PARTIAL REPLACEMENT OF CEMENT WITH RICE HUSK ASH (RHA) AS FILLER IN ASPHALT CONCRETE DESIGN

BY

UZOMA HENRY ONYEIWU

U09CV2003

A PROJECT SUBMITTED TO THE DEPARTMENT OF CIVIL ENGINEERING,

AHMADU BELLO UNIVERSITY, ZARIA-NIGERIA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE AWARD OF BACHELOR OF

ENGINEERING

(B. ENG) IN CIVIL ENGINEERING

FEBRUARY, 2014

1

DECLARATION

I hereby declare that the content of this project written by me is purely a record of my

research work, under the supervision of Engr. A.A. Murana. All quotations and literatures

cited from other sources have been duly acknowledged.

__________________________________

______________________

Uzoma Henry Onyeiwu Date

2

CERTIFICATION

The project entitled “Partial Replacement of Cement with Rice Husk Ash as Filler in Asphalt

Concrete” by Uzoma Henry Onyeiwu meets the regulations governing the award of the

degree of Bachelor of Engineering, Department of Civil Engineering, Faculty of Engineering,

Ahmadu Bello University, Zaria and is approved for its contribution to the knowledge and

literary presentation.

______________________________

__________________

Engr A. A Murana Date

Project Supervisor

______________________________

__________________

Dr I. Abubakar Date

Head of Department

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DEDICATION

This work is dedicated to Almighty God for His goodness, mercy and grace all through also

to my parents, siblings and friends for their prayers, support and encouragement during this

pursuit.

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ACKNOWLEDGEMENT

All gratitude goes to God almighty that in His love, guidance and protection has used several

individuals to contribute greatly to my educational career. I am highly indebted to my

supervisor, Engr. A. A. Murana for his time to supervise; give suggestions and advice during

the course of this research work despite his losses during the period may God reward you and

your family. My appreciation goes to all the lecturers of the Department of Civil Engineering

for their support, may God bless you all. To my lovely parents Mr. Emmanuel I. Onyeiwu

and Mrs. Veronica N. Onyeiwu, thanks for your prayers, care and love may God continue to

strengthen and grant you long life, good health and prosperity in all you do. I love you both.

My appreciation also goes to my Uncle Engr. Eric C. Onyeiwu and his family for their

support, may God continue to increase you.

Lastly, I sincerely appreciate my Siblings, my friends: Tolu, Samuel, Dorathy and Wisdom,

my Roommates, course mates, members of Quintessence theatre, G.O.D ministry, F.C.S and

the entire staff of ECO project services ltd. for their contribution. May God be with you all

and continue to bind us in love, good health and protection. Thank you all.

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TABLE OF CONTENT

Content Page

Title page i

Declaration ii

Certification iii

Dedication iv

Acknowledgement v

Table of content vi

Appendices xii

List of tables xiii

List of figures xv

Abstract xvi

CHAPTER ONE: INTRODUCTION 1

1.1 Background 1

1.1.2 Supplementary Cementitious Materials (SCMs) 1

1.1.3 Rice Hush 2

1.2 Aim and Objectives of the Research 3

1.2.1Aim 3

1.2.2Objectives 3

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1.3 Statement of the Problem 3

1.4 Justification for the Study 4

1.5 Scope of Research 5

CHAPTER TWO: LITERATURE REVIEW 6

2.1 Bituminous Pavement Structure 6

2.2 Desirable Properties of a Bituminous Mix 7

2.3 Rice Husk Ash 7

2.4 Use of RHA as supplementary cementitious material in Portland cement concrete 8

2.4.1 Temperature Effect 9

2.4.2 Workability 9

2.4.3 Setting Time 9

2.4.4 Compressive Strength 10

2.5 Effect of Rice Husk Ash as Cement Admixture 11

2.6 RHA as A Tundish Powder in Steel Casting Industries 12

2.7 RHA as an Active Pozzolan 13

2.8 Manufacturing Refractory Bricks 14

2.9 RHA as Silicon Chips 14

2.10 RHA as Adsorbent for Gold- Thiourea Complex 15

2.11 RHA as Vulcanizing Rubber 15

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2.12 RHA as Soil Ameliorant 15

2.13 RHA used in production of Asphalt 15

CHAPTER THREE: METHODOLOGY 16

3.1 Materials 16

3.2 Properties Considered In Mix Design 16

3.3 Test on Materials 16

3.3.1 Test on Coarse Aggregate 16

3.3.1.1 Sieve Analysis of Coarse Aggregates 16

3.3.1.2 Specific Gravity 17

3.3.1.3 Bulk Density and Void of Coarse Aggregate 18

3.3.1.4 Aggregate Impact Value 18

3.3.1.5 Aggregate Crushing Value 19

3.3.2 Tests on Fine Aggregates 19

3.3.2.1 Sieve Analysis of fine Aggregates 19

3.3.2.2 Specific gravity of fine aggregate 20

3.3.2.3 Bulk Density and Void of Fine Aggregate 21

3.3.3 Preliminary Tests on Bitumen 22

3.3.3.1 Penetration Test 22

3.3.3.2 Ductility Test 22

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3.3.3.3 Solubility Test 23

3.3.3.4 Flash and Fire Point Test 23

3.3.3.5 Viscosity Test

23

3.3.3.6 Softening Point (Ring and Ball) Test. 23

3.4Preliminary Tests on Filler Materials 24

3.4.1Test on Cement and RHA (OPC) 24

3.4.1.1 Consistency Tests 24

3.4.2Chemical Analysis of RHA and Cement 25

3.5 Marshall Method of Asphalt-Concrete Mix Design 26

3.5.1 Marshall Method of Mix Design 27

3.5.1.1 Preparation of test specimens 27

3.5.1.2 Bulk density of the compacted specimen 28

3.5.1.3 Stability test 28

3.5.2 Analysis of Results from Marshall Test 29

3.5.2.1 Bulk specific gravity of aggregate (Gbam) 29

3.5.2.2 Maximum specific gravity of aggregate mixture (Gmp) 30

3.5.2.3 Percent voids in compacted mineral aggregate (VMA) 30

3.5.2.4 Percent air voids in compacted mixture (Pav) 31

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3.5.3 Determination of Optimum Binder Content ` 31

3.5.4 Evaluation and Adjustment of mix Design 32

CHAPTER FOUR: ANALYSIS AND DISCUSSION OF RESULTS 34

4.1Tests on pure bitumen 34

4.1.1 Penetration Test 35

4.1.2 Viscosity Test 35

4.1.3 Flash and Fire Point Test 35

4.1.4 Solubility Test 35

4.1.5 Ductility Test 36

4.2 Tests on RHA 36

4.3 Test on cement 37

4.3.1 Setting Times 37

4.3.2 Soundness 38

4.4 Tests on Coarse and Fine Aggregate 38

4.4.1 Sieve Analysis Test 38

4.5 Marshall Test Result 40

4.5.1 Optimum Bitumen Content 45

4.5.2 Determination of Optimum RHA Percentage 45

CHAPTER FIVE: CONCLUSION AND RECOMENDATION 49

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5.1 Conclusion 49

5.2 Recommendation 49

REFERNCE 51

APPENDICES

Appendix A 57

Plate 1: Students carrying out preliminary and laboratory tests on materials. 57

Plate 2: Marshall Stability & Flow Test Setup 58

Plate 3: Marshall Specimen Extractor 59

Appendix B 60

Table: Stability Correlation Ratio 60

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LIST OF TABLES

Table

Page

3.1: Sieve analysis of 3000g of coarse aggregate 17

3.2: Specific Gravity Test results for coarse Aggregate 18

3.3: Bulk Density for Coarse Aggregate 18

3.4: Sieve analysis 1000g fine aggregate 20

3.5: Specific Gravity Test for Fine Aggregate 21

3.6: Bulk Density for fine Aggregate 21

3.7 Test results on Aggregate 22

3.8 Test Results on Bitumen 24

3.9: Initial and Final Setting Times of Cement and RHA 25

3.10: Chemical Analysis of RHA and Cement (Weight %). 25

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3.11 Summary of Marshall Analysis At 0% RHA/ 100% OPC 33

