International Journal of Geotechnical Engineering

The combined effect of wood ash and lime on the engineering properties of expansivesoils

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Full Title: The combined effect of wood ash and lime on the engineering properties of expansivesoils

Article Type: Research Paper

Keywords: Wood Ash, Lime, Expansive Soil, Stabilization, Geotechnical Properties

Order of Authors: Chukwuebuka Emeh, M.Sc.

Ogbonnaya Igwe, PhD

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The combined effect of wood ash and lime on the engineering properties of expansive soils 1

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Chukwuebuka Emeh and Ogbonnaya Igwe 3

Department of Geology, University of Nigeria, Nsukka 4

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Corresponding Author: 14

Chukwuebuka Odinaka Emeh 15

Department of geology 16

University of Nigeria Nsukka 17

+2347064860010 18

chubylingy@yahoo.com 19

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Manuscript Click here to download Manuscript Manuscript.docx

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ABSTRACT 21

This work assessed the combined effect of wood ash a waste product from a bread bakery and lime (calcium oxide) on 22

the geotechnical properties of expansive soils collected from Awgu (southeastern Nigeria). The mineralogical 23

composition of the soil and chemical composition of the wood ash were analysed using X-ray diffraction (XRD) and X-24

ray fluorescence (XRF) method respectively. The geotechnical properties of the soil such as grain size distribution, 25

consistency limits, free swell potential, compaction, and unconfined compressive strength of the natural soil and that of 26

the soil with varying proportion of wood ash and lime was also examined. The results revealed that the natural soil which 27

is classified as highly plastic inorganic soil, on addition of wood ash and lime in the optimum proportion of 78%-18%-28

4% by weight of soil-wood ash-lime admixture showed reduction in the plasticity index and linear shrinkage thus 29

improvement in the workability of the natural soil. There was also reduction in the free swell potential of the natural soil, 30

improvement in the compaction properties of the natural soil, and increase in the shear strength value of the natural soil 31

which drastically improved more after 28days of curing. It was therefore concluded that high plastic inorganic soils can 32

successfully be stabilized for use in pavement construction with the combined effect of wood ash and lime, which will 33

not only reduce the cost of carrying out engineering projects, but also reduces the environmental problems associated 34

with indiscriminate disposal of wood ash. 35

Keywords: Wood Ash, Lime, Expansive Soil, Stabilization, Geotechnical Properties 36

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INTRODUCTION 47

Expansive soils, which mostly originate from argillaceous sediments, are soils characterized by expansion in wet 48

conditions and shrinkage in dry conditions. Wetting and drying of expansive soils result to its heaving and cracking 49

respectively; a behaviour that results from its high clay mineral contents (over 65% of the total mineralogy). Most often, 50

this heaving and cracking result to failure of civil engineering structures supported by the expansive soil (Taylor and 51

Smith, 1986; Holtz, 1983; Uduji et al., 1994; Wray and Mayer, 2004). Due to the damages (failures) caused by expansive 52

soils, there is always need to improve their bearing capacity through mechanical or chemical stabilization. Works by Al-53

Rawas et al. (2005), Buhler and Cerato (2007) reveal that chemical stabilization using substances like lime and Portland 54

cement, which are the conventional stabilizers, is more effective and/or economical than mechanical stabilization like 55

vibro-flotation and heavy weight compaction of expansive soils. For example, Anifowose (1989) have shown that the 56

engineering properties of soils stabilized with lime (calcium oxide) are better than those that are mechanically stabilized. 57

This is because, while lime has high amount of calcium oxide (CaO) which undergoes cation exchange with the clay 58

minerals that cause the expansion, mechanical stabilization only reduces the void ratio of the soil (Sivapullaiah, 1996; 59

Show et al., 2003; Mitchell and Soga 2005, Eskisar, 2015). However, industrial stabilizing substances like lime, quick 60

lime and Portland cement are most often expensive which warrants the researching into alternative cheaper source of 61

stabilizers. 62

Works by Okagbue and Onyeobi (1999), Baser (2009) and Agrawal and Gupta (2011) reveal that the use of marble dust 63

as soil stabilizer reduced its (soil) plasticity, increased the strength (unconfined compressive strength and California 64

bearing ratio) and reduced the maximum dry density. Their works revealed that the maximum strength of the stabilized 65

soil was attained at about 8% marble dust and 92% soil admixtures but can only be successfully used as base of lightly 66

trafficked and sub-base of heavily trafficked flexible pavements. In using limestone ash waste to stabilize soil, Okagbue 67

and Yakubu (2000) discovered that the an addition of about 6% of limestone ash waste to 94% of soil improved the soil 68

by reducing the plasticity index and increasing the strength (California bearing ratio and shear strength) and also that 69

double quantity of the limestone ash waste may be required to achieve the same level of soil stabilization as would be 70

achieved by use of conventional lime. Brooks (2009) also reported reduction in swelling ability and strength gain of 71

expansive soil stabilized with rice husk ash, while Okagbue (2007) reported an improvement in the gradation, reduction 72

in the plasticity and maximum dry density of an expansive soil stabilized with wood ash (wood combustion by-product). 73

