stabilization of olokoro-umuahia lateritic soil using … · stabilization of olokoro-umuahia...
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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]
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
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
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
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
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
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 (%)
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
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
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
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
Moisture content (%)
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
Table 8: CBR for 6%PBA Stabilization of soil sample
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)
Penetration(mm) Dial reading for 8% Dial reading for 10% Dial reading for
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
Moisture content (%)
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
Figure 6: Moisture-Density relationship of 12% PBA stabilization
Table 10: CBR for 12%PBA Stabilization
Elapsed time
(minutes)
Penetration(mm) Dial reading for 8% Dial reading for 10% Dial reading for
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
Moisture content (%)
Dry
de
nsi
ty g
/cm
3
Moisture content (%)
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
Table 11: CBR for 15%PBA Stabilization of soil sample
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
STABILIZATION OF OLOKORO-UMUAHIA LATERITIC SOIL USING PALM BUNCH ASH (PBA) AS ADMIXTURE. Onyelowe and Ubachukwu, 2015
UJET Vol. 1, No. 2, December 2015 Page 10
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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