3.12 Summary of Marshall Analysis At 5.5% Optimum Bitumen Content 33

4.1: Result of preliminary tests on bitumen 34

4.2: Comparison of test on rice husk ash with standard 36

4.3: Comparison of Test Result on the Cement with Standard 37

4.4: Comparison of Test Results on Aggregates with Standards 40

4.5: Typical Marshall Mixture Design Criteria 41

4.6: Typical Marshal Mix Minimum VMA 44

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LIST OF FIGURES

Figure Page

3.1 Test Specimen Preparations 28

4.1: Graph showing the graduation curve of coarse aggregate 39

4.2: Graph showing the graduation curve of fine aggregate 39

4.3: Graph of Stability against Bitumen Content 42

4.4: Graph of Flow against Bitumen Content 42

4.5: Graph of CDM against Bitumen Content 43

4.6: Graph of VIM against Bitumen Content 43

4.7: Graph of VMA against Bitumen Content 44

4.8: Graph of VFB against Bitumen Content 45

4.9: Graph of Stability against Percentage RHA at 5.5% Bitumen Content 45

4.10: Graph of Flow against Percentage RHA at 5.5% Bitumen Content 46

4.11: Graph of CDM against Percentage RHA At 5.5% Bitumen Content 46

4.12: Graph of VIM against Percentage RHA At 5.5% Bitumen Content 47

4.13 Graph of VMA against Percentage RHA At 5.5% Bitumen Content 47

4.14: Graph of VFB (%) against Percentage RHA At 5.5% Bitumen Content 48

ABSTRACT

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This research work is based on the use of Rice Husk Ash (RHA) as filler in Asphalt concrete

pavement. Asphalt mix design was carried out using Marshall Stability method to test the

performance of the material in terms of its known engineering properties. Several trial mixes

with bitumen contents of 4.5%, 5.5%, 6.5% and 7.5% were produced in order to obtain the

optimum bitumen content. This investigation focuses on the partial replacement of cement

with Rice Husk Ash in the obtained optimum bitumen content in the following order 0%

(control), 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, and 25%. A total of 42 mix

specimens were produced for this experiment, 12 of these mix specimens were compacted

with each percentage of bitumen content, to determine the optimum bitumen content, and 30

specimens were produced to determine the optimum Rice Husk Ash content in terms of the

asphalt concrete strength. From the Marshall Stability-flow test and density-void analysis,

results obtained show that the performance of mix containing 0% of RHA (control), have

Stability, flow, Compacted density of mix (CDM), Void in Mix (VIM), Void in Mineral

Aggregate (VMA), and Void filled with Bitumen (VFB) as 6.7KN, 3.0mm, 1.49g/cm³,

39.4%, 47.27% and 16.63% respectively at an optimum bitumen content of 5.5%. The sample

prepared with 10% RHA as filler have Stability, flow, CDM, VIM, VMA, and VFB of

7.63%, 2.19mm, 1.78g/cm³, 28.23%, 36.77%, and 23.23% respectively at an optimum

bitumen content of 5.5% which satisfied the provision in the Standard Specification

requirement of Marshall Criteria by Asphalt Institute (1979). Thus for maximum strength,

10% RHA is recommended as partial replacement of cement as filler in Asphalt Concrete

mix.

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CHAPTER ONE

INTRODUCTION

1.1 Background

A pavement could be defined as a hard surface constructed over the natural soil for the

purpose of providing a stable, safe and smooth transportation medium for the vehicles

(Merriam, 2013).

Hot mix asphalt (HMA) is a generic term that includes many different types of mixtures of

aggregate and asphalt cement (binder) produced at elevated temperatures (generally between

300-350ºF) in an asphalt plant. Typically, HMA mixtures are divided into three mixture

categories: dense-graded; open-graded; and gap-graded as a function of the aggregate

gradation used in the mix (Griffiths and Thom, 2011).

1.1.2 Supplementary cementitious materials (SCMs)

Supplementary cementitious materials are often incorporated in Asphalt concrete mix to

reduce cement contents, improve workability, increase strength and enhance durability.

The use of SCMs dates back to the ancient Greeks who incorporated volcanic ash with

hydraulic lime to create a cementing mortar. The Greeks passed this knowledge on to the

Romans, who constructed such engineering marvels as the Roman aqueducts and the

coliseum, which still stands today. Early SCMs consisted of natural, readily available

materials such as volcanic ash or diatomaceous earth. More recently, strict air-pollution

controls and regulations have produced an abundance of industrial by-products that can be

used as supplementary cementitious materials such as flyash, silica fume and blast furnace

slag. The use of such by-products in concrete construction not only prevents these products

from being land-filled but also enhances the properties of concrete in the fresh and hydrated

states. SCMs can be divided into two categories based on their type of reaction: hydraulic or

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pozzolanic. Hydraulic materials react directly with water to form cementitious compounds,

while pozzolanic materials chemically react with calcium hydroxide (CH), a soluble reaction

product, in the presence of moisture to form compounds possessing cementing properties.

The word “pozzolan” was actually derived from a large deposit of Mt. Vesuvius volcanic ash

located near the town of Pozzuoli, Italy. Pozzolanic SCMs can be used either as an addition

to the cement or as a replacement for a portion of the cement. Most often an SCM will be

used to replace a portion of the cement content for economical or property-enhancement

reasons. Here is a brief overview of one of the more common pozzolans used in the

manufactured concrete products industry (Neuwald, 2010)

1.1.3 Rice husk

Rice husk is an agricultural residue which accounts for 20% of the 649.7 million tons of rice

produced annually worldwide. The produced partially burnt husk from the milling plants

when used as a fuel also contributes to pollution, and efforts are being made to overcome this

environmental issue by utilizing this material as a supplementary cementitious material.

The chemical composition of rice husk is found to vary from one sample to another due to the

differences in the type of paddy, crop year, climate and geographical conditions. Rice husk is

one of the most widely available agricultural wastes in many rice producing countries around

the world. Globally, approximately 600 million tons of rice paddy is produced each year. On

average 20% of the rice paddy is husk, giving an annual total production of 120 million

tonnes. In majority of rice producing countries much of the husk produced from processing

of rice is either burnt or dumped as waste. Burning of RH in ambient atmosphere leaves a

residue, called rice husk ash. For every 1000kg of paddy milled, about 220kg (22 %) of husk

is produced, and when this husk is burnt in the boilers, about 55kg (25 %) of RHA is

generated. The non-crystalline silica and high specific surface area of the RHA are

responsible for its high pozzolanic reactivity (Miyagawa and Gaweesh, 2001).

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A pozzolanic reaction occurs when a siliceous or aluminous material get in touch with

calcium hydroxide in the presence of humidity to form compounds exhibiting cementitious

properties (Papadakis et al., 2009). Data from reaction results between RHA and CH

indicates that the amount of CH by 30% RHA in cement paste begins to decrease after 3

days, and by 91 days it reaches nearly zero, while in the control paste, it is considerably

enlarged with hydration time (Yu et al., 1999).

1.2 Aim and Objectives of the research

1.2.1 Aim

The aim of this research work is the partial replacement of cement with rice husk ash (RHA)

using Marshall Stability Method.

1.2.2 Objectives

i. To carry out preliminary tests on rice husk ash and all other asphalt concrete

constituents, to determine its physical and chemical composition.

ii. Preparation of trail mix by varying aggregates, ordinary Portland cement, rice

husk ash, with predetermined percentages of bitumen content.

iii. To determine the engineering properties of the specimen mix, using Marshall

Stability method.

iv. Determination of optimum rice husk ash conten for Asphalt concrete.

1.3 Statement of the problem

The safe disposal of waste materials is an increasingly economic and environmental concern

in the several parts of the world (Ahmed and Lovell, 2003). The volume of waste materials

generated continues to increase even though the importance of recycling is being

acknowledged. Many of these wastes produced will remain in the environment for hundreds,

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perhaps thousands, of years. The production of non-degradable waste materials, combined

with a growing consumer population, has resulted in a waste disposal crisis. One solution to

this crisis lies in the recycling of the waste materials into useful by-products (Kandhal, 2002).

Recently, there have been several reported uses of crop waste material for pavement

construction. One of which is an investigation of the potential use of rice husk ash as a

supplemental cementing material for the replacement of Portland cement in PCC mixtures

(NAPA Special Report 152, 2001).

The replacement of cement up to 20% with an equal amount of the rice husk ash contributed

with an initial (1 to 3 days) increase in compressive strength, but as time passed the strength

was reduced due to effect of alkali aggregate reactivity (Mehta, 2002). It has also been

discovered that rice husk ash is efficient as a pozzolanic material; it is rich in amorphous

silica (88.32%) (Mahmud, 2009).

Since RHA has been proven to be an efficient pozzolanic material when tested in Portland

cement concrete (PCC) mixtures, this research will go a long way in helping us know its

behaviour when used as a supplementary cementitious material in asphalt concrete.

1.4 Justification for study

Several recent researches have focused on the need for producing durable and cost effective

concrete by using pozzolana as a partial replacement for Ordinary Portland cement

(Muhammad, 2010). According to Muhammad, the use of RHA significantly improves the

mortar strength at the 20% replacement level and at the later age. Also research has shown

that RHA has been used in lime pozzolana mixes and could be a suitable partly replacement

for Portland cement ( Nicole et al., 2000; Sakr 2006; Sata etal., 2007; etc).

Thus the use of agricultural waste (such as Rice Husk Ash) will considerably reduce the cost

of construction and as well reducing the environmental hazards they cause, this ultimately

suggests this research work.

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1.5 Scope of Research

This study is limited to the evaluation of compressive strength of asphalt concrete having its

filler been supplemented with rice husk ash. This will be achieved by carrying out

preliminary studies on the constituents of asphalt concrete, and the use of Marshall Stability

test in determining the mechanical properties of the asphalt concrete mix.

