Coffee husk ash as partial replacement for cement in concrete grade c25 final

INVESTIGATING THE EFFECT OF PARTIAL REPLACEMENT OF
CEMENT WITHCOFFEE HUSK ASH IN PRODUCTIONOF CONCRETE
GRADE C25
BY
ATEKA S PETER
REG NO: 111/05567
The project report submitted to the department of civil and construction
engineering in partial fulfilment of the award of the degree of bachelor of
engineering in civil engineering
SUPERVISOR
PROFESSOR GEORGE M. THUMBI
DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEER

DECLARATION
I declare and affirm to the best of my knowledge that this research is my original work and has
not been presented for a degree or any other award in this or any other university.
Signed: ……………………................. (Author); date…………………………………
PETER S ATEKA 111/05567
I confirm that the work reported in this research was carried out by the candidate under my
supervision.
Signed: ……………………................. (Supervisor); date………………………………
PROF.GEORGE M. THUMBI

ABSTRACT
The costs of conventional building materials continue to increase as the majority of the population
continues to lie below the poverty line.
Thus, there is the need to search for local materials as alternatives for the construction of
functional but low-cost buildings in both the rural and urban areas.
Continuous generation of wastes arising from industrial by-products and agricultural residue,
create acute environmental problems both in terms of their treatment and disposal.
This research considered the use of coffee husk ash as a pozzolan in the production of concrete
class 25. the study investigated the physical properties and chemical composition of coffee husk
ash (CHA) as well as the workability, and compressive strength properties of the concrete
produced by replacing 5%, 10%, 15%, 20% and 25% by weight of ordinary Portland cement with
CHA. Slump and compacting factor tests were carried out on the fresh concrete and compressive
strength, tensile strength test and bulk density was determined on hardened concrete. The concrete
cubes were tested at the ages of 7, 14 and 28 days. The results showed that CHA is a good pozzolan
with combined SiO2, Al2O3 and Fe2O3 of 73.07%. The slump and compacting factor decreased as
the CHA content increased indicating that concrete becomes less workable as the CHA content
increased. The compressive strength decreased with increasing CHA replacement. The
compressive strength of concrete with CHA was lower at early stages but improves significantly
up to 28 days. An optimum value of 21.02N/mm2 at 28 days was obtained for concrete with 5%
CHA replacement. It was concluded that 5% CHA substitution is adequate to enjoy maximum
benefit of strength gain.

DEDICATION
To almighty God for the life and strength He has granted me. To my parents, brothers and sisters,
thank you for your love, emotional and financial support. And especially to my Mother, all
would be lost without responsible parenthood. Thank you for your relentless sacrifices and
confidence so that I can be who I am today.

ACKNOWLEDGEMENT
I wish to sincerely acknowledge the contributions of all those who assisted me either directly or
otherwise towards the undertaking of this project. Special thanks to Prof. George M Thumbi my
supervisor, for rigorously guiding me through the research process.
The Civil engineering department for technical and material support throughout the entire
project.
To all my class mates thanks for your creative criticism and ideas and also for your friendship
and assistance. To all my friends, who have in one way or another contributed to the completion
of this project, I am entirely grateful for all your support.

LIST OF TABLES.
Table 2.1: Compound of cement…………………………………………………...16
Table 2.2: Chief compounds in cement clinker……………………………………16
Table 2.3: chemical properties of CHA…………………………………………….17
Table 3.1: Total amount of materials required for the project……………………. 28
Table 3.2: Batching proportion…………………………………………………….42
Table 4.1: Particle size distribution of the fine aggregates…………………………43
Table 4.2: The grading of aggregate of the size distribution the course
aggregate………………………….…………………………………………………45
Table 4.3: Showing slump test values………………………………………………46
Table 4.4: Compaction factor values of CHA concrete…………………………….47
Table 4.5: Compressive strength of cubes with various percentages of
CHA……………………………………………………………………………........49
Table 4.6: Loads failure…………………………………………………………….50
Table 4.7: Showing cylinder splitting values at 28 days……………………………51
Table 4.8: Bulk densities of concrete cubes with various percentages of
CHA…………………………………………………………………………………51
Table 5.1: Showing slumps test values……………………………………………...54

LIST OF FIGURES.
Figure 3.1: Preparation of coffee husk ash…………………………………………21
Figure 3.2: Different sieve sizes used for grading………………………………….21
Figure 3.3: Slump measurement………………………………………………….30
Figure 3.4: Compaction factor test…………………………………………………32
Figure 3.5: Casting of cubes……………………………………………………….33
Figure 3.6: Cubes unmoulded and ready for curing……………………………….34
Figure 3.7: Curing of cubes ………………………………………………............34
Figure 3.8: Application of compressing force of
15N/MM2………………………………………………………………………….39
Figure 3.9: Compressed block………………………………………………………39
Figure 3.10: Weighing balance …………………………………………………….41
Figure 3.11: Flow chart representing working in the
laboratory……………………………………………….........................................43
Figure 4.1: A graph showing the grading of sand…………………………………43
Figure 4.2: Particle size distribution curve for
fine………………………………………………………………………………...44
Figure 4.3: Showing slump test……………………………………………………45
Figure 4.4: Graph of compaction factor test……………………………………….45

