UNIVERSITY OF NAIROBI

AN INVESTIGATION OF THE PROPERTIES OF CONCRETE

CONTAINING MACADAMIA SHELLS AS A PARTIAL

REPLACEMENT OF COARSE AGGREGATES

BY

WAHOGO ALEX REBO

F16/35927/2010

A project submitted as a partial fulfillment

for the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015

SUPERVISOR: DR. (ENG.) JOHN MWERO

II

Abstract

The world, especially Kenya, is faced with the problem of solid waste. This solid waste also

constitutes agricultural waste. This experimental research is focused on the use of macadamia

shells, which is an agricultural waste, as a partial replacement of coarse aggregates in concrete. It

also looks into reducing the cost of producing concrete by replacing conventional coarse

aggregates obtained from quarries with macadamia shells obtained from the local farmers. The

research investigated the properties of macadamia shells in comparison with the properties of

conventional coarse aggregates based on strength properties required in concrete and in other

forms of construction. It also observed the properties of concrete with the addition of macadamia

shells and compared it with the control normal conventional concrete.

It the laboratory, various aggregates tests were done on the macadamia shells and significant

differences and similarities were observed. Macadamia shells exhibits higher toughness than

conventional aggregates. This is observed in the aggregates impact value test and the ten percent

fines tests. The particle size distribution of the macadamia was to some extent similar to the one

of the conventional aggregates.

In concrete, the coarse aggregates were replaced with macadamia shells by percentage masses of

10%, 20%, 30% and 50%. As the percentage replacement increased, the compressive and tensile

strength reduced. The workability at 10% replacement was higher than in normal concrete using

a constant water/cement ratio of 0.45. At 50% replacement, an increase in water/cement ratio to

0.55 yielded a much stronger concrete than using a water/cement ratio of 0.45. This increase in

strength due to higher water cement is not observed in normal conventional concrete. An

increase in percentage replacement yielded less dense concrete showing that macadamia shells

can be used to produce lightweight high strength concrete which is much cheaper than the

conventional concrete.

III

Dedication

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

loving parents and family who continually gave me hope, encouragement and support to

undertake all my studies.

IV

Acknowledgements

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

His comments and suggestions during the preparation of this project are gratefully

acknowledged. He has imparted invaluable knowledge and time dedication to my work.

Sincere appreciation to my friends for all the encouragement, morale, support and assistance

during this project.

I would also like to thank Jungle Nuts Company, Thika, for supplying me with the macadamia

shells used in this research project.

Special appreciation to the laboratory technicians, Mr Martin, Mr Muchina and Mr Nicholas for

their guidance and assistance in the whole experimental research.

Lastly but not least, I wish to thank my parents, brothers and sisters for their endless support

throughout my life.

May the Almighty God bless you all.

V

Table of Contents

Abstract ..................................................................................................................................... II

Dedication ................................................................................................................................. III

Acknowledgements .................................................................................................................. IV

Table of Contents ....................................................................................................................... V

List of Tables .......................................................................................................................... VII

List of Figures ........................................................................................................................ VIII

List of Plates ............................................................................................................................ IX

Chapter One ................................................................................................................................1

1.0 Introduction ...........................................................................................................................1

1.1 Experiment Justification ....................................................................................................2

1.2 Problem Statement .............................................................................................................2

1.3 Research Objectives ...........................................................................................................3

1.3.1 Overall Objective ........................................................................................................3

1.3.2 Specific Objectives ......................................................................................................3

1.4 Scope of Study ...................................................................................................................3

Chapter Two ...............................................................................................................................4

2.0 Literature Review ..................................................................................................................4

2.1 Concrete ............................................................................................................................4

2.1.1 Constituents of Concrete .............................................................................................4

2.1.2 Fresh Concrete ............................................................................................................9

2.1.3 Hardened Concrete .................................................................................................... 10

2.2 Macadamia Shells ............................................................................................................ 13

2.2.1 Introduction ............................................................................................................... 13

2.2.2 Macadamia Production .............................................................................................. 14

2.2.3 Uses of Macadamia Shells ......................................................................................... 15

2.2.4 Properties of Macadamia Shells ................................................................................. 16

Chapter Three ........................................................................................................................... 17

3.0 Methodology ....................................................................................................................... 17

3.1 Introduction ..................................................................................................................... 17

VI

3.2 Collection and Sampling of Material ................................................................................ 17

3.2.1 Sourcing Material ...................................................................................................... 17

3.2.2 Sampling ................................................................................................................... 18

3.3 Preparation and Testing Of Samples ................................................................................ 18

3.3.1 Preparation and Testing of Aggregates ...................................................................... 18

3.3.2 Preparation and Testing of Fresh Concrete ................................................................ 26

3.3.3 Preparation and Testing of Hardened Concrete .......................................................... 29

Chapter Four ............................................................................................................................. 32

4.0 Results and Discussions....................................................................................................... 32

4.1 Aggregates Tests Results ................................................................................................. 32

4.1.1 Moisture Content, Water Absorption and Specific Gravity ........................................ 32

4.1.2 Aggregate Crushing Value (A.C.V) ........................................................................... 33

4.1.3 Aggregate Impact Value (A.I.V) ................................................................................ 34

4.1.4 Ten Percent Fines Value ............................................................................................ 35

4.1.5 Particle Size Distribution ........................................................................................... 36

4.1.2 Flakiness Index ......................................................................................................... 37

4.2 Fresh Concrete Results .................................................................................................... 38

4.2.1 Slump test ................................................................................................................. 39

4.2.2 Compacting Factor Test............................................................................................. 40

4.3 Hardened Concrete Results .............................................................................................. 41

4.3.1 Compressive Strength ................................................................................................ 41

4.3.2 Tensile Strength ........................................................................................................ 45

4.3.3 Density and Mass ...................................................................................................... 47

Chapter Five ............................................................................................................................. 48

5.0 Conclusions and Recommendations ..................................................................................... 48

5.1 Conclusions ..................................................................................................................... 48

5.2 Recommendations............................................................................................................ 49

Chapter Six ............................................................................................................................... 50

6.0 References ........................................................................................................................... 50

VII

List of Tables

Table 4. 1 Moisture Content ...................................................................................................... 32

Table 4. 2 Water Absorption and Specific Gravity..................................................................... 32

Table 4. 3 Particle Size Distribution .......................................................................................... 36

Table 4. 4 Flakiness Index ......................................................................................................... 37

Table 4. 5 Slump Test ............................................................................................................... 39

Table 4. 6 Compaction Factor ................................................................................................... 40

Table 4. 7 7 Days Strength ....................................................................................................... 42

Table 4. 8 28 Days Strength ...................................................................................................... 43

Table 4. 9 Tensile Split Test ...................................................................................................... 45

Table 4. 10 Density and Mass.................................................................................................... 47

VIII

List of Figures

Figure 2. 1 Representation of Workability ................................................................................. 10

Figure 4. 1 Particle Size Distribution ......................................................................................... 36

Figure 4. 2 Slump Value............................................................................................................ 39

Figure 4. 3 7 Days Strength ....................................................................................................... 42

Figure 4. 4 28 Days Strength ..................................................................................................... 43

Figure 4. 5 7 Days and 28 Days Strength ................................................................................... 44

Figure 4. 6 Tensile Split Test ..................................................................................................... 46

Figure 4. 7 Average Density ...................................................................................................... 47

IX

List of Plates

Plate 2. 1 Crushed Macadamia Shells ........................................................................................ 14

Plate 2. 2 Burnt Macadamia Shells ............................................................................................ 15

Plate 3. 1 Ordinary Portland cement (32.5 N) and the River Washed Sand ................................ 18

Plate 3. 2 Sieves in the Sieve Analysis....................................................................................... 19

Plate 3. 3 Particle Size Distribution ........................................................................................... 20

Plate 3. 4 Pycnometer on a Weighing Balance ........................................................................... 21

Plate 3. 5 Soaked Macadamia Shells.......................................................................................... 22

Plate 3. 6 Macadamia Shells Being Tapped On the Cylindrical Metal ........................................ 24

Plate 3. 7 Compression Test Machine for Determination of Ten Percent Fines .......................... 26

Plate 3. 8 Preparations of the Iron Moulds ................................................................................. 27