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CHAPTER TWO

LITERATURE REVIEW

Aside from the use of rice husk ash (RHA) as supplementary material in concrete several

other uses of RHA which will be of importance in determining its characteristics are

discussed in this chapter. Asphalt concrete is one of the most important construction

materials, study of its constituents are essential for preparing desired mix design so as to

develop required strength necessary for structures. The durability of the structure depends on

the care with which ingredients of asphalt concrete are selected, mixed, placed and

compacted.

2.1 Bituminous pavement structure

Asphalt concrete pavements are flexible pavements. Flexible pavements are so named

because of the total pavement structure deflects, or flexes, under loading. A flexible

pavement structure is typically composed of several materials. Each layer receives the load

from the above layer, spreads them out, and then passes on the loads to the next layer below.

Thus the further down in the pavement structure a particular layer is, the less load it must

carry (Washington Asphalt Pavement Association (WAPA), 2010).

In order to take maximum advantage of this property, material layers are usually arranged in

order of descending load bearing capacity with the highest load bearing capacity material on

the top and the lowest load bearing capacity material on the bottom

[http//:www.asphaltwa.com/2010/09/17/pavementstucture].

Many factors affect the ability of a bituminous paving mixture to meet these requirements.

Mixture design, construction practices, properties of component materials, and the use of

additives all play important roles in the resulting structural characteristics of a pavement.

21

Factors affecting design include;

I. Volume and composition of traffic.

II. Environment and strength of the sub grade soil over which the road is to be built.

III. Selecting the most economically available materials for use and thickness of the layer.

It is therefore important to note that the design of new road pavement involves two

considerations, which are; Pavement Design and Mix Design Method.

2.2 Desirable properties of a bituminous mix

i. Stability to meet traffic demand

ii. Bitumen content to ensure proper binding and water proofing

iii. Voids to accommodate compaction due to traffic

iv. Flexibility to meet traffic loads, especially in cold season

v. Sufficient workability for construction

vi. Economical mix

2.3 Rice husk ash

Rice Husk is an agricultural waste obtained from milling of rice. About 108 tonnes of rice

husk is generated annually in the world. In Nigeria, about 2.0 million tonnes of rice is

produced annually, while in Niger state, about 96,600 tones of rice grains is produced in 2000

[5]. Meanwhile, the ash has been categorized under pozzolana, with about 67-70% silica and

about 4.9% and 0.95% Alumina and iron oxides, respectively [5]. The silica is substantially

contained in amorphous form, which can react with the CaOH librated during the hardening

of cement to further form cementations compounds (Aziz et al, 2005).

Rice plant is one of the plants that absorbs silica from the soil and assimilates it into its

structure during the growth (Smith et al., 1986). Rice husk is the outer covering of the grain

22

of rice plant with a high concentration of silica, generally more than 80-85% (Siddique,

2008). It is responsible for approximately 30% of the gross weight of a rice kernel and

normally contains 80% of organic and 20% of inorganic substances. Rice husk is produced in

millions of tons per year as a waste material in agricultural and industrial processes. It can

contribute about 20% of its weight to Rice Husk Ash (RHA) after incineration (Anwar et al.,

2001). RHA is a highly pozzolanic material (Tashima et al., 2004). The non-crystalline silica

and high specific surface area of the RHA are responsible for its high pozzolanic reactivity.

RHA has been used in lime pozzolana mixes and could be a suitable partly replacement for

Portland cement (Smith et al., 1986; Zhang et al., 1996; Nicole et al., 2000; Sakr 2006; Sata

et al., 2007; etc).

2.4 Use of RHA as supplementary cementitious material in Portland cement

concrete

Recently there are considerable efforts worldwide of utilizing indigenous and waste,

materials in concrete. One of such materials is the rice husk which under controlled burning,

and if sufficiently ground, the ash that is produced can be used as a cement replacement

material in concrete (Anwar et al, 2001). As a consequence of this characteristic, RHA is an

extremely reactive pozzolanic substance appropriate for use in lime-pozzolan mixes and for

Portland cement substitution. The reactivity of RHA associated to lime depends on a

combination of two factors: namely the non-crystalline silica content and its specific surface

(Dakroury et al., 2008). Cement replacement by rice husk ash accelerates the early hydration

of C3S. The increase in the early hydration rate of C3S is attributed to the high specific

surface area of the rice husk ash (Feng et al., 2004). This phenomenon specially takes place

with fine particles of RHA.

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2.4.1 Temperature effect

Cement blended with pozzolanic materials usually has decreased heat of hydration compared

to pure cement during the period of C3S hydration (Mostafa et al., 2005). The rate of

hydration heat of the cement added with pozzolanic material mainly depends on three factors,

C3S hydration, aluminate hydration and pozzolanic reaction (Hewlet, 1998). Likewise, RHA

demonstrate increase of hydration heat behaviour (positive values) during the first 12 h. The

increase in the hydration heat of cement blended with rice husk ash is due to (1) the

acceleration of the early hydration of C3S ascribed to the high specific surface area of the rice

husk ash ( Feng et al., 2004) and (2) pozzolanic reaction.

2.4.2 Workability

Studies by Owen (1979) and Jiang et al. (2000) have indicated that with high volume fly ash

concrete mixtures, up to 20% reduction in water requirements can be achieved. However,

there is the possibility of water reduction higher than 20% in the presence of RHA. This is

because fine particles of rice husk ash get absorbed on the oppositely charged surfaces of

cement particles and prevent them from flocculation. The cement particles are thus

effectively dispersed and will trap large amounts of water meaning that the system will have

a reduced water requirement to achieve a given consistency. The particle packing effect is

also responsible for the reduced water demand in plasticizing the system (Mehta, 2004).

2.4.3 Setting time

Initial and final setting time tests were shown to yield different results on plain cement paste

and pastes having rice husk ash (Dakroury et al., 2008). The studies by Ganesan et al. (2008),

and Bhanumathidas et al. (2004) showed that RHA increases the setting time of pastes. Just

like other hydraulic cement, the reactivity of rice husk ash cement depends very much upon

24

the specific surface area or particle size. The rice husk ash cement with finer particles

exhibits superior setting time behaviour.

2.4.4 Compressive strength

Inclusion of RHA as partial replacement of cement enhances the compressive strength of

concrete, but the optimum replacement level of OPC by RHA to give maximum long term

strength enhancement has been reported between 10% up to 30%. All these replacement

levels of RHA are in percentage by weight of the total binder material. Mahmud et al. (1996)

reported 15% cement replacement by RHA as an optimal level for achieving maximum

strength. Zhang et al. (1996) suggested 10% RHA replacement exhibited upper strength than

control OPC at all ages. Ganesan et al. (2008) concluded that concrete containing 15% of

RHA showed an utmost compressive strength and loss at elevated content more than 15%.

Dakroury et al. (2008) reported that using 30% RHA as a replacement of part of cement

could be considered optimum for all content of W/C ratios in investigated mortars because of

its high value of compressive strength. Zhang et al. (1996) reported that achieving higher

compressive strength and decrease of permeability in RHA blended concrete is perhaps

caused by the reduced porosity, reduced calcium hydroxide content and reduced width of the

interfacial zone between the paste and the aggregate. According to Rodriguez (2006) the

RHA concrete had higher compressive strength at 91 days in comparison to that of the

concrete without RHA. The increase in compressive strength of concretes with residual RHA

may also be justified by the filler (physical) effect. It is concluded that RHA can provide a

positive effect on the compressive strength of concrete at early ages.

In summary, the use of RHA in concrete has been associated with the following essential

assets:

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Increased compressive and flexural strengths (Zhang et al., 1996; Ismaila 1996;

Rodriguez 2006)

Reduced permeability (Zhang et al., 1996; Ganesan et al., 2007)

Increased resistance to chemical attack (Chindaprasirt et al., 2007)

Increased durability (Coutinho 2002)

Reduced effects of alkali-silica reactivity (ASR) (Nicole et al., 2000)

Reduced shrinkage due to particle packing, making concrete denser (Habeeb et al., 2009)

Enhanced workability of concrete (Coutinho 2002; Habeeb et al., 2009; Mahmud et al.,

2009)

Reduced heat gain through the walls of buildings (Lertsatitthanakorn et al., 2009)

Reduced amount of super plasticizer (Sata et al., 2007)

Reduced potential for efflorescence due to reduced calcium hydracids (Chindaprasirt et

al., 2007)

2.5 Effect of Rice Husk Ash as Cement Admixture

Rice husk ash is one of the promising pozzolanic materials that can be blended with Portland

cement for the production of durable concrete and at the same time it is a value added

product. Addition of rice husk ash to Portland cement does not only improve the early

strength of concrete, but also forms a calcium silicate hydrate (CSH) gel around the cement

particles which is highly dense and less porous, and may increase the strength of concrete

against cracking (Saraswathy and Ha- Won, 2007).

26

Many countries have the problem of shortage of conventional cementing materials. Recently

there are considerable efforts worldwide of utilizing indigenous and waste, materials in

concrete. One of such materials is the rice husk which under controlled burning, and if

sufficiently ground, the ash that is produced can be used as a cement replacement material in

concrete (Anwar et al, 2001). In the preparation of mortar cubes, 555g of standard sand, 185g

of cement sample and a certain volume of distilled water were mixed thoroughly. Similarly,

cement, rice husk ash (RHA) and sand, with percentage of cement replaced by RHA were

mixed together, until a homogeneous mixture was obtained (Table 1). The measured quantity

of water was then sprayed on to the mixture. The mixture was further mixed until a paste of

the required workability was obtained (Oyetola and Abdullahi, 2006).