Authors like Ene and Okagbue (2009) used pyroclastic dust while Cokca (2001), Kumar and Sharma (2004), Ji-ru and 74

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Xing (2002) and Wong (2015) used fly ash (by-product of coal power plant) to also improve the engineering properties 75

of expansive soil and each got result quiet similar to the cases earlier stated. 76

Some researchers also assessed the effect of two stabilizers (conventional and unconventional stabilizer) and discovered 77

that such combinations are better stabilizers than only one material. For example, Rao et al (2012) used rice husk ash and 78

lime to stabilize marine clay and discovered that on the addition of 25% rice husk ash, the plasticity index (PI), optimum 79

moisture content (OMC) and differential free swell (DFS) decreased by 30%, 18.5% and 72.8% respectively while the 80

maximum dry density (MDD) and California bearing ratio (CBR) increased by 17% and 282% respectively. Their work 81

further revealed that on addition of the two 25% rice husk ash and 9% lime, the PI, OMC and DFS decreased by 56.4%, 82

42.6% and 77.2% respectively while the MDD and CRB increased by 12% and 449% respectively. Other authors like 83

Ismaiel (2006) and Malhotra and Naval (2013) combined lime and fly ash while Amu et al. (2005) used cement and fly 84

ash also got higher improvement in the geotechnical property of the soil than using only one stabilizer. However, no 85

author has yet combined a conventional stabilizer and wood ash irrespective that Kersten et al. (1998) and Babayemi and 86

Dauda (2009) have shown that enormous wood ash is regularly generated and improperly disposed to the environment 87

from bakeries, restaurants and homes of some countries like Nigeria. 88

This work accesses the effect of combined wood ash and lime (CaO) on the engineering properties of soils and their best 89

admixture ratio in stabilizing expansive soil. 90

STUDY METHODOLOGY 91

Field observations and sampling 92

The observations that led to this study were done at Awgu town of south-eastern Nigeria where it was observed that most 93

of the civil engineering structures like roads and residential buildings develop cracks shortly after their construction and 94

in some cases lead to heaving or total failure of the structure. Reddish brown soil underlying the area that showed highest 95

structural damage was collected at 30cm depth, air-dried for two weeks to attain complete drying and preserved for 96

analyses. 97

The lime (calcium oxide) used was obtained from an industrially grade chemical store while the wood ash was obtained 98

from a bread bakery. Following Okagbue (2007), the wood ash was left undisturbed for 1 hour to cool to ambient 99

temperature after it was removed from the bakery furnace, passed through BS sieve of 63µm to obtain the size needed for 100

ash clay reaction and preserved in an airtight bag to eliminate its possible reaction with the atmospheric carbon dioxide. 101

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Analyses Procedure 102

The wood ash was subjected to X-ray florescence (XRF) analysis to determine its chemical composition and to specific 103

gravity test following BS 1377 (1975) standard to determine its specific gravity. The pH of the wood ash was determined 104

following ASTM C25-93a (1993) standard while the chemical composition and physical properties of the lime have 105

already been given on the container of the lime by the producing industry (specialty mineral incorporated, 2009). The soil 106

sample was subjected to X-ray diffraction (XRD) analysis using Shimadzu x-ray diffractometer (XRD-6000) to 107

determine its dominant mineralogical composition. It was further subjected to sieve analysis, Atterberg limits, specific 108

gravity, free swell index, linear shrinkage, compaction, and unconfined compressive strength tests. The sieve analysis/ 109

Atterberg limits, unconfined compressive strength and free swell index test were done according to ASTM D2487 110