Plate 3. 9 The Batched Concrete Mix ........................................................................................ 27

Plate 3. 10 Table Vibrator with Cast Cylinders on Top .............................................................. 28

Plate 3. 11 The Curing Tanks .................................................................................................... 30

Plate 3. 12 Compressive Test Machine and Its Setup ................................................................. 31

Plate 3. 13 Tensile Split Test Apparatus and Its Setup ............................................................... 31

Plate 4. 1 The Concrete Bath At 50% ....................................................................................... 38

Plate 4. 2 The Crushed Cubes .................................................................................................... 41

Plate 4. 3 Concrete cube and cylinder at 50% replacement ........................................................ 41

Plate 4. 4 Tensile Split Test Crushed Cylinder ........................................................................... 45

1

Chapter One

1.0 Introduction

Concrete is world’s most widely used construction material. The utilization of concrete is

increasing at a higher rate due to development in infrastructure and construction activities all

around the world. However, there are some negative impacts of more production of concrete like

continuous extensive extraction of aggregate from natural resources will lead to its depletion and

ecological degradation. Also, in the construction industry, increasing attention is being paid to

the concept of “green buildings”. The search for “green” or environmentally friendly materials in

the building industry involves the development of new materials, but might also lead to the

reconsideration of traditional conventional ones.

Researchers are in search of replacing normal granitic coarse aggregate from local quarries to

make concrete less expensive and to lead sustainable development. This environmental reason

has generated a lot of concern in the construction world. The use of sugarcane bagasse, wooden

chips, plastic waste, textile waste, polyethylene, rice husk ash, rubber tyres, vegetable fibers,

paper and pulp industry waste, waste glass, broken bricks are some examples which are being

investigated to replacing (partially or totally) aggregates in concrete. Macadamia shell is

categorized as light weight aggregate. The macadamia shell contains lignin, cellulose,

hemicelluloses and organic ash. All over the world, the construction industry is yet to realize the

advantages of light weight concrete in high rise buildings. Macadamia shells are not commonly

used in construction industry and are often dumped as agricultural waste. The aim of this

research is to investigate and experiment on the usage of macadamia shells as partial or total

replacement of coarse aggregate. It will also check the effects in terms of the properties of fresh

and hardened concrete when macadamia shells are used in place of conventional aggregates.

Until now, Industrial by products and domestic wastes have been utilized in concrete, but the use

of agricultural waste in concrete is in its infancy stage. Macadamia shell is an agricultural waste

and by utilizing it in concrete might lead to huge breakthroughs in the development of concrete.

The materials are proportioned by their weights. The water/cement ratio is predetermined based

2

on previous tests. The obtained results are compared with that of conventional mix of concrete.

Tests are as per the specified procedures of British Standard Codes.

1.1 Experiment Justification

Demands on building material have increased from time to time due to the increasing population

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

sustainability in construction, utilization of waste material has been encouraged because the use

of this material will help in protecting the environment from land fill disposal of the agricultural

waste and also the granitic quarrying of the coarse aggregate will be significantly reduced.

From an engineering standpoint, macadamia shells appear to be an excellent supplement for

replacement for natural aggregate in many construction applications. The study will define the

suitability of macadamia shells as a construction aggregate in terms of its engineering

performance and cost comparability with natural aggregates.

1.2 Problem Statement

The study aimed at evaluating the use of macadamia shells as a possible replacement of coarse

aggregate in concrete so as to reduce the amount of agricultural waste to be land filled and as

well as come up with light-weight and low cost concrete.

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

complemented with conventional aggregate to provide concrete of equivalent, or improved

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

new materials may not only be more economically advantageous than traditional granular

materials but may also outperform them. Hence macadamia shells could be considered as a

viable alternative. The factors to be considered were

Natural aggregate locally available.

3

How macadamia shells might supplement or complement the natural aggregate

supply,

Supply and quantity of macadamia shells

1.3 Research Objectives

1.3.1 Overall Objective

To investigate the possibility of either partial or total replacement of conventional coarse

aggregates with macadamia shells in the manufacture of concrete.

1.3.2 Specific Objectives

To determine the material properties of macadamia shells

To investigate the availability and economic feasibility of the use of macadamia

shells as coarse aggregates

To test the properties of concrete made with macadamia shells as a partial

replacement of conventional coarse aggregates.

1.4 Scope of Study

The scope of this project will be to evaluate the use of macadamia shells as a possible partial or

total replacement of conventional coarse aggregates in the manufacture of concrete.

4

Chapter Two

2.0 Literature Review

2.1 Concrete

Concrete is a man-made composite with major constituent of which is natural aggregates i.e.

sand and gravel, cement, water and admixture if required. Concrete development has evolved

over a long period of time. It is defined by properties in its fresh and hardened state, though fresh

concrete is a prerequisite of hardened concrete. The binding media binds aggregates together to

form a hard composite substance. Concrete properties typically depend on mix ratio of its

constituent (http://en.wikipedia.org/wiki/concrete).

2.1.1 Constituents of Concrete

2.1.1.1 Cement

These are finely ground powder and when mixed with water, a chemical reaction (hydration)

takes place, which in time produce a very hard strong binding medium for the aggregates

particles. In early stages of hydration, while in its plastic stage, cement mortar gives rise to the

fresh concrete its cohesive properties. Cement testing properties are specified in BS4550.

Performances of cement is subject to its fineness (BS 4550:Part3).

BS 4550:Part 3, gives requirement on setting time as not less than 45min and not more than

10hrs for final setting and strength of hardened cement paste in terms of compressive strength on

concrete cubes measured in 28 days of curing after casting of concrete.

2.1.1.2 Aggregates

Aggregates are much cheaper than cement and maximum economy is obtained by using much

aggregate as possible in concrete. Its use also considerably improves both the volume, stability

and the durability of the resulting concrete. The physical characteristic and in some cases its

5

chemical composition affect to varying states. Basic characteristics of aggregates test are

described in BS812: Part 102.

The properties of the aggregates known to have significant effect on concrete behavior are its

strength, deformation, durability, toughness, hardness, volume change, porosity, relative density

and chemical reactivity.

The grading of aggregates defines the proportion of particles of different size in the aggregates.

The size in the aggregates particles normally used in concrete varies from 37.5 to 0.15mm.BS

882 places aggregates into two main categories i.e. fine aggregates (commonly referred to as

sand) containing particles majority smaller than 5mm and coarse aggregates containing particles

larger than 5mm. Sieve analysis is used for determining the particle size distribution of

aggregates, BS 882:Part 103.

The following are the types of aggregates:

a) Heavyweight Aggregates

Heavyweight aggregates provide an effective and economical use for radiation shielding, by

giving the necessary protection against X-rays, Gamma rays and neutrons; and for weight-

coating of submerged pipelines. The effectiveness of heavyweight concrete, with a density from

4000 to 8500kg/m3, depends on the aggregate type, the dimension and degree of compaction. It

is frequently difficult with heavy aggregates to obtain a mix which is both workable and not

prone to segregation.

b) Normal Aggregates

These aggregates are suitable for most purposes and produce concrete with a density in the range

2300 to 2500 kg/m3. Rock aggregates are obtained by crushing quarried rock to the required

particle size or by extracting the sand and gravel deposits formed by alluvial or glacial action.

Some sand and gravels are also obtained by dredging from sea and river beds

The properties of rock aggregates depend on their composition, grain size and texture. For

example, granite has a low fire resistance because of the high coefficient of expansion of its

quartz content. Air-cooled blast-furnace slag aggregates produce concretes with similar strength

to natural aggregates but with improved fire resistance. Broken-brick aggregates are also very

6

fire resistant, but should not be used for normal concrete if its soluble sulphate content exceeds

1%.

c) Artificial Aggregates

These are manufactured mainly from industrial by – products, waste materials or sometimes

natural materials. They are mainly lightweight aggregates. Examples are:

i. Pulverized fuel or fly ash (PFA)

This is the residue of the combustion of pulverized coal used as a fuel in thermal power stations.