Figure4.5: Compressive strength of concrete cubes with varying percentage of
CHA………………………………………….........................................................48
Figure 4.6: Graph showing the variation in tensile strengths for various mixes
used…………………………………………..........................................................50
Figure 4.7: Effect of cha at different curing age…………………………………. 51

CONTENTS
DECLARATION .....................................................................................................................................i
ABSTRACT......................................................................................................................................- 0 -
DEDICATION...................................................................................................................................- 1 -
ACKNOWLEDGEMENT.....................................................................................................................- 2 -
CHAPTER ONE................................................................................................................................- 8 -
INTRODUCTION..............................................................................................................................- 8 -
1.0 Background information............................................................................................................- 8 -
1.1 Problem statement.................................................................................................................- 10 -
1.2 Problem justification...............................................................................................................- 10 -
1.3 Objective................................................................................................................................- 11 -
1.3.1 Main objective.....................................................................................................................- 11 -
1.3.2 Specific objectives................................................................................................................- 11 -
CHAPTER TWO .............................................................................................................................- 12 -
LITERATURE REVIEW.....................................................................................................................- 12 -
2.0 Concrete.................................................................................................................................- 12 -
2.1 Constituents of concrete .........................................................................................................- 12 -
2.1.1 Cement................................................................................................................................- 13 -
2.1.2 Aggregates...........................................................................................................................- 15 -
2.1.3 Water..................................................................................................................................- 15 -
2.1.4 Admixture............................................................................................................................- 15 -
2.2 Coffee husk ash (CHA).............................................................................................................- 16 -
CHAPTER THREE ...........................................................................................................................- 17 -
RESEARCH METHODOLOGY...........................................................................................................- 18 -
3.0 Introduction............................................................................................................................- 18 -
Coffee husk ash............................................................................................................................- 18 -
3.1 Preliminary preparations.........................................................................................................- 20 -
3.1.1 Sieve analysis of aggregate ...................................................................................................- 20 -
3.1.2 Mixing proportion ................................................................................................................- 23 -
Concrete mix design .....................................................................................................................- 23 -
3.1.3 Batching of concrete material ...............................................................................................- 28 -
3.2 Laboratory tests......................................................................................................................- 28 -
3.2.1 TESTING THE PROPERTIES OF FRESH CONCRETE.....................................................................- 29 -

3.2.1.1 Slump test.........................................................................................................................- 29 -
3.2.1.2 Compacting factor test.......................................................................................................- 30 -
3.2.1.3Casting of and curing of cubes.............................................................................................- 32 -
A. casting of cubes........................................................................................................................- 32 -
B. Curing of cubes ......................................................................................................................- 33 -
3.2.2 Testing the properties of hardened concrete .........................................................................- 35 -
3.2.2.1 Compressive strength test..................................................................................................- 35 -
3.2.2.2 Tensile Test.......................................................................................................................- 38 -
Tensile splitting test....................................................................................................................- 38 -
3.2.2.3 Bulk densities of hardened concrete cubes .........................................................................- 39 -
CHAPTER FOUR.............................................................................................................................- 42 -
RESULTS AND ANALYSIS................................................................................................................- 42 -
4.0 Sieve analysis..........................................................................................................................- 42 -
4.1 Results of slump test onfresh concrete samples.......................................................................- 46 -
4.2 Results of compacting factor test on fresh concrete samples.....................................................- 47 -
4.3 Results of Compressive Strength Tests on Concrete Cubes.........................................................- 49 -
4.5 Tensile strength of the samples................................................................................................- 52 -
4.6 Bulk densities of concrete cubes ..............................................................................................- 54 -
CHAPTER 5............................................................................................. Error! Bookmark not defined.
DISCUSSION ........................................................................................... Error! Bookmark not defined.
5.0 Grading ............................................................................................ Error! Bookmark not defined.
5.1 Workability....................................................................................... Error! Bookmark not defined.
5.2 Compressive strength........................................................................ Error! Bookmark not defined.
5.3 Tensile strength ................................................................................ Error! Bookmark not defined.
Summary of Discussion.................................................................................................................- 56 -
CHAPTER SIX ................................................................................................................................- 57 -
CONCLUSION AND RECOMMENDATION.........................................................................................- 57 -
6.0 CONCLUSIONS ........................................................................................................................- 57 -
6.1 Challenges..............................................................................................................................- 11 -
6.2 Recommendations..................................................................................................................- 58 -
References...................................................................................................................................- 59 -
APPENDICES.................................................................................................................................- 61 -