Compressive strength tests were carried out on six mortar cubes with cement replaced by rice

husk ash (RHA) at five levels (0, 10, 20, 30, 40 and 50%). After the curing age of 3, 7, 14 and

28 days, the compressive strengths of the cubes at 10% replacement were 12.60, 14.20,

22.10, 28.50 and 36.30 N/mm2 respectively and increased with age of curing but decreased

with increase in RHA content for all mixes. The chemical analysis of the rice husk ash

revealed high amount of silica (68.12%), alumina (1.01%) and oxides such as calcium oxide

(1.01%) and iron oxide (0.78%) responsible for strength, soundness and setting of the

concrete. It also contained high amount of magnesia (1.31%) which is responsible for the

unsoundness. This result, therefore, indicated that RHA can be used as cement substitute at

10% and 20% replacement and 14 and 28 day curing age (Dabai et al, 2002).

2.6 RHA as a Tundish Powder in Steel Casting Industries

RHA is used by the steel industry in the production of high quality flat steel. It is in

continuous casting that RHA plays a role. RHA is an excellent insulator, having low thermal

conductivity, high melting point, low bulk density and high porosity. It is this insulating

27

properly that makes it an excellent “tundish powder”. Tundish powders are used to insulate

the tundish, prevent rapid cooling of the steel and ensure uniform solidification (Harold,

2002).

2.7 RHA as an Active Pozzolan

Portland cement produces an excess of lime. Adding a pozzolan, such as RHA, combines

with lime in the presence of water, results in a stable and more amorphous hydrate (Calcium

Silicate). It is stronger, less permeable and more resistant to chemical attack (Chaiyanena,

1992). The potential for good but inexpensive housing in developing countries is especially

great. Studies have been carried out all over the world, such as in Nigeria, Kenya, Indonesia,

and Guyana on the use of low cost building blocks (RHA Market Study, 2003). Ordinary

Portland Cement (OPC) is expensive and unaffordable to produce low strength concrete

block. Generally around 7Mpa strength is achieved at 14 days with mix proportion of 20:80

ratio of lime: RHA as binder. A study showed that replacing 50% of Portland cement with

RHA was effective and the resultant concrete cost 25% less (Tuts, 1994).

After vehicle and utility emissions cement manufacturing is the largest industrial producer of

CO2 and accounts for over 50% of all industrial CO2 emissions; for every ton of cement

produced 1 to 1.25 tons of CO2 are produced (Muga et al., 2005). The potential economic

savings (U.S.dollars) and reduction of CO2 emissions(tons) if rice husk ash is utilized on a

global basis in the construction of either spring - boxes or gravity fed water systems for the

1billion people worldwide that do not have access to safe drinking water, $141 to $451

million could be saved while the total anthropogenic CO2 emissions could decrease from

0.95 million to 3.8 million tons if rice husk ash were substituted for Portland Cement at a

25% level (Muga et al., 2005).

28

2.8 Manufacturing Refractory Bricks

One of the potentially major profitable uses of RHA is in the in the manufacture of refractory

bricks (Adylov, et al., 2005) .Due to the insulating properties, RHA has been used in the

manufacture of refractory bricks. Refractory bricks are used in furnaces which are exposed to

extreme temperatures, such an in blast furnaces used for producing molten iron and in the

production of cement clinker. Bricks from RHA were reported to be good heat insulators up

to extreme temperatures, such as 1450°C, and have a low thermal conductivity of about

0.3Kcal/m hr °C and good resistance to compression. Such bricks normally contain 80-98%

ash and 2-20% CaO+MgO (Gidde et al., 2007).

2.9 RHA as Silicon Chips

The first step in semiconductor manufacture is the production of a wafer, a thin round slice of

semiconductor material, which is usually silicon. Purified polycrystalline silicon

(traditionally created from sand) is heated to a molten liquid and a small piece of silicon seed

placed in the molten liquid. As the seed is from the melt the liquid cools to form a single

crystal ingot which is then grand and sliced to form wafers that form the starting material for

manufacturing integrated circuits (RHA Market Study, 2003).Silicon dioxide though

naturally generated from sand is extracted after a fusion of high temperature whose procedure

requires energy and investment intensive driving the cost of silica higher. It is therefore

worthwhile extracting purer silica from rice husk ash with minimal cost which also

contributes to the practice of waste management engineering (Omatola, 2009).

The Indian Space Research Organization has successfully developed technology for

producing high purity precipitated silica from RHA that has a potential use in the computer

industry. A Consortium of American and Brazilian Scientists have also developed ways to

extract and purify silicon with the aim of using it in semiconductor manufacture (Science

29

News, 1994). A company in Michigan is purifying RHA into silica for silicon chip

manufacture.

2.10 RHA as Adsorbent for a Gold-Thiourea Complex.

Gold is often in nature as a compound with other elements. One way it is extracted is to leach

it by pumping suitable fluids through the gold bearing strata. RHA produced by heating rice

husks at 300°C has been shown to adsorb more gold – thiourea than the conventional used

activated carbon (RHA Market Study, 2003).

2.11 RHA as Vulcanizing Rubber

White RHA can be used as filler for natural rubber compounds (Siriwandena et al., 2001).

White RHA increases mechanical properties such as, tensile strength, tear strength, resilience

and hardness, if used as a partial replacement of silica as a bonding agent.

2.12 RHA as Soil Ameliorant

There are reports of RHA being used as a soil ameliorant to help break up clay soils and

improve soil structure (Confidential Report, 1998).Its porous nature also assists with water

distribution in the soil. Research in USA has also been carried out on using it as a potting

substrate for bedding plants .It has also been found to increase the pH of the soil, so was

recommended for use with plants that require alkaline soil.

2.13 RHA used in the Production of Asphalt

Rice husk ash and palm oil fiber have been used as filler for stone mastic asphalt. The

physical characteristics of stone asphalt with rice husk ash and palm oil fiber were favourable

for surfacing in road construction. The result of asphalt with RHA and palm oil fiber as filler

and binder passed standard specifications (Jeffrey et al., 2002).

30

CHAPTER THREE

METHODOLOGY

3.1 Materials

Materials used are the constituent materials of asphalt concrete; bitumen, aggregate (fine and

coarse) and filler material (cement and rice husk ash).

3.2 Properties considered in Mix Design

Good asphalt concrete pavement function well because they are designed, produced and

placed in such a way as to give them certain desirable properties. These are several properties

that contribute to the quality of asphalt concrete pavements. They include stability, durability,

impermeability, workability, flexibility, fatigue resistance and skid resistance (Asphalt

Institute, 1983).

3.3 Tests on material

Tests to determine the engineering properties of bitumen and aggregates, chemical

composition of RHA and ordinary Portland cement were conducted.

3.3.1 Tests on Coarse Aggregate

The following tests were carried out on aggregate in order to determine its suitability for use

in the asphalt concrete;

3.3.1.1 Sieve Analysis of Coarse Aggregates

Aggregate grading affects the strength of concrete mainly indirectly, through its important

effect on the water/cement ratio required for a given workability. A badly graded aggregate

31

requires a higher water/cement ratio and hence results in a weak concrete. This practical is

aimed at determining the grading of coarse aggregate and their zones.

Sieve Analysis Test Result:

percentageretained =mass retained

totalmassof sample ×100 3.1

Table 3.1: Sieve analysis of 3000g of coarse aggregate

Sieve size(mm)

Weight retained(g)

Percentage retained(%)

Percentage passing(%)

53.00 0 0.00 100

37.60 0 0.00 100

25.40 138 4.60 95.419.00 1456 48.53 46.8712.70 589 19.63 27.24

9.52 621 20.70 6.546.30 141 4.70 1.84

pan 55 1.83 0.00

3.3.1.2 Specific Gravity

The specific gravity of an aggregate is the ratio between the weight of a given volume of

the aggregate and the weight of an equal volume of water. Specific gravity provides a

means of expressing the weight-volume characteristics of materials. Specific gravity of an

aggregate considered as a measure of the quality of material in terms of strength.

