stabilization of olokoro-umuahia lateritic soil using … · stabilization of olokoro-umuahia...

UMUDIKE JOURNAL OF ENGINEERING AND TECHNOLOGY (UJET) VOL. 1.NO. 2. DECEMBER 2015 PAGE 67-77

STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH AS ADMIXTURE

*Onyelowe, K. C. and Ubachukwu, O. A.

Department of Civil Engineering, Michael Okpara University of Agriculture, Umudike. P.M.B.7267, Umuahia 440001,

Abia State.

ABSTRACT

The growing cost of known conventional stabilizing agents, the need to rid the environment of pollutant that could be

converted to usable engineering materials and the need for the economical utilization of industrial and agricultural waste

for beneficial engineering purposes have prompted an investigation into the stabilizing potentials of Palm Bunch Ash

(PBA) as admixture. In Nigeria especially in the southern and western parts, lots of engineering projects founded on soil

fail primarily as a result of foundation soil failure. Results from researches have shown that most of the engineering soils

(lateritic soil) borrow sites yield poor soil in terms of geophysical and geotechnical properties which eventually render

the soil material unfit to serve relevant engineering purposes. As a result, there is need to improve on the engineering

properties of the soil by using admixtures hence this research work that was targeted at improving the engineering

properties of Olokoro lateritic soil with PBA. Index properties of the soil material showed that it belongs to A–2–6 and

GP under the AASHTO and Unified Soil Classification Systems (USCS), respectively. Soils under these groups are of

poor engineering benefit. The soil was studied under varying proportions of the PBA at 3%, 6%, 9%, 12% and 15% and

subjected to soil Classification Test, Compaction Test, Atterberg Limit Test and CBR Test. The results show an increase

in MDD and OMC after an initial decrease with PBA variations. The California Bearing Ratio under unsoaked condition

for the natural soil was 39.8% and the peak CBR of the stabilized soil was 69.4% which satisfies the use of the stabilized

sample as sub-grade material at 15% PBA.

Keywords: Palm bunch ash, stabilization, olokoro-umuahia, lateritic soil, admixture

1. INTRODUCTION

A land based structure of any type is only as strong as its

foundation. For that reason, soil is a critical element

influencing the success of a construction project. Soil is

either part of the foundation or one of the raw materials

used in the construction process. Therefore,

understanding the engineering properties of soil is crucial

to obtain strength and economic permanence (Ameta et

al., 2007). Soil stabilization is the process of maximizing

the suitability of soil for a given purpose. The necessity of

improving the engineering properties of soil has been

recognized for as long as construction has existed. Many

ancient cultures, including the Chinese, Romans and

Indians, utilized various techniques to improve soil

stability, some of which were so effective that many of the

buildings and roadways they constructed still exist today.

Corresponding Author: ONYELOWE, K. C, Email: [email protected]

; [email protected].

In the united states, the modern era of soil stabilization

began during the 1960 and 70’s, when general shortages

of aggregates and petroleum resources forced engineers

to consider alternatives to the conventional technique of

replacing poor soils at building sites with shipped-in

aggregates that possessed more favourable engineering

characteristics (Higgin, 2005).

Soil stabilization then fell out of favor, mainly due to faulty

application techniques and misunderstanding. More

recently, soil stabilization has once again become a

popular trend as global demand for raw materials, fuel and

infrastructure has increased. This time however, soil

stabilization is benefiting from better research, materials

and equipment. Poor sub grade soil conditions can result

in inadequate pavement support and reduce pavement

life.

Soils may be improved through the addition of chemical or

cementitious additives (Dallas et al, 2010; Behzad and

Bujang, 2008; Obeta and Ohwoganohwo, 2015; Obeta

and Eze-Uzoamaka, 2013; Onyelowe and Agunwamba,

2012). These chemical additives range from waste

products to manufactured materials, these additives can

be used with a variety of soils to help improve their native

engineering properties. The effectiveness of these

mailto:[email protected]

STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015

additives depends on the soil treated and the amount of

additive used.

