partially replacement of waste plastics in bituminous
TRANSCRIPT
Partially Replacement of Waste Plastics in Bituminous Mixes as Road
Construction Material
Ethiopian Institute of Technology- Mekelle
School of Civil Engineering
Authors Name:
1) Abebe Welegabir
2) Brihane Fisshaye
3) Gebremeskel G/Korkos
4) Kena Debissa
5) Mekilit Demmissie
6) Asbeha Kalayu
B.Sc Degree in Civil Engineering
Submitted to: Ethiopian Road Authority
I. ABSTRACT
Now a day, in Ethiopia as the result of rapid industrial growth in various fields with highly
population growth an obvious increase the consumption of plastics. Disposal of large
consumed plastics cause an environmental pollution as they are considered non-
biodegradable materials.
The objective of this experimental study was partially replacement of plastic wastes mixing
with asphalt bitumen in road construction to improve the performance(quality) of the road
and to minimize the cost of bitumen spend for road construction in addition to solving
disposal problems.
The experimental study began with collection of waste plastics. The waste plastics, then
washed, dried and cut in desired shapes. Bitumen test, aggregate test and marshal mix design
were held during the study. The plastic modified asphalt requires three aggregates (aggregate
00, aggregate 01and aggregate 02 sizes) having different gradation to produce an aggregate
blend that meets gradation specification for particular mix. The different aggregates mixed
and heated at 160°C, transferred to the chamber. Similarly, the bitumen and plastic heated
together at 160°C, then mixed with the hot aggregate to get strong binding. Marshal mix
design started with 5%, 10%, 15% and 20% of plastic wastes by weight of the conventional
asphalt bitumen mixing with the prepared aggregate in hot mix. The marshal test designed to
determine the optimum plastic content and bitumen content added to the specific aggregate
bled resulting mix where the desired properties strength and durability were met.
The result indicates that, partially replacement of waste plastics in asphalt mix has 25%
higher stability than the conventional bitumen only. The plastic modified asphalt was lower
by 10.06% in cost comparing to conventional bitumen. The optimum plastic content was
determining 11.5% by weight of the conventional bitumen.
Generally, plastic wastes can be used as modifier for asphalt mix to improve the performance
of the mix design as well as sustainable management of plastic wastes.
Key words: plastic waste, optimum plastic content, optimum bitumen content, marshal
properties
1
II. INTRODUCTION
A. General Introduction
Due to increasing demand in highway construction, scientists and researchers are constantly
trying to improve the performance of bitumen pavement. Asphalt concretes are widely used
in pavements. Due to increase in vehicles in recent years the road surface has been exposed to
high traffic resulting in deformation of pavements due to excessive stress. Permanent
deformation happens when pavement does not have sufficient stability, improper compaction
and insufficient pavement strength.
As a result of rapid industrial growth in various fields together with population growth, an
obvious increase in waste generation rates for various types of waste materials is observed.
Disposal of that large amount of wastes especially non-decaying waste materials become a
problem of great concern in developed as well as in developing countries. Recycling waste
into useful products is considered to be one of the most sustainable solutions for this problem.
From practical experiences it is proved that the modification of asphalt binder with polymer
additives, offers several benefits. To enhance various engineering properties of asphalt many
modifiers such as low density plastics have been used in asphalt.
B. Problem statement
The high costs of bitumen spend for road construction and the low
performance (stability) of roads.
The huge discarded plastic wastes that cause environmental pollution.
C. Thesis objective
Partially replacement of waste plastics in bituminous mixes as road
construction material.
To minimize the cost of bitumen spend for road construction
To compare the stability of conventional bitumen mix with plastic modified
bitumen mix.
To identify the optimum percent of waste plastic to be added in the hot mix
asphalt.
To protect the environment pollution due to waste plastics.
D. Scope and limitation of the study
Used only low density plastics.
It does not include aging.
Absence of reagent that facilitate the chemical reaction between plastic and
bitumen.
2
III. LITRETURE REVIEW
A. Introduction
For many years, researchers have experimented with modified bitumen mainly for road
construction. It’s proven that the addition of certain polymer additive to asphalt mix can
improve the performance of road pavement.