PFA is used in the manufacture of lightweight aggregates in Germany and Great Britain to

reduce dead loads of high rise structures (L.J. Murdock 1991). PFA powder is pelletized with

water in a rotating pan and the pellets burnt in horizontal grate at a temperature of 12000–

13000C. They are then cooled and screened in different particle size fractions.

ii. Foamed slag

This is a by-product in the manufacture of pig iron in blast furnace. The slag is transformed into

molten state at 14000 – 15000C. Steam and compressed air is injected in the process. This

produces numerous bubbles which causes the slag to expand so that on cooling it becomes an

artificial rock like material with cellular structure internally porous and honey combed (The

concrete society 1980). The artificial rock is then crushed and screened to give different particle

sizes.

iii. Sintered glass aggregates

They are manufactured mainly north of France. The raw material used comes from waste glass

bottles. The bottles are crushed, dried and ground in a rotary mill at a fine state. Before grinding,

2.5% of calcium carbonate (CaCO3) is added as an expansive agent. The powder is well

homogenized and pelletized with water in a rotary pan. According to the speed and inclination of

the pan, it is possible to obtain several diameters. The pellets are then dried in hot air and pre-

heated up to 6800C and passed quickly through a rotary kiln at 8000C. They are then cooled and

screened (The concrete society Ci80, 1980).

7

iv. Furnace Clinker

It comes from the combustion of coal in domestic or firing systems. The clinker is sometimes

used as lightweight aggregate after being crushed and screened. Aggregates are dark in colour

with a sintered or slaggy appearance. This type of aggregate is relatively little used due to its

stability which must be verified by chemical and physical testing. It must not contain harmful

substances like burnt lime and magnesia, sulphides, and sulphates which are deleterious in

concrete.

d) Lightweight Aggregates

Artificial and processed aggregates, notably expanded clays, foamed slag and sintered fly ash

pellets, are used for lightweight structural concrete. The various methods of producing

lightweight concrete depend on either the presence of air voids in the aggregate; or the formation

of air voids in the concrete by omitting fine aggregate; or the formation of air voids in a cement

paste by the addition of some substance which causes foam.

Lightweight concrete is used not only on account of its light weight but also because of the high

thermal insulation compared to normal concrete. Generally, a decrease in density is accompanied

by an increase in thermal insulation, although there is a decrease in strength.

The tests done to test the properties of aggregates are:

i. Particle size distribution

The proportions of the different sizes of particles making up the aggregate are found by sieving

and are known as the grading of the aggregate. The grading is given in terms of the percentage

by mass passing the various sieves. Grading is carried out to determine the particle size

distribution.

ii. Flakiness Index

The flakiness index of an aggregate is the percentage by weight of particles in it whose least

dimension (thickness) is less than three fifths of their mean dimension. A flaky particle is one

whose least dimension is less than 0.6 of its mean size. The test is not applicable to material

passing a 6-35mm BS sieve.

8

iii. Aggregate impact value

The aggregate impact value gives the measure of the resistance of an aggregate to sudden shock

or impact, which in some aggregates differs from its resistance to a slow compressive load. With

aggregates of aggregate impact value 30% or higher, the result may be anomalous. Aggregate

impact value is an indicator of the toughness of aggregates.

The standard aggregate impact test is done on aggregates passing a 12.7mm and retained on a

9.52mm BS test sieve. Smaller sizes of aggregates will give a lower value of impact value but

the relationship between the values obtained with different sizes may vary from one aggregate to

another.

iv. Aggregate crushing value

The aggregate crushing value gives a relative measure of the resistance of an aggregate to

crushing under a gradually applied compressive load. It is also a measure of the mechanical

strength of the aggregate.

The standard aggregate crushing value test is done on aggregate passing a 14mm test sieve and

retained on 10mm test sieve

v. 10% fines value

The 10% fines value gives a measure of the resistance of an aggregate to crushing and is

applicable to both weak and strong aggregates; however, it is designed for relatively soft

aggregates having an aggregate crushing value of over 30% where a force of 400kN would crush

most or all of the aggregate.

2.1.1.3 Water

Water used in concrete, in addition to reacting with cement and thus causing it to set and harden,

also facilitates mixing, placing and compacting of the fresh concrete. Water is used also for

washing the aggregates and for curing purpose. Water fit for drinking is acceptable for mixing

concrete.

9

2.1.1.4 Admixture

These are substances introduced into a batch of concrete, during or immediately before its

mixing, in order to improve the properties of the fresh or hardened concrete or both. Changes

brought about in the concrete by the use of admixtures are effected through the influence of the

admixture on hydration, liberation of heat, formation of pores and the development of the gel

structure i.e. Retards, accelerating agents etc.

2.1.2 Fresh Concrete

Fresh concrete is concrete in its plastic state that can be virtually molded into any shape.

Handling of fresh concrete considerably affects the properties of hardened concrete i.e.

transporting, placing compacting and finishing. Factors influencing properties of fresh concrete

are;

2.1.2.1 Workability

Workability implies the ease with which concrete mix can be handled from the mixer to its

finally compacted shape. Its three main characteristic of workability are consistency, mobility

and compact-ability. Consistency is measure of wetness or fluidity. Mobility defines the ease

with, which mix can flow into and completely fill the formwork or mould. Compact-ability is the

ease with which a given mix can be fully compacted, all the trapped air being removed (Neil

Jackson and Ravinda K.Dhir, 1992).

It is essential that the correct level of workability is chosen to match the requirements of the

construction process. The ease or difficulty of placing concrete in sections of different sizes, the

type of compaction equipment, the complexity of reinforcement, the size and skills of the

workforce are amongst the items to be considered. In general, the more difficult it is to work the

concrete, the greater should be the level of workability. But the concrete must also have some

cohesiveness in order to resist segregation.

Workability is measured by slump test, compacting factor test and vebe time test (BS 1881: Parts

102,103 and 104; German standard Din 148). Workability in concrete is affected by water-

cement content and aggregates size distribution. Workability can be represented in a diagram as;

10

Figure 2. 1 Representation of Workability

2.1.2.2 Stability

It is the ability of fresh concrete to remain uniformly distributed in the concrete the period

between mixing and compaction and the period following compaction before the concrete

stiffens. It is affected by particles size distribution and generally in workability mixes.

2.1.2.3 Segregation

This is the tendency for large and fine particles to separate. It is governed by the total surface of

the solid particles including cement and the quantity of mortar in the mix. It affects strength and

durability of concrete. Use of macadamia shells is expected not to cause segregation as well

graded aggregates will be used.

2.1.3 Hardened Concrete

This is state at which concrete is a rock-like materials with high compressive strength. Listed

below are the properties of hardened concrete:

Workability

Stability Mobility

a. Bleeding

b. Separation

of

materials

Compact-

ability

Relative density a. Internal

friction angle

b. Bonding force

c. Viscosity

11

Strength

Concrete Creep

Shrinkage

Modulus Of Elasticity

Permeability

Rate of Strength gain of Concrete

In this experimental research, the investigation was mainly on the strength of concrete.

2.1.3.1 Strength

This is the maximum load (stress) concrete can carry. As strength increases, its other properties

are relatively improved. Concrete strength takes the form of;

i. Compressive strength

This is taken to be maximum compressive loads concrete can carry per unit area. Concrete cubes

of 150mmx150mmx150mm dimension are normally used to determine compressive strength

(BS1881: Part 116). Compressive strength is used to evaluate concrete strength development

over a period of time. Compressive strength is normally determined at age of 7, 14 and 28 day

and compared with set standards to give assurance on capability of concrete to carry subjected

loads in its life span of use.

ii. Tensile strength

Indirect tensile strength is normally determined by split of cylinder test (BS 1881: Part 117) and

entails diametrically loading cylinder in compression along its entire length. It is evaluated as;

Fct=2𝐹

𝜋𝑙𝑑

Where

o l and d are the cylinder length and diameter

o F is the maximum load applied

12

This varies from 5-13 percent of cube compressive strength. Indirect tensile strength of a

concrete is affected by cement ratio, water content and aggregates bond development (Munday

and Dhir 1984).

iii. Flexural strength test

Flexural strength is one of the measures of tensile strength of concrete. It is a measure of the

unreinforced concrete beam or slab to resist failure in bending. Although concrete is not

normally designed to resist direct tension, the knowledge of tensile strength is of value in

estimating the load under which the concrete will crack. The absence of cracking is of

considerable importance in maintaining the continuity of a concrete structure and in many cases

the prevention of corrosion of reinforcement. (Neville, 1981). The flexural strength is expressed

as Modulus of Rupture (MR). It is determined by the third point loading or the Center Point

loading. The MR determined by the Third Point Loading is less than that determined by the

Center Point Loading, sometimes by as much as 15%. (National Ready Mix Concrete

Association, CIP 16, 2000).

