UNIVERSITY OF NAIROBI

STRENGTH CHARACTERISTICS OF RUBBER

DERIVED CONCRETE (RUBCRETE)

BY

ODUOR VALENTINE OTIENO

F16/35879/2010

A project submitted as a partial fulfillment for the requirement for the

award of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015

i

Abstract

About 2 million waste tires were generated in Kenya in 2012. This amount increases every

year and an estimate of 2015 will be about 5 million waste tires.

Weight, compressive and tensile strengths of concrete with rubber tires as coarse aggregates

were investigated. Fifty four concrete (150x150x150) mm cubes and thirty six concrete

(150x300) mm cylinders were prepared for this study. The replacement of aggregates with

cut tires was partially in the concrete mixes according to the mix designs required in terms of

weight. Test Results indicated clear substantial reduction in strengths and weight of the tire

derived concrete as compared with the strengths of controls. Based on the results of tests, tire

derived concrete was still not recommended for structural uses because of the low unit

weight, compressive and tensile strengths comparing with the normal concrete containing

natural rock aggregates.

The study also tried to point out the fact that not all discarded materials classified are wastes

but can be converted to other uses by manipulating. Adding them as partial substitutes for

coarse aggregate in concrete mixes, cut rubber tire pellets could lower cost of production and

saving valuable funds, protect the environment and resources to be used for construction

projects.

ii

Dedication

I am greatly indebted to my mother Mrs. Olyvia Achieng Owera for her faith in me. Her

support, encouragement and advice were invaluable.

I would also like to give thanks to my friends, Clarise Akinyi Onyango and who gave me the

encouragement and unconditional support while carrying out this research. Besides, I am so

grateful to all the people who helped me in one way or the other while carrying out this

research.

iii

Acknowledgements

I am delighted to express my gratitude to my supervisor Eng. Evans Goro. He provided me a

lot of expert guidance, suggestions, comments and continuous support. His dedication and

excellence have always been an inspiration for my academic and professional career.

I am so thankful to the University for providing me the platform to undergo my

undergraduate studies and for delivering the financial support required for this project.

My Special thanks goes to Mr. M Mburu and his colleagues in the Material testing

laboratory for their cooperation and assistance while carrying out the various tests.

Beyond all, my usual thanks goes to the Almighty God for He is in all that exists

iv

Table of contents

Abstract .................................................................................................................................................... i

Dedication ............................................................................................................................................... ii

Acknowledgements ................................................................................................................................ iii

List of tables .......................................................................................................................................... vii

List of plates ......................................................................................................................................... viii

List of graphs .......................................................................................................................................... ix

LIST OF ACRONYMS ................................................................................................................................. x

CHAPTER 1: INTRODUCTION ................................................................................................................... 1

1.1 GENERAL INTRODUCTION ............................................................................................................. 1

1.2 BACKGROUND ............................................................................................................................... 1

1.3 PROBLEM STATEMENT .................................................................................................................. 6

1.4 PROBLEM JUSTIFICATION.............................................................................................................. 6

1.5 OBJECTIVES ................................................................................................................................... 6

1.5.1 GENERAL OBJECTIVES ..................................................................................................... 6

1.5.2 SPECIFIC OBJECTIVES ...................................................................................................... 6

1.6 RESEARCH METHODOLOGY .......................................................................................................... 7

1.7 SIGNICANCE OF THE STUDY .......................................................................................................... 8

1.8 LIMITATIONS OF THE STUDY ......................................................................................................... 9

1.9 SCOPE OF THE STUDY .................................................................................................................... 9

CHAPTER 2: LITERATURE REVIEW ......................................................................................................... 10

2.1. Composition of a Tire ................................................................................................................. 10

2.2 Methods of Recycling Tires ......................................................................................................... 11

2.3 Literature on concrete and rubberized concrete........................................................................ 12

2.3.1 Characteristics of Concrete .................................................................................................. 12

2.3.2 Constituents of Concrete ...................................................................................................... 13

2.3.3 Properties of Fresh Rubberized Concrete ............................................................................ 15

v

2.3.4 Properties of Hardened Rubberized Concrete ...................................................................... 16

CHAPTER 3: METHODOLOGY ................................................................................................................ 18

3.1 TESTS ON THE COARSE AND RUBBER AGGREGATE .................................................................... 18

3.1.1 DETERMINATION OF FLAKINESS INDEX ................................................................... 18

3.1.2 DETERMINATION OF AGGREGATE CRUSHING VALUE ......................................... 19

3.1.3 DETERMINATION OF AGGREGATE IMPACT VALUE .............................................. 20

3.1.4 SPECIFIC GRAVITY.......................................................................................................... 21

3.1.5 Determination of bulking density ........................................................................................ 23

3.2 TESTS ON CONCRETE................................................................................................................... 24

3.2.1 PREPARATION OF THE RUBBER AGGREGATE ......................................................... 24

3.2.2 Slump test ............................................................................................................................. 25

3.2.3 Compaction test ................................................................................................................... 26

3.3 TESTING OF DRY CONCRETE........................................................................................................ 27

3.3.1 COMPRESSIVE STRENGTH ............................................................................................ 28

3.3.2 TENSILE STRENGTH ........................................................................................................ 28

CHAPTER 4: RESULTS AND ANALYSIS .................................................................................................... 29

4.1 THE COARSE AND RUBBER AGGREGATE ......................................................................................... 29

4.1.1 FLAKINESS INDEX OF THE COARSE AGGREGATE .................................................. 29

4.1.2 ACV ..................................................................................................................................... 29

4.1.3 AIV ...................................................................................................................................... 30

4.1.4 SPECIFIC GRAVITY OF SAND ........................................................................................ 30

4.1.5 LAA ....................................................................................................................................... 30

4.1.6 COMPARING THE COARSE AND RUBBER AGGREGATE PROPERTIES ................ 31

4.2 MIX DESIGN ................................................................................................................................. 32

4.2.1 SIEVE ANALYSIS OF THE FINE AGGREGATE ........................................................... 32

4.2.2 COARSE AGGREGATE GRADING ................................................................................. 35

4.2.3 AGGREGATE COMBINATIONS ...................................................................................... 37

vi

4.2.4 TRIAL MIX ......................................................................................................................... 39

4.2.5 REPLACEMENT OF COARSE AGGREGATE WITH THE RUBBER TIRE ................. 41

4.3 RESULTS ON FRESH CONCRETE ................................................................................................... 42

4.3.1 SLUMP ................................................................................................................................ 42

4.3.2 COMPACTION FACTOR .................................................................................................. 43

4.4 RESULTS ON DRY CONCRETE ....................................................................................................... 45

4.4.1 UNIT WEIGHT ................................................................................................................... 45

4.4.2 COMPRESSIVE STRENGTHS .......................................................................................... 47

4.4.3 TENSILE STRENGTHS ..................................................................................................... 48

4.5 Cost Considerations in Rubberized Concrete ............................................................................. 49

4.5.2 Cost Savings due to Material substitution ............................................................................ 49

4.5.3 Cost Savings by Protecting the Environment....................................................................... 49

CHAPTER 5: CONCLUSION AND RECCOMENDATION ............................................................................ 51

5.1 CONCLUSION ............................................................................................................................... 51

5.2 RECCOMENDATIONS ................................................................................................................... 52

REFERENCE ............................................................................................................................................ 53

APPENDIX .............................................................................................................................................. 54

vii

List of tables

Table 1: Research methodology program ............................................................................................... 7

Table 2: Percentage Composition of Materials for a Passenger and a Truck car .................................. 11

Table 3: Flakiness Index ....................................................................................................................... 29

Table 4: Comparing aggregate properties ............................................................................................. 31

Table 5: Sieve analysis of the sand ....................................................................................................... 32

Table 6: Results on sieve analysis and Graph 1: Cumulative graph on fine aggregate ........................ 33

Table 7: Results on coarse aggregate grading and Graph 2: Cummulative curve on coarse aggregate 35

Table 8: Aggregate combinations and Graph 3: Aggregate combinations curve ................................. 37

Table 9: Results obtained from the trial mix ......................................................................................... 40

Table 10: Weight replacement in cubes ................................................................................................ 41

Table 11: Weight replacement in cylinders .......................................................................................... 41