The study was investigated using polyethylene as one sort of polymers to enhance asphalt
mixture properties, two types of polymers in two states were added to coat mix aggregates
(Grinded and not grinded low density Polyethylene (LDPE) and high density Polyethylene
(HDPE)). Optimum bitumen content (OBC) is first determined using Marshal mix design
procedure then seven proportions of polyethylene of each type and state by weight of OBC
were selected to be tested (6, 8, 10, 12, 14, 16 and 18%). The tests include the determination
of bulk density, stability and flow [1&2].
Another study was reported that the incorporation of waste polymeric packaging material
(WPPM) in the bituminous mixes enhances pavement performance as well as protect the
environment. Study includes reusing milk bags and other HDPE based carry bags as additives
in bituminous mixes. Results revealed that the optimum dose of WPPM is 0.3% to 0.4% by
weight of asphalt mix. Higher dose lead to undesirably higher stiffness of mix. It’s found that
using of WPPM in bituminous mixes substantially improving performance properties which
include reduction in rutting and deformation values [2, 3&4].
The addition of polymers typically exhibit improved durability, greater resistance to
permanent deformation in the form of rutting and thermal cracking. Besides, it increases
stiffness and decreased fatigue damage. Waste plastic bags (WPB) which is mainly composed
of Low Density Polyethylene (LDPE) has been found to be one of the most effective polymer
additives which would enhance the life of the road pavement and also solve many
environmental problems [5&6].
B. Hot Mix Asphalt
Hot-Mix Asphalt (HMA) is the most widely used paving material around the world. It's
known by many different names: HMA, asphaltic concrete, plant mix, bituminous mix,
bituminous concrete, and many others. It is a combination of two primary ingredients
aggregates and asphalt binder. Aggregates include both coarse and fine materials, typically a
combination of different size rock and sand. The aggregates total approximately 95% of the
3
total mixture by weight. They are mixed with approximately 5% asphalt binder to produce
HMA. By volume, a typical HMA mixture is about 85% aggregate, 10% asphalt binder, and
5% air voids. Additives are added in small amounts to many HMA mixtures to enhance their
performance or workability. Because asphalt concrete pavement is much more flexible than
Portland cement concrete pavement, asphalt concrete pavements are sometimes called
flexible pavements [7].
C. Aggregates
Aggregates (or mineral aggregates) are hard, inert materials such as sand, gravel, crushed
rock, slag, or rock dust. Properly selected and graded aggregates are mixed with the asphalt
binder to form HMA pavements. Aggregates are the principal load supporting components of
HMA pavement. Because about 95% of the weight of dense-graded HMA is made up of
aggregates [8].
D. Asphalt Binder (Bitumen)
Asphalt binder (bitumen) which holds aggregates together in HMA is thick, heavy residue
remaining after refining crude oil. Many asphalt binders contain small percentages of
polymer to improve their physical properties; these materials are called polymer modified
binders. Most of asphalt binder specification was designed to control changes in consistency
with temperature [8&9].
E. Plastic Polymers
Plastics are mainly organic polymers of high molecular mass. The raw materials for plastics
production are natural products such as cellulose, coal, natural gas, salt and crude oil.
Different plastics have different polymer chain structures which determine many of their
physical characteristics. The vast majority of these polymers are based on chains of carbon
atoms alone or with oxygen, sulfur, or nitrogen [10].
4
IV. METHODOLOGY
A. Selection and Collection of Plastic Materials
Now a day, in Ethiopia it is most common to see the plastic waste materials used for
packaging of drinking water in small plastic bottles. These water plastic bottles are very low
in cost and are highly available near bus stations, eating places, river side and many other
busy locations. Also the disposal of this non-decaying and non-biodegradable waste
polythene’s is a big problem for the present society. So, Plastics used in these experiments
were polythene material of these water bottles collected from the discarded place.
B. Selection of Aggregate Gradation
Selection of proper gradation for the mix is one of the most important parameter. In this
investigation there are three aggregates gradations (aggregate 00, aggregate 01and aggregate
02 sizes) having different gradation to produce an aggregate blend that meets gradation
specification for particular mix
C. Sample Preparation
The collected polythene wastes were washed, cleaned and dried. The polythene was then
cutting into tiny pieces. The required quantities of polythene to be added with specified
amount of bitumen for preparation of different percentage of polythene-bitumen blend were
weighted and added in required percentage by weight of bitumen to the hot bitumen and the
mixture was stirred well for optimum temperature.
