Partial Replacement of Cement with Rice Husk Ash (RHA) as Filler in Asphalt Concrete by Onyeiwu Uzoma

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 DECLARATION

1

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

3

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.

4

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 6

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 7

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 8

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

3.5.2.3 Percent voids in compacted mineral aggregate (VMA)

9

)

30 30

3.5.2.4 Percent air voids in compacted mixture (

Pav

)

31 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 10

4.5.2 Determination of Optimum RHA Percentage

45

CHAPTER FIVE: CONCLUSION AND RECOMENDATION

49

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

11

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 12

3.9: Initial and Final Setting Times of Cement and RHA

25

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

25

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

14

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.

CHAPTER ONE 15

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 pozzolanic. Hydraulic materials react directly with water to form cementitious compounds, while pozzolanic materials chemically react with calcium hydroxide (CH), a soluble reaction 16

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). 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 17

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

1.3

Objectives

i.

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

ii.

constituents, to determine its physical and chemical composition. Preparation of trail mix by varying aggregates, ordinary Portland cement, rice

iii.

husk ash, with predetermined percentages of bitumen content. To determine the engineering properties of the specimen mix, using Marshall

iv.

Stability method. Determination of optimum rice husk ash conten for Asphalt concrete. 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, 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).

18

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. 1.5

Scope of Research

19

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.

20

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. II. III.

Volume and composition of traffic. Environment and strength of the sub grade soil over which the road is to be built. 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. ii. iii. iv. v. vi.

2.3

Stability to meet traffic demand Bitumen content to ensure proper binding and water proofing Voids to accommodate compaction due to traffic Flexibility to meet traffic loads, especially in cold season Sufficient workability for construction Economical mix Rice husk ash

Rice Husk is an agricultural waste obtained from milling of rice. About 10 8 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 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

22

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.

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

23

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 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

24

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: 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) 25

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). 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, 26

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 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

27

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).

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 28

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 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.

29

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). CHAPTER THREE METHODOLOGY 3.1

Materials 30

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 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:

percentage retained

mass retained = total mass of sample

31

× 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

95.4

19.00 12.70

1456 589

48.53 19.63

46.87 27.24

9.52 6.30

621 141

20.70 4.70

6.54 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.

Table3.2:

Specific Gravity Test results for coarse Aggregate

Test number Weight of gravel (B) Weight of gas jar (P) Weight of gas jar + water + gravel (Ps) B Specific gravity (S.G) = P+ B−PS

Test 1 1000g 2520g 3135g 2.60

32

Test 2 1000g 2520g 3163g 2.80

sample 1+ sample 2 ` 2

Average specific gravity =

3.3.1.3

2.70

Bulk Density and Void of Coarse Aggregate

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

Table 3.3:

weight of sample volume of water

3.2

Bulk Density for Coarse Aggregate

Sample number

W1

W2

W3

Ww

Ws

Volume of cylinder (m3)

Bulk density (Kgm-3)

1 2

9.72 9.72

19.65 19.65

15.30 15.20

9.93 9.93

5.58 5.48

0.01 0.01

558 548

Void Ratio = 1 – ((

3.3.1.4

bulk density specific gravity ) ×1000)

= 1 – ((

553 2.7 ) ×1000)

=

0.8

3.3

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 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 33

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 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: 34

percentage retained

Table3.4:

mass retained = total mass of sample

×100

3.4

Sieve analysis 1000g fine aggregate

Sieve size

Weight retained (g)

Percentage retained (%)

Percentage passing (%)

5.00 mm 2.36 mm

15 48

1.5 4.8

98.5 93.7

1.18mm 600µm 300µm 150µm 75µm Pan

210 489 170 39 11 18

21.0 48.9 17.0 3.9 1.1 1.8

72.7 23.8 6.8 2.9 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 B Specific gravity (S.G) = P+ B−PS

Table3.5:

3.5

Specific Gravity Test for Fine Aggregate

Test number

Test 1

35

Test 2

Weight of sand (B)

500g

500g

Weight of pycnometer (P)

1600g

1600g

Weight of pycnometer + water + sand (Ps)

1908g

1915g

2.60

2.70

Specific gravity (S.G) =

B P+ B−PS

Average specific gravity =

3.3.2.3

sample 1+ sample 2 ` 2

2.65

Bulk Density and Void of Fine Aggregate

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

Table3.6:

weight of sample volume of water

3.6

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

740.74

2

1.40

4.05

3.50

2.65

2.10

2.65×10-3

792.75

Void Ratio = 1 – ((

bulk density specific gravity ) ×1000)

= 1 – ((

767 2.7 ) ×1000)

=

0.7

Table 3.7: Test results on Aggregate 36

3.7

PROPERTY

UNIT

TEST RESULTS

Aggregate Crushing Value (ACV) Aggregate Impact Value (AIV) Specific Gravity (Coarse Aggregate) Specific Gravity (Fine Aggregate) Bulk density/ Void ratio (Coarse Aggregate) Bulk density/Void ratio (Fine Aggregate)

%

20.50

%

16.70

-

2.70

-

2.65

(Kgm

)

553/0.8

-3

(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

105

Viscosity at 60 ˚ C

mm³/s

121.83

Flash and Fire point

˚ C

259

% cm

96 >100

Solubility Ductility

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.