(2011), ASTM D2166/D2166M-13 (2013) and IS: 2720-XL (1985) standards respectively while the, specific gravity and 111

compaction test were each done following BS 1377 (1975) standard. 112

About 940g of the soil and 60g of the wood ash (corresponding to 94% soil and 6% wood ash) were thoroughly mixed 113

with a hand trowel and the wood ash-soil admixture divided into 5 portions. The 5 portions were subjected to Atterberg 114

limits, free swell index, linear shrinkage, compaction, and unconfined compressive strength tests respectively in order to 115

determine the effect of wood ash on the geotechnical properties of the soil sample. The mixing, dividing and geotechnical 116

tests were repeated for 3 more times using 88% soil and 12% wood ash; 82% soil and 18% wood ash; 76% soil and 24% 117

wood ash. For each of the geotechnical tests, the soil-wood ash admixture that gave the best (optimum) geotechnical 118

property was selected and mixed with lime (calcium oxide) in the ratio of 49:1 (i.e 2% lime and 98% soil-wood ash 119

admixture). The wood ash-soil-lime admixture was also divided into 5 portions and subjected to Atterberg limits, free 120

swell index, linear shrinkage, compaction, and unconfined compressive strength tests in order to ascertain if the addition 121

of lime will improve or depreciate the tested geotechnical properties of the soil. The mixing, dividing and geotechnical 122

testing were repeated 3 more times using 4% lime and 96% soil-wood ash admixture; 6% lime and 94% soil-wood ash 123

admixture; and 8% lime and 92% soil-wood ash admixture. In each case, the geotechnical tests were done following the 124

earlier stated standards. 125

The wood ash-soil and wood ash-soil-lime admixtures were each further compacted at the optimum moisture content and 126

specimen was moulded using the split mould of dimension 38mm in diameter and 76mm in height. The moulded samples 127

were each carefully extruded and divided into 4 portions. Each of the 4 portions was cured moist (storing in polythene 128

bags at 98% humidity and 25oC) for 7, 14, 21, and 28 days respectively. The cured samples were thereafter subjected to 129

unconfined compressive strength test to determine their possible strength gain/lose. 130

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RESULTS AND DISCUSSION 131

The index properties and dominant mineralogy of the expansive soil are shown in Table 1 and 2 respectively. The 132

physical and chemical properties of the wood ash are shown in Table 3 while those of lime are shown in Table 4. 133

From Table 1, the soil was classified as high plasticity inorganic clay (CH) and of high expansivity. Based on findings 134

done by Prakash and Sridhara (2004), the free swell ratio of the soil showed that the soil contains both swelling and non-135

swelling clays, which corresponds with its (soil) montmorillonite and illite content shown in Table 2. Table 3 reveals that 136

the wood ash contains over 13 oxide compounds which agrees with works of Someshwar (1996) and Ayininuola and 137

Oyedemi (2013) that the high oxide content of wood ash is because it of plant part. Amongst the identified oxides 138

however, CaO predominates others, which renders the wood ash good stabilizer of expansive soil as it will not only 139

increase the alkalinity of the soil, which promotes solubility of silica and alumina, but will also provide enough Ca2+ for 140

cation exchange reaction (Nelson and Millner, 1992 and Okagbue, 2007). 141

EFFECT OF THE ADDITIVES ON THE GEOTECHNICAL PROPERTIES OF THE SOIL 142

Atterberg limits, shrinkage limits and free swell index 143

Figure 1a shows the variation of Atterberg limits, linear shrinkage and free swell index of the expansive soil with varying 144

quantities of wood ash. For the case of Atterberg limits, the addition of 6% wood ash resulted to a 12% increase in liquid 145

limit and 12.2% increase in plastic limit while an addition of 18% wood ash resulted to a 3% increase in liquid limit and 146

22.2% increase in plastic limit. This higher increase in plastic limit than in liquid limit resulted to the lowest decrease 147

(19%) in the plasticity index on addition of 18% wood ash. The lowest decrease of 9.5% was also recorded in the linear 148

shrinkage on addition of 18% wood ash. These results agree with those of Bhuvaneshwari (2005) and Ismaiel (2006) and 149

Okagbue (2007) who used fly ash and wood ash to stabilize expansive soil. Terzaghi and Peck (1967) and Nalbantoglu 150

and Gucbilmez (2001) explained that the reduction in plasticity of the soil was due to the decrease in the thickness of the 151

double layer of the clay particles as a result of cation exchange reaction which causes increase in the attraction force 152

therefore leading to the flocculation of the particles. Similarly, the lowest decrease (2.15%) in free swell index was also 153

recorded on addition of 18% wood ash. However, the trend of the free swell index was more fluctuating than others (see 154

Fig. 1a). This fluctuation is probably due to the variation in the mineralogical composition of the natural soil as the 155

reaction between clay and lime depends on the cation exchange capacity (CEC) of the minerals present and the 156

concentration of lime (Bell, 1996). Another explanation is that the wood ash does not quickly produce enough calcium 157

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ions (Ca2+) that can favourably go into cation exchange reaction since it (wood ash) contains other high valence ions 158