D. Bitumen Tests
a) Penetration test:
A needle of specified dimension was allowed to penetrate vertically in to bitumen-plastic
mixed material under specified load, temperature and time condition. The distance the needle
penetrated in units of 1/10mm was termed penetration value.
Figure 1.1: penetration test
5
b) Ductility:
A dumbbell shaped specimen was placed in a hot water bath and allowed equilibrate.
The sample was stretched until it broke. The distance at rupture in centimeter reported as
the ductility.
Figure 1.2: ductility test
c) Softening point test:
A steel ball of 3.5 gram placed on sample of binder contained in a brass ring which
suspended in water bathwater used for softening of 80°C.
The bath temperature raised at 5°C per minute, the binder gradually softens and eventually
deformed slowly as the ball falls through the ring.
Figure 1.3: softening point test
E. Aggregate Tests
a) Sieve Analysis:
After arranged the sieve in descending order poured the coarse or the fine aggregate on the
top of the sieve, then shacked by shaker machine or hand shaking, finally weighed the
aggregate retained in each sieve.
6
Figure 1.4: sieve analysis test
b) Flakiness index:
The flakiness index of an aggregate founded by separating the flaking particles and expressing
their mass as percentage of the sample.
Figure 1.5: flakiness index test
c) Los-Angeles Abrasion Test:
The los-Angeles abrasion test measured of degradation of minerals aggregate of standard
grading resulting from a combination of action including abrasion, impact and grinding in
rotating steel drum containing 12 steel spheres.
d) Relative Density and Water Absorption of Aggregate
A sample of about one kilogram of the aggregate shall be used. The sample shall be
thoroughly washed on the 5mm test sieve to remove finer partecles.eg clay, silt and dust. Two
tests shall be made. The preferred method described is a glass vessel method for aggregates
between 5mm and 40mm size. Subsidiary wire basket method for aggregates larger than
10mm is also described. It is the difference in mass between saturated surface dry and oven
dried aggregate expressed as a percentage of the oven dried sample mass. Coarse aggregate
having water. Absorption of 2% or less is considered durable. No value of water absorption is
given for fine aggregate.
7
F. Blending of Aggregates
Asphalt mix requires the combining of two or more aggregates, having different gradations,
to produce an aggregate blend that meets gradation specifications for a particular asphalt mix.
Available aggregate materials and sand are integrated in order to get the proper gradation
within the allowable limits according to ASTM Specifications using mathematical trial
method.
G. Marshall Test
Marshall Method for designing hot asphalt mixtures is used to determine the optimum
bitumen content to be added to specific aggregate blend resulting a mix where the desired
properties of strength and durability are met. Marshal molds were prepared for different
percentages of bitumen by varying the bitumen percentage from 4% – 5.5% by increment of
0.5%.
Figure 1.6: Marshal Test
8
V. RESULT AND DISCUSSION
A. General Introduction
Results of laboratory work had been obtained and analyzed in order to achieve study
objectives which include studying the effect of adding different percentages of plastics on the
mechanical properties of asphalt mix and identify the optimum percent of plastic to be added
to hot mix asphalt. Marshal Test is carried out with different percentages of bitumen which
are (4.0, 4.5, 5.0, and 5.5%) and the results are analyzed in order to obtain the optimum
bitumen content (OBC).After obtaining OBC, the following step is to study the effect of
adding different percentages of plastics on asphalt mix properties which are (5, 10, and 15%)
by the weight of bitumen. Finally marshal test results for modified asphalt mixes are
analyzed.
B. Bitumen Tests and Results
a) Penetration Test
The values that were obtained from this test were acceptable up to 20% plastic and 80%
asphalt.
Mass of asphalt taken= 128gm
Weight of plastic 5%of bitumen=0.05*128=6.4gm
Mixing of these materials at temperature of 160-180⁰c and waiting for one hour in air and
one hour in water bath maintained at 27⁰c the result that obtained was; for 20% plastic and
80% bitumen
Table 1.1: penetration test
Readings
Trial 1 Trial 2 Trial 3
Initial reading 140 140 142
Final reading 210 200 190
Penetration depth (final
reading- initial reading)
70 60 58
Then the average of these 3 values was = (70 + 60 + 58) /3=62.3cm.
