UNIVERSITY OF NAIROBI

AN INVESTIGATION OF THE PROPERTIES OF CONCRETE CONTAINING GRANULATED PLASTIC BOTTLE

WASTE AS A PARTIAL REPLACEMENT OF FINE AGGREGATES

BY

MUSILU JUDITH MALI

F16/2292/2009

SUPERVISOR: DR. (ENG) JOHN MWERO

A project submitted as a partial fulfillment of the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2014

1

ABSTRACT

Solid waste is one of the major environmental issues facing our country today. This study is

focused on the use of granulated plastics as a partial replacement of fine aggregates in concrete.

The aim was to investigate the characteristics of concrete with the addition of plastic and

comparing it with the control, thereby determining the advantages and disadvantages of doing

so.

In the lab concrete was mixed, cast, cured and tested. The fresh concrete was tested for slump

test and the compaction factor test, while the hardened concrete for compressive, tensile and

flexural strength. There were four batches, the control and 10%, 30% and 50% weight

replacement of sand with granulated plastic.

It was found that addition of plastic in concrete resulted in the formation of lightweight concrete.

The compressive, tensile, flexural strength of concrete reduced with the addition of plastic.

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DEDICATION

I dedicate this research work to the Almighty God who has brought me this far. To my parents

who continually gave to me love, moral and financial support to undertake my studies. You have

indeed helped me come this far. God bless you.

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ACKNOWLEDGEMENT

To the Almighty God for His strength, provision and protection during this project period. Special

thanks to my supervisor Dr. (Eng.) John Mwero, for the guidance, support and advice. His

comments and suggestions during the preparation of this project are gratefully acknowledged.

Further appreciation goes to the concrete laboratory technicians, Mr. Muchina and Mr. Martin

among others for guidance and assistance during the laboratory work period of this project.

To my good friends among them Sunday, Mwangi, Mevys and Bush for their encouragement.

Lastly, I would like to appreciate my family for their continuous prayers during the whole period

of my study.

To all I say thank you and may God bless you.

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Table of Contents

ABSTRACT……………………………………………………………………………………………………………………………………………….1

DEDICATION……………………………………………………………………………………………………………………………………………2

ACKNOWLEGMENT…………………………………………………………………………………………………………………………………3

TABLE OF CONTENTS…………………………………………………………………...............................................................4

LIST OF FIGURES……………………………………………………………………………………………………………………………………..7

LIST OF TABLES……………………………………………………………………………………………………………………………………….8

LIST OF PLATES……………………………………………………………………………………………………………………………………….9

CHAPTER 1 .............................................................................................................................................. 10

1.0 INTRODUCTION ................................................................................................................................ 10

1.1 Background ....................................................................................................................................... 10

1.2 Problem statement .......................................................................................................................... 11

1.3 Objectives ......................................................................................................................................... 11

1.3.1 Main objective. .............................................................................................................................. 11

1.3.2 Specific objectives ......................................................................................................................... 11

2.0. LITERATURE REVIEW ....................................................................................................................... 12

2.1 Introduction ...................................................................................................................................... 12

2.2 Plastic ................................................................................................................................................ 12

2.2.1 Types of plasic ........................................................................................................................ 12

2.2.3. Properties of plastic ............................................................................................................... 14

2.2.4. Waste plastic and its sources ................................................................................................. 15

2.2.5 Recycling of plastic ................................................................................................................. 15

2.2.6. Recycling methods and construction applications ................................................................ 16

2.3 Advantanges and disadvantages of using plastics .......................................................................... 17

2.4 Concrete ............................................................................................... Error! Bookmark not defined.

2.4.1 Constituents of concrete ............................................................................................................... 18

2.4.2 Curing ............................................................................................................................................. 19

2.4.3 Testing ........................................................................................................................................... 19

2.5 Previous research ............................................................................................................................. 20

2.5.1 Fresh concrete properties ............................................................................................................. 20

2.5.1.1 Workability ................................................................................................................................. 20

5

2.5.1.2 Density of concrete .................................................................................................................... 22

2.5.2 Hardened concrete properties ...................................................................................................... 22

2.5.2.1 Dry density ................................................................................................................................. 22

2.5.2.2 Compressive strength ................................................................................................................ 22

2.5.2.3 Tensile strength .......................................................................................................................... 25

2.5.2.4 Flexural strength ........................................................................................................................ 25

2.6 Information gap ................................................................................................................................ 26

3.0 METHODOLOGY ................................................................................................................................ 27

3.1 Material collection and preparations .............................................................................................. 27

3.1.1 Plastic ............................................................................................................................................. 27

3.1.2 Laboratory test of Particle Size Distribution of aggregates – (BS 812) ........................................ 28

3.1.3 Fine aggregates ............................................................................................................................. 29

3.1.3.1 Sieve Analysis and Grading of fine aggregates ......................................................................... 29

3.1.4 Coarse aggregates - (BS 882: 1992) ............................................................................................... 29

3.1.5 Determination of specific gravity and water absorption of plastic aggregates (BS 812: PART 107)

................................................................................................................................................................ 30

3.2 Concrete test equipment ........................................................................................................... ……30

3.2.1 Moulds ......................................................................................................................................... 300

3.2.2 Slump test equipment ................................................................................................................. 300

3.2.3 Compacting factor apparatus ....................................................................................................... 31

3.2.4 Compression Test Machine .......................................................................................................... 31

3.3 Batching ............................................................................................................................................ 32

3.3.1 Preparations of test samples ........................................................................................................ 32

3.3.2 Casting - (BS 1881 – 108:1983) ...................................................................................................... 32

3.3.3 Curing - (BS 1881 – 111:1983) ....................................................................................................... 33

3.4 Fresh concrete .................................................................................................................................. 33

3.4.1 Slump test ...................................................................................................................................... 33

3.4.2 Compacting factor test - (BS 1881 - 103:1983) ............................................................................. 34

3.5 Hardened concrete ........................................................................................................................... 35

3.5.1 Density - (BS 1881 - 107:1983) ...................................................................................................... 35

3.5.2 Compressive strength test - (BS 1881 - 116: 1983) ...................................................................... 36

3.3.4 Flexural strength test (BS 1881 - 107:1983) ................................................................................. 38

4.0 RESULTS AND DISCUSSION............................................................................................................... 40

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4.1 sieve analysis .................................................................................................................................... 40

4.1.2 Sieve analysis results of plastic particles ...................................................................................... 41

4.1.3 Sieve analysis results for coarse aggregates ................................................................................ 44

4.2 Specific gravity results...................................................................................................................... 46

4.3 Workability ....................................................................................................................................... 46

4.3.1 Slump test (BS 1881: Part 102) ..................................................................................................... 46

4.3.2 Compaction factor test……………………………………………………………..……………………………………………..47

4.4 Dry Density ....................................................................................................................................... 48

4.5 Compressive strength ...................................................................................................................... 50

