaction energy level respectively at 10% replacement after which the values reduced to

22 and 60 kN/m2 for BSL and BSH compaction energy levels respectively at 70% replacement. Stabilization of clay soil using cold reclaimed asphalt pavement (RAP) is also a form of mechanical stabilization (Alhaji et al., 2014). The result showed 7.2% increase in UCS and 9.2% increase in California Bearing Ratio (CBR). Mechanically stabilized clay soil using quarry dust was treated with cement kiln dust (Amadi and Osu, 2016). It was observed that curing time affects the strength of the specimen tremendously. The UCS increased from 1.25 to 5.25 times higher than the value of specimen tested immediately after preparation. Some other mechanical forms of stabilization are studies by (Ola, 1981; Louafi and Bahar 2012; Diouf et al., 1990) on the mechanical stabilization involving clay soils mixed with sandy soil.

Chemical stabilization entails mixture of chemical substance like cement, lime, or mixture of both, to a deficient soil in other to improve its strength and durability. Stabilization of soils  using  cement  or  mixture  of  cement  and  pozzolana  has  become  a  common phenomenon and has yield positive result in many instances. Portland cement alone have been used to stabilize soil for road base (Ismail et al., 2014). Tremendous improvement in strength and durability was recorded with the addition of Portland cement. Some other works include the stabilization of lateritic clay using cement and bagasse ash as pozzolana (Osinubi and Alhaji, 2009) variation of compressive strength of cement-treated marine clay with water content (Tsuchida and Tang, 2015), effect of sodium silicate and promoter on

the strength of cement stabilized clay (Ma et al., 2015), cohesive soil stabilized with a mixture of cement and rice husk ash (Prasad et al.,, 2017), improvement of weak residual soil using cement and rice husk ash (Basha et al.,, 2005). All these studies recorded higher strength compared to the use of cement alone.

The common biological stabilization in use is the application of enzymes for improvement of soils. The work by (Khan and Taha, 2015; Sahoo and Sridevi, 2018; Muguda and Nagaraj, 2019; Rao and Hanuma, 2019; Somireddy, 2019; Renjith et al., 2017) are indication of the potential of enzymes as soil stabilizers. Volcanic ash are products from volcanic eruptions and are deposited around the vents of the eruption epicenter. A lot of studies on the engineering use of volcanic ash have been carried out in Indonesia and some other countries in Africa. However, little or no study have been done on the volcanic ash found around the recent volcanic eruptions in Jos Plateau area of Nigeria. This research is intended to evaluate the effect of volcanic ash in Jos Plateau on the engineering properties of cement stabilized clay soil.

1.2      Statement of Research Problem

Clay exists in many regions of the world and has constituted one of the most troublesome soils for civil engineering construction. Most times, they exist on a large span of a region such that road construction must cut across the deposit. Where alternative suitable soil is not available, the clay must be treated to meet the specification for use in constructions. Improvement of these clay soils can be by modification or stabilization or combination of the two. Stabilization of clay soils are usually carried out using cement which is presently

uneconomical and its production is environmentally unfriendly. Production of cement have been understood to generate enormous carbon dioxide which pollutes the atmosphere. Any alternative that can substitute cement partially or holistically will assist to reduce air pollution and reduce the cost of construction.

Volcanic ash is a product of eruption of molten magma which was observed to constitute large deposit in Jos, Plateau State. This ash has been shown to be Pozzolanic in nature and can  react  with  calcium  hydroxide  (byproduct  of  cement  hydration)  to  give  enhanced strength gain. However, strength gain is a function of both the cement and volcanic ash. It is therefore pertinent to evaluate the optimal mixture of volcanic ash that give the highest strength and stability.

1.3    Aim and Objectives of Study

The aim of this study is to determine the effect of volcanic ash on cement stabilized with clay soil.

In order to achieve this aim, the following objectives will be considered:

i     Determine the index properties and compaction characteristics of the natural clay soil ii Determine the microstructural characteristics of the clay and clay mixed with selected composition of the stabilizing chemicals

iii Determine the unconfined compressive strength of untreated clay specimen and clay mixed with 0, 2, 4 and 6% cement admixed with 0, 3, 6, 9, 12 and 15% volcanic ash each.

Iv Determine the effect of volcanic ash on cement stabilized clay

1.4     Justification of Study

Due to scarcity of befitting soil material for road construction in some areas of the world, it is  very necessary to  stabilize  available  but  deficient  soils  so  as  to  meet  the  required specification for use in road construction. The common chemical used for soil stabilization over the years is cement. However, cement is fast becoming expensive and environmentally unfriendly due to emission of carbon dioxide in to atmosphere. The use of cheaply and environmentally friendly, available volcanic ash to substitute cement will go a long way to reduce the use of cement and increase the strength and durability of clay soil.

1.5      Scope of Study

Clay soil were collected at depth of between 0.7m to 1.5m using the method of disturbed sampling. The clay was air-dried and prepared according to the method highlighted in BS 1377 (1992) before use. Index properties test including mechanical sieve analysis, hydrometer analysis, liquid limit test, plastic limit test, plasticity test, specific gravity test, compaction tests were conducted on the natural clay soil. X-ray fluorescence test was conducted on the clay, cement and volcanic ash to determine their oxide composition. X- ray diffraction test and scanning electron microscopy tests were carried out on the natural clay, clay mixed with 6% cement, clay mixed with 6% volcanic ash and clay mixed with 6% cement and 6% volcanic ash. The specimen molded from the natural clay and clay mixed with 0, 2, 4 and 6% cement which in turn was admixed with 0, 3, 6, 9, 12 and 15% volcanic ash each,  were prepared  and  cured for 1, 7,  14, 28,  30 and  60 days  before unconfined compressive strength tests.

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