The main objective of this study includes:

(i) To establish PBA, a waste material as an

admixture to the stabilization of

engineering soil.

(ii) To evaluate and compute the amount of

Palm bunch ash (PBA) that is required to

meet the optimum load bearing capacity

requirements for the lateritic soil samples

collected from the borrow pit at Olokoro.

(iii) To determine the effects of the stabilizer on

other geotechnical properties of the soil;

such as liquid limit, plastic limit and

moisture content-dry density relationships.

In a broad sense, stabilization incorporates the various

methods employed for modifying the properties of a soil to

improve its engineering performance (Bowles, 1998).

Stabilization of soil means improving of soil strength under

applied load. The soil properties will be increased

reasonably with or without the help of admixtures so that

base/sub-base soil is capable of supporting the traffic load

in all weather condition (Ellen et al., 2006). In the recent

year the stabilization of soil with suitable admixture such

as lime, cement, calcium chloride, fly ash, bituminous

material etc. has been successfully used on increasing

scale for the construction of road foundation in

Bangladesh, India, United Kingdom, and U.S.A etc.

(Gopal and Rao, 2011; Bardet, 1997; AFM No. 32-1019,

1994). In this research work Palm Bunch Ash (PBA) is

considered.

Some admixtures improve poor soils and they become

capable of supporting greater loads but they are not

economical. If the volume of earth involved under a

pavement or under a foundation is huge, the result of the

quantity of stabilization becomes prohibitive. The high

pressure exerted on the pavement and base course

generally preludes using the stabilized soil for bases.

Therefore, stabilization, except for secondary roads is

centred on use in sub-grade and sub-bases. For

secondary roads, a stabilized material (particularly a

mechanically stabilized soil) can be used as the principal

component of the pavement. Secondary road construction

includes gravel surfaces of types, soil cement and oiled

earth surfaces. The choice of the proper admixtures,

which should be used, depends upon the use for which it

is independent. The quantity of stabilizer is generally

determined by means of arbitrary tests, which simulate

field condition of weathering and other durability

processes.

Palm Bunch Ash (PBA) stabilization

Palm trees are economic trees dominantly grown in the

south-east and south-south of Nigeria, where production

averages approximately 95% of the total production in

Nigeria. The two major economical produce from palm

tree processing are palm-wine and palm-oil. Palm fruits

are used for the palm-oil and are harvested from the palm

bunch. The empty palm bunches are the waste from the

processing of the palm fruits. These wastes presently are

used as organic fertilizers, fuel in the rural areas, soap

making (black soap) or as a sauce for local edibles. The

waste produced per day is approximately 4000 tones. It

has been reported that the palm-oil industry produces

considerable amount of solid waste by-products in the

form of fibers, shells and empty bunches which are

discharged from the mills. Presently, shell and fiber are

used extensively as fuel for the production of steam in the

palm-oil mills as a means of waste disposal and energy

recovery. Tables 1 and 2 below show the physical and

chemical constituents of PBA.

Table 1: Physical properties of Palm Bunch Ash (Ettu et

al, 2013)

Property PBA

Moisture content (%) 0.35

Specific gravity 2.33

P.H 7.1

2. MATERIALS AND METHODS

The lateritic soil sample used for this work was a disturbed

sample collected from a borrow pit at Olokoro, Umuahia

South L.G.A, Abia State, Nigeria located between latitude

05°28I36.900II North and longitude 07°32I23.170II East, a

distance of 5km along Ubakala road (Onyelowe and

Okafor, 2013). The PBA used for this investigation was

obtained from incinerated empty palm bunches collected

from Ezeigbo farms. Ezeigbo farms is a palm plantation

located at Eluoma Uzuakoli in

Table 2: Chemical properties of PBA


Constituent Percentage weight

in PBA (%)