Factors affecting Strength of concrete:

The following factors affect the strength of concrete:

i. Water-Cement ratio:

It is the water cement ratio that basically governs the property of strength. The lesser the water

cement ratio, greater will be strength.

ii. Type of cement:

The type of cement affects the hydration process and therefore strength of concrete.

iii. Amount of cementing material:

It is the paste that holds or binds all the ingredients. Thus greater amount of cementing material

greater will be strength.

13

iv. Type of Aggregate:

Rough and angular aggregates are preferable as they provide greater bonding.

v. Admixtures:

Chemical admixtures like plasticizers reduce the water cement ratio and increase the strength of

concrete at same water/cement ratio. Mineral admixtures affect the strength at later stage and

increase the strength by increasing the amount of cementing material.

2.2 Macadamia Shells

2.2.1 Introduction

The flexibility in use of concrete, and its adaptability to environmental conditions make concrete

suitable for applications in almost all civil engineering structures. Despite these attributes,

concrete still has a characteristics weight which presents problems and complications in

construction usually resulting to high cost of construction of underlying sections i.e. foundations

and the base columns. The introduction of lightweight concrete has to a large extent solved the

attendant problems in concrete constructions. Various lightweight concrete have been formulated

through different technical approaches, these are:

i. Inclusion of air voids into the concrete mix.

ii. Omission of fine aggregate phase.

iii. Replacing the normal natural aggregates with lightweight aggregates.

In the third approach, natural lightweight aggregate such as expanded slag, pumice, scoria, and

industrial, and agricultural wastes have been used as discussed earlier. Other wood waste such as

splinters and shavings, suitably treated chemically have been used to make non-load bearing

concrete with a density of 800 and 1200Kg/m3. Apart from being advantageous to construction,

the use of these alternative aggregates reduces the over dependence on the conventional

aggregates (river sand and crushed rock) which is increasingly becoming expensive, limited and

14

gradually degrading the natural habitat and causing ecological imbalance. Several

comprehensive studies during the past years have dealt with the subject of aggregate supplies and

needs and the possible use of waste materials as aggregates for concrete. Critical shortage of

natural aggregate for concrete is developing in many regions. Also, the needs for better methods

of solid waste disposal and probably energy conservation have contributed to the increased

interest in this technology. The use of agricultural waste products such as macadamia shells as

replacement for conventional coarse aggregates could reduce the cost of construction and helps

take care of the environment.

Plate 2. 1 Crushed Macadamia Shells

2.2.2 Macadamia Production

Macadamia nuts come from plants belonging to the family of Proteaceae and are native to

Australia. Australia is the world’s main commercial producer of macadamia nuts, producing

around 40,000 tonnes a year, out of a total global production of 100,000 tonnes globally

(www.macadamias.org). They are also commercially produced in Brazil, Costa Rica, Bolivia,

Hawaii and New Zealand.

In Kenya, the current macadamia production stands at around 12000 tonnes annually, about 10%

of the global production.

15

2.2.3 Uses of Macadamia Shells

The shells and other waste comprise almost 70% by weight of the macadamia nuts. Their main

uses include;

Active carbon- they are burned at high temperatures to create activated carbon and

charcoal

They are used to make carbon filters, both domestic and industrial

They are combined with the husks to help in mulching in macadamia farms where they

later decompose to get back the nutrients to the soil

The shell is ground to affine powder which is very hard. The powder can be used as an

industrial abrasive which is superior to sand and can be even marketed by the cosmetics

industry as the active ingredient in facial skin scrub

As a source of fuel (Having a calorific value of 5,500 Kcal/kg).

They are used as charcoal for grilling because the embers last a long time and the smoke

doesn’t leave an unpleasant taste on food. The below pictures shows macadamia shells

when they have undergone incomplete combustion and used as charcoal (photo below

courtesy of Jungle Nuts Company in Thika where they have been disposed as waste)

Plate 2. 2 Burnt Macadamia Shells

16

2.2.4 Properties of Macadamia Shells

The shell of the macadamia nut is hard and brittle. It has fracture toughness similar to those of

common ceramics and glass. The structure of the macadamia nut shell is reasonably isotropic

and uniform, very different from that of trees. The main components of the shell are lignin

(47%), cellulose (25%), hemicelluloses (11%) and ash (0-2%). The shells have a bulk density of

680 kg/m3, and a moisture content of around 10%.

Very limited work has been carried out on the use of macadamia shells in composites, with the

only product identified from the literature being Husque, a composite based on pulverized

macadamia shells bonded with resin

Over the years, macadamia shell constitutes common solid waste especially in the developing

parts of this world. Its potential as a useful engineering material has not been investigated. The

utilization of macadamia shells will promote waste management at little cost, reduce pollution by

these waste and increase the economic base of the farmer when such waste are sold thereby

encouraging more production.

17

Chapter Three

3.0 Methodology

3.1 Introduction

The main aim of this research project was to utilize macadamia shells as coarse aggregate for the

production of concrete. It was essential to know whether the replacement of macadamia shells in

concrete is inappropriate or acceptable. Three types of aggregates were used in this project which

include natural coarse aggregate, natural fine aggregate and macadamia shells. Natural coarse

aggregate used was crushed stone from quarries with maximum size of 20 mm. Natural fine

aggregate used was river sand and the macadamia shells used were obtained from the factory

where macadamia are processed and packed. Concrete cube and cylinders were then prepared for

0%, 10%, 20%, 30% and 50% and the same were tested at 7 and 28 days for the various strength

properties. The methodology involved collection, preparation and assessment of material

properties by carrying out the following activities:

Collection and sampling of materials

macadamia shells sorting, sieve analysis of coarse aggregates

Carrying out laboratory tests on the properties of coarse aggregates

Carrying out laboratory tests on the properties of fresh concrete

Carrying out laboratory tests on the properties of hardened concrete

3.2 Collection and Sampling of Material

3.2.1 Sourcing Material

Macadamia shells were obtained from Jungle Nuts Company located in the industrial area of

Thika town. The shells obtained had been crushed by first removing the outer husks and then

breaking them to remove the nut inside.

18

The cement, coarse and fine aggregates (sand) were obtained from the Concrete Laboratory here

in The University of Nairobi. Coarse aggregate was crushed granitic stone. Fine aggregate was

river-washed sand.

Plate 3. 1 Ordinary Portland cement (32.5 N) and the River Washed Sand

3.2.2 Sampling

Samples should show the true nature and conditions of the materials which they represent. They

should be drawn from points known to be representative of the probable variations in the

material. At the laboratory the main sample was reduced to the quantity required for testing. The

method used for sampling was riffling.

3.3 Preparation and Testing Of Samples

3.3.1 Preparation and Testing of Aggregates

The sampled macadamia shells were manually sorted to remove the presence of any unwanted

materials which may include unremoved nuts from the shells, leaves or the macadamia husks.

The properties of macadamia shells were then tested for their aggregates properties in

accordance with the respective BS codes. The following tests were carried out:

19

3.3.1.1 Particle Size Distribution (BS 812-103.1:1985)

Particle size distribution is used to analyze the composition of a certain sample of aggregates. It

is carried on both fine and coarse aggregates. Aggregates should be well distributed in all sizes

depending on their use and application.

The objective of the test was to determine the particle size distribution of the macadamia shells

and draw the respective grading curves. The apparatus used were a balance accurate to ±0.5% of

mass of test sample, the BS test sieves, a shaking mechanism, data sheets and brushes.