Table 12: Results on the workability test .............................................................................................. 42

Table 13: Results on compaction factors .............................................................................................. 43

Table 14: Unit weight of cubes (Kg) .................................................................................................... 45

Table 15: Unit weight of cylinders (Kg) ............................................................................................... 46

Table 16: Compressive strengths (N/mm2) ........................................................................................... 47

Table 17: Tensile strength (N/mm2) ...................................................................................................... 48

viii

List of plates

Plate 1: A waste tire dumping site .......................................................................................................... 3

Plate 2 : Uses of waste rubber tires in the art industry ............................................................................ 4

Plate 3 : Use of waste rubber tires in interior design .............................................................................. 4

Plate 4 : using waste rubber tires for recreational purposes .................................................................... 4

Plate 5: using tire rubber in construction ................................................................................................ 5

Plate 6 Sample of tire derived aggregate. ............................................................................................... 8

Plate 7: During the sieve analysis ......................................................................................................... 18

Plate 8: Manual cutting of the rubber Plate 9: Open drying of the tire pellets ................................. 25

Plate 10: The batch in the rotating machine .......................................................................................... 25

Plate 11: During the tamping Plate 12: Slump measurement .......................................................... 26

Plate 13: During the compaction process .............................................................................................. 26

Plate 14: Molding of some of the cubes Plate 15: Curing of specimens ............................................ 27

Plate 16: Part of a rubberized concrete cube after compression ........................................................... 28

Plate 17: The control cylinder specimen at testing. .............................................................................. 28

Plate 18: A sample of the rubber aggregate I used, about 20 mm ........................................................ 42

ix

List of graphs

Table 6: Results on sieve analysis and Graph 1: Cumulative graph on fine aggregate ........................ 33

Table 7: Results on coarse aggregate grading and Graph 2: Cummulative curve on coarse aggregate 35

Table 8: Aggregate combinations and Graph 3: Aggregate combinations curve ................................. 37

Graph 4: Graph of slump ...................................................................................................................... 43

Graph 5: Graph of compaction factor ................................................................................................... 44

Graph 6: Graph of Cubes Unit weight .................................................................................................. 45

Graph 7: Graph of Cubes Unit weight .................................................................................................. 46

Graph 8: Graph of compressive strengths ............................................................................................. 47

Graph 9: Graph of tensile strengths ...................................................................................................... 48

x

LIST OF ACRONYMS

SSS – Sodium Sulphate Soundness

ACV- Aggregate crushing value

LAA- Los Angeles Abrasion

AIV- Aggregate Impact Value

w/c – Water cement ratio

S.G- Specific gravity

F.I- Flakiness Index

C25/20- concrete class 25 with 20 mm aggregate

WTMK- Waste Tire Management of Kenya

1

CHAPTER 1: INTRODUCTION

1.1 GENERAL INTRODUCTION

Concrete is a composite material composed of coarse granular material (the aggregate or

filler) embedded in a hard matrix of material (the cement or binder) that fills the space

between the aggregate particles and glues them together. Aggregates can be obtained from

many different kinds of materials, in this study; shredded tires are used as filler in concrete

instead of common natural rock aggregates. The replacement of aggregates was partially or

completely in the concrete according to the mix designs required in terms of weight and

strength.

1.2 BACKGROUND

Concrete is the most used material in the construction industry and it comprises cement,

aggregate and water. The scarcity and availability at reasonable rates of sand and aggregate

are now giving anxiety to the construction industry since large volumes of concrete are used

all over the world on a daily basis. Natural aggregates are obtained from river beds and

quarries. Research is being undertaken to produce a cost effective and high quality concrete.

Problems caused by mining of aggregates,

a) Mining of aggregates causes deformation of the landscapes and landslides.

b) Flooding and erosion

c) Removal of virtually all natural vegetation, top soil and subsoil; this causes loss of

existing wildlife and huge loss of biodiversity as plants and aquatic habitats are

destroyed.

d) Noise, dust pollution and contamination of water.

e) Disruption of existing movement of surface water and groundwater; Interrupt natural

water and reduces quantity and quality of drinking water downstream.

f) After mining, large excavations and pits left behind trap rain and this act as death

traps or breeding grounds for mosquitoes

2

Pneumatic tires are made from synthetic rubber, natural rubber, fabric, wire, carbon black

and other chemical compounds. With the development of modern societies in Kenya there

has been increased need for mobility and thus growth of the automobile sector. This

revolution has come with problems associated with waste management of the worn out

rubber tires. Tires are known to be non-biodegradable.

Aggregate is cheaper than cement and it is, therefore, economical to put into the mix much of

the former and as little of the latter as possible. Nevertheless, economy is not the only reason

for using aggregate: it confers considerable technical advantages on concrete, which has a

higher volume stability and better durability than hydrated cement paste alone.

The goal of sustainability is that life on the planet can be sustained for the foreseeable future

and there are three components of sustainability environment, economy, and society. To

meet its goal, sustainable development must ensure that these three components remain

healthy and balanced. Furthermore, it must do so simultaneously and throughout the entire

planet, both now and in the future. At the moment, the environment is probably the most

important component and an engineer uses sustainability to mean having no net negative

impact on the environment.

Problems caused by misused waste tires,

a) Tires are used in industries like thermal water plant, cement kilns, brick kilns thus

polluting air.

b) Fire hazards

c) Piles in garages and residential places provide breeding grounds for mosquitoes

d) Tires are burnt illegally in dumps to recover the steel straps

e) Due to their heavy metal and other pollutant contents, tires pose a risk of leaching of

toxins into the groundwater when placed in wet soils.

Waste tires in Kenya have always been used for making sandals, to guard seedlings, cement

kilns, for erosion prevention and to make straps. This constitutes a smaller percentage on the

recycle management. A journal by Waste tire management Kenya (WTMK) showed that

about 2 million waste tires were generated in Kenya in 2012. This amount increases every

year and an estimate of 2014 will be about 5 million waste tires. The research went ahead and

showed that citizens burn tire illegally to recover the steel wire and sell to scrap dealers at

3

average revenue of 15- 40 ksh. per Kg. Only 10 % is recycled unlike Europe where 32% is

recycled.

Various waste tire dumping sites were visited and large piles of truck and car used tires were

noticed.

Plate 1: A waste tire dumping site

One methodology of recycling waste tire is by cutting or scraping actual waste materials into

smaller sizes and then down to powder particles, and finally reused in many industrial fields,

so-called reclaimed rubber. One suitable application of this rubber is to use it as an additive

for conventional asphalt in production of asphalt concrete for road pavement.

Tires are not desired at landfills, due to their large volumes and 75% void space, which

quickly consume valuable space. Tires can trap methane gases, causing them to become

buoyant, or bubble to the surface. This ‘bubbling’ effect can damage landfill liners that have

been installed to help keep landfill contaminants from polluting local surface and ground

water.

Shredded tires are now being used in landfills, replacing other construction materials, for a

lightweight backfill in gas venting systems, leachate collection systems, and operational

4

liners. Shredded tire material may also be used to cap, close, or daily cover landfill sites.

Scrap tires as a backfill and cover material are also more costly.

In Europe, U.S.A and other developed countries waste rubber tires have been put in quiet a

number of uses ;

Art

Plate 2 : Uses of waste rubber tires in the art industry

Furniture

Plate 3 : Use of waste rubber tires in interior design

Recreation

Plate 4 : using waste rubber tires for recreational purposes

5

Construction

Plate 5: using tire rubber in construction

Other uses of whole tire wastes include boat bumpers, artificial reefs, in basketball courts and

retreading; retreading involves reusing of waste tire by replacing the steel treads, this saves

landfill space, saves resources and cut costs up to 30% to 70% less to make a new tire.

Pyrolysis is a method that is used on waste tire to break it down into potentially usable end

products; it is the heating of organic compounds in a low oxygen environment. Outputs

include oil, char and fuel gas. In Kenya pyrolysis is not common because of lack of

equipment, environmental considerations, availability and steady flow of tires.

“THE BEAD”

The “bead” is the edge of the tire. On most tires, the bead consists of loops of strong steel

cable. The beads hold the tire onto the rim, and are, in a sense, the backbone of a tire. Most

beads are high carbon steel. In Kenya, the beads are obtained illegally by burning waste tire

to recover the steel wire and sold to scrap dealers at average revenue of 15- 40 Ksh. Per Kg.