32

Table3.2: Specific Gravity Test results for coarse Aggregate

Test number Test 1 Test 2Weight of gravel (B) 1000g 1000gWeight of gas jar (P) 2520g 2520gWeight of gas jar + water + gravel (Ps) 3135g 3163g

Specific gravity (S.G) = B

P+B−PS2.60 2.80

Average specific gravity = sample1+sample2

2 ` 2.70

3.3.1.3 Bulk Density and Void of Coarse Aggregate

Aim: To determine the bulk density and void ratio of fine and coarse aggregate

Bulk density = weight of samplevolumeof water 3.2

Table 3.3: Bulk Density for Coarse Aggregate

Sample number

W1 W2 W3 Ww Ws Volume of cylinder (m3)

Bulk density (Kgm-3)

1 9.72 19.65 15.30 9.93 5.58 0.01 5582 9.72 19.65 15.20 9.93 5.48 0.01 548

Void Ratio = 1 – (( bulk density

specific gravity ) ×1000) 3.3

= 1 – (( 5532.7 ) ×1000)

= 0.8

3.3.1.4 Aggregate Impact Value

Toughness is the property of a material to easiest impact. Due to moving loads the

aggregates are subjected to pounding action or impact and there is possibility of stones

breaking into smaller pieces. Therefore a test designed to evaluate the toughness of stones

i.e., the resistance of the stones to fracture under repeated impacts may be called Impact

33

test on aggregates. The aggregate Impact value indicates a relative measure of the

resistance of aggregate to a sudden shock or an Impact, which in some aggregates differs

from its resistance to a slope compressive load in crushing test. A modified Impact test is

also often carried out in the case of soft aggregates to find the wet Impact value after

soaking the test sample.

The maximum allowable aggregate Impact value for water bound Macadam; Sub-Base

coarse 50% where as cement concrete used in base course is 45%. WBM base course with

Bitumen surface in should be 40%. Bituminous Macadam base course should have A.I.V

of 35%. All the surface courses should possess an A.I.V below 30%.

3.3.1.5 Aggregate Crushing Value

This is one of the major Mechanical properties required in a road stone. The test evaluates

the ability of the Aggregates used in road construction to withstand the stresses induced by

moving vehicles in the form of crushing. With this the aggregates should also provide

sufficient resistance to crushing under the roller during construction and under rigid tyre

rims of heavily loaded animal drawn vehicles.

The aggregate crushing value of the coarse aggregates used for cement concrete pavement

at surface should not exceed 30% and aggregates used for concrete other than for wearing

surfaces, shall not exceed 45% as specified by Indian Standard (IS) and Indian Road

Congress (IRC).

3.3.2 Tests on Fine Aggregates

3.3.2.1 Sieve Analysis of fine Aggregates

Aggregate grading affects the strength of concrete mainly indirectly, through its important

effect on the water/cement ratio required for a given workability. A badly graded

34

aggregate requires a higher water/cement ratio and hence results in a weak concrete. This

practical is aimed at determining the grading of coarse aggregate and their zones.

Sieve Analysis Test Result:

percentageretained =mass retained

totalmassof sample ×100 3.4

Table3.4: Sieve analysis 1000g fine aggregate

Sieve size Weight retained(g)

Percentage retained(%)

Percentage passing(%)

5.00 mm 15 1.5 98.52.36 mm 48 4.8 93.71.18mm 210 21.0 72.7600µm 489 48.9 23.8300µm 170 17.0 6.8150µm 39 3.9 2.975µm 11 1.1 1.8Pan 18 1.8 0.0

3.3.2.2 Specific gravity of fine aggregate

The specific gravity of an aggregate is the ratio between the weight of a given volume of the

aggregate and the weight of an equal volume of water. Specific gravity provides a means of

expressing the weight-volume characteristics of materials. Specific gravity of an aggregate

considered as a measure of the quality of material in terms of strength.

Specific Gravity Test result

Specific gravity (S.G) =B

P+B−PS 3.5

Table3.5: Specific Gravity Test for Fine Aggregate

35

Test number Test 1 Test 2

Weight of sand (B) 500g 500g

Weight of pycnometer (P) 1600g 1600g

Weight of pycnometer + water + sand (Ps) 1908g 1915g

Specific gravity (S.G) = B

P+B−PS2.60 2.70

Average specific gravity = sample1+sample2

2 ` 2.65

3.3.2.3 Bulk Density and Void of Fine Aggregate

Aim: To determine the bulk density and void ratio of fine and coarse aggregate

Bulk density = weight of samplevolumeof water 3.6

Table3.6: Bulk Density for fine Aggregate

Sample number

W1 W2 W3 Ww Ws Volume of cylinder (m3)

Bulk density (Kgm-3)

1 1.40 4.10 3.40 2.70 2.00 2.70×10-3 740.742 1.40 4.05 3.50 2.65 2.10 2.65×10-3 792.75

Void Ratio = 1 – (( bulk density

specific gravity ) ×1000) 3.7

= 1 – (( 7672.7 ) ×1000)

= 0.7

Table 3.7: Test results on Aggregate

36

PROPERTY UNIT TEST RESULTS

Aggregate Crushing Value (ACV)

% 20.50

Aggregate Impact Value (AIV)

% 16.70

Specific Gravity (Coarse Aggregate)

- 2.70

Specific Gravity (Fine Aggregate)

- 2.65

Bulk density/ Void ratio (Coarse Aggregate) (Kgm-3)

553/0.8

Bulk density/Void ratio (Fine Aggregate) (Kgm-3)

767/0.7

3.3.3 Preliminary Tests on Bitumen

3.3.3.1 Penetration Test

Penetration value below 20 is associated with bad cracking of road surfacing. While cracking

rarely occurs when the penetration exceeds 30 for normal road work 30 – 500 penetration

bitumen is in common use. Generally, higher penetration bitumen is preferred for use in cold

climate and smaller penetration bitumen is used in hot climate areas.

3.3.3.2 Ductility Test

The ductility test is a measure of the internal cohesion of bitumen. The ductility of

bituminous material is measured by the distance in centimetre to which it will elongate before

breaking when a standard briquette specimen of the material is pulled apart at a specified

speed and a specified temperature. Bitumen possessing high ductility is normally

cementitious and adheres well to aggregates.

3.3.3.3 Solubility Test

37

Determines the purity of bitumen in relation to the possibility of contamination by foreign

materials. A solubility of 99.5% in carbon disulphide (CS2) is found in all British

specifications. For refinery bitumen, (CS2) is highly inflammable, hence the safer is carbon

tetrachloride (CCl4) or methylene chloride can be used for normal solubility tests without

significant loss of accuracy .And for tars, we use toluene.

3.3.3.4 Flash and Fire Point Test

Flash and fire point is safety related which suitable caution should be taken to eliminate fire

hazards during heating and manipulation of bitumen. Flash point is the temperature of the

flame application that causes a bright flash. The point at which the material gets ignite band

continues to burn for five seconds is the fire point.

3.3.3.5 Viscosity Test

It determines in a large measure how the material will function when used, such as the

readiness to flow at a given temperature required for correct application.

3.3.3.6 Softening Point (Ring and Ball) Test.

This is in order that specifications of many bituminous binders for the particular purposes are

often with or without softening point requirements. It is used to specify hand bitumen and it

helps characterise its rate of setting. It may indicate the adequacy to flow in service.

Table 3.8 Test Results on Bitumen

38

TEST UNIT TEST RESULTS

Penetration at 25˚C mm 105Viscosity at 60˚C mm³/s 121.83

Flash and Fire point ˚C 259Solubility % 96Ductility cm >100

3.4 Preliminary Tests on Filler Materials

3.4.1 Test on Cement and RHA (OPC)

Dangote brand of ordinary Portland cement was used in the experiment. Some preliminary

tests like setting times and soundness tests were carried out. The initial and final setting times

were considered using cement and different percentages of rice husk (RHA).

3.4.1.1 Consistency Tests

The setting time is determined by observing the penetration of a needle into cement paste of

Standard Consistence until it reaches a specified value.

The soundness is determined by observing the volume expansion of cement paste of Standard

Consistence as indicated by the relative movement of two needles.

Cement paste of standard consistence has a specified resistance to penetration by a standard

plunger. The water required for such a paste is determined by trial penetrations of pastes with

different water contents.

Table 3.9: Initial and Final Setting Times of Cement and RHA

39

Cement (%) RHA (%) Initial Setting Time (Mins)

Final Setting Time (Mins)

100 0 122 18390 10 136 22780 20 154 25570 30 165 27560 40 213 35050 50 281 402

3.4.2 Chemical Analysis of RHA and Cement

The chemical analysis of the samples was conducted at the centre for energy research and

training (CERT), Ahmadu Bello University, Zaria, using minipal which is a compact energy

dispersive X-ray spectrometer designed for the elemental analysis of a wide range of samples.

The results of the analysis are shown below in comparison with the chemical composition of

cement, and will be discussed in subsequent chapter.

Table 3.10: Chemical Analysis of RHA and Cement (Weight %).

Constituents Concentration Unit in RHA Concentration Unit in OPCSiO2 68.12 23.43

CaO 1.01 64.40

Al2O3 1.06 4.84

Fe2O3 0.78 4.08

K2O 21.23 0.29SO3 0.137 2.79

LOI 18.25 5.68

Free Lime - 1.50

3.5 Marshall Method of Asphalt-Concrete Mix Design

40

Bituminous mixes (sometimes called asphalt mixes) are used in the surface layer of road and

airfield pavements. The mix is composed usually of aggregate and asphalt cements. Some

types of bituminous mixes are also used in base-coarse. The design of asphalt paving mix, as

with the design of other engineering materials is largely a matter of selecting and

proportioning constituent materials to obtain the desired properties in the finished pavement

structure.