MgO 0.89

Fe2O2 0.45

CaO 14.59

Al2O3 15.49

SiO2 60.96

TiO2 Trace

Na2O 0.81

ZnO 0.99

MnO 0.89

MgO 0.40

PbO 0.24

CuO Trace

CdO Trace

LOI 5.8

Source: Ettu et al. (2013)

Umuahia, Abia State, Nigeria, covering a land area of

5562 hectares and produces approximately 4000 tonnes

of palm bunches/day. Open burning method (collecting

the palm bunch wastes in heaps and burning) was

adopted. At the end of the burning, the ashes were

allowed to cool before pulverizing by grinding with mortar

and pestle and sieving using a 150µ BS sieve. The

physical and chemical properties of the PBA are as shown

in Tables 1 and 2.

The experimental work consists of the following; Specific

gravity of soil; determination of soil index properties

(Atterberg Limits); Liquid Limit by Casagrande’s

apparatus, Plastic Limit and Plasticity Index; Particle Size

Distribution by sieve analysis, determination of the

Maximum Dry Density (MDD) and the corresponding

Optimum Moisture Content (OMC) of the soil by Standard

Proctor compaction test, California bearing ratio (CBR),

preparation of modified soil samples. PBA is added in

different percentages of 3%, 6%, 9%, 12% and 15% and

subsequent experimentation was carried out on the

stabilized soil. The stabilized soil and the natural soil

samples respectively will have their results compared to

ascertain the trend in changes in strength characteristics

of the soil samples due to the stabilization (BS 1377, 1995;

BS 1924, 1990; Gopal and Rao, 2011; Gulhati and Datta,

2009).

3. RESULTS AND DISCUSSION

Table 3: Particle Size Distribution

Sieve size Weight retained (g) Actual weight (g) Cumulative (g) passing

4.75 0 100

2 2.8 1.73 1.73 98.27

1.18 39.2 24.17 25.9 74.1

0.6 35.6 21.95 47.85 52.15

0.42 17.0 10.48 58.33 41.67

0.15 52.7 32.49 90.82 9.18

0.075 14.1 8.69 99.51 0.49

0.075 0.8 0.49 100


Table 4: Specific Gravity of natural soil sample

Bottle No. 1 2

Weight of bottle + soil+ water (M3) 1982 1979

Weight of Bottle + soil(M2) 1524 1535

Weight of bottle full of water (M4) 1373 1383

Weight of Bottle (M1) 595 597

Weight of water used 458 444

Weight of soil used 656 657

Volume of soil 778 786

Specific Gravity 2.84 2.73

Average specific gravity 2.79

Figure 1: Moisture-Density relationship of the natural soil.

Dry

De

nsi

ty g

/cm

3

Moisture Content (%)


Figure 2: Liquid Limit graph

Table 5: Summary of compaction test results

PBA (%) 0 3 6 9 12 15

OMC (%) 18.90 25.05 24.73 26.30 24.46 20.78

MDD (gm/cm3 1.65 1.47 1.53 1.52 1.64 1.63

Table 6: California Bearing Ratio of natural soil

Elapsed time

(minutes)

Penetration (mm) Dial reading for

4%

Dial reading for

6%

Dial reading for

8%

0.5 0.625 15 40 25

1 1.250 45 80 50

1.5 1.875 65 115 70

2 2.500 80=17.36% 155=33.6% 95=20.6%

2.5 1.125 170 170 120

3 3.750 200 200 145

3.5 4.375 245 245 160

4 5.000 275=39.8% 275=39.8% 190=27.5%

y = 0.6181x + 14.734R² = 0.4131

Mo

istu

re c

on

ten

t (%

)

No of blows


Table 7: CBR for 3%PBA Stabilization of soil sample

Elapsed time

(minutes)