CHAPTER ONE
INTRODUCTION
1.0 Background information
There is a need for affordable building materials particularly Ordinary Portland Cement in order
to provide accommodation for the teaming populace of the World. The costs of conventional
building materials continue to increase as the majority of the population continues to lie below the
poverty line.
Thus, there is the need to search for local materials as alternatives for the construction of functional
but low-cost buildings in both the rural and urban areas. Supplementary cementitious materials
have been proven to be effective in meeting most of the requirements of durable concrete and
blended cements are now used in many parts of the World (Bakar, Putraya, and Abdulaziz, 2010).
Various research works have been carried out on the binary blends of Ordinary Portland Cement
with different pozzolans in making cement composites (Adewuyi and Ola, 2005; De Sensale, 2006;
Saraswathy and Song, 2007).
Some of the materials that have been used are; earthen plaster (Svoboda and Prochazka, 2012),
laterite interlocking blocks (Raheem et al., 2012), Palm kernel shell (Raheem et al., 2008), Saw
dust ash (Raheem, Olasunkami and Folorunso, 2012) and Rice husk ash (Obilande et al., 2012).
Continuous generation of wastes arising from industrial by-products and agricultural residue,
create acute environmental problems both in terms of their treatment and disposal. The
construction industry has been identified as the one that absorbs the majority of such materials as
fillers in concrete (Antiphons et al., 2005). If the fillers have pozzolanic properties, they impart
technical advantages to the resulting concrete and also enable larger quantities of cement
replacement to be achieved (Hossain, 2003). Appropriate utilization of these materials brings
ecological and economical benefits.

The construction materials are obtained from either river beds or on ground then some are
processed in industries to have final product to be used in construction one of the major material
processed in industry is limestone which is the chief material for cement. Chemical composition
of limestone is mainly Calcium Carbonate (CaCO3)
In the industry, limestone is heated at elevated temperatures to produce quicklime (CaO) and
Carbon (IV) oxide (CO2). Carbon (IV) oxide is one of the major causes of global warming-
greenhouse effect. In 2006, at Kyoto scientific convention agreed that emission of carbon (IV)
oxide to the environment should be minimized by all countries. This set conditions and
mitigation measures that should be followed to minimize emission of this gas.
It is due to this measures that has led to scientific research on cement replacement materials that
is, finding alternatives of cement manufacturing materials. Through this research it has been
discovered that there exist organic materials with same pozzolanic properties as limestone. These
materials are;
 Rice husk ash (RHA)
 Saw dust ash (SDA)
 Sugarcane straw ash (SCSA)
 Sugar cane bagasse ash (SCBA)
 Coffee husk ash (CHA)
These materials are waste product from rice mill, sugar cane and coffee factories respectively. If
they are not carefully controlled, they are becoming major land and air pollutants and therefore
more effort is applied on disposal or recycling of these wastes. In Uganda for example, coffee
husk is being proposed to be used as a source of energy in cement production industry and in
Brazil which is major coffee producer in the world is using coffee husk as untreated sorbents for

removal of methylene blue (BM) from aqueous solutions- application of Langmuir and
Freundlich adsorption models.
Therefore, this project is aimed at reducing cost of building materials, emission of carbon (IV)
oxide gas from cement production process and re-use of agricultural by-products hence reducing
pollution due to this wastes as the research aims at replacement of cement with coffee husk
which is cheaply available.
1.1 Problem statement
Challenges facing the construction industry in Kenya are the increased cost of building materials
which eventually leads to increased construction costs, environmental pollution control from
industrial manufacture of cement, control of carbon (IV) oxide gas emission into the environment,
and energy consumption during production of cement. Disposal of agricultural waste is also a
challenge since these wastes pollutes environment.
In order to reduce the overall cost of construction, environmental pollution and lowering energy
consumption, a cheap construction material which can give high strength and durability as
compared to the normal concrete is required. The use of coffee husk ash as partial replacement of
cement in concrete will therefore reduce this challenges.
1.2 Problem justification
Since it is clearly known and understood that the rising cost of concrete production has impaired
the construction industry, a study on the alternative readily available alternatives (like coffee
husk ash) to replace cement justifies the research. Also from environmental point of view,
recycling of these wastes would help in the protection of environment that is, exploitation of
limestone through quarrying would be significantly reduced and emission of carbon (iv)oxide to

the environment. Agricultural wastes such as coffee husk also pollutes environment that is, land
and air. Therefore, using them in construction will reduce their environmental pollution.
1.3 Objective
1.3.1 Main objective
The main objective of this research is to investigate the effect of coffee husk ash as partial
replacement of Portland cement in concrete C25.
1.3.2 Specific objectives
 To determine workability of concrete before and after replacing with CHA
 To evaluate the effect of concrete mix ratio on compression strength, tensile strength and
bulk densities of concrete cubes with different percentages of coffee husk ash.
1.4 limitations
For optimum replacement, higher amount of coffee husks is needed which is expensive for this
research. For example, a bag of 90 kg produces 5 kg of CHA. Onother side this is good for disposal
of coffee husk but it utilises high amount of energy to be combusted.
Pre-burning should be done on open air on which wind causes problems like blowing away coffee
husks as they are light.
The process produces a lot of carbon (ii) oxide if not supplied with a lot of air.