(like Fe3+, Cr3+, Ti4+) that may mask the effect of Ca2+. 159

Since the lowest plasticity index (PI), linear shrinkage (LS) and free swell index (FSI) were obtained on the addition of 160

18% wood ash to 82% soil; this was taken as the optimum wood ash-soil admixture and was added varying percentages 161

of lime. Figure 1b shows the variation of the Atterberg limits, linear shrinkage and free swell index at their optimum 162

wood ash-soil admixture with varying percentage of lime. The Figure shows that the addition of 4% lime increases the 163

liquid and plastic limits by 5% and 2% respectively but an addition of 8% lime decreases the liquid and plastic limits by 164

11% and 21% respectively. The result is that the plasticity index showed a 6% and 10% increase on addition of 4% and 165

8% lime respectively. Similar progressive increase shown by plasticity index is also shown by the linear shrinkage (see 166

Fig. 1b). The addition of 4% and 8% lime to the optimum wood ash-soil admixture showed a 1.5% and 3.5% increase in 167

the linear shrinkage. Ismaiel (2006) also gave similar report on stabilization of expansive soils with the combined effect 168

of fly ash and lime. It implies that the addition of lime to the optimum wood ash-soil admixture does not significantly 169

improve the plasticity index and linear shrinkage of the soil. 170

Figure 1b however reveals that an addition of 4% and 6% lime to the optimum wood ash-soil admixture (OWSA) causes 171

a further 18.66% and 18.44% decrease in the free swell index (i.e. relative to that of OWSA) respectively. It is expected 172

that the addition of 5% lime to the OWSA shall result to the lowest decrease (19.13%) in the free swell index. These 173

results agree with those of Buhler and Cerato (2007), Malhotra and Naval (2013) in using fly ash and lime to stabilize 174

soil and also that of Rao et al. (2012) in using rice husk ash and lime to stabilize soil. The reduction in the swell potential 175

of the natural soil was achieved by the initial reaction of lime which releases calcium ion (Ca2+) that migrates to the 176

surface of the clay particles displacing water and other ions thereby reducing the swell tendency. A process regarded as 177

flocculation and agglomeration and it generally occurs in a matter of hours, though can substantially improve with time 178

of curing and pozzolanic reaction (Dempsey and Thompson, 1968; National lime association, 2004). 179

Maximum dry density and optimum moisture content of the soil 180

The optimum moisture content (OMC) and maximum dry density (MDD) with varying quantities of wood ash are shown 181

in Figures 2a and 2b while the variation of the OMC and MDD at their optimum wood ash (18%) with varying quantities 182

of lime are shown in Figure 2c and 2d. The compaction curves of the soil, soil-wood ash and soil-wood ash-lime 183

admixtures are shown in Figure 2e. 184

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Figures 2a and 2b show that there is an initial sharp decrease in the maximum dry density (MDD) from 1.49 to 185

1.46mg/m3 and a corresponding 4.5% increase in optimum moisture content (OMC) on the addition of 6% wood ash to 186

the natural soil. There was then gradual increase to the highest MDD (1.48mg/m3) and a corresponding decrease to the 187

lowest OMC (3.5%) on the addition of 18% wood ash. The initial sharp decrease was also observed and explained by 188

Okagbue and Yakubu (2000) to have been caused by flocculation and agglomeration of the clay particles but their reason 189

for the subsequent gradual drop did not agree with the result obtained in the present work. An explanation for the gradual 190

drop in the MDD may be that the lime content in the 6% wood ash added was enough only for the initial flocculation and 191

agglomeration reaction and thus an increase in the quantity of wood ash resulted to a slower reaction rate. Generally, as 192

the amount of wood ash increases, the OMC and MDD fluctuate in which case none of the wood ash-soil OMC 193

decreased up to that of the natural soil and none of the wood ash-soil MDD increased up to that of the natural soil. 194

Figures 2c and 2d reveal a general progressive increase in OMC and decrease in MDD as lime is added to the optimum 195

wood ash-soil admixture. The OMC increased by 12.5% while the MDD decreased by 0.15mg/m3 on the addition of 8% 196

lime to the optimum wood ash-soil admixture. Okagbue (2007) explained that the decrease in the MDD is due to 197

flocculation and agglomeration of the clay particles (caused by cation exchange reaction) resulting to increase in void 198

volume consequential reduction in the weight-volume ratio. The increase in the optimum moisture content is because of 199

the hydration of quick lime (reaction of quick lime and water to form calcium hydroxide). An exothermic reaction that 200

normally leads to the drying of soil and thus requires more water for the subsequent reaction, which is disassociation of 201

the calcium hydroxide into Ca2+ and OH- ions (Okagbue and Yakubu, 2000; National lime association, 2004). 202