Penetration(mm) Dial reading for 4% Dial reading for

6%

Dial reading for

8%

0.5 0.625 15 40 20

1 1.250 35 70 40

1.5 1.875 75 145 80

2 2.500 95=20.6% 180=39.1% 105=135%

2.5 1.125 115 210 135

3 3.750 135 235 160

3.5 4.375 170 255 175

4 5.000 195=28.2% 275=39.8% 200=28.9%

Figure 3: Graph of Moisture Density Relationship of 3% PBA Stabilization

Figure 4: Moisture Density Relationship of 6% PBA

Dry

De

nsi

ty g

/cm

3

Moisture content (%)

Dry

De

nsi

ty g

/cm

3




Elapsed time

(minutes)

Penetration(mm) Dial reading for 6% Dial reading for 8% Dial reading for

10%

0.5 0.625 35 75 30

1 1.250 65 135 80

1.5 1.875 85 170 105

2 2.500 100=21.7% 210=43.6% 140=30.4%

2.5 1.125 115 240 170

3 3.750 145 260 190

3.5 4.375 160 275 215

4 5.000 180=26% 290=42% 235=34%

Figure 5: Moisture Density Relationship of 9% PBA stabilization

Table 9: CBR for 9% Stabilization of soil sample

Elapsed time

(minutes)


12%

0.5 0.625 70 90 65

1 1.250 105 124 120

1.5 1.875 130 153 150

2 2.500 160=34.7% 185=40.1% 180=39.1%

2.5 1.125 190 255 220

3 3.750 210 280 245

3.5 4.375 217 305 270

4 5.000 242=35.0% 330=47.7 293=42.4%

Dry

De

nsi

ty g

/cm

3



Figure 6: Moisture-Density relationship of 12% PBA stabilization

Table 10: CBR for 12%PBA Stabilization

Elapsed time

(minutes)


12%

0.5 0.625 55 88 65

1 1.250 85 140 90

1.5 1.875 150 217 170

2 2.500 175=38% 295=64.0% 214=46.4%

2.5 1.125 210 310 240

3 3.750 255 350 270

3.5 4.375 290 385 285

4 5.000 335=48.5% 405=58.6% 315=45.6%

Figure 7: Moisture Density Relationship for 15% PBA stabilization

Dry

De

nsi

ty g

/cm

3


Dry

de

nsi

ty g

/cm

3




Elapsed time (minutes) Penetration(mm) Dial reading for 10% Dial reading for 12% Dial reading for 14%

0.5 0.625 95 100 70 1 1.250 160 165 140 1.5 1.875 205 240 185 2 2.500 255=55.3% 335=72.7% 230=50% 2.5 1.125 280 370 270 3 3.750 305 405 290 3.5 4.375 340 455 325 4 5.000 370=53.5% 480=69.4% 345=50%

Table 12: Geotechnical Properties of Olokoro Lateritic Soil

Property Quantity

Percentage passing

BS No 200 sieve

Natural moisture

content, (%)

Liquid limit, (%)

Plastic limit, (%)

Plasticity index, (%)

Coefficient of

curvature

Coefficient of

uniformity

Specific gravity

AASHTO

classification

USCS

Optimum Moisture

content, %

Maximum Dry

Density, g/cm3

California bearing

ratio, %

Colour

0.49

19.33

36.25

18.39

17.86

0.91

4.38

2.79

A-2-6

GP

18.5

1.89

39.8

Reddish

brown

Index Properties

Preliminary tests results were conducted for the

identification of the natural soil and the determination of

its properties that are summarized in the Tables 3, 4, 5, 6

and 12 and Figures 1 and 2. The soil is classified under

the A–2–6 subgroup of the American Association of State

Highway and Transportation (AASHTO) classification

system, poorly graded (GP) according to Unified Soil

Classification system (USCS) and found to be highly

plastic with a PI of above 17%.

The test results revealed that the stabilized soil sample

with constituents of silty-clayey, gravel and sand is

suitable for use as sub- grade material for pavement

construction.