CHAPTER TWO
LITERATURE REVIEW
2.0 Concrete
Concrete has been used in construction since prehistoric times in Israel, Egypt and Rome. The
constituent of concrete that has been changed over time is cement or binder. The earliest
civilization used lime or volcanic ash as a binder in place of present day cement.
Concrete is a mixture of cement, water, fine and coarse aggregates in which water and cement
have hardened by chemical reaction to form a binder. In addition, other materials are included in
the mixture; the admixture (G.D Taylor and B.J Smith, 1986).
Concrete is used for various purposes in the construction industry; for building, airport runway,
road pavement, water pipeline, fencing posts, electric poles, subway and tunnels, and water
retaining structures.
Concrete strength is assessed by measuring the crushing strength of cubes or cylinders of
concrete made from the mixture. These are usually cured and tested after twenty-eight days
according to standard procedures. Concrete of given strength is identified by its grade for
example; concrete class C25 means that it has a characteristic cube crushing strength of
25N/mm2 (W.H. Mosley et al., 1999).
In some circumstances it may be useful to replace some of the cement by materials such as
pulverized fuel ash or ground granulated blast furnace slag which has slowly developing
cementitious properties (W.H. Mosley et al., 1999).
2.1 Constituents of concrete
Concrete is a mixture of cement, water and aggregates. Aggregates are divided into fine
aggregates of size 0.2 to 0.5 mm, and coarse aggregates of size exceeding 5mm but less than

20mm for most building. For high strength coarse aggregate of size 12.7mm are of good use
(David Otieno Kotieng’, 2015).
2.1.1 Cement
Portland cement is the most common type of cement in general usage. It is a basic ingredient of
concrete, mortar, and plaster. English engineer Joseph Aspdin patented Portland cement in 1824;
it was named because of its similarity in colour to Portland limestone, quarried from the English
Isle of Portland and used extensively in London architecture. It consists of a mixture of oxides of
calcium, silicon and aluminium. Portland cement and similar materials are made by heating
limestone (a source of calcium) with clay, and grinding this product (called clinker) with a
source of sulphate (most commonly gypsum). The manufacturing of Portland cement creates
about 5 percent of human CO2emissions (A.M. Neville, 2002).
Cement is a material with adhesive and cohesive properties which makes it capable of binding
mineral particles into a compact whole. Most important cements are Portland cements which are
hydraulic that is, they set and harden by the action of water only (G.D Taylor and B.J Smith,
1986).
Cement is produced in accordance to KS EAS18, KEBS, 2005, cement Part (I). The cement
produced are blended cements in which cement replacing materials are added to clinker at the
time of grinding. The cements available in the market are Portland Pozzolana Cement PPC
CEMII/B-P containing 21-35% natural pozzolana, Pozzolanic Cement PC CEMIV/A with 11-
35% pozzolanic material and Portland limestone cement PLC CEMII/A-CC with 6-20%
limestone addition. A limited quantity of Ordinary Portland Cement OPC CEMI is produced for
specific use (David Otieno Kotieng’, 2015).

Chemically, cement is composed of the following compounds, shown in table 2.1 (G.D Taylor
and B.J Smith, 1986).
Table 2.1 compounds of cement
Compound name Chemical formula Common name Abbreviation
Clay or shale SiO2
Fe2O3
Al2O3
Silica (silicon oxide)
Ferrite (iron oxide)
Alumina (Aluminum oxide)
S
F
A
Limestone CaCO3 Calcium Carbonate C
Microscopic examination of cement clinker shows that there are four chief compounds present as
shown in table 2.2 (G.D Taylor and B.J Smith, 1986).
Table 2.2 chief compounds in cement clinker
Name Abbreviations Approximate
%
Properties Heat of
hydration
(J/g)
Di- calcium
silicate
C2S 30 Slow strength gain
responsible for long term
strength
260
Tri-calcium
silicate
C3S 45 Rapid strength gain
responsible for early
strength e.g. 7days
500
Tri -calcium
aluminates
C3A2 12 Quick setting controlled by
gypsum susceptible to
sulphate attack
865
Tetra -calcium
aluminoferrite
C4AF 8 Little contribution to setting
or strength responsible for
grey colour of Ordinary
Portland Cement
420