Interestingly, the wood ash-lime-soil admixture moisture-density curves (see Fig. 2e) showed a more flattened 203

compaction curve than that of wood ash-soil admixture. This was also observed by Sweeney et al. (1988) who explained 204

that the flattening is due to the short term pre-compaction cementation reactions caused by the lime. This cementation 205

mostly concentrates between the inter-clay particles edges/faces offering greater resistance to compaction. Nicholson et 206

al. (1994) and Ismaiel (2006) further explained that the flattening of compaction curves makes it easier to achieve the 207

required density over a wider range of moisture contents thereby conserving time, effort/energy and hence reduction in 208

cost of operation. 209

Unconfined compressive strength (UCS) and Curing 210

From Figure 3a it can be seen that, as in the case of OMC and MDD, the unconfined compressive strength (UCS) of the 211

soil did not show significant increase or decrease as wood ash is progressively added to it. The UCS increased by only 212

7kpa on the addition of 18% wood ash to the soil. In order to determine if the increase in calcium oxide content of the 213

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wood ash will cause increase in strength value of the natural soil, again this soil mixed with 18% wood ash taken as the 214

optimum wood ash-soil admixture was mixed with varying quantities of lime as shown in Figure 3b. The result revealed 215

that there was a significant increase in the UCS. The UCS increased by 206.4kpa on addition 2% lime to the optimum 216

wood ash-soil admixture and further increased by 181kpa on the addition of 4% lime to the optimum wood ash-soil 217

admixture and decreased on the addition of more lime. Therefore, 4% lime and 96% optimum wood ash-soil admixture 218

was taken as the optimum wood ash-soil-lime admixture. However, Figure 3b indicates that the highest UCS shall be 219

attained (about 400kpa total increase) on the addition of about 4.5% lime to the optimum wood ash-soil. The optimum 220

wood ash-soil admixture (18% wood ash content) and optimum wood ash-soil-lime admixture (4% lime content) were 221

selected and each cured for 7, 14, 21, and 28 days with the aim of determining the strength gain of the admixtures with 222

time, bearing in mind that Pozzolanic reaction is time dependent (Show et al., 2003), and this reaction as shown below 223

produces calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH): 224

Ca2+ + 2(OH) - + SiO2 (Clay Silica) → CSH 225

Ca2+ + 2(OH) - + Al2O3 (Clay Alumina) → CAH. 226

The calcium silicate gel formed initially coats and binds lumps of clay together which then in time crystallizes to form an 227

interlocking structure which binds the soil particles together thus, strength of the soils increases (Terrel et al., 1979; Hadi 228

et al, 2008). 229

Comparing Figures 3a and 3b with 4a, it can be seen that the lower strength gained by the wood ash-soil admixture is 230

due to the calcium oxide in the wood ash is not readily available for the Pozzolanic reaction which is time dependent, 231

noting that the natural soil contains appreciable amount of Na-montmorillonite (see Table 2) and excessive quantities of 232

exchangeable sodium affects the lime reactivity of soil (Mallela et al., 2004), therefore at this point the wood ash has no 233

Pozzolanic value to the mix but only as a filler (Abdullahi, 2006). This could be justified by the increase in the strength 234

value of the wood ash-soil-lime admixture as compared with the one obtained with the optimum wood ash admixture 235

alone, i.e. from 200.6 kPa to 407 kPa on addition of 2% lime which subsequently increases as more lime is added, and 236

also the surge up of the strength value after 7days of curing from 200.6 kPa before curing to 1050 kPa and to 1590 kPa 237

after 28days of curing, and at this point the wood ash must have produced enough lime for Pozzolanic reaction. 238

This strength gain was also revealed in the stress-strain curves of the natural soil, the optimum admixtures, and 28 days 239

cured optimum admixtures shown in Figure 4b. The stress-strain curves of the uncured samples showing a plastic 240

deformation as they showed very high deformation (strain) with little stress while the cured samples that showed brittle 241

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deformation as their deformation increased with the stress applied. These behaviours are likely due to hardening of the 242

cured clay particles with time and agree with works of Popescu et al. (1997) and Nasrizer et al. (2011). Curing of the 243

samples in this work did not only serve the purpose of determining the durability of the wood ash-lime stabilized soil, but 244

also revealed that the calcium oxide content in the wood ash is not readily available or not adequate enough for 245