Test sieves were arranged from top to bottom in order of decreasing aperture sizes with pan and

lid to form a sieving column. The aggregate sample was then poured into the sieving column and

thoroughly shaken, manually. The sieves were removed one by one starting with the largest

aperture sizes (top most), and each sieve shaken manually ensuring that no material is lost. All

the material which passed each sieve was returned into the column before continuing with the

operation with that sieve. The retained material on the sieve with the largest aperture size was

weighed and its weight recorded with its corresponding sieve size. The same operation was

carried out for successive sieves in the column and their weights recorded. The screened material

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

Plate 3. 2 Sieves in the Sieve Analysis

20

Plate 3. 3 Particle Size Distribution

3.3.1.2 Specific Gravity and Water Absorption of Aggregates (BS 812-107)

The specific gravity of an aggregate is considered to be a measure of strength or quality of the

material. The specific gravity test helps in the identification of stone.

Water absorption gives an idea of strength of aggregate. Aggregates having more water

absorption are more porous in nature and are generally considered unsuitable unless they are

found to be acceptable based on strength, impact and hardness tests

The specific gravity of a substance is a comparison of its density and the density of water. A

value of greater than 1 indicates that the substance has a higher density than water while a value

of less than 1 indicates that the substance is less dense than water.

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

done using a pycnometer, funnel and the weighing balance machine. The weight of a clean

pycnometer was determined and recorded as WP. 10g of dry sample was placed in the

pycnometer and the weight recorded as WPS. Distilled water was added to fill the pycnometer to

the mark, while making sure no air was being trapped. The sample was allowed to soak for 10

minutes. The surface of the pycnometer was wiped dry using a cloth and weighed. The weight

was then recorded as WB. The pycnometer was then emptied and cleaned. After which it was

21

filled with distilled water only up to the mark. It was then wiped dry and weighed. This weight

was recorded as WA.

Specific Gravity = 𝑊𝑃𝑆 − (𝑊𝑃𝑆−𝑊𝑃) + (𝑊𝐴−𝑊𝐵) … Equation 3. 1

Plate 3. 4 Pycnometer on a Weighing Balance

3.3.1.3 Moisture Content

This is a measure of the amount of water present in a given aggregate material compared to its

total mass. The objective of the test was to determine the moisture content of the macadamia

shells

A sample of the macadamia shells was crumbled and placed loosely in the weighing container

and the cover was replaced and weighed (M2).

22

The container was cleaned, dried and weighed to the nearest 0.01g (m1) the cover was then

removed and placed below the container and then inserted in the oven having a temperature of

105o C for 24 hours.

The weight of the dried sample was then weighed (m3)

W= 𝐦𝟐−𝐦𝟑

𝐦𝟑−𝐦𝟏 𝐱 𝟏𝟎𝟎 … Equation 3. 2

Where;

W= moisture content in %

Plate 3. 5 Soaked Macadamia Shells

3.3.1.4 Flakiness Index (B.S. 812)

The flakiness index of an aggregate is the percentage by weight of particles in it whose least

dimension (thickness) is less than three fifths of their mean dimension. A flaky particle is one

whose least dimension is less than 0.6 of its mean size. The main objective was to determine the

flakiness index of the macadamia shells.

23

The apparatus used was special sieves having elongated slots. The width of the slot used in the

gauge is specified for the appropriate fractions. A balance accurate to 0.5% of the weight of the

test sample was used to measure the masses passing.

A quantity sufficient enough to provide at least 200 pieces for each size fraction which

constitutes more than 15% of the sample and at least 100 pieces for each size fraction which

constitutes between 5-15% of the sample was taken. Size fraction constituting of less than 5% of

the sample was not tested. The sample was then separated into the appropriate size fractions by

sieving. Each appropriate fraction was gauged in turn for thickness on the special sieves.

The total amount passing the thickness gauge or special sieves was then weighed to an accuracy

of at least 0-5% of the weight of the test sample.

3.3.1.5 Aggregate Impact Value (BS 812)

The aggregate impact value gives the measure of the resistance of an aggregate to sudden shock

or impact, which in some aggregates differs from its resistance to a slow compressive load. With

aggregates of aggregate impact value 30% or higher, the result may be anomalous. Aggregate

impact value is an indicator of the toughness of aggregates.

The apparatus used were as described in BS 812. The material for the standard test consisted of

aggregate passing a 12.7mm and retained on a 9.52mm BS test sieve.

The measure was then filled with three equal layers of aggregates and tamped with 25strokes

using the round end of the tamping rod after each layer was added. The final layer was filled to

overflowing before tamping, and the surplus aggregate struck off, using the straight edge of the

tamping rod after tamping.

Test Procedure.

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

that it was rigid and the hammer guide columns were vertical. The cup was then fixed firmly in

position on the base of the machine and the whole of the test sample placed in it and compacted

by a single tamping of 25 strokes by the tamping rod.

24

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

in the cup, and allowed to fall freely on to the aggregates. The test sample was subjected to a

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

The crushed aggregates were then removed from the cup without further breaking of the sample,

and then sieved on the2.36mm BS test sieve for the standard test until no further amount passed

in one minute. The fraction passing the sieve was weighed to an accuracy of 0.1g (weight B).

The fraction retained on the sieve was also weighed (weight C)

Plate 3. 6 Macadamia Shells Being Tapped On the Cylindrical Metal

3.3.1.6 Aggregate Crushing Value (BS 812)

The aggregate crushing value gives a relative measure of the resistance of an aggregate to

crushing under a gradually applied compressive load. It is also a measure of the mechanical

strength of the aggregate. The higher the aggregate crushing value of an aggregate, the stronger

is the aggregate in resisting compression. The apparatus used were in accordance to BS 812.

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

added in three equal layers, with each layer being subjected to 25 strokes evenly distributed over

25

the surface of the layer, by the tamping rod which was dropped from a height of approximately

50mm above the surface of the aggregates. The surface of the aggregates was then leveled off

and a plunger was inserted so that it rests horizontally on this surface, taking care to ensure that

the plunger did not jam in the cylinder. The apparatus was then placed with the test sample and

plunger in position, between the platens of the testing machine and loaded at a uniform rate of

40kN/min up to a force of 200kN. The loading was supposed to reach to a value of 400kN but

the machine could not press further due to high strains by the macadamia shells.

The load was released and the crushed material was removed. The fine particles adhering to the

inside of the cylinder, the base plate and the underside of the plunger were transferred to the tray

by means of a stiff hair brush. The whole sample on the tray was then sieved using a 2.36mm test

sieve and the fraction passing the sieve was then weighed.

3.3.1.7 Ten Percent Fines Value (BS 812-111:1990)

The 10% fines value gives a measure of the resistance of an aggregate to crushing and is

applicable to both weak and strong aggregates; however, it is designed for relatively soft

aggregates having an aggregate crushing value of over 30% where a force of 400kN would crush

most or all of the aggregate. The force at which 10% of fines are produced is noted as the Ten

Percent Fines Value. The standard test is made on aggregates passing a 14mm test sieve and

retained on a 10mm test sieve. The objective was to determine the ten percent fines value of the

macadamia shells.

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

in three equal layers with each layer being subjected to 25 strokes by the tamping rod, distributed

evenly over the surface of the layer and dropped from a height of approximately 50mm above the

surface of the aggregate. The surface was then carefully leveled off and the plunger inserted so

that it rested horizontally on the surface, taking care to ensure that the plunger did not jam in the

cylinder.

The apparatus was then placed with the test sample and plunger in position, between the platens

of the testing machine. Force was applied at a uniform rate so as to cause a total penetration of

plunger in 10min of about 24 mm. The maximum force required to produce the required

26

penetration was recorded. The force was then released and the crushed materials removed. The

fine particles adhering to the inside of the cylinder, the base plate and the underside of the

plunger were transferred to the tray by means of a stiff hair brush. The whole sample on the tray

was then sieved using a 2.36mm test sieve. The fraction passing the sieve was then weighed and

expressed as a percentage of the mass of the test sample

Plate 3. 7 Compression Test Machine for Determination of Ten Percent Fines

3.3.2 Preparation and Testing of Fresh Concrete

3.3.2.1 Batching of Concrete Materials (BS 1881-108:1983)

Weight batching method was used and five batches were obtained. Substitution of coarse

aggregates with macadamia shells was done at percentages of 0%, 10%, 20%, 30% and 50% for

the five batches respectively. The water content was kept constant at 0.45 however at 50%

replacement, an additional batch was added containing a water cement ratio of 0.55. Mix ratio

adopted was (1: 1: 2) to obtain class 30 concrete.