9
Table 1.2: Final Result of Penetration test
Content of plastics (%) Penetration value
(mm)
Range(mm) Remark
0 72.6 60-80 Ok
5 68 60-80 Ok
10 65 60-80 Ok
15 63.2 60-80 Ok
20 62.6 60-80 Ok
b) Ductility Test
Conducting this test, results obtained are acceptable values up to 15% plastic and 85% of
bitumen.
Table 1.3: Ductility Reading For 100% Asphalt And 0% Plastic
Sample Trial 1 Trial 2
Reading (mm) 105 106.3
Ductility value(mm)→ (reading1+reading2)/2= 105.65
.
Table 1.4: Final Ductility Result for Plastic and Bitumen
Content of plastic (%) Ductility value
(cm)
Range Remark
0 105.65 >60 Ok
5 94.6 >60 Ok
10 84.7 >60 Ok
15 76.8 >60 Ok
20 44.2 >60 Not ok
From the table, as the plastic content increases ductility decrease because plastic are rigid.
c) Softening Point Test
Heating the bitumen and pour into the ring then add normal stones in place of standard ring
balls because the ring balls are not found in the laboratory. Adjusting into the machine
obtained the following results:
10
Table 1.5: softening point result
In degree centigrade
Plastic content in % Ring 1 Ring 2 Average value
0 55 56 55.5
5 55 57 56
10 59.25 60.75 60
15 59.8 67 63.55
From the above result, the asphalt can use for a temperature of < 55.5⁰C but as the plastic
modified asphalt its resistance to temperature is increased to 63.55⁰C.
C. Aggregate Testes and Result
Table1.6: summary of aggregate tests
no
Aggregate tests
Test result
obtained
Remarks according ERA
manual specifications
1 Flakiness index 26.14% Max 35%
2 Los-Angeles Abrasion 31% -
3 Bulk specific gravity for coarse
aggregate
2.67 2.5-3.0
4 Bulk specific gravity for the mineral
filler
2.69
5 Bulk specific gravity for fine
aggregate
2.74
6 Water absorption of aggregates 0.55% Max 2%
a) Sieve Analysis
Taking 10kg sample of aggregate and obtained cumulative percentage retained.
Table 1.7: Sieve Analysis result
Sieve size (mm) % pass % retained Cumulative % retained
37.5 100 0 0
28 98.27 1.73 1.73
20 69.39 30.61 32.34
11
14 60.33 39.67 84.46
10 47.15 52.85 93.52
5 44.42 55.58 95.25
Pan - - 95.25
Figure 1.7: gradation graph for asphalt binder
The “S” shape of the graph indicates that, it is well graded that contains proportional ratio of
coarse and fine aggregate.
D. Marshal Test
A number of 16 samples each of 1000 gm. in weight were prepared using 4 different bitumen
contents (from 4 – 5.5% with 0.5 % incremental) in order to obtain the optimum bitumen
content.
Table 1.8: Aggregate Characteristics
Aggregate type Percent by weight (%) Bulk specific gravity
Coarse 45 2.67
Fine 35 2.74
Filler 20 2.69
Mixing the above proportion of aggregate with asphalt bitumen and preparing a mold
compacting with 75 numbers of blows for heavy traffic, obtained the following result:
0
20
40
60
80
100
120
0 2 4 6 8
cum
mu
lati
ve (
%)
sieve size (mm)
sieve analysis
12
7
7.5
8
8.5
9
9.5
10
4 4.5 5 5.5 6
stab
lity
(K
N)
% bitumen
Stablity (KN)
Table 1.9: Properties of bituminous mix before adding waste plastic for 60/70 grade bitumen
Bitumen
%
(By total
weight)
Stability
(KN)
Flow
(mm)
Gbcm
(g/cm3)
VA (%) VMA (%)
4 7.6 10.16 2.43 3.57 13.6
4.5 9.2 10.84 2.46 3.14 12.98
5 9.3 12.8 2.46 3.17 14.14
5.5 7.8 14.4 2.44 2.42 14.95
Figure 1.8: stability Vs bitumen content
Figure1.9: Flow Vs bitumen content
9
10
11
12
13
14
15
3.5 4 4.5 5 5.5 6
flo
w (
mm
)
% bitumen
flow(mm)
13
Figure 2: Bulk density Vs bitumen content
Figure2.1: VMA Vs bitumen content
Figure2.2: air void Vs bitumen content
E. Determination of Optimum Bitumen Content
Bitumen content at the highest stability=4.8%