Pozzolanic reaction within hours but has to last for a period of at least 7 days before significant strength gain could be 246

observed. However, Pozzolanic reaction have been observed to last for months even years as long as the pH of the soil 247

remains above 10 (Biczysko, 1996; Ismaiel, 2006). 248

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CONCLUSIONS 250

The following conclusions are drawn from this work: 251

1. The addition of wood ash into the studied expansive soil reduced the plasticity index and linear shrinkage of the soil 252

and thus generally improved the workability of the soil. The mixing of 18% wood ash and 82% soil (regarded as the 253

optimum wood ash-soil admixture) gave the least reduction in plasticity index (decreased by 19.00%) and linear 254

shrinkage (decreased by 9.50%) of the soil. Addition of lime to the optimum wood ash-soil admixture did not show 255

any significant improvement in the plasticity index and linear shrinkage. 256

2. The optimum wood ash-soil admixture (OWSA) resulted to only 2.15% decrease in free swell index of the soil while 257

the addition of 4% lime to the OWSA resulted to a further 18.66% decrease in the free swell index. 258

3. Addition of wood as to the soil has no significant effect on its (soil) optimum moisture content and maximum dry 259

density but the addition of lime to the OWSA resulted to a progressive increase in optimum moisture content and 260

progressive reduction in the maximum dry density. On the addition of 8% lime to the OWSA, the optimum moisture 261

content increased by 12.50% while the maximum dry density decreased by 0.15mgm3. Similarly, the addition of 262

wood ash to the soil has no immediate significant effect on its unconfined compressive strength (UCS) while the 263

addition of 4% lime to the OWSA resulted to 387.4kpa increase in the UCS of the soil. There is evidence that it will 264

attain a maximum increase (by 400kpa) on the addition of 4.5% lime to the OWSA. 265

4. The strength of both wood ash-soil and wood ash-soil-lime admixtures increases with curing duration. After 28 days 266

curing at 98% humidity and a temperature of 25oC, UCS of the wood ash-soil admixture increased by 1389kpa while 267

that of wood ash-soil-lime admixture increased by 1912kpa. Curing of the samples in this work did not only serve 268

the purpose of determining the durability of the wood ash-lime stabilized soil, but also revealed that the calcium 269

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oxide content in the wood ash is not readily available or not adequate enough for Pozzolanic reaction within hours 270

but has to last for a period of at least 7 days before significant strength gain could be observed. 271

5. The addition of industrial calcium oxide (CaO) to wood ash in the right proportion improves the stabilizing ability of 272

the wood ash. 273

6. Since wood ash is regarded as a waste material and it is cheap, using it as a stabilizing material for expansive soils 274

will reduce the cost of carrying out engineering constructions on expansive soils and also reduce the environmental 275

problems associated with indiscriminate disposal of wood ash. 276

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ACKNOWLEDGEMENT 293

Authors are grateful to Mr Ojo Johnson, and Mr Ganiyu of National Steel Raw Materials Exploration Agency, Kaduna, 294

for providing geotechnical services. They are also grateful to the management of Ife-best bakeries for providing the wood 295

ash used in this work and to Chinenye for her financial supports. 296

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Abdullahi M (2006) Characterestics of wood ash/OPC concrete. Leonardo electronic journal of practices and 326 technologies 8:9-16 327

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Amu O, Adewumi IK, Ayodele AL, Mustapha RA, Ola OO (2005) Analysis of California bearing ratio values of lime 333 and wood ash stabilized lateritic soil. Journal of Applied Sciences 5: 1479 – 1483 334 335 Anifowose AYB (1989) The performance of some soils under stabilization in Ondo state, Nigeria. Bull IAEG 400: 79- 336 183 337 338 ASTM C25 (1993). American Society for Testing and Material. Standard test methods for chemical analysis of 339 limestone, quicklime and hydrated lime. Annual book of ASTM standards 4.01:9-36 340 341 ASTM D2166/D2166M-13 (2013) Standard test method for unconfined compressive strength of cohesive soil. ASTM 342 international, West Conshohocken, PA, 2013. Vol. 04.08 343 344 ASTM D2487-11 (2011). American Society for Testing and Material. Standard practice for classification of soils for 345 Engineering purposes (Unified Soil Classification System), ASTM international, West Conshohocken, PA, 2011. Vol. 346 04.08 347 348 Ayininuola GM, Oyedemi OP (2013) Impact of hardwood and softwood ashes on soil geotechnical properties. 349 Transnational Journal of Science and Technology 3(10):1-7 350 351 Babayemi JO, Dauda KT (2009) Evaluation of solid waste generation, categories and disposal options in developing 352 countries: A case study of Nigeria. Journal of applied sciences and environmental management 13(3):1-10 353 354 Baser O (2009) Stabilization of expansive soils using waste marble dust. MSc. thesis, Department of civil engineering, 355 Middle-East Technical University 356 357 Bell FG (1996) Lime stabilization of clay minerals and Soils. Engineering Geology 42(4):223-227 358