The wires can be used in construction industries to link reinforcing bars and in a number of

uses but it is evident that the method used to obtain it is environmentally unfriendly and

costly.

6

1.3 PROBLEM STATEMENT

The study was aimed at evaluating the use of waste tire as a possible replacement of coarse

aggregate in concrete so as to mitigate the risks involved with misuse of waste ground rubber

tire to produce a light-weight, low cost concrete mix.

What was needed was an aggregate comprising material of low commercial value, which can

be complemented with natural aggregate to provide concrete of equivalent, or improved

physical properties. With respect to the construction industry and engineering profession,

these new technique may be of beneficial use.

1.4 PROBLEM JUSTIFICATION

Demands on building material have increased due to the increasing population and

urbanization. Among the material demanded is coarse aggregate and in the phase of

sustainability in construction, utilization of waste material is encouraged because it will help

in conserving the environment and in reducing costs.

1.5 OBJECTIVES

1.5.1 GENERAL OBJECTIVES

To evaluate the technical aspects of using rubberized concrete in Portland cement concrete

1.5.2 SPECIFIC OBJECTIVES

a) To examine the components of rubber derived concrete

b) To study the failure characteristics of rubber derived concrete

c) To formulate guidelines indicating how tire derived concrete can be utilized in

construction.

d) To investigate the availability and economic feasibility of the use for waste rubber

as aggregates

7

1.6 RESEARCH METHODOLOGY

Research was carried out on the use of waste tire as a replacement of coarse aggregate in

concrete. Materials used were;

a) Cement

b) Waste rubber tire

c) Fine and coarse aggregate

Mix proportions were formulated for the coarse aggregate with the rubber cuttings.

Proportions were formulated by weight. Coarse aggregate were then replaced as percentages

to the coarse aggregate.

Table 1: Research methodology program

Percentages

No. of cubes

No. of cylinders

7 days

14 days

28 days

7 days

28 days

1 0% 3 3 3 3 3

2 5% 3 3 3 3 3

3 10% 3 3 3 3 3

4 15% 3 3 3 3 3

5 20% 3 3 3 3 3

6 30% 3 3 3 3 3

18 18 18 18 18

TOTAL

54

36

8

In total 63 cubes and 36 cylinders were used to carry out the compressive and tensile tests

since statistical work requires quiet a number of data to reduce risks of extremes. Weight

tests, workability and strength tests were then carried out.

Tests were then carried out on the coarse aggregates and waste rubber pieces. (Flakiness

index, ACV, Los Angeles Abrasion test, water absorption, sieve analysis, Aggregate impact

value)

Waste tire rubber was got locally and cut into small sizes as indicated, they were then

roughened to increase bonding in the concrete mix. For uniformity I used the truck, lorries,

busses and heavy vans tires.

Plate 6 Sample of tire derived aggregate.

1.7 SIGNICANCE OF THE STUDY

The findings of this study would help reduce the environmental issues associated with mining

of aggregate and that of misusing waste rubber tire.

It would also help future researchers interested in furthering the study on recycling ground

rubber tire.

If done in a large scale, cutting and roughening the rubber waste may provide employment

thus benefiting the entire participating society.

9

1.8 LIMITATIONS OF THE STUDY

This research was limited to lack of equipment to carry out some tests on the concrete mixes

like fire resistance, permeability, air content, sodium sulphate soundness and flexural

strength.

The research was also limited to only Portland cement and to a specific water/cement ratio of

0.5 and a cement strength of 32.5 portland pozzolanic.

Even though waste tire management is a global issue, my study will only be limited to

establishing the availability, capacity and feasibility in Kenya.

1.9 SCOPE OF THE STUDY

The scope of the study was rubber waste generated from the discarded tires and possibility of

using waste tire rubber as replacement of coarse aggregate in Kenya.

One concrete control was designed. The coarse aggregate of the mixture was replaced in

30%, 20%, 15%, 10% and 5% by weight using the tire chips.

The research was conducted in the premises of the University of Nairobi concrete laboratory

between December 2014 and February 2015

10

CHAPTER 2: LITERATURE REVIEW

2.1. Composition of a Tire

A tire is an assembly of numerous components that are built up on a drum and then cured in a

press under heat and pressure. Heat facilitates a polymerization reaction that crosslinks

rubber monomers to create long elastic molecules. These polymers create the elastic quality

that permits the tire to be compressed in the area where the tire contacts the road surface and

spring back to its original shape under high-frequency cycles [1].

The fundamental materials of modern tires are rubber and fabric along with other compound

chemicals. Their constructive make-up consists of the tread and the body. The tread provides

traction while the body ensures support. Before rubber was invented, the first versions of tires

were simply bands of metal that fit around wooden wheels in order to prevent wear and tear.

The most recent and popular type of tire is pneumatic, pertaining to a fitted rubber based ring

that is used as an inflatable cushion and generally filled with compressed air. Pneumatic tires

are used on many types of vehicles [2].

Table 1 below shows the typical composition of a passenger tire and track tire respectively by

listing the major classes of materials used to manufacture tires with the percentage of the total

weight of the finished tire that each material class represents. From the percentage values of

the composition, it can be observed that the main difference between the passenger car and

truck car is in the composition of natural rubber and synthetic rubber. Otherwise, the other

constituent materials are added in the same quantity for both types.

11

Table 2: Percentage Composition of Materials for a Passenger and a Truck car

The Rubber Manufacturers Association, http://www.rma.org, 2009

Material Passenger car Truck car

Natural rubber 14% 27%

Synthetic rubber 27% 14 %

Carbon black 28% 28%

Steel 14-15 % 14-15%

Fabric, fillers,

accelerators,

Antiozonants

16-17% 16-17 %

2.2 Methods of Recycling Tires

The numerous techniques and technologies available for processing postconsumer tires are

enumerated below.

1. Shredding and Chipping: This is mechanical shredding of the tires first in to bigger sizes

and then into particles of 20 – 30 mm in size.

2. Crumbing: It is the processing of the tire into fine granular or powdered particles using

mechanical or cryogenic processes. The steel and fabric component of the tires are also

removed during this process.

3. DeVulcanising: This is the treatment of tire with heat and chemicals to reverse the

vulcanisation process in the original tire production.

4. Pyrolysis and Gasification: These are two thermal decomposition processes carried out

under different conditions. The processes produce gas, oil, steel, and carbon black (char).

5. Energy Recovery: It is the incineration of tires to generate energy.

12

2.3 Literature on concrete and rubberized concrete

2.3.1 Characteristics of Concrete

Concrete is a composite material composed of coarse granular material (the aggregate or

filler) embedded in a hard matrix of material (the cement or binder) that fills the space

between the aggregate particles and glues them together [3]. In its simplest form, concrete is

a mixture of paste and aggregates. The paste, composed of Portland cement and water, coats

the surface of the fine and coarse aggregates. Through a chemical reaction called hydration,

the paste hardens and gains strength to form the rock-like mass known as concrete.

Concrete is the world’s most important construction material. The quality and performance of

concrete plays a key role for most of the infrastructures including commercial, industrial,

residential and military structures, dams, power plants and transportation systems. Concrete is

the single largest manufactured material in the world and accounts for more than 6 billion

metric tons of materials annually.

Good quality concrete is a very durable material and should remain maintenance free for

many years when it has been properly designed for the service conditions and properly

placed. Of course, proper use of the structure for the intended function can have a significant

role. Through choice of aggregate or control of paste chemistry and microstructure, concrete

can be made inherently resistant to physical attack, such as from cycles of freezing and

thawing or from abrasion and from chemical attack such as from dissolved sulfates or acids

attacking the paste matrix or from highly alkaline pore solutions attacking the aggregates.

Judicious use of mineral admixtures greatly enhances the durability of concrete. The main

advantages of concrete as a construction material are the ability to be cast, being economical,

durability, fire resistance, energy efficiency, on-site fabrication and its aesthetic properties.

Whereas the disadvantages are low tensile strength, low ductility, volume instability and low

strength to weight ratio [3]

13

2.3.2 Constituents of Concrete

a) Cement

Cement is a generic name that can apply to all binders. The chemical composition of the

cements can be quite diverse but by far the greatest amount of concrete used today is made

with Portland cements [3]. For this reason, the discussion of cement in this report is mainly

about the Portland cement.