4.6 Tensile strength……………………………………………………………………………………………………………………………53

4.7 Flexural strength .............................................................................................................................. 55

5.0 CONCLUSION AND RECOMMENDATION ......................................................................................... 57

5.1General .............................................................................................................................................. 57

5.2 Conclusion ........................................................................................................................................ 57

5.3 Recommendation ............................................................................................................................. 57

REFERENCES ............................................................................................................................................ 58

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LIST OF FIGURES

Fig. 4.1.1 particle distribution for sand ……………………………………………………………………………………41

Fig 4.1.2 Particle distribution for plastic particles…………………………………………………………………….43

Fig 4.1.3 particle distribution for coarse aggregates…………………………………………………………………45

Fig. 4.2 slump in (mm) against percentage replacement of sand with plastic particles in

concrete……………….………………………………………………………………………………………………………………….47

Fig 4.3.1 cube dry density against percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..48

Fig 4.3.2 cylinder dry density against percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..49

Fig 4.4.1 7days compressive strength vs percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..51

Fig 4.4.2 28days compressive strength vs percentage replacement of sand with plastic particles

in

concrete…………………………………………………………………………………………………………………………………..51

Fig 4.4.3 compressive strength ratio depending on age of concrete, age 1 and 2 represent 7days

and 28days respectively…………………..………………………………………………………………………………….…..52

Fig 4.5.1 7days tensile split strength vs percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..53

Fig 4.5.2 28days tensile split strength vs percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..54

Fig 4.5.3 split tensile strength ratio depending on the age of concrete, age 1 and 2 represent

7days and 28days respectively…………………..…………………………………………………………………………….54

Fig 4.6 flexural strength vs percentage replacement of sand with plastic particles in

concrete…………………………………………………………………………………………………………………………………..56

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LIST OF TABLES

Table 2.1 Cone Slump test results(Al-manaseer and Dalal 1997)………………………………………………20

Table 2.2 Mixture proportions and slump test results (Batayneh et al, 2007)…………………………..21

Table 2.3 Compressive strength of hardened concrete results (Choi et at 2005)………………………23

Table 2.4 Percentage reduction in compressive strength vs percentage plastics for different water

content (Ghaly et al 2004)………………………………………………………………………………………………………..24

Table 3.3.1 Batch mix proportions…………………………………………………………………………………………….32

Table 4.1.1 Sieve analysis results for sand…………………………………………………………………………………40

Table 4.1.2 Particle distribution for plastic particles………………………………………………………………….42

Table 4.1.3 particle size distribution for coarse aggregates……………………………………………………….44

Table 4.1.4 Determined specific gravity and water absorption………………………………………………….46

Table 4.2.1 Slump test results……………………………………………………………………………………………………46

Table 4.2.2 Compaction factor test results………………………………………………………………………………..47

Table 4.3 Determined dry density…………………………………………………………………………………………….48

Table 4.4 Determined compressive strength…………………………………………………………………………….50

Table 4.5 Variation of split tensile strength due to replacement of sand with plastic particles……53

Table 4.6 Flexural strength……………………………………………………………………………………………………….55

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LIST OF PLATES

Plate 3.1 Granulated plastic particles used for testing……………………………………………………………..27

Plate 3.2 compaction factor apparatus and the Determination of the slump respectively………..35

Plate 3.3 Cube crushing for the determination of compressive strength………………………………….36

Plate 3.4 Cylinder for the determination of the tensile split strength……………………………………….37

Plate 3.5 Cylinder for the determination of the tensile split strength……………………………………….38

Plate 3.6 Dial gauge reading for the flexural Load…………………………………………………………………….39

Plate 3.7 sieves…………………………………………………………………………………………………………………….…..40

Plate 4.1 Hourglass failure mode concrete cube…………………………………..……………………………………50

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CHAPTER 1

1.0 INTRODUCTION

1.1 Background

In Kenya, most industrial and domestic activities are associated with significant amounts of non-

biodegradable solid waste, which include a wide range of plastic waste. The research study to be

undertaken intended to determine the efficiency of reusing waste plastic in production of

concrete.

Utilization of these waste materials is a partial solution to environmental and ecological

problems. Use of plastic not only helps in getting them utilized in concrete, it helps in reducing

the cost of concrete making, numerous indirect benefits such as reduction landfill cost, saving

energy, and protecting the environment from possible pollution effects.

At a time when landfill space is becoming almost impossible due to increasing land value, then

recycling and reuse of wastes as beneficial products should be strongly encouraged and

examined. One potentially strong and viable market is to develop recyclable wastes into granular

aggregates, a common material used throughout the construction industry. The reuse of waste

materials in building construction is a great idea, and the high demand for construction materials

makes them a favorable medium in which to reuse recyclable materials.

Aggregates are used in a variety of building applications, and can be said to be the largest quantity

of material used in any industry. Almost all aggregates are produced from natural resources such

as gravel pits, river beds and rock quarries. In addition to depleting these natural resources,

mining for aggregates also poses serious environmental risks like disturbance of natural habitats

and creating open areas with no vegetation.

Most concrete structures are produced using normal weight aggregates. However there are

certain instances where light weight concrete is desirable, raising the need for partial or total

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replacement of the aggregate with a lighter substitute. Plastic recycling efforts have increased

but are still insufficient. The preferred plastic material for use as an aggregate should be available

in large quantities such as post-consumer wastes which has little or no resale value.

In Kenya, there is a great strain placed on the environment at the moment, specifically by waste

plastic. A very small percentage of it is recycled, probably due to lack of investment or a low

demand for recycled plastic waste. As a result, most of it usually ends up dumped in landfills, or

just burned. The effect of such actions on the environment is degrading, at a time when the world

is focusing its efforts on tackling pollution and environmental issues such as global warming.

The evolution of concrete mix production has taken massive steps over the years. During this

period, various types of aggregates have been used. The major role of aggregates in concrete is

to provide strength. In instances where light weight concrete are required, a lighter aggregate

made from plastic can be adopted.

1.2 Problem statement

The cost of construction materials has been increasing and the ever-present problem of plastic

waste requires an urgent and efficient solution. The use of waste plastic as an aggregate

substitute in concrete will give a good approach to reduce the cost of materials and solve some

of the solid waste problems posed by plastics.

1.3 Objectives

1.3.1 Main objective.

To investigate the properties of concrete when waste plastics in granulated form is used as partial

replacement of fine aggregates in concrete.

1.3.2 Specific objectives

• To study the material (concrete constituents and plastic particles) characteristics.

• To study the characteristics of Concrete with plastic as fine aggregates.

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CHAPTER 2

2.0 LITERATURE REVIEW

2.1 Introduction

Concrete is defined as a mixture of cement, water and aggregates in which the cement and water

combine to act as a binder to hold the aggregate particles together into a plastic mixture. The

mixture of water and cement results in a chemical exothermic reaction called hydration as

concrete changes from plastic to a solid state, in a process called curing. It has been observed

that concrete continues to gain strength as it cures.