The apparatus used were iron moulds as specified in the BS codes, a steel trowel, a vibrator,

spade and a mixing trough. The specimens were cast in iron moulds of 150mm cubes and

150mm diameter by 300mm height cylinders (BS 1881:1983). The moulds were cleaned and

oiled on their inside surfaces first in order to prevent sticking of concrete on the surfaces. The

27

moulds were then assembled and bolts and nuts tightened to prevent leakage of the plastic

concrete mix.

After preparing the mixes in accordance with the mix ratio, the moulds were filled with concrete

in three layers, each layer being compacted using a vibrating table to remove as much entrapped

air as possible and to produce full compaction of concrete without segregation. The moulds were

filled until the concrete overflowed and excess concrete removed by cutting across the surface of

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

the moulds undisturbed for 24 hours and protected against dehydration at a temperature of about

20°C by covering them with a moist inorganic sack. They were then demoulded and placed in

curing tanks for curing.

Plate 3. 8 Preparations of the Iron Moulds

Plate 3. 9 The Batched Concrete Mix

28

Plate 3. 10 Table Vibrator with Cast Cylinders on Top

3.3.2.2 Slump Test (BS1881-102:1983)

Unsupported fresh concrete flows to the sides and a sinking in height takes place. This vertical

settlement is known as slump. Workability may be described as the consistence of a mix such

that the concrete can be transported, placed and finished sufficiently, easily and without

segregation.

The objective was to determine slump of fresh concrete mix. The apparatus included a standard

slump cone, a base plate, a standard tamping rod, steel rule, scoop and a drying duster.

The inside surfaces of the mould were cleaned and oiled to prevent adherence of fresh concrete

on the surfaces. The mould was then placed on the base plate and firmly held in place by

standing on the base plate on a smooth hard surface. The cone was then filled with fresh concrete

in three layers with each layer compacted with 25 drops of the tamping rod. After filling the

mould, the top surface was smoothed off using the tamping rod as a straight edge. The surface of

the cone and the base plate were wiped clean. The cone was carefully lifted, keeping it vertical as

much as possible.

As soon as the concrete collapsed, the degree of slump was measured. This was done by first

resting the rod across the top of inverted empty cone so that it reaches over the mould of

concrete. The distance of the highest point of the concrete to the underside of the rod was

measured and recorded to the nearest 5mm as the slump.

29

3.3.2.3 Compacting Factor Test (BS 1881-103:1993)

The compaction factor test measures the degree of compaction resulting from the application of a

standard amount of work

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

used were compacting factor apparatus, tamping rod and a weighing balance

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

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

was released opened to allow concrete to fall into the cylinder. The excess concrete was cut

across the top of the cylinder and the net mass of the concrete in the cylinder was determined.

The cylinder was emptied and then refilled and placed in a vibrating table so as to compact it and

then the weight of the compacted concrete measured. The compacting factor is then calculated as

follows;

Compacting factor = 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒑𝒂𝒓𝒕𝒊𝒂𝒍𝒍𝒚 𝒄𝒐𝒎𝒑𝒂𝒄𝒕𝒆𝒅 𝒄𝒐𝒏𝒄𝒓𝒆𝒕𝒆

𝒎𝒂𝒔𝒔 𝒐𝒇 𝒇𝒖𝒍𝒍𝒚 𝒄𝒐𝒎𝒑𝒂𝒄𝒕𝒆𝒅 𝒄𝒐𝒏𝒄𝒓𝒆𝒕𝒆 … Equation 3. 3

3.3.3 Preparation and Testing of Hardened Concrete

3.3.3.1 Curing of Cubes

Curing may be defined as the procedures used for promoting the hydration of cement, and

consists of a control of temperature and of the moisture movement from and into the concrete.

The objective of curing was to keep concrete as nearly saturated as possible, until the originally

water-filled space in the fresh cement paste was filled to the desired extent by the products of

hydration of cement. The temperature during curing also controls the rate of progress of the

reactions of hydration and consequently affects the development of strength of concrete. The

cubes were placed in a curing pond/tank at a temperature of 20 ± 2◦C for the specified period of

time. After setting and demoulding, the cubes were marked before being placed in a curing tank.

30

Plate 3. 11 The Curing Tanks

3.3.3.2 Compressive Test (BS EN 12390-3:2002)

The compressive test is used to get the strength of concrete in terms of the compressive axial

load.

The objective of the test is to determine the cube strength of hardened concrete. The apparatus

included the concrete specimens and a compression machine in accordance with BS EN 12390.

The specimen was placed in the machine with two cast faces in contact with the plates of the

testing machine. The load was applied at a constant rate. The ultimate load was read and

recorded. The procedure was repeated for all the sample cubes cast and the readings were

recorded.

31

Plate 3. 12 Compressive Test Machine and Its Setup

3.3.3.3 Tensile Split Test (BS 1881-117:1983)

Tensile strength is an important property of concrete because concrete structures are highly

vulnerable to tensile cracking due to various kinds of effects and applied loading itself. However,

tensile strength of concrete is very low compared to its compressive strength.In the experiment,

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

with the load application line and perpendicular to the trowelled face. The load was then applied

until failure.

Plate 3. 13 Tensile Split Test Apparatus and Its Setup

32

Chapter Four

4.0 Results and Discussions

4.1 Aggregates Tests Results

4.1.1 Moisture Content, Water Absorption and Specific Gravity

Table 4. 1 Moisture Content

Contents Mass(g)

Pan + wet aggregate (M1) 283.2

Pan + dry aggregate (M2) 274.7

Pan (M3) 126.8

Table 4. 2 Water Absorption and Specific Gravity

Contents symbol Mass(g)

Mass of saturated shells in air A 172.8

Vessel + water + shells B 1233.7

Vessel + water C 1198.2

Oven dry sample + pan 262.1

Pan 126.9

Oven dry sample D 135.2

Moisture content=M1−M2

M2−M3*100%

=283.2−274.7

274.7−126.8*100%

= 6.16%

33

Water absorption =A−D

D∗ 100%

= 172.8−135.2

135.2*100%

= 27.8%

Relative density on a saturated and surface dried basis

=A

A−(B−C)

= 172.8

172.8−(1233.7−1198.2) = 1.26

Relative density on an oven dried sample

= 𝐷

𝐴−(𝐵−𝐶)

= 135.2

172.8−(1233.7−1198.2)

= 0.98

The relative density of aggregates used in normal road construction varies between about 2.5 and

3.0, with an average value of about 2.7 and in general, a high specific gravity is associated with a

hard stone. In our case, the results show that the aggregate has failed in moisture content, water

absorption and specific gravity. However, our project objective requires a less dense aggregate to

reduce on the mass of concrete which our sample aggregate achieves.

4.1.2 Aggregate Crushing Value (A.C.V)

The test was compressed up to a force of 200kN instead of the standard 400kN specified in the

BS 812.

2.36 BS sieve results

Mass passing = 7.4g

34

Mass retained = 1045.5g

A.C.V. = 𝑀𝑎𝑠𝑠 𝑝𝑎𝑠𝑠𝑖𝑛𝑔

𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 * 100%

= 7.4

1052.9∗ 100%

= 0.7%

According to the set standards in BS 812, a value of less than 10% signifies an exceptionally

strong aggregate whereas values above 35% are regarded as of weak aggregates. In our case, the

aggregates show that they are exceptionally strong. This strength is usually referred to as

toughness. This is the resistance of an aggregate to resist breakage. However; the force used was

200kN instead of the standard 400kN because the compression machine would not press further

due to the high strains exhibited by the macadamia shells. The high strains observed are

advantageous in concrete because they help concrete in flexural behavior and help in its elastic

behavior.

4.1.3 Aggregate Impact Value (A.I.V)

Mass passing = 4g

Mass retained = 202.3g

A.I.V. = 𝑀𝑎𝑠𝑠 𝑝𝑎𝑠𝑠𝑖𝑛𝑔

𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 * 100%

= 4

206.3∗ 100%

= 1.94%

Aggregate Impact Values below 10 are regarded as strong, and AIV's above 35 would normally

be regarded as too weak for use in road surfaces and construction.