Bitumen content at highest bulk density=4.6%
Bitumen with allowed air void=5%
Then, the OBC= (4.8%+4.6%+5%)/3=4.8%
2.425
2.43
2.435
2.44
2.445
2.45
2.455
2.46
2.465
3.5 4 4.5 5 5.5 6
bu
lk d
ensi
ty o
f th
e m
ix(G
bcm
)
% bitumen
Gbcm(g/cm3)
12.5
13
13.5
14
14.5
15
15.5
3.5 4 4.5 5 5.5 6
volu
me
of
min
eral
ag
gre
gate
% bitumen
VMA
2
2.5
3
3.5
4
3.5 4 4.5 5 5.5 6
% a
ir v
oid
% bitumen
Air void
14
Table 2: Properties of bituminous mix after adding waste plastic for 60/70 grade bitumen
Plastic %( by
weight of
OBC)
OBC (%) Stability
(KN)
Flow
(mm)
Gbcm
(g/cm3)
VA (%) VMA (%)
0 4.8 8.00 11.98 2.440 3.16 12.36
5 4.8 8.8 9.875 2.453 3.07 13.460
10 4.8 11.8 8.98 2.443 3.09 13.814
15 4.8 12.8 8.63 2.444 3.06 12.830
20 4.8 11.20 8.20 2.441 3.00 12.260
Figure 2.3: stability Vs plastic content
Generally, the stability of modified asphalt mixes is higher than the conventional asphalt mix.
All the values of stability for different modifier percentages are higher than stability of
conventional mix. The maximum stability value is found nearly 12.8 KN at plastic content of
around 15%.
The improvement of stability in plastic modified asphalt mixes can be explained as a result of
the better adhesion developed between bitumen, plastics and aggregates due to intermolecular
bonding, these intermolecular attractions enhanced strength of asphalt mix, which in turn help
to enhance durability and stability of the asphalt mix.
0
2
4
6
8
10
12
14
0 5 10 15 20 25
stab
ilit
y(K
N)
% of plastic waste
stability
15
Figure 2.4: Flow Vs plastic content
Generally, the flow of modified asphalt mix is lower than the conventional asphalt mix. The
graph shows that the flow decreases continuously as the plastic modifier content increase.
Figure 2.5: Bulk density of plastic modified Vs %plastic content
The general trend shows that the bulk density of plastic modified decreases as the plastic
content increase. This decrease of bulk density can be explained to be as a result of the low
density of added plastic material.
0
2
4
6
8
10
12
14
0 5 10 15 20 25
Flow(mm)
2.438
2.44
2.442
2.444
2.446
2.448
2.45
2.452
2.454
0 5 10 15 20 25
bulk
den
sity
(g/c
m3)
% plastic wastes
Bulk density (g/cm3)
16
Figure 2.6: Air void Vs plastic content
In general, the air voids proportion of modified asphalt mixes is higher than
conventional asphalt mix. From the graph as the percentage of plastic increases
the air void is gradually decreasing. Generally modified asphalt mixes have air
void content within specifications range.
Figure 2.7: VMA Vs plastic content
Generally, the VMA of plastic modified is lower than conventional asphalt. The
graph indicates that, as the plastic content increase the VMA also increases still
it reaches the peak point 13.81% VMA then gradually decrease.
2.98
3
3.02
3.04
3.06
3.08
3.1
3.12
3.14
3.16
3.18
0 5 10 15 20 25
air
vo
id(%
)
% plastics
Air void(%)
12
12.2
12.4
12.6
12.8
13
13.2
13.4
13.6
13.8
14
0 5 10 15 20 25
VMA(%)
17
F. Determination of Optimum Modifier Content
A set of controls is recommended in order to obtain the optimum modifier content that
produce an asphalt mix with the best mechanical properties. Asphalt mix with optimum
modifier content satisfies the following.
Maximum stability
Maximum bulk density
VA % within the allowed range of specifications.
Table 2.1: Summery Of Optimum Modifier Content
Property Optimum plastic wastes in percentage
Maximum stability 15%
Maximum bulk density 15%
Air void with allowed range 4.5%
The optimum plastic content is the average of the three properties.