2.2 Plastic

Plastic entails of substances that have plasticity, and also those formed in a soft state and used

in a solid state. The origin of plastic is traced back to the processing methods of natural polymers

such as horns, tusks and amber as well as substances like clay, glass and metals. The natural

polymers are not uniform in quality and lack adequate productivity due to their scarcity. Hence

the need to process plastics easily, faster and in better quality, artificial materials are used to

replace the natural polymers. These artificial materials are celluloid, synthetic rubber, rayon, and

ebonite.

2.2.1 Types of plastic

Plastics can be classified in many ways, but most commonly by their physical properties. Plastics

may be classified also according to their chemical sources. There are twenty or more known basic

types which fall into six general groups:-

1. Cellulose Plastics

2. Synthetic Resin Plastics

3. Protein Plastics

4. Natural Resins

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5. Elastomers

6. Fibers

They can also be classified depending on their physical properties, as thermoplastic and

thermosetting materials. Thermoplastic materials can be formed into desired shapes under heat

and pressure and become solids on cooling. If they are subjected to the same conditions of heat

and pressure, they can be remolded. They include; polyethylene, polyamide, polyoxymethylene,

polypropylene, polyethylene terephthalate, and polytetrafluorethylene.

Thermosetting materials those that once shaped cannot be softened or remolded by the

application of heat. This is because their molecular chains are bonded together by firm meshed

crosslinks. This type include; phenolic, melamine, unsaturated polyester, epoxy resin, silicone

and polyurethane. It is disposed off by either burning or burying, which are quite costly processes.

To save the environment from pollution especially the one caused by the burning process and

also to reduce the cost of waste management efforts the reuse of thermosetting plastics is put.

To achieve this, they are being applied as construction materials where light weight concrete is

produced. They are used for interior and exterior walls of buildings, and for walls not designed

for lateral loads.

The types of plastics which are mostly used are:-

1. Polyethylene Terephthalate (PET)

2. High Density Polyethylene (HDPE)

3. Polyvinyl chloride (PVC)

4. Low density Polyethylene (LDPE)

5. Polypropylene (PP), Polystyrene (PS)

Among them, HDPE and LDPE produces major share of volume in post-consumer plastic waste.

14

2.2.3. Properties of plastic

Plastic is a non-biodegradable material and researchers found that the material can remain on

earth for 4500 years without degradation.

Plastic characteristics that make it a good material in concrete production and other building

activities include:-

a) Not easily biodegradable/ durability - This property shows that plastic can be used as an

inert matter in cement matrix.

b) Versatility - Plastic can be used in many areas in the industry. It is capable of being used

in many different situations. This makes it an economically attractive choice.

c) Lightness - Plastic is very light in terms of weight.

d) Hardness - Plastic is made up of strongly bond together particles that make it hard to

break.

e) Low linear dilation coefficient

f) Good chemical resistance

g) High heat resistance

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2.2.4. Waste plastic and its sources

Low Density Polyethylene (LDPE)

Carry bags, sacks, milk pouches, bin lining, cosmetic and detergent bottles.

High Density Polyethylene (HDPE)

Carry bags, bottle caps, house hold articles etc.

Polyethylene Teryphthalate (PET)

Drinking water bottles etc.,

Polypropylene (PP)

Bottle caps and closures, wrappers of detergent, biscuit, vapors packets, microwave trays

for readymade meal etc.,

Polystyrene (PS)

Yoghurt pots, clear egg packs, bottle caps. Foamed

Polystyrene

Food trays, egg boxes, disposable cups, protective packaging

Polyvinyl Chloride (PVC)

Mineral water bottles, credit cards, toys, pipes and gutters; electrical fittings, furniture,

folders and pens, medical disposables.

2.2.5 Recycling of plastic

Recycling is the process of recovering used materials from waste and incorporating them into the

manufacturing process.

Recycling is a critical issue in this environmental conscious times.

It aims to:-

• Preserve natural resources

• Minimize transportation and its associated cost

• Reduce the environmental load caused by waste material especially land requirement

16

Since plastic products do not decompose in landfill and are difficult to reduce in size, the need to

recycle plastic is clear even though the whole process is faced with technological and economic

constraints that limit its efficiency to convert plastic waste into useful products.

2.2.6. Recycling methods and construction application

Prior to using plastics in concrete it is recycled through some modification and process techniques

which includes:-

a. Mechanical technique

This refers to the processes which involve melting, shredding or granulation of the plastics. The

plastics are sorted out before mechanical recycling. This can be done manually by hand picking

or by sorting out automatically by a technology being introduced such as the use of x-ray

fluorescence, infrared, electrostatics and flotation.

After the sorting out, the plastic is either melted, moulded or shredded into flakes and then

processed into granules which can be used to replace natural aggregates in concrete.

b. Chemical technique

Plastic can be recycled by depolymerization, which is done in two ways:-

• Hydrolysis – which involves chemical decomposition.

• Pyrolysis – which is thermal decomposition.

It is a relatively easy technique especially when the plastic contains single condensed polymers

for example urethanes, polyethylene terephthalate, nylon and many others. It is however

complicated when it comes to mixed plastics hence it becomes more difficult to recycle such

plastics to produce useful and economical product.

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c. Thermal reprocessing

This is a recycling process that involves heating the thermoplastic at very high temperatures until

it flows. Then it is converted to new products as it cools.

This method does not change the chemical composition of the plastics e.g thermoplastic

polyester can be heated and reprocessed into fence posts, building panels, fibres for carpeting.

It however cannot be repeated since a repetitive of heating could affect the properties of plastic.

It is easy when applied to pure thermoplastics but cannot be applied to thermosets which cannot

melt at high temperatures without degrading.

In the case of mixed thermoplastics thermal reprocessing becomes more involving because it will

need either separation of the various plastics depending on the source of the waste or by use of

a special machine that takes into account the different thermal properties.

d. Fillers

Plastic waste can be used as filler in concrete and in road construction. When used in this case

chemical composition of the plastics is generally not very significant.

It is therefore an easy way to recycle thermosets or contaminated plastics. Plastic wastes can

hence be used as partial replacement of inorganic aggregates in concrete applications to reduce

the dead weight of structures. Recycled rubber can also be used in asphalt concrete mixes.

2.3 Advantages and disadvantages of using plastics

Advantages

Plastic has many beneficial properties, these include:-

• Extreme versatility and ability to be modified to meet specific technical needs.

• Lighter weight than other materials.

• Durability and not easy to fail.

• Resistance to chemicals, water and impact.

18

• Excellent thermal and electrical insulation properties.

• Lesser production cost compared to other materials.

• Superior aesthetic appeal.

• Ability to combine with other materials like adhesives.

• Reduction in solid wastes hence better use of land than landfills.

Disadvantages

The following are the main disadvantages of using plastic in concrete:-

• Plastic have low bonding properties so that the strength of concrete gets reduced such as

compressive, tensile and flexural strength.

• In high temperatures plastic gets melted because it has low melting point.