The desirable properties of Asphalt mixes are:

1. Resistance to permanent deformation: The mix should not distort or be displaced when

subjected to traffic loads. The resistance to permanent deformation is more important at high

temperatures.

2. Fatigue resistance: the mix should not crack when subjected to repeated loads over a period

of time.

3. Resistance to low temperature cracking. This mix property is important in cold regions.

4. Durability: the mix should contain sufficient asphalt cement to ensure an adequate film

thickness around the aggregate particles. The compacted mix should not have very high air

voids, which accelerates the aging process.

5. Resistance to moisture-induced damage.

6. Skid resistance.

7. Workability: the mix must be capable of being placed and compacted with reasonable

effort.

8. Low noise and good drainage properties: If the mix is to be used for the surface (wearing)

layer of the pavement structure.

41

3.5.1 Marshall Method of Mix Design

In this method, the resistance to plastic deformation of a compacted cylindrical specimen of

bituminous mixture is measured when the specimen is loaded diametrically at a deformation

rate 53 of 50 mm per minute. There are two major features of the Marshall method of mix

design. (i) density-voids analysis and (ii) stability-flow tests. The Marshall stability of the

mix is defined as the maximum load carried by the specimen at a standard test temperature of

60°C. The flow value is the deformation that the test specimen undergoes during loading upto

the maximum load. Flow is measured in 0.25 mm units. In this test, an attempt is made to

obtain optimum binder content for the type of aggregate mix used and the expected traffic

intensity.

3.5.1.1 Preparation of test specimens

The coarse aggregate, fine aggregate, and the filler material should be proportioned so as to

fulfil the requirements of the relevant standards. The required quantity of the mix is taken so

as to produce compacted bituminous mix specimens of thickness 63.5 mm approximately.

1200 gm of aggregates and filler are required to produce the desired thickness. The

aggregates are heated to a temperature of 175° to 190°C the compaction mould assembly and

rammer are cleaned and kept pre-heated to a temperature of 100°C to 145°C. The bitumen is

heated to a temperature of 121°C to 138°C and the required amount of first trial of bitumen is

added to the heated aggregate and thoroughly mixed. The mix is placed in a mould and

compacted with number of blows specified. The sample is taken out of the mould after few

42

minutes using sample extractor.

Figure 3.1 Test Specimen Preparations

3.5.1.2 Bulk density of the compacted specimen

The bulk density of the sample is usually determined by weighting the sample in air and in

water. It may be necessary to coat samples with paraffin before determining density. The

specific gravity Gb(cm) of the specimen is given by

Gb(cm)= Wa

Wa−Ww 3.8

Where,

W a = weight of sample in air (g)

W w = weight of sample in water (g)

3.5.1.3 Stability test

In conducting the stability test, the specimen is immersed in a bath of water at a temperature

of 60° ± 1°C for a period of 30 minutes. It is then placed in the Marshall Stability testing

machine and loaded at a constant rate of deformation of 5 mm per minute until failure. The

total maximum in kN (that causes failure of the specimen) is taken as Marshall Stability. The

43

stability value so obtained is corrected for volume. The total amount of deformation is units

of 0.25 mm that occurs at maximum load is recorded as Flow Value. The total time between

removing the specimen from the bath and completion of the test should not exceed 30

seconds.

3.5.2 Analysis of Results from Marshall Test

Following results and analysis is performed on the data obtained from the experiments.

3.5.2.1 Bulk specific gravity of aggregate (Gbam)

Since the aggregate mixture consists of different fractions of coarse aggregate, fine aggregate,

and mineral filler with different specific gravities, the bulk specific gravity of the total

aggregate in the paving mixture is given as

Gbam=

Pca+Pfa+Pmf

Pca

Gbca+Pfa

G bca+Pmf

Gbca

3.9

Where,

Gbam = bulk specific gravity of aggregates in paving mixtures.

Pca , Pfa ,Pmf = percent by weight of coarse aggregate, fine aggregate, and mineral filler in

paving mixture.

Gbca ,Gbfa ,Gbmf = bulk specific gravities of coarse aggregate, fine aggregate and mineral filler,

respectively.

44

3.5.2.2 Maximum specific gravity of aggregate mixture (Gmp)

The maximum specific gravity of aggregate mixture should be obtained as per ASTM D2041,

however because of the difficulty in conducting this experiment an alternative procedure

could be utilized to obtain the maximum specific gravity using the following equation:

Gbam=

Pca+Pfa+Pmf

Pca

Gbca+Pfa

Gbca+Pmf

Gbca

3.10

Where,

Gmp = maximum specific gravity of paving mixtures.

Pca , Pfa ,Pmf = percent by weight of coarse aggregate, fine aggregate, and mineral filler

in paving mixture.

Gbca ,Gbfa ,Gbmf = bulk specific gravities of coarse aggregate, fine aggregate, and mineral

filler, respectively.

3.5.2.3 Percent voids in compacted mineral aggregate (VMA)

The percent voids in mineral aggregate (VMA) is the percentage of void spaces between the

granular particles in the compacted paving mixture, including the air voids and the volume

occupied by the effective asphalt content

VMA = 100 - GbcmPta

G bam3.11

Where,

VMA = percent voids in mineral aggregates.

Gbcm = bulk specific gravity of compacted specimen

45

Gbam = bulk specific gravity of aggregate.

Pta = aggregate percent by weight of total paving mixture.

3.5.2.4 Percent air voids in compacted mixture (Pav)

Percent air voids is the ratio (expressed as a percentage) between the volume of the air voids

between the coated particles and the total volume of the mixture.

Pav=100Gmp−Gbcm

Gmp3.12

Where,

Pav = percent air voids in compacted mixture

Gmp = maximum specific gravity of the compacted paving mixture

Gbcm = bulk specific gravity of the compacted mixtures

3.5.3 Determination of Optimum Binder Content

Five separate smooth curves are drawn (Figure 11.4) with percent of asphalt on x-axis and the

following on y-axis

unit weight

Marshall stability

Flow

VMA

Voids in total mix (Pav)

Optimum binder content is selected as the average binder content for maximum density,

maximum stability and specified percent air voids in the total mix. Thus

46

B0=B1+B2+B3

33.13

Where,

B0 = optimum Bitumen content.

B1 = % asphalt content at maximum unit weight.

B2 = % asphalt content at maximum stability.

B3 = % asphalt content at specified percent air voids in the total mix.

3.5.4 Evaluation and Adjustment of mix Design

The overall objective of the mix design is to determine an optimum blend of different

components that will satisfy the requirements of the given specifications (Table 11.3). This

mixture should have:

1. Adequate amount of asphalt to ensure a durable pavement.

2. Adequate mix stability to prevent unacceptable distortion and displacement when traffic

load is applied.

3. Adequate voids in the total compacted mixture to permit a small amount of compaction

when traffic load is applied without bleeding and loss of stability.

4. Adequate workability to facilitate placement of the mix without segregation.

If the mix design for the optimum binder content does not satisfy all the requirements of

specifications (table 11.3) it is necessary to adjust the original blend of aggregates. The trial

mixes can be adjusted by using the following guidelines.

1. If low voids: The voids can be increased by adding more coarse aggregates.

47

2. If high voids: Increase the amount of mineral filler in the mix.

3. If low stability: This condition suggests low quality of aggregates. The quality of

aggregates should be improved. (Use different aggregate or use cement coated aggregate)

Table 3.11 Summary of Marshall Analysis At 0% RHA/ 100% OPC

Bitumen content (%)

Stability (kN)

Flow (mm)

CDM (g/cm³)

VIM (%) VMA (%) VFB (%)

4.5 3.97 2.43 1.78 28.51 36.22 21.315.5 6.70 3.0 1.49 39.40 47.27 16.636.5 2.73 5.64 1.53 36.78 46.33 20.617.5 3.81 3.56 1.55 35.15 46.75 24.818.5 2.96 4.1 1.65 30.08 43.88 31.45

Table 3.12 Summary of Marshall Analysis At 5.5% Optimum Bitumen Content

RHA content (%)

Stability (kN)

Flow (0.25mm)

CDM (g/cm³)

VIM (%) VMA (%) VFB (%)

0.0 6.70 3.0 1.49 39.40 47.27 16.63

5.0 5.75 3.06 1.80 27.13 35.93 24.49

7.5 7.27 2.73 1.77 28.63 37.17 22.98

10.0 7.63 2.19 1.78 28.23 36.77 23.23

12.5 5.02 2.56 1.79 27.82 35.40 23.5715.0 4.46 3.06 1.78 28.23 36.75 23.19

17.5 5.30 2.19 1.79 27.82 36.38 23.53

20.0 4.56 2.54 1.80 27.13 35.79 24.20

22.5 5.85 2.08 1.81 36.46 45.23 19.39

25.0 3.45 2.19 1.81 36.46 45.07 19.10

48

CHAPTER FOUR

ANALYSIS AND DISCUSSION OF RESULTS

4.1 Tests on pure bitumen

From the table presented in chapter three on the various preliminary tests on bitumen, the

results obtained are now compared with the standard code of practice to assess for its quality

for usage. The results obtained in the test conducted are within the limits of code

specifications, therefore the bitumen can be judge as good for usage. The table below

interprets the results obtained

Table 4.1: Result of preliminary tests on bitumen

Test Test Method (ASTM)

Specification by codes for penetration Grade*

Results obtained

40/50 60/70 80/100

Penetration at 25˚C (mm)

D5 40-50 60-70 80-100 98

Flash point and fire point (˚C) Min.