Bhuvaneshwari S, Robinson RG, Gandhi SR (2005) Stabilization of expansive soils using fly ash. Fly Ash Utilization 359 Programme, (FAUP), Technology Information Forecasting & Assessment Council (TIFAC), Department of Science and 360 Technology (DST), New Delhi, India 361 362 Biczysko SJ (1996) Long-Term Performance of Lime Stabilized Road Subgrade. Lime stabilization, Thomas Telford 363 Publisher 364 365 Brooks RM (2009) Soil stabilization with fly ash and rice husk ash. International journal of research and reviews in 366 applied sciences 1(3): 209-217 367 368 BS 1377. British Standard Institute (1975). Method of testing soils for civil engineering purposes. 369 370 Buhler LR, Cerato BA (2007) Stabilization of Oklahoma expansive soil using lime and class C flyash. In: Problematic 371 soils and rocks an insitu characterization, ASCE Geotechnical special publication 162:1-10 372 373 Buhler LR, Cerato BA (2007) Stabilization of Oklahoma expansive soil using lime and class C flyash. In: Problematic 374 soils and rocks an insitu characterization, ASCE Geotechnical special publication 162:1-10 375 376 Cokca E (2001) Use of class C fly ash for stabilization of expansive soil. Journal of geotechnical geoenvironmental 377 engineering, 127(7):568-573 378 379 Dempsey BJ, Thompson MR (1968) Durability properties of lime-soil mixtures. Highway Research Record 235, 380

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National Research Council, Washington, D. C. pp 61-75 381 382 Ene E, Okagbue C (2009) Some basic geotechnical properties of expansive soil modified using pyroclastic dust. 383 Engineering geology 107: 61-65 384 385 Eskisar T (2015) Influence of Cement Treatment on Unconfined Compressive Strength and Compressibility of Lean Clay 386 with Medium Plasticity. Arabian Journal for Science and Engineering 40(3): 763-772 387

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Uduji ER, Okagbue CO, and Onyeobi TUS (1994) Geotechnical properties of soils derived from the Agwu and Mamu 458 Formations in the Agwu-Okigwe area of South-eastern Nigeria and their relation to Engineering problems. Journal of 459 mining and geology 30:177-123 460 461 Wong LS (2015) Formulation of an optimal mix design of stabilized peat columns with fly ash as a pozzolan. Arabian 462 Journal for Science and Engineering 40(4):1015-1025 463

Wray WK, Mayer KT (2004) Expansive clay soil: a widespread and costly geohazard. geostrata, ASCE 464 GeoInstitute 5: 24-28 465 466 467

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Figure captions 481

Fig1a Variation of Atterberg limits, linear shrinkage, and free swell index with varying percentages of wood ash 482

Fig1b Variation of Atterberg limits, linear shrinkage, and free swell index with 18% wood ash and varying percentages 483

of lime 484

Fig 2a Variation of optimum moisture content (OMC) with varying percentages of wood ash 485

Fig 2b Variation of maximum dry density (MDD) with varying percentages of wood ash 486

Fig 2c Variation of optimum moisture content (OMC) with 18% wood ash and varying percentages of lime 487

Fig 2d Variation of maximum dry density (MDD) with 18% wood ash and varying percentages of lime 488

Fig 2e Compaction curves of the natural soil and at varying proportions of additives 489

Fig 3a Variation of unconfined compressive strength (UCS) with varying percentages of wood ash 490

Fig 3b Variation of unconfined compressive strength (UCS) with 18% wood ash and varying percentages of lime 491

Fig 4a The effect of curing on the unconfined compressive strength (UCS) 492

Fig 4b Stress-stain relationship of the natural soil, optimum wood ash admixture uncured and 28days cured, and 493

optimum lime-wood ash admixture uncured and 28 days cured 494

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497

498

499

500

501

502

503

504

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List of Tables 505

Table 1: Index properties and classification of the natural soil 506

Table 2 Dominant mineralogy of the expansive soil 507

Table 3 Chemical and physical properties of the wood ash 508

Table 4 Chemical and physical properties of the lime (after specialty minerals Inc., 2009) 509

510

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Figure 1a Variation of Atterberg limits, linear shrinkage, free swell index with varying percentages of wood ash

Figure 1b Variation of Atterberg limits, linear shrinkage, free swell index with 18% wood ash and varying percentages of

lime

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25

Mo

istu

re c

on

ten

t (%

)