2.4 Concrete

2.4.1 Constituents of concrete

Cement

Cement is a material with adhesive and cohesive properties, which make it capable of bonding

mineral particles into a compact whole.

It is produced by mixing ground limestone, iron ore, alumina and silica. The mixture is heated in

a rotary kiln to temperatures of about 1600o C, which cause the material to break down and

recombine into new compound is called clinker. After cooling clinker is ground to a fine powder

now the cement.

Aggregates

Aggregate is granular material such as sand, gravel, crushed stone, and blast furnace slag that

usually occupies approximately 60-70% of the volume of concrete. It reduces volume changes

due to drying shrinkage of the cement-water paste.

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Aggregate properties affect workability of plastic concrete and the durability, strength, thermal

properties and density of hardened concrete. Aggregates can be classified as fine and coarse

aggregates depending on size and also as natural or artificial, with respect to source and method

of preparation.

2.4.2 Curing

Curing is a process that involves the maintenance of a suitable moisture content and temperature

in concrete for a suitable period of time immediately after placing and finishing so that desired

properties of concrete are achieved.

Since concrete produces a lot of heat due to the reaction of water and cement (hydration) curing

should be properly done to avoid cracking because of excess expansion of the particles. Hence

curing involves pouring of water to cool the surfaces of concrete and also covering to minimize

loss of the water through evaporation and effects of hydration.

2.4.3 Testing

During the preparation of concrete the amount of water used compared to the amount of cement

(water/cement ratio) should be carefully mixed. This ratio majorly indicates the strength of

concrete in that the lower it is the higher the final concrete strength. Although a minimum

water/cement ratio of 0.3 by weight is necessary so that all the cement particles are in contact

with water for complete hydration.

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2.5 Previous research

2.5.1 Fresh concrete properties

2.5.1.1 Workability

Effects of plastic as a partial replacement of sand on the workability of concrete

(Koehler and Fowler, 2003) The main property to check for in fresh concrete is its workability.

Workability is the ease with which concrete can be mixed, placed and finished easily without

segregation. Workability has a broad range from very low, having a slump of 0-25mm applied for

vibrated concrete in large sections to high workability of slump 100-180mm for sections with

congested reinforcement.

(Al-manaseer and Dalal 1997) determined the slump of concrete mixes made with plastic

aggregates. Their report showed that there was increase in slump when plastic aggregates were

added to concrete. Concrete with 50% plastic replacement of aggregates had a higher cone slump

than that without plastic aggregates. Their conclusion was that plastic aggregates did not absorb

or add any water to the concrete mix. Due to the not absorbing water characteristic of plastic

concrete containing plastic aggregates had more free water in the mix hence the increasing

slump.

Table 2.1 Cone Slump test results(Al-manaseer and Dalal 1997)

Plastic aggregates % Workability of w/c 0.5

0 55

10 45

30 50

50 50

(Choi et al 2005) researched on the influence of polyethylene terephthalate (PET) waste bottles

as lightweight aggregate (WPLA) on the workability of concrete. Water-cement ratios were in the

21

proportions 45%, 49% and 53% and the replacement ratios of WPLA were 0%, 25%, 50% and 75%

by volume of fine aggregate. Their report showed that waste PET bottles lightweight aggregate

concrete (WPLAC) slump value increased with increase in water-cement ratio and the

replacement ratio. The increase in workability represent 52%, 104%, and 123% comparing to that

of normal concrete at water-cement ratio of 45%, 49%, and 53% respectively. They therefore

concluded that this was because of the spherical and smooth shape and the non-absorption

characteristic of the waste PET bottles lightweight aggregate (WPLA).

(Batayneh et al, 2007) investigated the effect of ground plastic on the slump of concrete.

Concrete mixes of up to 20% of plastic particles are proportioned to partially replace the fine

aggregates. It was observed that there was a decrease in the slump with the increase in the plastic

content. In fact at the 20% replacement the slump decreased by 25% of the original slump value

with 0% plastic replacement. The decrease in slump value was attributed to the shape of the

plastic particles which had sharper edges than the fine aggregate. Besides plastic, glass and

crushed concrete was also used as replacement of aggregate.

Table 2.2 Mixture proportions and slump test results (Batayneh et al, 2007)

Plastic

replacement

%

Mix proportions (Kg/M3 ) Slump

(mm) Water Cement Coarse

aggregate

Fine

aggregate

Plastic Water

cement

0 252 446 961 585 0 0.56 78

5 252 446 961 555.7 17.8 0.56 73

10 252 446 961 526.5 35.5 0.56 69

15 252 446 961 497.2 53.2 0.56 63

20 252 446 961 468 71 0.56 57

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2.5.1.2 Density of concrete

For concrete the density is measured in three types, as bulk, fresh and dry densities.

Effects of plastic as a partial replacement of sand on the bulk density of concrete

The effect of plastic aggregates on the bulk density of concrete is that the bulk density reduces

with the increase in plastic aggregate content. This reduction is directly proportional to the plastic

aggregates content. The density reduced by 2.5%, 6%, and 13% for concrete having 10%, 30%

and 50% plastic aggregate respectively. It was concluded that this was due to the lower unit

weight of the plastics compared to natural aggregates.(Al- Manaseer and Dalal 1997).

2.5.2 Hardened concrete properties

2.5.2.1 Dry density

Effects of plastic as a partial replacement of sand on the dry density of concrete

Ismail and Hashmai (2007) studied that the dry density of each curing age tend to decrease with

increasing the waste plastic ratio in each concrete mixture, but the dry densities tend to increase

with age for each concrete mixture at all curing ages. The use of waste plastic for each curing age

reduces the dry densities of all mixtures with increasing the waste plastic ratio, because the

density of plastic is lower than that of sand by 69.7%.

2.5.2.2 Compressive strength

Effects of plastic as a partial replacement of sand on the compressive strength

(Choi et at 2005) Effects of polyethylene terephthalene PET bottles lightweight aggregate (WPLA)

on the compressive strength of concrete. The mixture proportions were as mentioned earlier

that water-cement ratios were in the proportions 45%, 49% and 53% and the replacement ratios

23

of WPLA were 0%, 25%, 50% and 75% by volume of fine aggregate. It was found out that the

compressive strength of concrete decreased with the increase in the amount of PET aggregates

and also that for a certain particular amount of PET aggregate the compressive strength increase

with a reduction in the water- cement ratio.

Table 2.3 Compressive strength of hardened concrete results (Choi et at 2005)

Water-cement ratio PET aggregate % Compressive strength (Mpa)

7days 28days

53 0 24 3.27

25 23.4 2.65

50 21.5 2.25

75 19.2 2.04

49 0 27.8 3.27

25 26.7 2.76

50 24.3 2.35

75 21.6 1.98

45 0 31.3 3.32

25 27.4 2.80

50 26.5 2.55

75 24.8 2.04

(Marzouk 2007) Did an experiment on the use of consumed plastic bottle waste as sand-

substituting aggregate within composite materials for building application. (PET) polyethylene

terephthalate were used as partial and complete replacement of sand in concrete composites.