Portland cement, the basic ingredient of concrete, is a closely controlled chemical

combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to

which gypsum is added in the final grinding process to regulate the setting time of the

concrete. Lime and silica make up about 85% of the mass. Common among the materials

used in its manufacture are limestone, shells, and chalk or marl combined with shale, clay,

slate or blast furnace slag, silica sand, and iron ore

b) Aggregates

Aggregates generally occupy 70 to 80 % of the volume of concrete and can therefore be

expected to have an important influence on its properties. They are granular materials derived

for the most part from natural rock and sands. Moreover, synthetic materials such as slag and

expanded clay or shale are used to some extent, mostly in lightweight concrete. In addition to

their use as economical filler, aggregates generally provide concrete with better dimensional

stability and wear resistance. Based on their size, aggregates are divided into coarse and fine

fractions. The coarse aggregate fraction is that retained on the 4.75 mm sieve. While the fine

aggregate fraction is that passing the same sieve [3]

c) Water

Water is a key ingredient in the manufacture of concrete. Attention should be given to the

quality of water used in concrete. The time-honored rule of thumb for water quality is “If you

can drink it, you can make concrete with it.” A large amount of concrete is made using

14

municipal water supplies. However, good quality concrete can be made with water that would

not pass normal standards for drinking water [3].

Mixing water can cause problems by introducing impurities that have a detrimental effect on

concrete quality. Although satisfactory strength development is of primary concern,

impurities contained in the mix water may also affect setting times, drying shrinkage, or

durability or they may cause efflorescence. Water should be avoided if it contains large

amounts of dissolved solids, or appreciable amounts of organic materials [3].

d) Chemical Admixtures

Admixtures are ingredients other than water, aggregates, hydraulic cement, and fibers that are

added to the concrete batch immediately before or during mixing. A proper use of admixtures

offers certain beneficial effects to concrete, including improved quality, acceleration or

retardation of setting time, enhanced frost and sulfate resistance, control of strength

development, improved workability, and enhanced finish ability

e) Natural Aggregates in Rubberized Concrete

Rubberized concrete is produced by partially replacing the mineral aggregates with rubber.

Therefore, the mineral aggregates are still part of the constituents as in the conventional

concrete. Natural aggregates are usually obtained by mining or from natural sources like river

in the case of sand. The coarse and fine aggregates are usually mined separately.

Occasionally, aggregate is obtained as a by-product of some other processes (e.g., slag or

recycled concrete). Aggregates may be crushed and may be washed . They are usually

separated into various size fractions and reconstituted to satisfy the grading requirements.

They may need to be dried. A modest amount of energy is involved in all these processes.

f) Cement in Rubberized Concrete

The choice of cement for a particular application depends on the availability, the cost and on

the particular circumstances of equipment, skilled labor force, speeds of construction and of

course on the exigencies of the structure and its environment [4]. Wide varieties of cements

have been used to produce rubberized concrete by different researchers.

15

2.3.3 Properties of Fresh Rubberized Concrete

a) Workability

A decrease in slump was observed with increase in rubber aggregate content. For rubber

aggregate contents of 40% by total aggregate volume, the slump was close to zero and the

concrete was not workable by hand. Such mixtures had to be compacted using a mechanical

vibrator. Mixtures containing fine crumb rubber were, however, more workable than mixtures

containing either coarse rubber aggregate or a combination of crumb rubber and tire chips

[5]. It was found that increasing the size or percentage of rubber aggregate decreased the

workability of the mix and subsequently caused a reduction in the slump values obtained.

Reduction of around 85% on slump has been reported when comparing traditional aggregate

concrete with mixes containing recycled rubber. Other researchers found out that roughly

textured, angular, and elongated particles require more water to produce workable concrete

than smooth, rounded compact aggregate [6].

b) Air content

There is a higher air content in concrete mixtures containing rubber when compared to

control mixtures. Even without any air-entrainment admixtures being introduced, it has been

reported that the air content is significant. The higher air content of rubberized concrete

mixtures may be due to the non-polar nature of rubber aggregates and their ability to entrap

air in their jagged surface texture. When non-polar rubber aggregate is added to the concrete

mixture, it may attract air as it repels water [6]. This increase in air voids content would

certainly produce a reduction in concrete strength, as does the presence of air voids in plain

concrete [4]. Since rubber has a specific gravity greater than 1, it can be expected to sink

rather than float in the fresh concrete mix. However, if air is trapped in the jagged surface of

the rubber aggregates, it could cause them to float

16

2.3.4 Properties of Hardened Rubberized Concrete

a) Unit Weight

The replacement of natural aggregates with rubber aggregates tends to reduce the density of

the concrete. This reduction is attributable to the lower unit weight of rubber aggregate

compared to ordinary aggregate. The unit weight of rubberized concrete mixtures decreases

as the percentage of rubber aggregate increases [6]. The unit weight (density) of concrete

varies, depending on the amount and density of the aggregate, the amount of air that is

entrapped or purposely entrained, and the water and cement contents, which in turn are

influenced by the maximum size of the aggregate.

Because of low specific gravity of rubber particles, unit weight of mixtures containing rubber

decreases with the increases in the percentage of rubber content. Moreover, increase in rubber

content increases the air content, which in turn reduces the unit weight of the mixtures. At

30% rubber content, the dry density diminished to about 95 % of the normal concrete.

However, the decrease in dry density of rubber is negligible when rubber content is lower

than 10-20 % of the total aggregate volume . The reduction in the unit weight of the

rubberized concrete mix increases as the percentage crumb rubber added increases [7].

b) Compressive Strength

Compressive strength tests are widely accepted as the most convenient means of quality

control of the concrete produced. Tests conducted by Kumaran S.G. et al on rubberized

concrete behavior, using tire chips and crumb rubber as aggregate substitute of sizes 38, 25

and 19 mm exhibited reduction in compressive strength by 85% and tensile splitting strength

by 50% but showed the ability to absorb a large amount of plastic energy under tensile and

compressive loads [7].

Kaloush K.E. et al also noted that the compressive strength decreased as the rubber content

increased. Part of the strength reduction was contributed by the entrapped air, which

increases as the rubber content increases. Investigative efforts showed that the strength

reduction could be substantially reduced by adding a de-airing agent into the mixing truck

just prior to the placement of the concrete [7].

17

In most of the previous studies, a reduction in compressive strength was noted with the

addition of rubber aggregate in the concrete mix but there is still a possibility of greatly

improving the compressive strength by using de-airing agents [4].

c) Tensile Strength

The tensile strength of rubber containing concrete is affected by the size, shape, and surface

textures of the aggregate along with the volume being used indicating that the strength of

concretes decreases as the volume of rubber aggregate increases. As the rubber content

increased, the tensile strength decreased, but the strain at failure also increased. Higher tensile

strain at failure is indicative of more energy absorbent mixes [7].

d) Impact Strength and other mechanical properties

Previous investigations have shown that the addition of rubber aggregate into the concrete

mixture produces an improvement in toughness, plastic deformation, impact resistance and

cracking resistance of the concrete. For concrete, it is found that the higher the strength, the

lower the toughness. It is difficult to develop high strength and high toughness concrete

without modifications. Owing to the very high toughness of waste tires, it is expected that

adding crumb rubber into concrete mixture can increase the toughness of concrete

considerably. Laboratory tests have shown that the introduction of waste tire rubber

considerably increase toughness, impact resistance, and plastic deformation of concrete [8].

e) Flexural Strength

Kaloush K.E. et al found that the flexural strengths of rubberized concrete decreased as the

rubber content in the mix increased [7]. On the contrary, Kang Jingfu et al reported that there

is an improvement in flexural strength by the addition of rubber aggregates in roller

compacted concrete. In comparison with the control concrete, when the compressive strength

was kept constant for roller compacted concrete, the flexural strength, and ultimate tension

elongation increased with the increase of rubber content [9].

18

CHAPTER 3: METHODOLOGY

3.1 TESTS ON THE COARSE AND RUBBER AGGREGATE

3.1.1 DETERMINATION OF FLAKINESS INDEX

Objective

To determine the flakiness index of given aggregate sample.