OPWC= (15%+15%+4.5%)/3=11.5%
G. Stability Comparison of Bitumen Content with Plastic Modified
Content
From the stability table for 11.5% of plastic modifier is 12.8KN and for 4.8% of conventional
bitumen is 9.30KN. There for, the stability of plastic modified mix in %=( 12.8KN-
9.3KN)/12.8KN*100=25%, this means the stability of plastic modified mix is 25% higher
than conventional bitumen mix.
H. Cost Analysis
For the following parameter of a road section:
Width of road=7m
Length of road =1Km
Thickness of road=7cm
Data obtained from analysis
Density of modified asphalt mix=2.45gm/cm3
Optimum plastic waste content=11.5%(by weight of optimum bitumen content)
Optimum bitumen content=4.8%
Data obtained (source from high-way engineers in ERA)
Cost of 1Kg plastic waste=3birr
Cost of 1Kg of bitumen=33.33birr
18
Asphalt needed for 1m3 road section=47.36Kg
I. Calculations
The amount of plastic material needed=Optimum waste plastic*density*volume of road
section
=0.115*2.45*0.07*1000*7=56350Kg of plastics
Weight of optimum plastic content=11.5 %( by weight of bitumen content)
56350Kg=0.115*weight of bitumen
Weight of bitumen=490000Kg
Total weight of plastic and asphalt =490000+56350=546350Kg
Cost of 1Kg of plastic=3birr*56350=169050birr/Kg
Cost of the shredding machine (for plastic) =30000birr
Cost of 1Kg bitumen =490000*33.33birr=16331700birr/Kg
Total cost of asphalt and plastic mixed=16331700+169050+30000birr=16530750birr/Kg
Total cost when, 100% asphalt used =546350*33.33=18209845.5birr/Kg
Therefore the cost difference between plastic modified asphalt and asphalt only
% difference in cost= (18378895.5-16530750)/18378895.5*100=10.06%
19
VI. CONCLUTION
A. Stability
Plastic modified asphalt mix has 25% higher stability value compared to the conventional
asphalt mix. The improvement of stability in plastic modified asphalt mixes can be explained
as a result of the better adhesion developed between bitumen, plastics and aggregates due to
intermolecular bonding, these intermolecular attractions enhanced strength of asphalt mix,
which in turn help to enhance durability and stability of the asphalt mix.
B. Cost Reduction
Plastic modified asphalt mix has 10.06% lower in cost than the conventional asphalt mix.
C. Optimum Plastic Content
The optimum amount of waste plastic to be added as a modifier of asphalt mix was found
11.5 % by weight of optimum bitumen content. And the optimum bitumen content found for
marshal mix was 4.8%.
D. Softening Point
The temperature resistance of plastic modified asphalt is higher than the conventional asphalt
(63.55⁰c>55.55⁰c) due to the rigid property of plastic.
E. Plastic Management
Due to plastics are utilized within bituminous mixes as road construction materials,
environmental pollution caused by plastics is solved.
VII. AKNOWLEDGMENT
First of all we would like to thank our almighty God for providing us to courage and to carry
out this research. Also we thank for Ethiopian road authority which invite us to participating
in road and research 3rd
annual conference.
20
VIII. REFERENCE
[1] ERA Manual, Flexible road pavement volume 1, A.A, 2002.
[2] American assosation of state high and transportation officials, Washigiton ,DC., 1993.
[3] J. SH, Highway engineering structural design, Palestine: Dar El- manara library, 2000.
[4] M. Sadd, Micro structural Simulation of Asphalt material, paelsetaine: Jourals of materials in
civil engineering, 2014.
[5] Chen, Evalution of rutting performance on hot mix asphalt modified with plastic bottels, Malasia,
2009.
[6] Awwad ,M and Shabeeb, "Use of polyethele in hot mix asphalt mixtures," American journal of
appiled science, pp. 390-396, 2007.
[7] Al-Hadidy,A & Tan, The effect of plastomers polymer type and concentration on asphalt and
moisture damage of SMMA mixture, Al-Rafidain Engineering Journal, 2011.
[8] Giriftinoglu, "The use of plastic waste matreials in asphalt pavment," Turky, 2007.
[9] P. Soyal, 07 oct 2015. [Online].
[10] M. A. J. Chavan, "International Journal of application or innovation in engineering and
managment," 4 April 2013. [Online].