Several volume percentages of sand from 2% to 100% were replaced by the same volume of

granulated plastic. The conclusion was that replacing sand at a level below 50% by volume with

granulated PET, whose upper granular limit equals 5mm, affected the compressive strength of

composites and plastic bottles shredded into small PET particles may be used successfully to

24

replace sand. The advantage of the composites was low cost material with consistent properties,

and also resolved solid waste problems created by plastics.

Batayneh et at (2007) He studied the reduction of strength in the addition of plastic particles. For

a 20% replacement, the compressive strength showed a sharp reduction up to 72% of the control

strength. For a 5% replacement the compressive strength reduces by 23%.(insert graph)

(Ghaly et al 2004) Researched on plastic chips used as a partial replacement of coarse aggregates

in concrete mixtures. Plastic aggregate were replaced by 5, 10, 15% by mass of coarse aggregates.

As the plastic content in the mix increases the lower the compressive strength of concrete.

Digital imaging of the concrete cube sections with plastic showed that the plastic were dispersed

in the concrete. It revealed that the reduction in compressive strength is directly proportional to

the area of plastic chips in the section.

Table 2.4 Percentage reduction in compressive strength vs percentage plastics for different water content (Ghaly et al 2004)

Water content % plastics % average area of

plastics

% reduction in

compressive strength

0.42 5 4.95 14.75

0.42 10 8.54 18.04

0.42 15 11.69 28.64

0.54 5 4.25 6.37

0.54 10 7.59 20.37

0.54 15 10.52 29.28

0.69 5 5.02 15.17

0.69 10 10.87 18.65

0.69 15 15.48 34.78

Naik et al (1996) Investigated the effect of post-consumer waste plastic in concrete as a soft filler.

The results showed lower compressive strength of the mix made with plastics compared with the

25

control. This was attributed to lower compressive strength of the plastic particles compared to

cementitious matrix as well as fine and coarse aggregates. It was also concluded that alkaline

bleach treatment of plastics is the best for compressive strength of concrete containing plastics.

2.5.2.3 Tensile strength

Effects of plastic as a partial replacement of sand on the split tensile strength

Al-Manaseer and Dalal(1997) researched on the effects of plastic aggregates on the splitting

tensile strength of concrete. They measured the strength of concrete at different water content

ratios and for various percentages of plastic aggregates. They concluded that the splitting tensile

strength decreased with the increase in plastic aggregates percentages, while for a given plastic

aggregate content, the splitting tensile strength was found to decrease when the water ratio was

increased. It was also found that concrete with plastic had a gradual failure and not the typical

brittle failure observed in conventional concrete. It was hence concluded that specimens

containing plastic aggregates are more capable of resisting the splitting load after failure without

full disintegration because the plastic content made them more ductile.

Batayneh et al (2007) observed that the splitting and flexural strength reduced due to the fact

that the strength of plastic particles is lower than that of the natural aggregates. Hence the use

of plastic particles and its percentage of replacement should be controlled to the allowable

strength of the structure under construction.

2.5.2.4 Flexural strength

Marzouk et al (2007) studied that the flexural strength of new composites decreased as the

volume of PET was increased.

Choi et al (2005) observed that the flexural strength of new composites decreases regularly with

the increase in percentage of plastics in concrete. For 50% replacement of aggregate by plastics,

the flexural strength is 32.8% of the control concrete.

26

2.6 Information gap

Previous studies have shown that plastic can only be used as a sand replacement in concrete only

in small percentage replacement. Research has shown that waste plastic particles when used as

a partial replacement of sand in concrete causes a decrease in dry density, compressive, tensile

split and flexural strengths. This research project presents a study on workability, compressive

strength and density variation, tensile split strength and flexural strength for increasing

percentage replacement of sand with plastic particles. More research on the same is required for

other concrete properties such as bleeding and segregation.

27

CHAPTER 3

3.0 METHODOLOGY

3.1 Material collection and preparations

3.1.1 Plastic

Samples of the waste granulated plastic particles mostly soda and water bottles, were collected

from a plastic collection company near the Dandora dump site, Nairobi. They were thoroughly

cleaned before use to ensure that the debris and other forms of impurities that could alter the

hydration and bonding of cement water paste are removed. At the laboratory, the plastic samples

were then sieved to ensure that they fit in the limit sieve requirements.

Plate 3.1 Granulated plastic particles used for testing

28

3.1.2 Laboratory test of Particle Size Distribution of aggregates – (BS 812)

The sieves used for making a sieve analysis conformed to BS 410. The tests were carried out in

accordance with the procedure given in BS 812. The objective of the test was;

(i) To determine the particle size distribution of plastic particle aggregates.

(ii) To draw grading curves for the aggregates specified.

The procedure involved arranging the test sieves from top to bottom in order of decreasing

aperture sizes with pan and lid to form a sieving column. The aggregate sample of 1kg by mass

was then poured into the sieving column and shaken thoroughly manually. The sieves were

removed one by one starting with the largest aperture sizes (top most), and each sieve shaken

manually ensuring no material is lost. All the material which passed each sieve was returned into

the column before continuing with the operation with that sieve.

The retained material was weighed for the sieve with the largest aperture size and its weight

recorded. The same operation was carried out for all the sieves in the column and their weights

recorded. The screened material that remained in the pan was weighed and its weight recorded.

Various masses were recorded on a test data sheet. The cumulative mass retained and passing

on each sieve is calculated as a percentage of the original dry mass.

The results of sieve analysis are represented graphically in charts known as grading curves/charts.

By using these charts, it is possible to see at a glance if the grading of a given sample conforms

to that specified or it is too fine or coarse or deficient on a particular size. In the curves, the

ordinates represent cumulative percentages passing and the abscissa the sieve sizes plotted in a

logarithm scale.

Grading is of importance as it affects the workability of concrete. The development of strength

corresponding to a given water/cement ratio requires full compaction and this can only be

achieved with a sufficiently workable mix. It is necessary to produce a mix that can be compacted

to a maximum density with a reasonable amount of work. The main factors governing the desired

aggregate grading are;

29

a) Surface area of aggregate. This determines the amount of water necessary to wet all the

solids/particles.

b) The relative volume occupied by the aggregate.

c) The workability of the mix. The aggregate must contain a sufficient amount of material

passing 300𝛍m sieve to improve workability.

d) The tendency to segregation. It is essential for the voids in the combined aggregate to be

sufficiently small to prevent the cement paste from passing through and separating out.

3.1.3 Fine aggregates

3.1.3.1 Sieve Analysis and Grading of fine aggregates

The sieve sizes in general used for particle size distribution of fine aggregates were 10, 5, 2.36,

1.18 mm and 600, 300,150 and 75μm. This test consisted of dividing up and separating by means

of a series of test sieves named here above, a material into several particle size classifications of

decreasing sizes. The mass of the particles retained on the various sieves was related to the initial

mass of the material. The cumulative percentages passing each sieve were reported in numerical

and graphical form.