D92 232 232 219 240 and 259 respectively.

Solubility in carbon tetrachloride (CCl4) Min. (%).

D2042 99 99 99 99

Specific gravity at 25˚C Min.

D70 0.97-1.02 0.97-1.02 0.97-1.02 1.00

Ductility at 25˚C Min (mm)

D113 - 50 75 100

Viscosity(mm³/s) D4402 220-400 120-250 75-150 138

49

4.1.1 Penetration Test

Penetration is a measure of consistency of bitumen. It serves as a yardstick in classification of

bitumen into standard grades. It is used to classify bitumen for purchasing and identification

purposes.

From the result obtained (98mm), the penetration falls within penetration grade 80-100 which

is suitable for HMA design.

4.1.2 Viscosity Test

This test determines the readiness of bitumen to flow at a given temperature required for field

application or spray on site.

From the viscosity test carried out, the result obtained (138mm³/sec) conforms to the

viscosity requirement (75-150mm³/sec) for penetration grade of 80-100; it is therefore

suitable for HMA design.

4.1.3 Flash and Fire Point Test

This is a safety precaution test. It is used to determine the temperature at which the bitumen

material will ignite with fire when subjected to heat. From the flash and fire point carried out,

the result obtained (240˚C) conforms to the ASTM D92 requirement (219˚C) for penetration

grade of 80-100; it is therefore suitable for HMA design.

4.1.4 Solubility Test

Solubility test is a quality control test done to determine in relation to the possibility of

contamination with mineral matter or improperly refined. From the solubility test carried out,

the

50

Result obtained (99%) conforms to the ASTM D2042 requirement (99%) for penetration

grade of 80-100; it is therefore suitable for HMA design.

4.1.5 Ductility Test

This is a measure of the internal cohesion of bitumen. High ductility bitumen is normally

cementitious and adheres well to aggregates. It’s also a measure of tensile property of

bitumen. High ductility bitumen has greater flexibility and tenacity. Conversely, low ductility

bitumen is more likely to crack under heavy load and severe changes in temperature.

From the ductility test carried out, the result obtained (100mm) conforms to the ASTM D113

requirement (75mm) for penetration grade of 80-100; it is therefore suitable for HMA design.

4.2 Tests on RHA

The test result obtained was compared with those specified by ASTM C 618-78 for use

admixture in concrete.

Table 4.2: Comparison of test on rice husk ash with standard

Mineral admixture class Test resultN F C

Silicon dioxide (SiO2), plus aluminum oxide (Al2O3), plus iron oxide (Fe2O3) min, %

70.0 70.0 50.0 69.96

Sulfur trioxide (SO3), max, % 4.0 5.0 5.0 0.14

From the table, it I observed that Rice husk ash is composed of several oxides and according

to ASTM C618-78 which specifies that a material having a combined weight of silica,

aluminium and iron oxides of a minimum value of 50% (for class C), 70%(for class N), 70%

(for class F) by weight of fraction is considered a pozzolana. The Rice husk ash used for this

research is of class C.

Thus from the result table, we have;

51

Silica (SiO2) = 68.12%

Aluminium (Al2O3) =1.06%

Iron (Fe2O3) = 0.78%

Total weight = 69.96

Therefore, it can be said that rice husk ash is pozzolanic and can be used as mineral filler in

HMA design as a partial replacement of cement.

4.3 Test on cement

The following are the main properties of cement which are important to civil engineering:

fineness, consistency, setting times, soundness, crushing strength and heat of gyration. It is

these properties that the engineer uses to judge the suitability of cements.

Three out of these properties were tested on the sample of cement used for this project work,

which are; consistency, setting times and consistency of cement.

Table 4.3: Comparison of Test Result on the Cement with Standard

Property Unit Test results Code used Code specificationInitial setting time Min 122 BS EN 196 PART 3

(1995)>45mins

Final setting time Hr-min 3hrs 3mins BS EN 196 PART 3 (1995)

<10hrs

soundness mm 4.2 BS EN 196 PART 3 (1995)

<10mm

Specific gravity - 2.43 ASTM C188 3.15

4.3.1 Setting Times

Initial setting time is defined as the period elapsing between the time when water is added to

cement and the needle of 1mm square section fails to pierce the test block to a depth of about

52

5mm from the bottom of the mould. A period of 45 minutes is the minimum initial setting

time (specified by BS 12, 146 and AASHTO T-129, E-131) for ordinary Portland cement,

which agrees with the test result obtained.

Final setting time is defined as the period elapsing between the time when water is added to

the cement and the time at which the needle of 1mm square section with 5mm attachment

makes an impression on the test sample. A period of 600 minutes (10 hours) is the maximum

time specified for the final set for Portland cement. Therefore, since the standards are in

agreement with the test result obtained, it is then concluded that the cement used for this

study is an ordinary Portland cement.

4.3.2 Soundness

The test specifies that the increase in the distance between the indicator of the le-chatelier

mould, after the heating of the cement paste in the required manner (chapter 3), should not

exceed 10mm (BS 12, AASHTO- 129).

From the test conducted, the difference between the lengths was 4.2mm which is less than

10mm; therefore the cement is ordinary Portland cement and is suitable for engineering

purposes.

4.4 Tests on Coarse and Fine Aggregate

4.4.1 Sieve Analysis Test

Table in the previous chapter ,showed the result of the laboratory test (sieve analysis ) carried

out to obtain standard grading for fine and coarse aggregate as shown in table and graphs

plotted respectively. For fine aggregate fell within the limits of BS 882 zone 1, therefore the

aggregate is well graded and suitable for use in the concrete mix. While for coarse aggregate,

the grading curve fell within the specified unit by BS 882, this showed that the 20mm

53

maximum size aggregate is well graded and suitable for use in the asphalt concrete mix. The

graduation curve for both coarse and fine aggregates are shown in figures 4.1 and 4.2 below.

1 10 1000

10

20

30

40

50

60

70

80

90

100

sieve size (mm)

perc

enta

ge p

assin

g (%

)

Figure 4.1: Graph showing the graduation curve of coarse aggregate

0.01 0.1 1 100

10

20

30

40

50

60

70

80

90

100

sieve size (mm)

perc

enta

ge p

assin

g (%

)

Figure 4.2: Graph showing the graduation curve of fine aggregate

54

The table below shows the strength properties which are measures of mechanical properties

(crushing and impact tests) of the aggregate and specific gravity is a measure of aggregate

density.

Table 4.4: Comparison of Test Results on Aggregates with Standards

Property Unit Test

Result

Code used Code specification

Aggregate crushing value % 20.50 BS 882 PART112 <30

Aggregate impact value % 16.70 BS 882 PART111 <30

Specific gravity (Coarse) 2.70 ASTM C136 2.6-2.9

Specific gravity (Fine) 2.65 ASTM C136 2.6-2.9

The values obtained from the tests on aggregates are substantial typical value of Aggregate

Crushing Value (ACV), Aggregate Impact Value (AIV) and Specific Gravity (SG) for the

aggregate favourable to the quoted code of specifications as such the aggregate is suitable for

HMA design.

4.5 Marshall Test Result

The Marshall stability of the mix is defined as the maximum load carried by the specimen at

a standard test temperature of 60˚C. The flow value is the deformation that the test specimen

undergoes during loading up to the maximum load. Flow is measured in 0.25mm units. In this

test, an attempt is made to obtain optimum binder content for the type of aggregate mix used

and the expected traffic intensity.

55

Table 4.5: Typical Marshall Mixture Design Criteria

DescriptionType IBase course

Type IIBinder orleveling course

Type IIIWearing course

Min. Max. Min. Max. Min. Max.

Marshallspecimens(ASTM D 1559)No. of comp.Blows, each end ofspecimen

75 75 75

Stability, kN. 2224 3336 6672Flow (0.25mm or 0.01 inch) (mm)

8[ 2]

16[ 14]

8[ 2]

16[ 14]

8[ 2]

16

[14]

VMA

Air voids, %

Aggregate voids

filled with

bitumen, %

Immersion

compression

specimen

(AASHTO T 165)

index of retainedstrength, %

13

3

60

70

8

80

14

3

65

70

8

85

15

4

70

70

6

85

56

4.5 5.5 6.5 7.5 8.50

1

2

3

4

5

6

7

8

Bitumen Content (%)

Stab

ility

(kN

)

Figure 4.3: Graph of Stability against Bitumen Content

Stability is the maximum load developed during the test; it is an indication of strength in the

compacted material. The stability of the sample increased initially up to a bitumen content of

5.5%, and then began to fall with an increase of bitumen content, as shown in figure 4.3. The

stability of the sample was optimum at a bitumen content of 5.5% with a value of 6700N

which is greater than the minimum value of 6672N specified by the standard as given in table

4.5 for heavy traffic.