Wood ash content (%)

liquid limit

Plastic limit

Plasticity index

linear shrinkage

free Swell index

0

10

20

30

40

50

60

70

0 2 4 6 8

Mo

istu

re c

on

ten

t (%

)

Lime content (%)

liquid limit

Plastic limit

Plasticity index

linear shrinkage

free Swell index

Figure Click here to download Colour figure (online only) Figures.docx

Figure 2a Variation of optimum moisture content (OMC) with varying percentages of wood ash

Figure 2b Variation of maximum dry density (MDD) with varying percentages of wood ash

10

12

14

16

18

20

22

24

26

0 5 10 15 20 25

OM

C (

%)

WOOD ASH CONTENT (%)

1.4

1.42

1.44

1.46

1.48

1.5

0 5 10 15 20 25

MD

D (

mg/

m3)

WOOD ASH CONTENT (%)

Figure 2c Variation of optimum moisture content (OMC) with 18% wood ash and varying percentages of lime

Figure 2d Variation of maximum dry density (MDD) with 18% wood ash and varying percentages of lime

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8

Op

tim

um

Mo

istu

re c

on

ten

t (%

)

Lime content (%)

1.32

1.34

1.36

1.38

1.4

1.42

1.44

1.46

1.48

1.5

0 1 2 3 4 5 6 7 8

Max

imu

m d

ry d

en

sity

Lime content (%)

Figure 2e Compaction curves of the natural soil and at varying proportions of additives (S= soil, W= wood ash, L=

lime)

Figure 3a Variation of unconfined compressive strength with varying percentages of wood ash

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

1.5

0 5 10 15 20 25 30 35 40

DEN

SITY

(m

g/m

3)

MOISTURE CONTENT (%)

S

S+6%W

S+12%W

S+18%W

S+24%W

S+18%W+2%L

S+18%W+4%L

S+18%W+6%L

S+18%W+8%L

0

50

100

150

200

250

0 5 10 15 20 25

Un

con

fin

ed c

om

pre

ssiv

e st

ren

gth

(kp

a)

WOOD ASH CONTENT (%)

Figure 3b Variation of unconfined compressive strength with 18% wood ash and varying percentages of lime

0

100

200

300

400

500

600

700

0 1 2 3 4 5 6 7 8

UC

S (k

Pa)

LIME CONTENT (%)

Figure 4a The effect of curing on the unconfined compressive strength (W=wood ash, L=lime)

Figure 4b Stress-stain relationship of the natural soil, optimum wood ash admixture uncured and 28days cured, and

optimum lime-wood ash admixture uncured and 28 days cured (W=wood ash, L=lime, 28DAYS=28 days of curing)

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30

Un

con

fin

ed c

om

pre

ssiv

e st

ren

gth

(kP

a)

CURING PERIOD (Day)

18%W

18%W+4%L

0

0.5

1

1.5

2

2.5

3

0 0.02 0.04 0.06 0.08 0.1 0.12

STR

ESS

(N/m

m2 )

STRAIN

S

18%W

18%W28DAYS

18%W+4L

18%W+4L28DAYS

Table 1 Index properties and classification of the natural soil

Property Numerical value

Specific gravity (g/cm3) 2.43

Liquid limit (%) 57.00

Plastic limit (%) 26.84

Linear shrinkage (%) 16.51

Plasticity index 30.17

Sand (%) 49.00

Silt (%) 36.00

Clay (%) 15.00

Soil classification (USCS) CH

Free swell ratio 1.23

Activity 2.00

Swell potential 8.80

Table 2 Dominant mineralogy of the expansive soil

Mineral present Percentage abundance

Na-montmorillonite 6.21

Illites 33.01

Kaolinites 12.14

Sepiolite 18.69

Sanidine 8.97

Tables Click here to download Colour figure (online only) Tables.docx

Table 3 Chemical and physical properties of the wood ash

Table 4 Chemical and physical properties of the lime (after specialty minerals Inc., 2009)

Compounds/Property Concentration unit

P2O5 3.40%

SO3 1.82%

K2O 15.1%

CaO 71.58%

TiO2 0.46%

Cr2O3 0.02%

V2O5 0.091%

MnO 2.37%

Fe2O3 2.30%

CuO 0.070%

ZnO 0.17%

Ag2O 2.10%

BaO 0.40%

Re2O7 0.2%

LOI 20.01%

pH 12-13

Specific gravity 2.81

Compounds Concentration unit

CaO 96%

Mg 0.8%

Fe2O3 0.1%

LOI 0.1%

pH 13-14

Percent fines (%) 98

Bulk density 1.12g/cm3