3.1.4 Coarse aggregates - (BS 882: 1992)

Well graded natural coarse aggregates obtained from Ndarugu quarry near Juja. Aggregates

passing 19 mm sieve but retained in 10 mm sieve were used. The natural coarse aggregates were

further sieved in order to remove traces of quarry dust and other small particles.

The sieve sizes in general used for particle size distribution of coarse aggregates were 50, 37.5,

25, 19, 10, and 4.75 for coarse aggregate. The aggregates were collected approximately 2kg by

mass. The proportions of the different sizes of particles making up the aggregates are found by

sieving and are known as the 'grading' of the aggregates, the grading is given in terms of the

percentage by mass passing the various sieves. Continuously graded aggregates for concrete

contain particles ranging in size from the largest to the smallest.

30

3.1.5 Determination of specific gravity and water absorption of plastic aggregates (BS 812: PART

107)

The objective of the test was to determine the specific gravity of plastic aggregates. The test was

done using a pycnometer, funnel and the weighing balance machine.

The weight of a clean pycnometer was determined and recorded as WP.

10g of dry sample was placed in the pycnometer and the weight recorded as WPS.

Distilled water was added to fill the pycnometer to the mark, while making sure no air was being

trapped. The sample was allowed to soak for 10 minutes. The surface of the pycnometer was

wiped dry using a cloth and weighed. The weight was then recorded as WB.

The pycnometer was then emptied and cleaned. After which it was filled with distilled water only

upto the mark. It was the wiped dry and weighed. This weight was recorded as WA.

Specific Gravity = 𝑊𝑃𝑆−𝑊𝑃

(𝑊𝑃𝑆−𝑊𝑃)+(𝑊𝐴−𝑊𝐵) …equation 3.1

3.2 Concrete test equipment

3.2.1 Moulds

Iron moulds of 100mm x 100mm x 100mm were prepared where the concrete would be cast. Oil

was applied to the moulds before casting was done to act as a release agent. Demoulding was

done after 48 hours.

3.2.2 Slump test equipment

Slump test apparatus consisted of a metallic frustum of a cone 305 mm high and a base of 205

mm diameter placed on a smooth surface with the smaller opening of 102 mm diameter at the

top. The concrete was filled inside and each layer was tamped 25 times with a standard 16 mm

diameter steel rod. The inside surface was oiled to reduce friction.

31

3.2.3 Compacting factor apparatus

The apparatus consisted essentially of two hoppers, each in the shape of a frustum of a cone, and

one cylinder, the three being above one another. The inside surface was oiled to reduce friction.

3.2.4 Compression Test Machine

Compression test machine consisted of load platens where the compression load is applied.

There were dial gauges that recorded the compression load upon failure of the cube that depends

on the compressive strength of the cube to be tested.

32

3.3 Batching

3.3.1 Preparations of test samples

Weight batching method was used and four batches were obtained. Mass substitution of sand

with plastic particles was made at percentages of 0%, 10%, 30% and 50% for the four batches

respectively. The water content was kept constant for all the batches. Mix ratio adopted was

class 25 of (1:1.5:3).The following table outlines the mix proportions by mass of each batch.

Table 3.1.1 Batch mix proportions

%

Replacement

Sand ( kg ) Cement (kg) Coarse

aggregates (kg)

Plastic

particles(kg)

0 14 9 28 0

10 12.6 9 28 1.4

30 9.8 9 28 4.2

50 7 9 28 7

3.3.2 Casting - (BS 1881 – 108:1983)

The specimens were cast in iron moulds of 100mm cubes, 150mm diameter by 300mm height

cylinders and timber beams of 100mm by 100mm by 500mm. This conforms to the specifications

of BS 1881:1983. The moulds were cleaned and oiled on their inside surfaces first in order to

prevent sticking of concrete on the surfaces. The moulds were then assembled and bolts and nuts

tightened to prevent leakage of the plastic concrete mix.

After preparing trial mixes, the moulds were filled with concrete in three layers, each layer being

compacted using a vibrating table to remove as much entrapped air as possible and to produce

33

full compaction of concrete without segregation. The moulds were filled until the concrete

overflowed and excess concrete removed by cutting across the surface of the mould. Surface

finishing was then done using a trowel. The test specimens were then left in the moulds

undisturbed for 48 hours and protected against shock, vibration and dehydration at a

temperature of about 20°C.

3.3.3 Curing - (BS 1881 – 111:1983)

The specimens were removed from the moulds and marked with details of; type of mix, date of

casting, duration for curing and the determined crushing date, using a water proof marker then

placed in water of temperature about 200C such that they were completely submerged. Some

samples were cured for 7days and others 28days so as to determine how the duration of curing

would affect strength of concrete. Curing took place by hardening of the concrete. The

temperature controlled the rate of progress of the reactions of hydration and consequently

affected the development of strength of concrete.

3.4 Fresh concrete

3.4.1 Slump test

The slump test is used to determine variations in the uniformity of mix of given proportions. The

objective of the test was to determine slump of fresh concrete mix.

The apparatus used were;

A standard mould which is a frustum of a cone complying with BS 1881 – 102: 1983

A standard flat base plate preferably steel.

A standard tamping rod.

Standard graduated steel rule from 0 to 300mm at 5mm intervals.

A scoop approximately 100mm wide.

The procedure of the test involved cleaning and oiling the inside surfaces of the mould to prevent

sticking of fresh concrete on the surfaces of the mould. The mould was placed on the base plate

34

and held. It was then filled with fresh concrete in three layer with each layer compacted with 25

strokes of the tamping rod. When filled, the top surface was struck off using a straight blade.

The cone was then slowly lifted and removed leaving the moulded concrete unsupported. Then

its height was measured. The difference between that height and that of the cone was recorded

as the slump.

3.4.2 Compacting factor test - (BS 1881 - 103:1983)

The objective of the test was to measure the compacting factor of the concrete.

The apparatus used were;

Compacting factor apparatus

Tamping rod

Weighing balance

The upper hopper of the compacting apparatus was filled with fresh concrete and the bottom of

the hopper released open to allow the concrete fall down to the lower hopper. The bottom

hopper was released opened to allow concrete to fall into the cylinder.