39

Table 3.9: Initial and Final Setting Times of Cement and RHA Cement (%)

RHA (%)

100 90 80 70 60 50

0 10 20 30 40 50

Initial Setting Time (Mins) 122 136 154 165 213 281

Final Setting Time (Mins) 183 227 255 275 350 402

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 SiO2

Concentration Unit in RHA 68.12

Concentration Unit in OPC 23.43

CaO

1.01

64.40

Al2O3

1.06

4.84

Fe2O3

0.78

4.08

K2O

21.23

0.29

SO3

0.137

2.79

LOI

18.25

5.68

Free Lime

-

1.50

40

3.5

Marshall Method of Asphalt-Concrete Mix Design

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. 41

8. Low noise and good drainage properties: If the mix is to be used for the surface (wearing) layer of the pavement structure. 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, Wa

= weight of sample in air (g)

43

Ww

= 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 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=

P ca + Pfa + Pmf Pca Pfa P mf + + Gbca Gbca Gbca

3.9

Where, Gbam

= bulk specific gravity of aggregates in paving mixtures.

44

Pca , P fa , Pmf

= percent by weight of coarse aggregate, fine aggregate, and mineral

filler in paving mixture. Gbca , G bfa , Gbmf

= bulk specific gravities of coarse aggregate, fine aggregate and mineral

filler, respectively.

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=

P ca + Pfa + Pmf Pca Pfa P mf + + Gbca Gbca Gbca

3.10

Where, Gmp = maximum specific gravity of paving mixtures. Pca , P fa , Pmf

= percent by weight of coarse aggregate, fine aggregate, and mineral

filler in paving mixture.

45

Gbca , G bfa , 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 -

Gbcm P Gbam

ta

3.11 Where, VMA = percent voids in mineral aggregates. Gbcm

= bulk specific gravity of compacted specimen

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 =100

Gmp−G Gmp

bcm

3.12

46

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

B 0=

B 1+ B2 +B3 3

3.13 Where, B 0 = optimum Bitumen content. B 1 = % asphalt content at maximum unit weight.

47

B 2 = % asphalt content at maximum stability. B 3 = % 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. 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 48

Bitumen content (%) 4.5 5.5 6.5 7.5 8.5

Stability (kN) 3.97 6.70 2.73 3.81 2.96

Flow (mm) 2.43 3.0 5.64 3.56 4.1

CDM (g/cm³) 1.78 1.49 1.53 1.55 1.65

VIM (%)

VMA (%)

VFB (%)

28.51 39.40 36.78 35.15 30.08

36.22 47.27 46.33 46.75 43.88

21.31 16.63 20.61 24.81 31.45

Table 3.12 Summary of Marshall Analysis At 5.5% Optimum Bitumen Content RHA content (%) 0.0

Stability (kN) 6.70

Flow (0.25mm) 3.0

CDM (g/cm³) 1.49

VIM (%)

VMA (%)

VFB (%)

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 15.0

5.02 4.46

2.56 3.06

1.79 1.78

27.82 28.23

35.40 36.75

23.57 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

49

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* 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

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

D2042

99

99

99

240 and 259 respectively . 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

50

Results obtained

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 51

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

O2

Silicon dioxide (Si aluminum oxide ( iron oxide (

Al 2 O3

Fe2 O3

Sulfur trioxide (

Mineral admixture class N F 70.0 70.0 ), plus

Test result C 50.0

69.96

5.0

0.14

), plus

) min, %

SO3

), max, %

4.0

5.0

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%

52

(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;

Silica (Si

O2

Aluminium (

Iron (

) = 68.12%

Al 2 O3

Fe2 O3

) =1.06%

) = 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 Initial setting time

Unit Min

Test results 122

Final setting time

Hr-min

3hrs 3mins

soundness

mm

4.2 53

Code used BS EN 196 PART 3 (1995) BS EN 196 PART 3 (1995) BS EN 196 PART 3 (1995)

Code specification >45mins