Apparatus

a) A metal thickness gauge or special sieves having elongated slots.

b) Test sieves.

c) A balance

Procedure

A sieve analysis was carried out. All aggregates retained on a 63 mm were disregarded and

test sieve was carried out on all aggregates passing a 63 mm test sieve. Each of the individual

size fractions retained on the sieves were weighed and stored separately with the rest (except

6.3cm test sieve). The total weight, was obtained for all the fractions not recording any

fraction that constituted less than 5% of total weight of the fractions.

The thickness was selected appropriately to each size fraction, under test and each particle

separately by hand.

The weight of all particles passing the gauge for each size fraction was obtained.

Plate 7: During the sieve analysis

19

3.1.2 DETERMINATION OF AGGREGATE CRUSHING VALUE

Objective

To determine the aggregate crushing value of the given sample

Apparatus

a) An open ended steel cylinder of nominal diameter with plunger and base plate.

b) Round steel tamping rod, 16mm diameter by 600mm long, one end rounded.

c) An accurate balance.

d) Test sieves.

e) Compression testing machine

f) A cylindrical metal measure of internal dimensions, 115 mm diameter by 180 mm

deep.

Procedure

The cylinder of the test apparatus was put in position of the base plate, and the test sample in

the three equal layers being subjected to 25 strokes from the tamping rod distributed evenly

over the surface of the layer and dropping from a height of 50 mm above the surface of the

aggregate. The surface of the aggregates was leveled and the plunger inserted so that it rested

horizontally on the surface, taking care to ensure that the plunger does not jam in the

cylinder.

The apparatus were placed with thee test sample and plunger in position, between the platens

of the testing machine and loaded at a uniform rate of 40KN/min up to a maximum of

400KN.

The load was released and the crushed material removed by holding the cylinder over a clean

tray and hammering on the outside with a rubber mallet to enable the sample to fall freely on

to the tray. The fine particles were transferred adhering to the inside of the cylinder, the base

plate and the underside of the plunger to the tray by means of a stiff hair brush. The whole

sample was sieved on the tray and the 2.36 mm test sieve. The fraction passing the sieve was

weighed.

ACV = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑝𝑎𝑠𝑠𝑖𝑛𝑔 2.36 𝑚𝑚 𝑠𝑖𝑒𝑣𝑒

𝑚𝑎𝑠𝑠 𝑜𝑓𝑠𝑢𝑟𝑎𝑐𝑒 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒 𝑥 100

20

3.1.3 DETERMINATION OF AGGREGATE IMPACT VALUE

Objective

To determine the aggregate impact value of a sample of aggregates

Apparatus

An impact testing machine

Preparation of test sample

The material for the test sample shall consist of aggregate passing a 14mm and retained on a

10mm BS test sieve and shall be separated on these, sieves before testing. For smaller sizes

the aggregate shall be prepared in a similar manner using the appropriate sieve.

The aggregate shall be tested in a surface- dry condition. If dried by heating, the period of

drying shall not exceed four hours, the temperature shall not exceed 110℃ and the samples

shall be cooled to room testing before testing.The net weight of aggregate in the measure was

determined to the nearest gram

Test procedure

The impact machine rested without wedging or packing upon the level plate, floor, so that it

is rigid and the guide columns were vertical.

The cup was fixed firmly in position on the base of the machine and the whole of the test

sample placed in place in it and compacted by a single tamping of 25 strokes of the tamping

rod.

The hammer was raised until its lower face was 38 cm above the upper surface of the

aggregate in the cup and allowed to fall on to the aggregate. The test sample was subjected to

a total of 15 such blows, each being delivered at an interval of not less than one second.

The crushed aggregate was then removed from the cup without further breaking of the

sample, and the whole of it sieved on the No 7 BS test sieve for the standard test until no

further significant amount passed in one minute. The fraction passing the sieve was weighed.

The fraction retained on the sieve was also weighed.

21

3.1.4 SPECIFIC GRAVITY

Objective

To determine the relative density and water absorption of a sample of aggregate of not more

than 5mm nominal size

AGGREGATES OF NOMINAL SIZE 5mm AND SMALLER:

Apparatus

a) A balance of capacity not less than 3kg and accurate to 0.5g.

b) A well ventilated oven, capable of maintaining a temperature of 105±5˚C.

c) A pycnometer of about 1litre capacity having a brass conical screw top with a hole.

approximately 6mm diameter at its apex.

d) A watertight tray of area not less than 0.03m2.

e) A container of a size sufficient enough to contain the sample covered with water a

f) A 75micron test sieve and a nesting1.13mm sieve.

g) A supply of water free from any impurity

h) Hair drier.

Test sample

A sample of about 1kg of material having a nominal size of between 10-5mm or about 500g

of material if finer than 5mm is used.

Two tests are carried out and the mean of the two tests is taken.

The sample is thoroughly washed to remove all materials finer than 75micron test sieve using

the following procedure:

The test sample is placed in the container and enough water is added to cover it. The

container is agitated vigorously and the wash water is poured over the sieves, which are

wetted on both sides before the experiment and arranged with the coarser sieve on top.

The agitation is sufficiently vigorous to result in the complete separation of all the particles

finer than the 75micron test sieve from the coarse particles, and to bring the fine material into

suspension in order that they can be removed by decantation of the wash water. Care is taken

to avoid decantation of coarse particles of the sample. The operation is repeated until the

water is clear then all the materials retained on the sieves is returned to the washed sample.

22

Test Procedure

The washed aggregates were transferred to the tray and water was further added to ensure

that the sample was completely immersed. Soon after immersion, bubbles of entrapped air

were removed by gently agitation with a rod. The sample was kept immersed in water for

24±0.5hrs, with the water temperature being maintained at 25±5˚C for at least the last 20hrs

of immersion.

The water was then carefully drained out by decantation through a 75micron BS test sieve

covered by the protective coarser sieve. Any material retained was returned to the sample.

The aggregates were then exposed to a gentle current of warm air to evaporate the surface

moisture. It was stirred frequently at intervals to ensure uniform drying until no surface

moisture can be seen. The saturated and surface dry sample was then weighed (mass A).

The aggregates were then placed in the pycnometer and the pycnometer was filled with

water. The cone was screwed into place and any trapped air was eliminated by rotating the

pycnometer on its side, with the hole in the axis of the cone being covered by a finger. The

pycnometer was topped up with water to remove any froth from the surface and to ensure the

surface of the water in the hole was flat. Then it was dried on the outside and weighed (mass

B).

Thereafter, the contents of the pycnometer were emptied in to the tray, with care being taken

to ensure all the aggregates were transferred. The pycnometer was then refilled with water to

the same level as before, dried on the outside and it weight measured (mass C).

Water was then carefully drained out of the sample by decantation through a 75micron test

sieve and any material retained was returned to the sample. The sample was placed back in

the tray and placed in the oven at a temperature of 105±5˚C for 24±0.5hrs, during which it

was stirred periodically to facilitate drying. Thereafter it was cooled in an airtight container

and weighed (mass D).

23

3.1.5 Determination of bulking density

Objective

To determine the bulk density and percentage of voids

Apparatus

a) Cylinder to be used should conform to the table 1 below. It should be fitted with

handles, be smooth inside, water tight, rigid enough to retain its form under rough

conditions and be protected against corrosion.

b) Balance accurate to 50g and of adequate capacity.

c) Steel rod of 16mm diameter by 600mm long and rounded at one end.

Calibration – The container shall be calibrated y determining the mass of water at 25±5˚C

required to fill it so that no meniscus is percent above the rim of the container, and dividing

the mass in kilograms by 1000 to obtain the volume in m3.

Test Sample

The test is made on material at oven-dry or saturated surface dry condition. The test for voids

is made on material oven-dry and then at the required test moisture content.

Procedure

The container was filled about one third full with the aggregate being discharged as near as

possible above the top of the container. Compactive blows were then given by allowing a

tamping steel rod to fall freely from a height of 50mm above the surface of the aggregate,

with the blows being evenly distributed over the surface. A further two similar quantities of

aggregates is added in the same manner, to fill the container.