2.1.2 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 chemical
composition affect to varying states. Basic characteristics of aggregates test is 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 refer as sand) containing
particles majority smaller than 5mm and coarse aggregates containing particles larger than 5mm.
Sieving analysis is used for determining the particle size distribution of aggregates, BS 882: Part 103.
2.1.3 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 (BS31480).
2.1.4 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 (Rixom1997; Concrete Society Technical Report
No.18,1980).
2.2 Coffee husk ash (CHA)
Coffee husk ash is produced after burning coffee husk which is believed to have high reactivity
and pozzolanic property.
Early studies conducted on rice husk revealed that rice has also same properties as those
mentioned above though energy released by coffee husk is much higher than for rice husk. Some
countries like India has included in her standards the use of rice husk cement for example IS456-
2000 recommends use of RHA for plain concrete
Chemical composition of coffee husk ash cement varies with variation of temperature and
burning process. Silica content in ash increases with higher temperature CHA produced by
burning coffee husk between 6000C and 7000C temperatures for two hours contains 90-95%
silica, 1-3% Potassium Oxide and <5% unburnt carbon.
Under controlled burning condition in industrial furnace, conducted by Mentha, P.K (1992) RHA
contains silica in amorphous and highly cellular form with 50-1000 cm3 /g surface area. Same
case has been revealed by Lee- Kuo Lin, Tsung-Min-Kuo and Yi-Shu- Hsu April 2013 of
Taiwan University on coffee husk cement research.

It has also been discovered that the use of coffee husk ash cement improves workability and
stability, impermeability and durability by strengthening transition zone, modifying the pore
structure, blocking the large voids in the hydrated cement paste through Pozzolanic reaction.
CHA minimizes alkali aggregate reaction, reduces expansion, refines pore structures and hinders
diffusion of alkali ions to the surface of aggregate by micro-porous structures.
Chemical properties of CHA
Table 2.3: chemical properties of CHA
Chemical constituents Percentage composition
SiO2 60.00
Fe2O3 3.00
CaO 9.52
MgO 4.08
SO3 1.07
Na2O 0.08
K2O 2.00
CaCO3 7.92
Total SiO2 + Al2O3 70.98
Total SiO2 + Al2O3 + Fe2O3 73.07

CHAPTER THREE
RESEARCH METHODOLOGY
3.0 Introduction
The research methodology was split into two phases;
1.0 Preliminary preparations, Laboratory tests and collection of data
2.0 Analysis and data application
Materials that were used in this research were;
 Ordinary Portland cement which was purchased from dealers in Nairobi. The choice
was made to conform to the requirement of BS EN 197-1:2002.
 Aggregates- fine aggregate used was river washed sand free from organic material
and clay, and crushed coarse aggregate of 12mm, both from dealers in Nairobi. Fine
aggregate was free from impurities so that it can conform to BS882-1992.
 Water which was free from organic material, suspended solids and impurities so that
strength of concrete was not weakened and conform to the requirement of BS
EN1008:2002.
Coffee husk ash
Coffee husks were obtained from Ruiru, Kofi Naf and were pre-burned to reduce carbon
content and bulkiness before they were incinerated a furnace at 7000C. Pre-burning was done
on open air, furnace product was white-greyish ash.
Then the pre-burned CHA was incinerated in oven temperatures varying from 100C to 7000C
then allowed to cool to room temperature to obtain coffee husk ash. This process was carried
out at the University of Nairobi, soil laboratory.

Precaution was taken during this process, major being constantly monitoring the oven
temperature as if not so, no ash would have been obtained as it was noted that, at very high
temperature coffee husk burns completely leaving no residue. The best method of cooling
noted was to open oven after the required temperature has been attained so that there is
complete combustion.
The ash obtained was whitish, it was grounded to the required level of fineness and sieved
through 600µm sieve in order to remove any impurity and large size particles.
Figure 3.1: Preparation of coffee husk ash

In this process, patience is very paramount or else nothing is expected.
Problems encountered were: -
1. In pre-burning, wind became nuisance as it blows away coffee husks as they are light.
One cannot avoid open air as at the beginning a lot of smoke is produced which has
chocking smell.
2. Constant turning needed as if not, first burned goes off, so to keep burning, one needs to
be constantly turning husks.
3. Coffee husks burns with fire that has glare effect on eyes
3.1 Preliminary preparations
3.1.1 Sieve analysis of aggregate
This involved determination of coefficient of uniformity (Cu) and coefficient of curvature (CC)
for fine aggregates and coarse aggregate. The sieve sizes that were used for the coarse
aggregates, according to BS812: Part 1:1975 were from 50mm to 2.36 mm.
The sieve sizes for fine aggregates were from 5mm -75ųm.
Coarse aggregate is defined as aggregate mainly retained on a 5.0 mm BS 410 test sieve and
containing no more-finer material than is permitted for the various sizes in this specification (CL
2.2).
Coarse aggregate may be described as gravel (uncrushed, crushed or partially crushed) as defined
in 2.2.1, or as crushed rock as defined in CL2.2.2, or as blended coarse aggregate as defined in
CL2.2.3.
When determined in accordance with BS 812-103.1 using test sieves of the sizes given in Table
3, complying with BS 410, full tolerance, the grading of the coarse aggregate should be within
the appropriate limits given in Table 3.