4.5 5.5 6.5 7.5 8.50

1

2

3

4

5

6

Bitumen Content (%)

Flow

(0.2

5mm

)

Figure 4.4: Graph of Flow against Bitumen Content

57

The flow is the deformation of the sample up to the moment when the maximum load occurs.

The flow of the sample increased with increase in bitumen content up to a bitumen content,

which is the conventional form, as shown in figure 4.4. The test yielded a maximum flow

value of 5.64mm, which falls within the range of 2-14mm as specified by standard as shown

in table 4.5 for a heavy traffic.

4.5 5.5 6.5 7.5 8.51.3

1.4

1.5

1.6

1.7

1.8

1.9

Bitumen Content (%)

CDM

(g/c

m³)

Figure 4.5: Graph of CDM against Bitumen Content

The compacted density of the mix is maximum at a bitumen content of 4.5%, and then it

began to fall with further increase in bitumen content, as shown in figure 4.5. The maximum

value was gotten to be 1.78g/cm³.

4.5 5.5 6.5 7.5 8.505

1015202530354045

Bitumen Content (%)

VIM

(%)

Figure 4.6: Graph of VIM against Bitumen Content

58

The volume of void in the mix obtained increased up to a bitumen content of 5.5%, and then

it began to fall with further increase in bitumen content as shown in figure 4.6. The value for

VIM at which stability is maximum was 36.78% and at a bitumen content of 5.5%.

4.5 5.5 6.5 7.5 8.520

25

30

35

40

45

50

Butimen Content (%)

VMA

(%)

Figure 4.7: Graph of VMA against Bitumen Content

The voids in mineral aggregates (VMA) increase with an increase in bitumen content, which

gave a maximum value of 47.27% of void in the mixed aggregate as shown in figure 4.7. The

value obtained is greater than the minimum value of 16% for a maximum aggregate size of

9.5 (used for the mix) as stated in table 4.6 below.

Table 4.6: Typical Marshal Mix Minimum VMA

Minimum VMA (%) (mm) (inch)63 2.5 1150 2.0 11.537.5 1.5 1225 1.0 1319 0.75 1412.5 0.50 159.5 0.375 164.75 0.19 182.36 0.094 211.18 0.047 23.5

59

The maximum particle size used was 9.5mm; which implies that minimum VMA is 16%.

4.5 5.5 6.5 7.5 8.50

5

10

15

20

25

30

35

Bitumen Content (%)

VFB

(%)

Figure 4.8: Graph of VFB against Bitumen Content

The voids filled with bitumen continuously increased with an increase in bitumen content,

with a maximum value of 31.45% at a bitumen content of 8.5%, as shown in figure 4.8.

4.5.1 Optimum Bitumen Content

From the above analysis, the optimum binder content was calculated to be 5.5%, which has

been adopted for usage in subsequent analysis.

60

4.5.2 Determination of Optimum RHA Percentage

0 5 10 15 20 25 302345678

RHA (%)

Stab

ility

(KN

)

Figure 4.9: Graph of Stability against Percentage RHA at 5.5% Bitumen

Content

From figure 4.9, the obtained stability is maximum at 10% RHA, with an optimum value of

7630N which is greater than the minimum stability specified according to ASTM D 1559,

shown in Table 4.5 above. It is also observed that at 0% RHA (i.e. 100% Ordinary Portland

Cement), the stability is 6700N which is also above the minimum specification.

0 5 10 15 20 25 302

2.22.42.62.8

33.2

RHA (%)

flow

(0.2

5mm

)

Figure 4.10: Graph of Flow against Percentage RHA at 5.5% Bitumen Content

61

From figure 4.10, the maximum flow was obtained at 15% RHA to be 3.06 (12.24mm), and

the minimum flow at 22.5% RHA to be 2.08 (8.32mm) which falls between 2-14mm

specification for heavy traffic according to Table 4.5 above.

0 5 10 15 20 25 301.4

1.451.5

1.551.6

1.651.7

1.751.8

1.85

RHA (%)

CDM

(g/c

m³)

Figure 4.11: Graph of CDM against Percentage RHA At 5.5% Bitumen Content

From figure 4.11 above, the compacted density of the mix (CDM) was observed to be

maximum at 22.5% RHA with a value of 1.81, and minimum at 7.5% RHA with a value of

1.77. It was also observed that at 0% RHA (i.e. 100% Ordinary Portland cement), a minimum

CDM value of 1.49g/cm³ was obtained.

0 5 10 15 20 25 3015

20

25

30

35

40

45

RHA (%)

VIM

(%)

Figure 4.12: Graph of VIM against Percentage RHA At 5.5% Bitumen Content

62

From figure 4.12 above, the percentage void in mix (VIM) was observed to be maximum at

0%. It then continued to maintain a constant range of values of 27-28% with increase in

RHA; it then increases to a value of 36.46% at 22.25% RHA.

0 5 10 15 20 25 303032343638404244464850

RHA (%)

VMA

(%)

Figure 4.13 Graph of VMA against Percentage RHA At 5.5% Bitumen Content

As observed in figure 4.13, the void in mineral aggregate (VMA) continues to maintain a

steady range of values of 35-37%. It then increases to a maximum value of 45.23% at 22.5%

RHA. It was also observed that at 0% RHA, VMA had a value of 47.27%, which is more than

that obtained at optimum RHA.

0 5 10 15 20 25 30101214161820222426

RHA (%)

VFB

(%)

Figure 4.14: Graph of VFB (%) against Percentage RHA At 5.5% Bitumen Content

63

From figure 4.14, the voids from bitumen (VFB %) is steady with increase in percentage

RHA values, with a constant value range of 22-24% it then decreases at 22.5% RHA to

19.39%. It was also observed that at 0% RHA, (VFB %) was minimum.

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.1 Conclusion

Based on the number of tests conducted, the following conclusions were reached;

The initial and final setting times of cement were determined to be 122 minutes and 3hours 3

minutes respectively, also the soundness of the cement was observed to be 4.2mm.

The Aggregate Crushing Value (ACV), Aggregate Impact value (AIV), Specific Gravity of

coarse aggregate (SG), specific gravity of fine aggregate (SG) were obtained as 20.50%

(ACV), 16.70% (AIV), 2.70 (SG coarse) and 2.65 (SG fine aggregate) respectively.

The RHA used in this research work is a pozzolana and conforms to the ASTM C618

requirement which has great potential use in concrete.

64

The value for the required properties of bitumen as a binder as regards its penetration,

viscosity, flash and fire point, durability and solubility are 80/100 penetration grade,

138mm³/s viscosity, 240˚C and 259˚C flash and fire point, 100cm ductility, and 99%

solubility which all conform with those specified in ASTM standard specification of the

design of asphalt concrete.

The trial mix obtained using 10.0% RHA and 90% OPC meets the standard specified in terms

of stability, flow, VIM, and VMA, at an optimum bitumen content of 5.5%.

5.2 Recommendation

It is important that engineers and material scientists understand the basic principles behind

pozzolanas, so as to provide solutions to constructional problems.

In this study, one rice husk sample was used for the experiment. Future studies should use

more than one sample from various sources. It is important to study the different behaviours

of RHA in asphalt concrete from different rice husk, to look into the performance

contingency of the samples.

Mechanical properties such as tensile strength, flexural strength, and elastic modulus should

be investigated in future research, as this will widen the application of RHA in asphalt

concrete.

While determining mechanical properties of asphalt concrete using Marshall Stability

method, crushing should be done immediately after curing, while cubes temperature is still

high, and the samples are still wet, as doing otherwise could lead to variation in results.

65

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71

Appendix A

Plate 1: Students carrying out preliminary and laboratory tests on materials.

72

Plate 2: Marshall Stability & Flow Test Setup

73

Plate 3: Marshall Specimen Extractor

74

Appendix B

Table: Stability Correlation Ratio

Volume of specimen, cm3

Approximate thickness of specimen mm in.

Correlation ratio

200 to 213214 to 225226 to 237238 to 250251 to 264265 to 276277 to 289290 to 301302 to 316317 to 328329 to 340341 to 353354 to 367368 to 379380 to 392393 to 405406 to 420421 to 431432 to 443444 to 456457 to 470471 to 482483 to 495496 to 508509 to 522523 to 535536 to 546547 to 559560 to 573574 to 585586 to 598599 to 610611 to 625

25.427.028.630.231.833.334.936.538.139.741.342.944.446.047.649.250.852.454.055.657.258.760.361.963.564.065.166.768.371.473.074.676.2

11 1/161 1/81 3/161 1/41 5/161 3/81 7/161 1/21 9/161 5/81 11/161 3/41 13/161 7/81 15/1622 1/162 1/82 3/162 1/42 5/162 3/82 7/162 1/22 9/162 5/82 11/162 3/42 13/162 7/82 15/163

5.565.004.554.173.853.573.333.032.782.502.272.081.921.791.671.561.471.391.321.251.191.141.091.041.000.960.930.890.860.830.810.780.76

75