The container was filled to over-flowing and the tamping rod was rolled across and in contact

with the top of the container to obtain a smooth surface flush with the top. The mass of the

aggregate in the container was then determined and the bulk density calculated using the

calibrated volume.

24

3.2 TESTS ON CONCRETE

OBJECTIVES

The aim of the experiment was to;

a) To measure the slump of wet concrete

b) To get the compaction factor of the wet concrete

c) To measure the compressive and tensile strengths of the dry concrete

APPARATUS

a) water

b) cement

c) sand

d) 19- 20 mm aggregate

e) Rubber aggregate

f) Bucket

g) Weighing machine

h) Rotating machine

i) Tamping rod

j) Ruler

k) Slump test mold

l) Compaction factor apparatus consisting of 2 hoppers and a cylinder fixed to a rigid

stand.

3.2.1 PREPARATION OF THE RUBBER AGGREGATE

The rubber tire was bought at Kariokor Market, cut and roughened at the market by the

salesmen dealing with scrap tire. The cost of purchase was relatively low. Before making the

batch the rubber was washed in water and later soaked for like two hours then dried on the

opened and turned for maximum exposure of sunlight. This was all done to remove

impurities that may compromise the concretes chemical composition.

25

Plate 8: Manual cutting of the rubber Plate 9: Open drying of the tire pellets

PROCEDURE

The weight of the empty bucket was measured. Using the bucket, measuring cylinder and the

weighing machine all the ingredients (cement, water, sand and aggregate) were measured.

The quantities measured were then placed in the rotating machine with the order; coarse

aggregate, sand, cement and lastly water. The quantities were then mixed with a rotating

machine.

Plate 10: The batch in the rotating machine

3.2.2 Slump test

Concrete was then placed into the frustum. The mold needs to be on a level, rigid surface,

free of vibration. Concrete was then put in the molds in 3 layers and a steel rod was jabbed

into each layer of concrete 25 times to consolidate the concrete in the mold. The top concrete

was then cut off and the mold was carefully lifted off. A ruler was then used to measure the

new height since the previous height of the mold was known.

26

Plate 11: During the tamping Plate 12: Slump measurement

3.2.3 Compaction test

With both trap doors in the hoppers closed and the cylinder covered, the upper hopper was

filled with concrete. Its trap door was then opened so that the concrete fell into the lower

hopper. The trap door of the lower hopper was then opened such that the concrete fell into the

cylinder. The surplus concrete on top was cut off and the mass of the concrete in the cylinder

determined. (This concrete is said to be partially compacted)

The concrete was then emptied and refilled with the same concrete. The cylinder was then

placed in the vibrating machine and concrete was added till when it was to level, the steel rod

was then used to clear off free concrete on the top. The mass of the fully compacted concrete

was then measured.

Plate 13: During the compaction process

27

The remaining concrete was then placed in cylindrical molds and other cubic molds; all of

them having been compacted on the vibrating machine. The cubes and cylinders were

covered with rags for 24 hours then placed under water for curing until after a week when

compressive and tensile strengths were conducted.

Plate 14: Molding of some of the cubes Plate 15: Curing of specimens

3.3 TESTING OF DRY CONCRETE

INTRODUCTION

The cubes are cast in lubricated steel molds with smooth and parallel opposite faces. The

concrete is fully compacted by external vibration. After demolding when set, the cube is

cured under water at constant temperature until testing. The load is applied to two of the faces

against the mold and therefore smooth. This ensures that there are no local stress

concentrations, which would affect the result. The rate of loading affects the strength and this

must be controlled to reach the ultimate strength gradually.

Compressive strength is the capacity of a material or structure to withstand axially directed

pushing forces. When the limit of compressive strength is reached, the concrete crushes.

28

3.3.1 COMPRESSIVE STRENGTH

The cubes were each put in the compressing machine and loaded until they crushed. The

crushing force was then recorded. This was to determine the compressive strength of the

concrete.

Plate 16: Part of a rubberized concrete cube after compression

3.3.2 TENSILE STRENGTH

The cylinder was then placed on the compression machine lengthwise. This was to determine

the tensile strength. A pair of splints was placed on the cylinder one on top and the other one

at the bottom. The machine was then switched on and the force used to split the cylinder

along the centroid measured. This was repeated for the other cylinders.

Tensile strength = (2P/πDL) Kg/cm2

Plate 17: The control cylinder specimen at testing.

29

CHAPTER 4: RESULTS AND ANALYSIS

4.1 THE COARSE AND RUBBER AGGREGATE

4.1.1 FLAKINESS INDEX OF THE COARSE AGGREGATE

Table 3: Flakiness Index

SIEVE

NO.

WEIGHT

RETAINED

(g)

F.I

PASSING RETAINED

2 -

1.5 -

1 -

0.75 996 246 750

0.5 2405 444 1961

0.375 580 94 486

0.25 71 22 49

SUM 836 3246

FLAKINESS INDEX = 836

836+3246

=20.4 %

4.1.2 ACV

𝟕𝟐𝟎

4000 𝑿 𝟏𝟎𝟎 = 𝟏𝟖 %

30

4.1.3 AIV

𝟑𝟎𝟎

3750 𝑿 𝟏𝟎𝟎 = 𝟖 %

4.1.4 SPECIFIC GRAVITY OF SAND

W1 (Weight of oven dried bottle to the nearest 0.001 gms) = 58.5 g

W2 (About 15 gms + density bottle) = 75.5 g

W3 (w2 + water) = 178.0 g

W4 (density bottle cleaned and filled with water) = 168.1 g

Specific gravity = 𝑊2−𝑊1

(𝑊4−𝑊1)−(𝑊3−𝑊2)

=75.5−58.5

(168.1−58.5)−(178.0−75.5)

= 2.41

4.1.5 LAA

𝟒𝟎𝟎𝟎 − 𝟖𝟎𝟎

4000 𝑿 𝟏𝟎𝟎 = 𝟐𝟎 %

31

4.1.6 COMPARING THE COARSE AND RUBBER AGGREGATE

PROPERTIES

Table 4: Comparing aggregate properties

TEST COARSE AGGREGATE RUBBER AGGREGATE

Specific gravity 2.58 1.1

Flakiness index (%) 20.4 4

Aggregate crushing value

(%)

18 5

Aggregate impact value

(%)

8 1

Water absorption (%) 0.4 0.0

Bulk density (Kg/m3) 1600

Los Angeles Abrasion (%) 20 2

32

4.2 MIX DESIGN

4.2.1 SIEVE ANALYSIS OF THE FINE AGGREGATE

Table 5: Sieve analysis of the sand

SIEVE NO.

WEIGHT RETAINED (g)

PASSING (%)

14 3.7 100.0

10 6.3 99.4

5 23 98.4

2.36 67 94.0

1.18 165.5 83.0

0.6 208.8 56.0

0.3 100.7 21.5

0.15 22.4 5.2

0.075 3.2 1.7

33

Table 6: Results on sieve analysis and Graph 1: Cumulative graph on fine aggregate

Pan mass (gm) 127

Initial dry sample mass + pan (gm) 761

Initial dry sample mass (gm) 634 Fine mass (gm) 11

Washed dry sample mass + pan (gm) 750 Fine percent (%) 1.7

Washed dry sample mass (gm) 623

Acceptance

Criteria (%)

Sieve size (mm)

Retained

mass

(gm)

% Retained

(%)

Cumulative

passed

percentage

(%)

Acceptance Criteria

Min(%)

Max

(%)

14 0 0.0 100.0

10 4 0.6 99.4 100

4.76 6 0.9 98.4 89 100

2.36 28 4.4 94.0 60 100

1.18 70 11.0 83.0 30 100

0.6 171 27.0 56.0 15 100

0.3 219 34.5 21.5 5 70

0.15 103 16.2 5.2 0 15

0.075 22 3.5 1.7 0 3

623

34

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Pass

ing

(%)

Sieves (mm)

SIEVE ANALYSIS

35

4.2.2 COARSE AGGREGATE GRADING

Table 7: Results on coarse aggregate grading and Graph 2: Cummulative curve on coarse

aggregate

Dry sample mass (gm) 4052

Sieve size

(mm)

Retained

mass (gm)

% Retained

(%)

Cumulative

passed

percentage

(%)

Acceptance Criteria

Min (%) Max (%)

37.5 0 0.0 100.0 100

20 996 24.6 75.4 90 100

14 2405 59.4 16.1 40 80

10 580 14.3 1.8 30 60

5 71 1.8 0.0 0 10

0.075 0 0.0 0.0

4052

36

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Pass

ing

(%)

Sieves (mm)

37

4.2.3 AGGREGATE COMBINATIONS

Table 8: Aggregate combinations and Graph 3: Aggregate combinations curve

AGGREGATES

Sample no Nominal Size Description Source

1 5-20 mm Coarse Aggrgates

2 0-6 mm

Fine Aggregates-River

Sand

SIEVE ANALYSIS % PASSING

Sample Number 1 2 THEO.