In the above analysis of our experiment, the AIV of the sample of aggregates used was found to

be 1.94%. These aggregates are therefore regarded as very strong aggregates and are deemed fit

for construction for they can resist impact without failure.

35

The AIV gave a very high value because the sample aggregates acted in an elastic way to bounce

back the hammer. This elastic tendency would prove a good way to prevent failure from impact

loadings.

4.1.4 Ten Percent Fines Value

Force required to produce 10% fines, F

F = 14𝑁

𝑌+4

Where; N = reading

= 120 kN

Y = percentage fines

= 𝑀𝑎𝑠𝑠 𝑝𝑎𝑠𝑠𝑖𝑛𝑔

𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 * 100%

= 3.9

1031.2∗ 100%

= 0.38 %

F = 14∗120

0.38+4

= 383.56 kN

= 384 kN

Due to the results obtained in the ACV and AIV, a 10% fines value was needed to further

establish on the toughness of the sample aggregate.

According to BS 812-111:1990, the percentage fines (Y), should be in the range of 7.5 – 12.5

and the ten percent fines value to be greater than 100kN. In our experiment, the percentage fines

gave a much lower value of 0.38% and the 10% fines value gave a very high value of 384kN

rounded off to the nearest whole number as stated in the BS code. A high numerical result of

36

10% fines value is associated with a strong aggregate, and the higher the value, the more suitable

it is for construction.

4.1.5 Particle Size Distribution

Table 4. 3 Particle Size Distribution

BS Sieve size

(mm)

Mass retained

(g)

Percentage

Retained

(%)

Cumulative

percentage

retained (%)

Percentage

passing

(%)

37.5 0 0 0 100

25.4 0 0 0 100

20 151.7 14 14 86

14 445.05 40 54 46

10 343.64 31 85 15

5 170.22 15 100 0

∑ = 1110.61

Figure 4. 1 Particle Size Distribution

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45

PA

SSIN

G (%

)

SIEVES (MM)

Min Max

37

The macadamia shells partially conformed to the specifications of BS 882:1990 which from the

graph shows the red graph as the minimum limit while the green graph as the maximum limit.

The shells generated the blue graph which indicated that aggregates above 17mm were more than

the required quantity.

4.1.2 Flakiness Index

Table 4. 4 Flakiness Index

BS sieve size (mm) Mass retained (g) Mass passing (g)

20 34.2 117.4

14 130.3 313.4

∑ = 164.5 ∑ = 430.8

Flakiness index = 𝑀𝑎𝑠𝑠 𝑝𝑎𝑠𝑠𝑖𝑛𝑔

𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 * 100%

= 430.8

164.5+430.8∗ 100%

= 72.3%

British standards for single-sized aggregates require that the maximum flakiness index shall be

35% or 40% according to the nominal size of aggregate. In our experiment, the sample gave a

flakiness index of 72.3% which was a very large value compared to the expected.

Its large flakiness value may be the source of the large differences observed in the previous

aggregates tests. The high flakiness leads to lower strength in concrete due to reduced aggregate

interlock.

38

4.2 Fresh Concrete Results

In our experiment, the water/cement ratio was predetermined to be 0.45 so as to produce a class

30 concrete, however, at 50% replacement of coarse aggregates, the concrete produced

comprised of relatively lumps of “coarse aggregates” coated with a cement and sand paste .i.e.

the concrete was composed of a very high percentage of aggregates coated with cement-sand

paste. After casting the first batch of 50% replacement of coarse aggregates using a water/cement

ratio of 0.45, the water/cement ratio was increased to a value of 0.55 to give a concrete which

was a bit more homogeneous and then the batching and casting was done.

Plate 4. 1 The Concrete Bath At 50% Replacement Showing the Non-Fluid Concrete (W/C

Ratio of 0.45)

39

4.2.1 Slump test

Table 4. 5 Slump Test

Percentage replacement (%) Slump value (mm)

0 (0.45 w/c ratio) 20

10 (0.45 w/c ratio) 25

20 (0.45 w/c ratio) 15

30 (0.45 w/c ratio) 10

50 (0.45 w/c ratio) Shear failure

50 (0.55 w/c ratio) 5

Figure 4. 2 Slump Value

The value of slump increases at 10% replacement but then falls gradually with an increase in

percentage replacement. This trend shows that, at minimal replacement, the concrete achieves a

higher workability than the normal conventional concrete using a constant water cement ratio.

The reduction in slump is due to the increasing bulking of the volume of concrete and due to the

high water absorption of the macadamia shells as observed in the previous aggregates tests

discussed earlier.

0

5

10

15

20

25

30

0 10 20 30

Slu

mp

val

ue

(mm

)

Percentage replacement (%)

Slump value (mm)

40

4.2.2 Compacting Factor Test

Table 4. 6 Compaction Factor

Percentage replacement (%) Compaction factor

0 (0.45 w/c ratio) 0.87

10 (0.45 w/c ratio) 0.79

20 (0.45 w/c ratio) 0.82

30 (0.45 w/c ratio) 0.78

50 (0.45 w/c ratio) 0.80

50 (0.55 w/c ratio) 0.74

The compacting factor did not give a continuous trend however its value should range from 0.82-

0.95 as stated in the BS 1881-103:1993. At 50% replacement, using the w/c ratio of 0.45, the

compacting factor was higher compared to the w/c of 0.55. This was due to the former having

little fluidity compared to the latter. The lack of fluidity reduced the compaction ability leading

to higher compaction factor. Our values do not deviate much from the set standard which makes

the concrete made from replacement by macadamia to be relatively suitable for use in regards to

compaction.

0.65

0.7

0.75

0.8

0.85

0.9

0 (0.45 w/cratio)

10 (0.45 w/cratio)

20 (0.45 w/cratio)

30 (0.45 w/cratio)

50 (0.45 w/cratio)

50 (0.55 w/cratio)

Co

mp

acti

on

fact

or

Percentage replacement(%)

Compaction factor

41

4.3 Hardened Concrete Results

4.3.1 Compressive Strength

Plate 4. 2 The Crushed Cubes (The Macadamia Shells Can Be Seen Embedded Inside the

Concrete Matrix) and Showing the Hourglass Failure Mode

Plate 4. 3 Concrete cube and cylinder at 50% replacement (note the low cement paste

content)

42

4.3.1.1 7 Days Strength

Table 4. 7 7 Days Strength

Percentage replacement (%) Average load (kN) Average strength (N/mm2)

0 (0.45 w/c ratio) 430 19.1

10 (0.45 w/c ratio) 400 17.8

20 (0.45 w/c ratio) 320 14.2

30 (0.45 w/c ratio) 220 9.8

50 (0.45 w/c ratio) 150 6.7

50 (0.55 w/c ratio) 190 8.4

Figure 4. 3 7 Days Strength

At 7 days, the difference in strength between the control and 10% replacement was quite small

however the strength reduced gradually with an increase in percentage replacement. At 50%

replacement, there was an increment in strength due to an increase in water/cement ratio. This

was an abnormal observation as the strength of concrete normally decreases as the water/cement

ratio increases.

0

5

10

15

20

25

0 (0.45 w/c ratio) 10 (0.45 w/cratio)

20 (0.45 w/cratio)

30 (0.45 w/cratio)

50 (0.45 w/cratio)

50 (0.55 w/cratio)

aver

ege

stre

ngt

h (N

/mm

2)

percentage replacement (%)

7 days strength

43

4.3.1.2 28 Days Strength

Table 4. 8 28 Days Strength

Figure 4. 4 28 Days Strength

At 28 days, the trend of the strength of concrete was the same as at that for 7 days and the control

concrete reached the class 30 concrete as expected. A similar trend was also observed at 50%

replacement of coarse aggregates.