The excess concrete was cut across the top of the cylinder and the net mass of the concrete in

the cylinder was determined. The cylinder was emptied and then refilled and placed in a vibrating

table so as to compact it and then the weight of the compacted concrete measured. The

compacting factor is then calculated as follows;

Compacting factor = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑎𝑙𝑙𝑦 𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑐𝑜𝑛𝑐𝑟𝑒𝑡𝑒

𝑀𝑎𝑠𝑠 𝑜𝑓 𝑓𝑢𝑙𝑙𝑦 𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑐𝑜𝑛𝑐𝑟𝑒𝑡𝑒

…equation 3.2

35

Plate 3.2 Compaction factor apparatus and the determination of slump respectively

3.5 Hardened concrete

3.5.1 Density - (BS 1881 - 107:1983)

The test was done to determine the density of hardened concrete after 7days and 28 days. The

procedure involved measuring the weight of the cubes after their curing period. The dry cured

specimens were placed on a weighing machine and their masses recorded. The volume of the

cubes was known since the standard 100mm x100mm x 100mm cubes were used and that of the

cylinder was 150mm diameter by 300mm height. The density of the concrete for each plastic

replacement was then calculated as;

Density = 𝑚𝑎𝑠𝑠

𝑣𝑜𝑙𝑢𝑚𝑒

…equation 3.3

36

3.5.2 Compressive strength test - (BS 1881 - 116: 1983)

After curing the cubes, cylinders and beams for 7days and 28 days periods, they were uncovered

in readiness for compression and tensile tests. The cubes were then placed with the cast faces in

contact with the platens of the testing machine that is the position of the cube when testing

should be at right angle to that of casting. The load was then gradually applied until failure

occurred. i.e the cube crashed.

Plate 3.3 Cube crushing for the determination of compressive strength

37

3.5.3 Tensile split test (BS 1881 - 107:1983)

The cylinder was placed in a position that the line of connection formed by the mould was in line

with the load application line as shown in the plate below. The load was then applied until failure.

Plate 3.4 Cylinder for the determination of the tensile split strength

38

Plate 3.5 Cylinder for the determination of the tensile split strength

3.3.4 Flexural strength test (BS 1881 - 107:1983)

The beam on the other side was placed such that the distances to each support were equal and

it was simply supported. The load was then applied gradually to failure. The readings were taken

from the dial gauge shown below.

39

Plate 3.6 Dial gauge reading for the flexural Load

40

CHAPTER 4

4.0 RESULTS AND DISCUSSION

4.1 sieve analysis

4.1.1 Sieve analysis for sand

Plate 3.8 BS 410 Sieves

Table 4.1.1 Sieve analysis results for sand

Sieve size

(mm)

Mass retained

(g)

% mass

Retained

% cumulative mass

Passing

4.75 0.0 0 100.00

2.38 11.08 5.54 94.46

1.18 20.98 10.49 83.97

0.6 56.26 28.13 55.39

0.3 71.72 35.86 19.53

0.15 13.62 6.81 12.27

0.075 25.44 12.72 0.45

Pan 0.90 0.45 0.0

41

Fig. 4.1.1 particle distribution for sand

Sand used for the study is within the limits of BS 882-1992. Its grading curve is in the envelope of

maximum and minimum curves as shown in Fig 4.1.1 above.

42

4.1.2 Sieve analysis results of plastic particles

Table 4.1.2 Particle distribution for plastic particles

Sieve size (mm) Retained mass

(gm)

% Retained (%) Cumulative passed

percentage (%)

10 0 0 100

4.75 17.00 8.5 91.5

2.38 58.80 29.4 62.1

1.18 57.60 28.8 33.3

0.6 28.98 14.49 18.81

0.3 28.56 14.28 4.53

0.15 3.24 1.62 2.91

0.075 2.93 1.46 1.45

Pan 2.72 1.40 0

43

Fig 4.1.2 Particle distribution for plastic particles

The granulated plastic particles used for this study conform to the requirements BS 882-1992.

Their grading curve is within the grading envelop of good fine aggregates although they were

coarser than sand as the curve is more to the right of the envelope as shown in Fig4.1.2above.

44

4.1.3 Sieve analysis results for coarse aggregates

Table 4.1.3 particle size distribution for coarse aggregates

Sieve size(mm) Retained mass(g) % Retained % Cumulative passing

50 0 0 100

37.5 0 0 100

25 26.3 1.3 98.7

19 569 28.5 70.2

12.5 713.7 35.7 34.5

9.5 367 18.4 16.1

4.75 174.5 8.7 7.4

Pan 149.5 7.4 0

45

Fig 4.1.3 particle distribution for coarse aggregates

The Coarse aggregates did not lie within the required limits of BS 882:1992 as shown in Fig 4.1.3

above. The

46

4.2 Specific gravity results

Table4.1.4 Determined specific gravity

Specific gravity pertains to the relative density of the solid material making up the constituent

particles not including the pore space within the particles that is accessible to water.

The results in table above show that the plastic particles are lighter than natural soil. This

indicates that a lighter concrete was achieved when sand was replaced by plastic aggregates.

4.3 Workability

4.3.1 Slump test (BS 1881: Part 102)

Table 4.2.1 Slump test results

Percentage replacement Slump (mm)

0 23

10 13

30 8

50 Shear failure

Type of sample Specific gravity

Natural fines 2.68

Plastic particles 0.833

47

Fig. 4.2 slump in (mm) against percentage replacement of sand with plastic particles in concrete

Fig 4.2 above shows that there is a reduction of slump with increasing amount of plastic in the

concrete. This indicates that the concrete becomes less workable with an increase in the

percentage replacement of sand with plastic particles as fine aggregates, which is attributed to

the plastic not mixing well with the other concrete constituents. At 10% replacement the mix was

workable enough at the same water content as the control, it was fairly workable at 30%, while

the concrete failed the slump test at 50% replacement. The results show that the concrete mixes

with higher plastic content required higher water content to achieve a reasonable workability

and flow characteristics.

4.3.2 Compaction factor test Table 4.2.2 compaction factor results

Percentage replacement Compaction factor

0 2.3

10 3.6

30 6.9

50 2.5

0

5

10

15

20

25

0 10 20 30 40 50 60

slu

mp

(m

m)

percentage replacement

slump vs %replacement of sand with plastic in concrete

48

4.4 Dry Density

Table 4.3 Determined dry density

Percentage

replacement

Cube

Average weight and density

Cylinder

Average weight and density

Weight(Kg) Density (KG/M3)

Weight (Kg) Density (KG/M3)

0 3.0 3000 12.65 2386.15

10 2.7 2700 12.45 2348.42

30 2.375 2375 12.35 2329.56

50 2.075 2075 10.5 1980.60

Fig 4.3.1 cube dry density against percentage replacement of sand with plastic particles in

concrete

0

500

1000

1500

2000

2500

3000

3500

0 10 20 30 40 50 60

Dry

Den

sity

(Kg/

Mᶟ)

percentage replacement

cube dry density

49

Fig 4.3.2 cylinder dry density against percentage replacement of sand with plastic particles in

concrete

From the Fig 4.3.1 and Fig 4.3.2 above it is evident that the density reduce with increase in the

plastic content in concrete. For the cubes there is a 10% decrease in density as compared to the

control for the 10% replacement of sand with plastic, a 20.83% decrease for the 30% replacement

and 30.83% for the 50% replacement. For the cylinders there is a 1.6% decrease in density as

compared to the control for the 10% replacement of sand with plastic, a 2.4% decrease for the

30% replacement and 17% for the 50% replacement. It shows that the rate of reduction of the

density of concrete also increases with every increase in the plastic content, although this rate is

more significant for cubes where there is a drastic reduction in density for every percentage

increase of plastic. This reduction in density is advantageous in that it will lead to reduced dead

load of the structure hence less complicated foundations can be use, which means a reduction in

the general cost of construction.