Compaction Characteristics

Maximum dry density

The Standard proctor compaction showed an increase in

maximum dry density with increasing dosage of PBA up

to about 9% shown in Table 5 and Figures 1, 3, 4, 5, 6 and

7. The increase in the MDD is due to the flocculation and

agglomeration leading to volumetric decrease in

density (Ettu et al., 2013).The decrease in MDD initially for

compaction was due to the presence of large, low density

aggregate of particles.

Above 9% PBA content there was a decrease in the MDD;

this decrease could be as a result of the void within the

coarse aggregate being filled with palm bunch ash

particles (Osinubi and Stephen, 2006).

This result is in conformity with the general trend and

earlier findings by (Osinubi, 1998a & b)

However, above 12% PBA content there was a possibility

that the formation of new compounds occurred, which

consequently led to an increase in the MDD at 15% of

PBA content with the general trend. The MDD for the

compactive effort was in agreement with the trend of

decreasing OMC with increasing MDD as shown in Tables


UJET Vol. 1, No. 2, December 2015

16 and 18 and Figures 6 and 7. At specific ash contents,

the results indicate a decrease in MDD with increasing

PBA contents. The initial decrease in the MDD can be

attributed to the replacement of the soil by the PBA which

has lower specific gravity compared to that of the soil

(Osinubi and Stephen, 2007). It may also be attributed to

coating of the soil by the ash content which resulted to

large particles with larger voids and hence less density.

The increase in density from the minimum attained value

at 12% PBA to 15% PBA contents was due to molecular

rearrangement in the formation of “transitional

compounds” which have high density at 15% PBA

(Osinubi, 1998a).

Optimum Moisture Content

From Table 5 and Figures 1, 3, 4, 5, 6 and 7, it can

observed that; there was an initial increase in OMC with

increase in PBA for the Standard Proctor compactive

efforts. The initial increment was as a result of increasing

demand for water by various cations and the clay mineral

particles to undergo hydration reaction (Steven and

Osinubi, 2006). The subsequent decrease at 6% PBA was

due to cation exchange reaction that caused the

flocculation of clay particles. The final decrease in OMC

recorded was due to self – desiccation in which all the

water was used, resulting in low hydration. The water is

used up in the hydration reaction, until too little is left to

saturate the solid surfaces and hence the relative humidity

within the paste decreases. The process described above

affected the reaction mechanism of stabilized soil

(Osinubi, 2000).

Strength Characteristics

California bearing ratio (CBR)

The California bearing ratio (CBR) value, of the stabilized

soils is an important parameter in establishing the

suitability of the stabilized soils. Thus, it gives an indication

of the strength and bearing ability of the soil; which will

assist the designer in recommending or rejecting the

suitability of the soil for base or sub-base material. Tables

6, 7, 8, 9, 10 and 11 have shown considerable increase in

CBR from 39.8% at control to 42% at 6% PBA to 47.7% at

9% PBA to 58.6% at 12% PBA and to 69.4% at 15% PBA.

The peak un-soaked CBR value obtained was at 15%

PBA with a CBR value of 69.4% less than 80%.

4. CONCLUSION

The Olokoro soil is poorly graded silty sandy gravel and

was classified as A-2-6 under the AASHTO soil

classification system and poorly graded (GP) according to

Unified Soil Classification system (USCS). Requirement

for the use of sub-grade is given that CBR (min of 5-11),

LL (max 50), Plastic Index (max 30), and Percentage

passing sieve 200 (max 35).

It can then be deduced that Olokoro lateritic soil satisfies

the use as sub-grade material but fails to meet the

requirement for that of base course and sub-base course.

It was observed that even after stabilization of the soil

using PBA the CBR value of (69.4%) increased by almost

50% from the CBR value (39.8%) of the natural soil but

still did not satisfy the requirement for use as base and

sub-base in road construction but improved well above

15% which satisfies sub-grade material condition for

highway pavement construction.

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stabilization of olokoro-umuahia lateritic soil using … · stabilization of olokoro-umuahia...

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