DESIGN

MIX

% in Mix 100 0 0 0 60 40 COMBINED SPEC.

Sieve Size (mm) GRADING Table 5:BS

882:1990

50 0 0 0 100 100 100.0 100

37.5 0 0 0 100 100 100.0 95 100

20 0 0 0 78 100 86.8 45 80

5 0 0 0 0 98 39.2 25 50

0.6 0 0 0 0 56 22.4 8 30

0.15 0 0 0 0 5 2.0 0 8

0.075 0 0 0 0 2 0.8 0 3

38

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

% P

AS

SIN

G

Sieve (mm)

39

4.2.4 TRIAL MIX

Concrete class 25

Aggregate size = 20 mm

Table 17-1: Standard specifications for roads and bridges construction

C25/20 moderate and intermediate exposure gives 28 days strength as 25N/mm2 and a water

to cement ratio of 0.5

Table 17-2: Standard specifications for roads and bridges construction

Minimum cement content for C25/20 = 370 kg/m3

Water = 0.5 x 370 = 185 kg/m3

Total aggregate content = 2400 – (370+185) = 1845 kg/m3

Proportion of aggregates = 60% / 40 %

Coarse aggregate = 60 % x 1845 = 1107 kg/m3

Fine aggregate = 738 kg/m3

a) Batching of the cubes

Volume of a cube = 0.15x0.15x0.15 = 0.0033750 m3

For each mix proportion 9 cubes were required but 12 were designed for because of wastages

during the process.

0.0033750 m3 x 12 = 0.0405 m3

The rotating mixer had a volume of 0.065 m3

PROPORTIONS

Cement = 0.0405 x 370 = 14.99 Kg

Water = 0.0405 x 185 = 7.5 Kg

Coarse aggregate = 0.0405 x 1107 = 44.83 Kg

Fine aggregate = 0.0405 x 738 = 30 Kg

40

b. Batching of the cylinders

Volume of a cube = 𝜋0.0752𝑥 0.3 = 0.0053014 m3

For each mix proportion 6 cylinders were required but 8 were designed for because of

wastages.

0.0053014 m3 x 8 = 0.042413 m3

PROPORTIONS

Cement = 0.042413 x 370 = 15.7 Kg

Water = 0.042413 x 185 = 7.85 Kg

Coarse aggregate = 0.042413 x 1107 = 46.95 Kg

Fine aggregate = 0.042413 x 738 = 31.3 Kg

In total making 9 cubes and six cylinders required about 0.083 m3 but the mixer had a volume

of 0.065 m3 therefore I did the mixing of each proportion in three stages for efficient mixing.

Design of slump was to be around 10 t0 35mm, compation factor between 0.95 to 0.8 with 28

days compressive strength of around 25 N/mm2 and tensile strength of around 3.0 N/mm2

Table 9: Results obtained from the trial mix

COMPRESSIVE STRENGTH

(N/mm2)

TENSILE STRENGTH

(N/mm2)

C.FACTOR SLUMP

(mm)

7 days 14 days 28 days 7 days 28 days

16

23

30

2.3

3.1

0.92

37

The design was therefore rendered fit.

41

4.2.5 REPLACEMENT OF COARSE AGGREGATE WITH THE RUBBER

TIRE

Apart from the control mix five other mix proportions were adopted i.e. 5%, 10%, 15%, 20 %

and 30 %.

Proportions for cement, water and fine aggregate remained the same.

Replacement of the coarse aggregate was by weight.

Cubes

Table 10: Weight replacement in cubes

MIX

PROPORTIONS

COARSE

AGGREGATE

(Kg)

RUBBER

AGGREGATE

(Kg)

Control (0 %) 44.83 -

5 % 42.59 2.24

10 % 40.35 4.48

15 % 38.11 6.72

20 % 35.86 8.97

30 % 31.38 13.45

SUM 233.12 35.86

Cylinders

Table 11: Weight replacement in cylinders

MIX

PROPORTIONS

COARSE

AGGREGATE

(Kg)

RUBBER

AGGREGATE

(Kg)

Control (0 %) 46.95 -

5 % 44.60 2.35

10 % 42.25 4.70

15 % 39.91 7.04

20 % 37.55 9.40

30 % 32.86 14.09

SUM 244.12 37.58

For all the batches I used therefore approximately 75 kg of rubber aggregate.

42

Plate 18: A sample of the rubber aggregate I used, about 20 mm

4.3 RESULTS ON FRESH CONCRETE

4.3.1 SLUMP

Table 12: Results on the workability test

MIX

PROPORTIONS

SLUMP (mm)

Control (0 %) 38

5 % 41

10 % 45

15 % 46.5

20 % 47

30 % 50.5

43

Graph 4: Graph of slump

The introduction of recycled rubber tires to concrete significantly increased the slump and

workability. The trial mix was designed to have a slump of around 30 mm.

4.3.2 COMPACTION FACTOR

Table 13: Results on compaction factors

0

10

20

30

40

50

60

0% 5% 10% 15% 20% 25% 30% 35%

Slu

mp

,mm

Mix proportions

Graph of Slump

MIX

PROPORTIONS

C.F

Control (0 %) 0.92

5 % 0.895

10 % 0.888

15 % 0.856

20 % 0.834

30 % 0.823

44

Graph 5: Graph of compaction factor

As the rubber content in the concrete increased it was noted that the compaction factor

reduced.

0.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0% 5% 10% 15% 20% 25% 30% 35%

Co

mp

acti

on

fac

tor

Mix Proportion

Graph of Compaction Factor

45

4.4 RESULTS ON DRY CONCRETE

4.4.1 UNIT WEIGHT

CUBES

Table 14: Unit weight of cubes (Kg)

MIX

PROPORTIONS

7 days Ave. 28 days Ave.

SAMPLES 01 02 03 01 02 03

Control (0 %) 8.20 8.22 8.15 8.19 8.30 8.28 8.34 8.31

5 % 7.81 7.77 7.63 7.71 8.01 8.10 7.95 8.02

10 % 7.60 7.53 7.58 7.57 7.83 7.79 7.80 7.81

15 % 7.38 7.41 7.49 7.43 7.65 7.61 7.58 7.61

20 % 7.23 7.31 7.27 7.27 7.35 7.30 7.39 7.35

30 % 7.01 7.19 7.07 7.09 7.25 7.31 7.08 7.21

Graph 6: Graph of Cubes Unit weight

6

6.5

7

7.5

8

8.5

0% 5% 10% 15% 20% 30%

Wei

ght,

kg

Mix Proportions

Cubes Unit Weights

7 day Ave. 28 day Ave.

46

CYLINDERS

Table 15: Unit weight of cylinders (Kg)

MIX

PROPORTIONS

7 days Ave. 28 days Ave.

SAMPLES 01 02 03 01 02 03

Control (0 %) 13.5 13.78 13.53 13.60 14.30 14.38 14.40 14.36

5 % 13.10 13.11 13.21 13.14 13.90 13.88 13.96 13.91

10 % 12.80 12.88 12.75 12.81 13.50 13.56 13.48 13.51

15 % 12.53 12.49 12.48 12.50 13.10 13.13 13.26 13.16

20 % 12.01 11.98 12.24 12.08 12.73 12.86 12.88 12.82

30 % 11.32 11.48 11.43 11.41 12.40 12.00 12.13 12.18

Graph 7: Graph of Cubes Unit weight

Because of low specific gravity of rubber particles, unit weight of mixtures containing rubber

decreases with the increase in the percentage of rubber content.

Moreover, increase in rubber content increases the air content, which in turn reduces the unit

weight of the mixtures.