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50 60

Dry

dD

ensi

ty (

Kg/

Mᶟ)

percentage replacement

Cylinders densities

50

4.5 Compressive strength

4.1 Plate Hourglass failure mode of concrete cube

Table 4.4 Determined compressive strength

Percentage

replacement

7days

Cube

failure

load(KN)

28days

Cube 1

failure

load(KN)

28days

Cube 2

failure

load(KN)

28days

Average

cube failure

load(KN)

7days

Compressive

strength(N/mm2)

28days

Compressive

strength(N/mm2)

0 125 275 270 272.5 12.5 27.25

10 122 245 255 250 12.2 25.00

30 120 225 195 210 12.0 21.00

50 58 120 125 122.5 5.8 12.25

51

Fig 4.4.1 7days compressive strength vs percentage replacement of sand with plastic particles

in concrete

Fig 4.4.2 28days compressive strength vs percentage replacement of sand with plastic particles

in concrete

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60

com

pre

ssiv

estr

engt

h

percentage replacement

7days

0

5

10

15

20

25

30

0 10 20 30 40 50 60

com

pre

ssiv

e st

ren

gth

percentage replacement

28days

52

Fig 4.4.3 compressive strength ratio depending on age, age 1 and 2 represent 7days and 28days

respectively

In this research the values of compressive strength for different replacement of plastic contents

(0%, 10%, 30% and 50%) at the end of different curing periods ( 7days, and 28 days) as given in

Table 4.4 above. The Fig.4.4.1 and Figs.4.4.2 graphs above represents varying strength of

concrete cubes in each of various percentages of sand replacement with plastic particles for 7

days. From the Fig 4.4.1 graph above, there is gradual decrease in compressive strength from 0%

– 10% sand replacement with a decrease of about 0.3N/mm2.Between 10% - 30% sand

replacement the slope becomes less steep with an decrease of 0.2N/mm2.Above 30% the

compressive strength has the steepest slope with a decrease of 6.2N/mm2 from 30% to 50%. Fig

4.4.2 shows that the compressive strength at 28 days decreases by 8.3 %, 23 %, and 55% compared

to ordinary mix. Therefore the compressive strength decreases with every addition of plastic

content replacing sand at all ages although the strength of all mixtures continued to increase with

the age. Fig.4.4.3 Show the compressive strength ratio (at 7 and 28 days) with respect to

percentage replacement of sand by plastic.

0

5

10

15

20

25

30

1 2

com

pre

ssiv

e st

ren

gth

Age

Compressive strength ratio for 7days and 28days respectively

control

10% sand replacement

30% sand replacement

50% sand replacement

53

4.6 Tensile split strength

Table 4.5 Variation of split tensile strength due to replacement of sand with plastic particles

Percentage

replacement

7days Cylinder

failure

Load(KN)

28days cylinder

failure load(KN)

7days Tensile

split

strength(N/mm2)

28days Tensile

split

strength(N/mm2)

0 120 185 1.70 2.62

10 85 170 1.20 2.41

30 75 135 1.06 1.91

50 40 60 0.57 0.85

Fig 4.5.1 7days tensile split strength vs percentage replacement of sand with plastic particles

in concrete

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 10 20 30 40 50 60

Ten

sile

sp

ilt s

tren

gth

percentage replacement

7days

54

Fig 4.5.2 28days tensile split strength vs percentage replacement of sand with plastic particles

in concrete

Fig 4.5.3 split tensile strength ratio depending on the age of concrete, age 1 and 2 represent

7days and 28days respectively

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60

ten

sile

sp

lit s

tren

gth

percentage replacement

28days

0

0.5

1

1.5

2

2.5

3

1 2

split tensile strength ratio for 7days and 28days respectively

control

10% sand replacement

30% sand replacement

50% sand replacement

55

It was found that split tensile strength of concrete containing plastic (using 10 %, 20 % and 30 %

replacement percentages with fine aggregate and a w/c of 0.5) depended on the percentage

plastic used. The variation of split tensile strength was shown in the table 4.5 above.

Fig.4.5.1 shows the variation of split tensile strength with replacements of sand with various

percentages of fine aggregate at 7days. Fig. 4.5.2 shows that split tensile strength decreases with

the increase in replacement of percentage of sand with plastic at 28days. Comparing with the

control mix, split tensile strength reduced by 29%, 38%, and 66% with respect to different

replacement levels of sand with foundry sand at 7days. At 28days the split tensile strength

reduces by 8%, 27% and 68% from control mix without plastic to the various replacement of sand

with plastic.

In Fig.4.5.3 the bar chart shows the split tensile strength ratio (at 7 and 28 days) with respect to

age at various replacement percentages of fine aggregates by plastic particles.

4.7 Flexural strength

Table 4.6 Flexural strength

percentage replacement

Beam load (KN) Flexural strength

0 1360 0.68

10 1220 0.61

30 780 0.39

50 480 0.24

56

Fig 4.6 flexural strength vs percentage replacement of sand with plastic particles in concrete

The results in table 4.6 above are for the concrete age of 28days. The flexural strength of the

concrete decreases with every percentage increase of plastic in the mix. The Fig 4.6 is a graph

showing that the variation in strength is almost linear. For 10%, 30%, 50% replacement of sand

with plastic particles the percentage decrease in strength was 10.3%, 43%, 65% respectively

comparing with the control mix.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50 60

flex

ura

l str

engt

h

percentage replacement

Chart Title

57

CHAPTER 5

5.0 CONCLUSION AND RECOMMENDATION

5.1General

In this research, waste granulated plastics were used as a partial replacement of sand in concrete,

and the resultant mix was studied and compared with the control mix having normal aggregates.

The conclusions are drawn based on the results obtained from this study.

5.2 Conclusion

1. For a given water content, the use of plastics in the mix lowers the density, compressive

strength and tensile strength.

2. Plastics can be used to replace some of the aggregates in a concrete mixture. This

contributes to reducing the unit weight of the concrete. This can be very applicable when

requiring lightweight concrete.

3. From observation of the mix, the cement paste and plastic aggregates did not mix as well

as the natural aggregates leading to a formation of a weak bond between the two, hence

the failure of concrete occurs under lower stresses compared to the control due to failure

of the bond.

4. Plastic aggregates can be used to cool the inside of buildings in areas of high temperatures

because it does not conduct heat.

5.3 Recommendation

The use of plastic in concrete lowered its resultant strength, therefore research should be done

to come up with methods of overcoming this drawdown before the use of plastic can actively be

adopted in concrete construction. The use of plastic in concrete is a new technology on which a

lot of research is required.

58

REFERENCES

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