Functions of the aggregates in a mix
Aggregates serve the following purposes;
 They reduce the cost of the concrete. Natural aggregates require only extraction, washing
and grading prior to transportation to the site.
 Correctly graded aggregates produce workable, yet cohesive concrete.
 They reduce heat of hydration of the concrete since they are chemically inert and act as
heat sink for hydrating cement.
Test apparatus
Wire brush
Balance
Drying oven
Tray
Receiving pan
Sieve series (50 mm, 38.1mm, 20mm, 15mm, 10mm ,5mm, 2.36mm, 2mm, 1.18mm, 0.6mm,
0.3mm,0.15, 0.075mm)
Procedure
 The sample sieved were representative of the source hence was firstly quartered using
a riffle box.

 The aggregate samples were air dried and then oven dried at 1050C for 24 hours. For
the coarse and fine aggregates, the dry samples were weighed before sieved. The
samples were then passed through a series of sieves starting with the largest mesh unit
and then proceeding with decreasing mesh seizes up to the receiving pan at the bottom.
 The material that were retained were weighed, while the material that passed through
the sieve were transferred to the next sieve. A soft brush was used to clean the sieve.
 The procedure was repeated with each sieve and the material passed through the last
one collected in the pan at the bottom.
 From the obtained results a grading chart was drawn.
Figure 3.2: Showing different sieve sizes used for grading test

3.1.2 Mixing proportion
This research was conducted on concrete C25 and therefore mix design was needed. For concrete
C25, a ratio of 1:2:4 (binder, fine aggregate and coarse aggregate) with water to binder ratio that
will be between 0.6, was be used.
Concrete mix design
Concrete mix design was carried out to determine the proportions of constituents of concrete that
met the desired strength and other properties. This was done according to accepted standards and
specifications.
Mix design enables in choosing of a mix that will be recommended in the casting of precast
element for testing.
It entailed coming up with adequate water/ cement ratio that will give adequate compressive
strength. This is aimed at achieving
 Workability
 Compressive strength
 Durability
Characteristic strength of 25N/mm2, crushed coarse aggregate of 12mm were used. Expected
slump of 30-60mm, age of loading being 7-28 days and cement used was ordinary Portland cement
(OPC)
The procedure is as follows:

Stage 1: Selection of target class strength
The standard deviation to be adopted in determining the target strength should be that obtained
from line A, from the graph showing the relationship between standard deviation and
characteristic strength.
The margin can then be derived from
M=k x s
Where;
M= margin
k = a value appropriate to the percentage defectives permitted below the characteristic
strength = 1.64
s = the standard deviation
s = 8
The target mean strength is determined through
fm = fc +M
Where
fm = the target mean strength
fc = the specified characteristic strength
fc = 25N/mm2
M = the margin
Fm = 25+ (1.64 x 8)

= 38.12N/mm2
Using this value, the water/cement ratio is obtained from the graph showing the relationship
between compressive strength and free water/cement ratio.
Stage 2: water/ cement ratio
Appendix 4 figure 4
w/c = 0.6
Stage 3: determination of free water content
Consists simply of determining the free water content depending upon the type and maximum
size of the aggregate to give a concrete of the specified slump.
Specific gravity of aggregate =2.63
Density of wet concrete =2400 kg/m3
Free water content =210 kg/m3 figure 4 in appendix
Stage 4: Determination of cement content
Cement content = (𝑓𝑟𝑒𝑒 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡)/(𝑓𝑟𝑒𝑒 𝑤𝑎𝑡𝑒𝑟/𝑐𝑒𝑚𝑒𝑛𝑡 𝑟𝑎𝑡𝑖𝑜)
Wet density = 2400kg/m3
Free water content = 210kg/m3
Cement content = 210/0.6
= 350kg/m3

The resulting value should be checked against any maximum or minimum value that may be
specified. If the calculated cement content is below a specified minimum, this minimum value
must be adopted and a modified free water/cement ratio calculated.
Stage 5: Determination of total aggregate content
Stage 5 requires an estimate of the density of the fully compacted concrete which is obtained
depending upon the free water content and the relative density of the combined aggregate in the
saturated surface dry condition (SSD).
Total aggregate content = D – C - W
Where;
D = the wet density of concrete (kg/m3) = 2400 kg/m3
C = the cement content (kg/m3) = 350 kg/m3
W = the free water content (kg/m3) = 210 kg/m3
Total aggregate = wet concrete mix – cement content – free water content
= 2400-350-210
= 1840kg/M3
Stage 6: Coarse aggregate
Total maximum aggregate size = 12 mm
Slump =30-60 (mm)

35% of fine aggregate passing 600 microns sieve, from fig 6
Proportional fine aggregate = 35/100 x 1840kg/m3
= 644kg/m3
Coarse aggregate = 1840-644
= 1196kg/m3
Quantity of constituents
Number of cubes = 18 cubes
Volume = 0.15 x 0.15 x 0.15
= 3.375 x 103m3
For 18 cubes = 18 x 3.375 x 10 -3
=6.075 x 10-2m3
Allowing for wastage of 10%
= 1.1 x 0.06075
= 0.0668 m3
= 0.07 m3 (approx.)
Volume of constituents = 0.07 x calculated amount in kg/m3
Table 3.1: total amount of materials required for the project
Proportions Calculated amount (kg/m3) Total required in experiment
(kg)
CEMENT 350 25
FINE AGGREGATE 644 46
COARSE AGGREGATE 1196 84
WATER 210 15