0

5

10

15

20

Control (0 %) 5% 10% 15% 20% 30%

Wei

ght,

kg

Mix Proportions

Graph of Cylinders weight

7 day Ave. 28 day Ave.

47

4.4.2 COMPRESSIVE STRENGTHS

Table 16: Compressive strengths (N/mm2)

MIX

PROPORTI

ONS

7 days Ave

.

14 days Ave

.

28 days Ave

.

SAMPLES 01 02 03 01 02 03 01 02 03

Control (0

%)

16.0 15.5

6

15.5

8 15.7

1

25.3

8

26.4

1

26.4

4 26.0

7

30.0

1

29.8

8

29.7

8 29.8

9

5 % 15.0

0

15.1

5

15.1

1 15.0

9

23.0

0

23.4

8

23.5

5 23.3

4

28.0

2

28.0

0

28.0

5 28.0

2

10 % 14.0

7

13.9

8

13.7

6 13.9

4

21.9

8

22.3

2

21.8

5 22.0

5

27.0

0

27.5

5

27.2

6 27.2

6

15 % 13.2

4

12.8

5

12.7

7 12.9

5

20.0

0

21.0

7

19.9

9 20.3

5

25.0

7

25.3

4

25.0

1 25.1

4

20 % 11.6

6

11.5

9

11.9

8 11.7

4

18.9

8

19.1

1

18.8

7 18.9

9

24.0

8

24.1

3

24.1

7 24.1

3

30 % 10.9

8

11.0

4

11.0

3 11.0

2

19.6

7

18.0

0

19.4

3 19.0

1

23.5

5

23.4

7

22.9

8 23.3

3

Graph 8: Graph of compressive strengths

0

5

10

15

20

25

30

35

Control (0 %) 5% 10% 15% 20% 30%Co

mp

ress

ive

stre

ngt

h, N

/mm

2

Mix Proportion

Graph of compressive strength

7 day Ave. 14 day Ave. 28 day Ave.

48

4.4.3 TENSILE STRENGTHS

Table 17: Tensile strength (N/mm2)

MIX

PROPORTIONS

7 days Ave. 28 days Ave.

SAMPLES 01 02 03 01 02 03

Control (0 %) 2.5 2.45 2.53 2.49 3.01 3.05 2.94 3.00

5 % 2.46 2.37 2.36 2.40 2.90 2.86 2.74 2.83

10 % 2.30 2.35 2.40 2.35 2.79 2.83 2.84 2.82

15 % 2.24 2.33 2.34 2.30 2.64 2.71 2.62 2.66

20 % 2.28 2.21 2.15 2.21 2.56 2.45 2.57 2.53

30 % 2.0 2.15 2.19 2.11 2.41 2.39 2.44 2.41

Graph 9: Graph of tensile strengths

0

0.5

1

1.5

2

2.5

3

3.5

0% 5% 10% 15% 20% 30%

Ten

sile

str

en

gth

,N/m

m2

Mix proportions

Graph of tensile strengths

7 day Ave.

28 day Ave.

49

4.5 Cost Considerations in Rubberized Concrete

The use of recycled tires in concrete construction is an infant technology and the number of

used tires that are recycled in civil engineering applications is very low at the current time.

However, any new concrete products developed for the market need to be feasible in terms of

cost, including material costs and production processes or the resulting advantage of

improved properties should surpass any cost increment that may occur.

4.5.2 Cost Savings due to Material substitution

The other approach is to consider the replacement value of materials used in current products.

This calculates the acceptable price for rubber aggregate based upon the current price of

virgin materials less an allowance for the cost of process changes.

In this approach, the principle is that the use of rubber aggregate should be cost neutral. The

cost of rubber aggregates also varies widely depending on the source of the rubber and the

amount of processing during production.

4.5.3 Cost Savings by Protecting the Environment

The accumulation of used tires at landfill sites presents the threat of uncontrolled fires,

producing a complex mixture of chemicals harming the environment and contaminating soil

and vegetation. Reuse and recycling generally costs the environment less in resources to the

benefit of wider society.

Additional benefits from using used rubber tires in landscaping applications include benefits

related to avoided disposal space savings (landfill space, land space), reduced risks to human

health from tire piles, and avoided emissions from tire pile fires. The need for quarrying and

waste disposal is reduced with the associated environmental impacts as well.

50

Provided that the cost of rubber aggregate can be kept to the lower end of the range, it can be

seen that the cost increase should not be onerous for manufacturers. The less stringent

processing requirements for rubber aggregate used in concrete are likely to further reduce the

cost of rubber aggregate in this application.

Waste tire at the Market was bought at KES 5 per Kg because the small tyre was going at

KES 50 and the truck tyre at KES 250.

Cutting was done at KES 15 per Kg, a total of 75 Kg was used for the project amounting to

around KES 1500.

51

CHAPTER 5: CONCLUSION AND RECCOMENDATION

5.1 CONCLUSION

Reduced weight, compressive and tensile strengths of rubber derived concrete do limit its use

in some structural applications, but it has few desirable benefits;

a) Reduction in dead loads making savings in foundations and reinforcements.

b) Better sound insulation

c) Toughness resistance

d) Higher impact

e) Lower density; the lower the density the better the heat insulation.

f) Improved fire resistance

g) Less water absorption

The introduction of recycled rubber tires into concrete significantly increased the slump and

workability. Even though SSS was not conducted it is evident that rubberized concrete can’t

resist chemical attacks arising from ground water and polluted air. It can therefore not be

used in septic systems even though it has less absorption.

The light unit weight qualities of rubberized concrete may be suitable for various

construction applications;

a) Partition walls

b) Casting structural steel to protect against fire and corrosion

c) Where vibration damping is required such as in foundation, bunkers and for trench

filling.

d) Stone baking

e) In building as an earthquake shock wave absorber

f) Rendering of roof top surfaces for insulation and water proofing

g) Highway embankments

h) Pipe bedding, paving slabs and retaining walls

Adhesion between rubber particles and other constituents materials can be improved by pre-

treating the rubber aggregates.

52

5.2 RECCOMENDATIONS

Since the use of rubber aggregates in concrete construction is not a common trend in a

country like Kenya. Many studies and research works need to be carried out in this area and

academic institutions should play a major role.

Tire manufacturers and importers should be aware of the environmental consequences

of waste tires and they should have research centers that promote an environmental

friendly way of tire reprocessing.

Most of the time, it is observed that designers and contractors go to a high strength and

expensive concrete to get few improved properties such as impact resistance in parking

areas and light weight structures for particular applications. Nevertheless, these properties

can be achieved through the application of rubberized concrete by first conducting laboratory

tests regarding the desired properties.

Since the long -term performance of these mixes were not investigated in the present

study, the use of such mixes is recommended in places where high strength of

concrete is not as important as the other properties.

Future studies should be continued in the field of rubber derived concrete as part of the

extension of this research work.

53

REFERENCE

[1] Wikipedia the Free Encyclopedia

[2] The Rubber Manufacturers Association, http://www.rma.org, 2009

[3] Sidney Mindess, Young J.F. and David Darwin, Concrete, 2nd edition, New Jersey:

Prentice hall, 2003

[4] Neville A.M., Properties of Concrete, 4th edition, Addison Wesley Longman ltd, 1996.

[5] Cairns R., Kew H.Y. and Kenny M.J., The Use of Recycled Rubber Tires in

Concrete Construction, Glasgow: The Onyx Environmental Trust, 2004.

[6] Michelle Danko, Edgar Cano and Jose Pena, Use of Recycled Tires as Partial

replacement of Coarse Aggregate in the Production of Concrete, Purdue University

Calumet, 2006

[7] Kaloush K.E, George B. W. and Han Z., Properties of Crumb Rubber Concrete,

Arizona: Arizona State University, 2004.

[8] Ling T.C. and Hasanan M.N., Properties of Crumb Rubber Concrete Paving Blocks

with and without Facing Layer, Kuala lumpur, 2006.

[9] Kang Jingfu, Han Chuncui and Zhang Zhenli, Roller-Compacted Concrete using

Tire-Rubber Additive, Tianjin, 2008

[10] BS 882, Testing aggregate, 1988

[11] Standard Specifications for Roads and Bridge Construction

54

APPENDIX