0

5

10

15

20

25

30

35

0 (0.45 w/c ratio) 10 (0.45 w/c ratio) 20 (0.45 w/c ratio) 30 (0.45 w/c ratio) 50 (0.45 w/c ratio) 50 (0.55 w/c ratio)

Ave

rage

str

engt

h (N

/mm

2)

Percentage replacement (%)

28 days strength

Percentage replacement (%) Average load (kN) Average strength (N/mm2)

0 (0.45 w/c ratio) 750 33.3

10 (0.45 w/c ratio) 630 28.0

20 (0.45 w/c ratio) 480 21.3

30 (0.45 w/c ratio) 340 15.1

50 (0.45 w/c ratio) 170 7.6

50 (0.55 w/c ratio) 230 10.2

44

Figure 4. 5 7 Days and 28 Days Strength

A comparison of the 7 day and 28 day strength generated the graph shown above. It was

observed that, as the percentage of replacement increased, the concrete did not increase its

strength as much as the control concrete .i.e. the 28 day strength increased by a small value

compared to the control. For example, at 50% replacement, the 7 day strength was 6.7N/mm2

while the 28 day strength was 7.6N/mm2 (at 0.45 w/c ratio), while the control had a strength of

19.1N/mm2 at 7 days and a strength of 33.3N/mm2 at 28 days.

The cause of reduction in achieving much higher strength is due to minimal cement content

observed by reduction of cement-sand paste as the percentage replacement increases. This is

because there is little cement content to continue being hydrated with time.

0

5

10

15

20

25

30

35

0 (0.45 w/cratio)

10 (0.45 w/cratio)

20 (0.45 w/cratio)

30 (0.45 w/cratio)

50 (0.45 w/cratio)

50 (0.55 w/cratio)

aver

age

str

engt

h (N

/mm

2)

Percentage replacement (%)

7 day and 28 day strengths

7 day strength 28 days strength

45

4.3.2 Tensile Strength

Plate 4. 4 Tensile Split Test Crushed Cylinder

Table 4. 9 Tensile Split Test

Percentage replacement (%) Average Load (kN) Average tensile split

strength (N/mm2)

0 (0.45 w/c ratio) 190.0 2.7

10 (0.45 w/c ratio) 137.7 1.9

20 (0.45 w/c ratio) 77.5 1.1

30 (0.45 w/c ratio) 50.0 0.7

50 (0.45 w/c ratio) 42.6 0.6

50 (0.55 w/c ratio) 45.0 0.64

46

Tensile split strength, Ϭct = 2𝐹

𝜋∗ 𝑙 ∗ 𝑑

Where,

F is the maximum load (in N);

L is the length of the specimen

d is the cross-sectional dimension of the specimen

Figure 4. 6 Tensile Split Test

The tensile strength reduces gradually with increase in percentage replacement. This trend

continues until when the water/cement is increased to 0.55 when the tensile strength increases by

a small value of 0.04 N/mm2.

0

0.5

1

1.5

2

2.5

3

0 (0.45 w/c ratio) 10 (0.45 w/c ratio) 20 (0.45 w/c ratio) 30 (0.45 w/c ratio) 50 (0.45 w/c ratio) 50 (0.55 w/c ratio)

Ten

sile

sp

lit s

tren

gth

(N/m

m2)

Percentage replacement (%)

Average tensile split strength - 28 days

47

4.3.3 Density and Mass

Table 4. 10 Density and Mass

Percentage

replacement

(%)

CUBE

average mass and density

CYLINDER

average mass and density

Average density

(kg/m3)

(cube + cylinder) Mass(kg) Density(kg/m3) Mass(kg) Density(kg/m3)

0 8.20 2429.6 13.45 2537.1 2483.4

10 7.85 2325.9 12.70 2395.6 2360.8

20 7.30 2163.0 11.80 2225.8 2194.4

30 6.95 2059.3 11.04 2084.4 2071.9

50 6.25 1851.9 9.80 1848.6 1850.3

Figure 4. 7 Average Density

The total average density reduced with an increment in percent replacement of coarse aggregates.

The reduction in density was directly proportional to the mass of the concrete produced leading

to a lighter concrete with an increment in percentage replacement.

0

500

1000

1500

2000

2500

3000

0 10 20 30 50

Ave

rage

den

sity

(kg/

m3)

Percentage replacement (%)

Average density

48

Chapter Five

5.0 Conclusions and Recommendations

5.1 Conclusions

From this research project, macadamia shells were used partially in place of coarse aggregates.

Total replacement of coarse aggregate could not be achieved with the available set standards.

The properties of macadamia shells were tested and compared to normal aggregates in terms of

the tests required by the British standards. The conclusions made were as follows:

Macadamia shells have a high water absorption rate which can be a great concern when

used in concrete. This high water absorption rate can however, prove to be an advantage

with time because it can provide additional water for the hydration of cement in concrete.

The aggregate crushing value of the macadamia shells is quite high; however, the test

was not done as specified because they gave high strains compared to the stresses

required. The high strains were not associated with failure as the percent of fines

recorded were very minimal. This was evidently seen in the ten percent fines test which

gave very positive results.

Macadamia shells can handle very high impact loads comfortably without failure as seen

in the aggregate impact value test which recorded high values as compared to the set

British standards.

The macadamia shells are very flaky materials. Their flakiness is very high but with

further research, blending with other materials can produce better materials which can be

of beneficial use.

The particle size distribution of the shells did not conform fully to the requirements of BS

882:1990 showing that blending with other coarse is needed.

Replacement of coarse aggregates with macadamia increases the workability of concrete

up to a certain level which then reduces as the percentage replacement increases.

Replacing at values exceeding 50% reduces the fluidity nature of the resultant concrete.

49

The compressive strength and tensile strength of concrete reduces with percentage

increment in replacement of coarse aggregates with macadamia shells at a constant

water/cement ratio. However, an increment in the water/cement ratio yields a much

higher strength than the corresponding concrete containing the same level of replacement.

Replacing coarse aggregates with macadamia produces concrete with a lower density and

mass. There was a reduction of 25% in density at 50% replacement.

At 50% replacement of coarse aggregates, the concrete was porous as seen on the surface

of the cubes and cylinders. The higher the porosity of concrete, the higher the insulation

of concrete. This shows that the insulation of concrete increases with additional

replacement of coarse aggregates with macadamia shells.

5.2 Recommendations

From the overall overview of the aggregates tests on macadamia shells, the shells proved to be

quite a good coarse aggregate if not better. However, when used partially in concrete they caused

a reduction in strength and an increment in workability up to a certain level. The strength

increased with a change in parameters (i.e. Water/cement ratio).

A cost analysis of the macadamia shells in comparison with conventional coarse aggregates

shows that the shells would be the ideal aggregate. This is because at the current Kenyan market,

one tonne of coarse aggregate is sold at a price of approximately Kshs 1600.00 while macadamia

shells are available freely from the nut manufacturers where they are usually disposed or burnt

off as seen earlier in this report.

This report clearly shows that macadamia shells can produce a high strength lightweight concrete

by using a high water/cement ratio (unlike in normal concrete) and an increased workability at a

much reduced price. Such concrete can be used in construction of non-load bearing walls and

panels. Further research on an ideal mix design for macadamia shells in concrete can produce

such kind of concrete which would make concrete a much better and economical material to

construct with.

50

Chapter Six

6.0 References

The study, research and experiments were based on extracts, theories and definitions from the

following titles:

William H. Langer, Lawrence J. Drew, Janet S. Sachs (2004). “Aggregates and the

Environment” American Geological Institute.

Henry G. Russell, Henry G. Russell, Inc., Glenview, IL, (2009) “Light weight concrete-

Material properties for structural design”. LWL Bridges Workshop. St Louis, MO.

Neville A. M. (2000), “Properties of Concrete”, 5th edition, New York. Pitman

Dr. N. Suresh Professor, NIE, Mysore, “Workability of Concrete”

Kosmatka and Panarese (1994) Design and Control of Concrete Mixtures, Portland

Cement Association, Skokie, Illinois

Mehta and Monteiro. (1993) Concrete Structure, Properties, and Materials,

Prentice-Hall, Inc., Englewood Cliffs, NJ

British Standard Institution, BS 1881-116:1983, “Method for Determination of

Compressive Strength of Concrete Cubes”, London, (1983)

BS 812: Part 110:1990,”Methods of determination of aggregates crushing value (ACV)”,

Testing Aggregates, British standards Institution, London, (1990).

BS 812: Part 1:1975,”Sampling, shape, size and classification”, Testing Aggregates,

British Standards Institution, London, (1975).

BS 812: Part 2:1975: Methods for determination of physical properties”, Testing

Aggregates, British Standards Institution, London, (1975).

51