3.1.3 Batching of concrete material
Batching of materials was done by weight. The percentage replacement of ordinary Portland
cement by CHA was 0%, 5%, 10%, 15%, 20% and 25%. The 0% replacement served as control
for other samples.
Table 3.2: Batching proportion
Percentage
Replacement
of CHA
Cement
kg
Coffee
huskash
kg
Fine
aggregate
kg
Coarse
aggregate
kg
Water
m3
w/c
0 1.20 0.00 2.30 4.60 0.80 0.60
5 1.14 0.06 2.30 4.60 0.80 0.60
10 1.08 0.12 2.30 4.60 0.80 0.60
15 1.02 0.18 2.30 4.60 0.80 0.60
20 0.96 0.24 2.30 4.60 0.80 0.60
25 0.90 0.30 2.30 4.60 0.90 0.65
3.2 Laboratory tests
The tests that were conducted were on properties of;
1. fresh concrete
 Slump
 Compacting factor test

2. hardened concrete
 Compressive strength test
 Tensile strength test
 Density of hardened concrete
3.2.1 TESTING THE PROPERTIES OF FRESH CONCRETE
3.2.1.1 Slump test
This involved determination of compacting values of CHA of different percentages replacement
of cement, that is, at 0%, 5%, 10%, 15%, 20% and 25%. This was important as it helped to know
whether this concrete had cohesion to resist segregation and also to test for consistence. This test
was carried out according to BS 1881-103:1983. This was a test used to detect variations in the
uniformity of a mix of given nominal proportions, and gave an indication of the workability of the
mix.
Apparatus
Slump cone
Standard 16mm diameter Steel rod
Flat steel base
Procedure
 The inside of the cone and its base was oiled at the beginning of every test.
 The slump cone was placed on the flat base and filled with concrete in three layers.
 Each layer was tamped 25 times with the steel rod, and the top surface struck off by
means of a screeding and rolling motion of the tamping rod.

 The area around the base of the cone was cleaned from concrete that had dropped
accidently.
 The cone was held firmly against its base during the entire operation, facilitated by
foot-rest brazed to the mould.
 Immediately after filling, the cone was lifted, and the unsupported concrete was
allowed to slump. The decrease in height of the Centre of the slumped concrete was
measured and recorded as the slump.
Figure 3.3: slump measurement
3.2.1.2 Compacting factor test
This is the degree of compaction measured by the density ratio that is the ratio of density actually
achieved in the test to the density of the same concrete fully compacted.
Objective
 To determine the workability of concrete mix by compacting factor method

Apparatus
Compacting factor apparatus
Weighing balance
Standard rod
A scoop approximately 100mm wide
A trowel or a float
Procedure
 The inside surfaces of the hoppers and the cylinder was cleaned, dried and oiled
to reduce friction between the hopper surfaces and the concrete.
 The upper hopper was then filled with concrete mix; the concrete being placed
gently so that no work was done on concrete.
 The door of the hopper was released so that the concrete fell on to the lower
hopper.
 The door of the lower hopper was released so that the concrete fell on to the
cylinder. Excess concrete was then cut by a trowel or a float. Concrete adhering to
the cylinder outside surfaces were then removed.
 The weight of the concrete in the cylinder was weighed. This gave the weight of
the partially compacted concrete.
 Using the same cylinder, the concrete was re-filled in three layers, each layer
vibrated to achieve full compaction. The concrete was weighed. This gave the
weight of fully compacted concrete.

Fig 3.4: compaction factor test
3.2.1.3 Casting of and curing of cubes
A. casting of cubes
Cubic specimens of concrete with size 150×150×150mm were casted for determination of all
measurements. 18 mixes were prepared using different percentages as indicated in 3.1.3 above.
The concrete was mixed, placed and compacted in three layers then demoulded after 24 hours.
Before assembling the mould, it’s mating surfaces and insides was covered with a thin layer of
oil, to prevent concrete and the mould bonding. The mould was filled in three layers, each layer
of concrete being compacted by not less than 35 strokes of the punner, until sufficient
compaction was achieved. After the top surface was levelled using a trowel, the moulds were
stored undisturbed for 24 hours, after which they were stripped and the cubes further cured in
water. The cubes were finally tested at 7, 14, and 28 days on the compression testing machine.

Figure 3.5: casting of cubes
B. 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 ± 20C for the specified period of
time. Before placing cubes into a curing tank they must be marked with a water proof marker.
Details to be marked on the cubes are mainly; type of mix, date of casting, duration for curing
and crushing day.

