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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).