Figure 3.6 cubes unmoulded and ready for curing
Figure 3.7: curing ofcubes

3.2.2 Testing the properties of hardened concrete
3.2.2.1 Compressive strength test
The main aim of this test was to determine the compressive strength of hardened concrete at a
specified time. This involved determination of compressive strength through cube crushing test.
Cubes with varying percentages of CHA are used and test is done at 7th, 14th and 28th day
The crushing strength is influenced by a number of factors in addition to the water/cement ratio
and degree of compaction. These are;
 The type of cement and its quality. Both the rate of strength gain and the ultimate
strength may be affected.
 Type and surface of aggregate. Affects the bond strength.
 Efficiency of curing. Loss in strength of up to 40% may result from premature drying
out.
 Temperature. In general, the initial rate of hardening of concrete is increased by an
increase in temperature but may lead to lower ultimate strength. At lower temperatures,
the crushing strength may remain low for some time, particularly when cements of slow
rate of strength gain are employed, but may lead to higher ultimate strength, provided
frost damage does not occur.
 Age. When moisture is available, concrete will increase in strength with age, the rate
being greatest initially and progressively decreasing over time. The rate will be
influenced by the cement type, cement content and internal concrete temperature.
 Moisture condition.Concrete allowed to dry will immediately exhibit a higher strength
due to the dry process but will not gain strength thereafter unless returned to and

maintained in moist conditions. Dry concrete will exhibit a reduced strength when
moistened.
The compressive strength of the concrete is determined from the following formula
Fc=F/Ac
Where;
Fc =is the compressive strength in N/mm2
F = is the maximum load at failure in Newton
Ac =is the cross sectional area of the specimen on which the compressive force acts,
calculated from the compressive strengths act.
Apparatus
Cubical steel moulds (150mm cubes)
25 mm square steel punner.
Compression testing machine
Procedure.
Cubes were left to stand on sun for one hour to dry them and then their weight measured and
recorded.
After curing the cubes for the specified period, they were removed and wiped to remove surface
moisture in readiness for compression test. The cubes were then placed with the cast faces in
contact with the platens of the testing machine that is the position of the cube when tested should

be at right angles to that as cast. The load was applied at a constant rate of stress of
approximately equal to 15 N/mm2 to failure. The readings on the dial gauge were then recorded
for each cube.
Figure 3.8: application of compressing load of 15N/mm2
figure 3.9: compressed block

3.2.2.2 Tensile Test
The tensile strength of concrete is very important to concrete because concrete structures are
very vulnerable to tensile cracking due to various effects and applied loading. The tensile
strength of concrete is very low however compared to its compressive strength.
Due to difficulty in applying uniaxial tension to a concrete specimen, the tensile test is obtained
by indirect methods. For the experiments carried out, the method used was the split cylinder test.
Preparation of the cylinder specimens
The method adopted was the indirect tensile splitting test of cylindrical concrete specimens.
Concrete mixes were prepared and the fresh concrete cast in 150mm diameter moulds.
Compaction were done in three layers using a poker vibrator to achieve the required compaction.
The upper surfaces of the cylinders were smoothened using a plasterer’s float and the outside of
the moulds wiped clean.
The specimens were stored in an undisturbed environment for 24 hours then cured in a curing
tank for the required number of days.
Tensile splitting test
The split-cylinder test is a method of determining the tensile strength of concrete in an indirect
way. A cylinder of 150mm by 300mm length was placed horizontally on a compression testing
machine. The load was applied diametrically and uniformly along the length of the cylinder. To
allow for uniform distribution of load and to avoid high compressive stress at the point of
application, plywood strips were placed between the loading specimen and the compressive
surface of the compression test machine. Concrete cylinders split in half along the vertical plane
due to indirect tensile strength generated by poisons effect. The load will then be applied and

gradually increased at a normal rate of 0.02 – 0.04N/ (mm2s) and maintained until failure of the
specimens. The maximum loads applied to each specimen will be recorded.
Due to the compressive loading, an element lying across the vertical diameter of the cylinder was
subjected to compressive stress and horizontal stress. The loading conditions produce high
compressive stress immediately beneath the loading points. It is estimated that the compressive
stress acts to about a 1/6th depth and the rest is subject to tensile stress due to Poisson’s effect.
Assuming concrete specimen behaves as an elastic body, a uniform tensile force Ft acting along
the vertical plane causes failure of the specimen which can be calculated as follows
FT=2P/ΠDL
Where P = Compressive load at failure
L = length of cylinder
D = Diameter of cylinder
The above test result represents the Splitting Tensile Strength that varies between 1/8th and a
1/12th of the cube compressive strength results.
3.2.2.3 Bulk densities of hardened concrete cubes
It involved determination of densities of the concrete cubes with different percentages of CHA in
the concrete that is, at 0%, 5%, 10%, 15%, 20% and 25% of CHA in 7th ,14 days and 28 days.
This was done in accordance to BS EN 12390-7:2009
The main aim was to determine the density of hardened concrete.

Apparatus
Weighing balance
Figure 3.10: weighing balance
Procedure
Weight of hardened concrete was measured on the weighing balance and recorded in kg, and
then the volume of hardened cubes was calculated in M3. The density was obtained by applying
formula:
Density = 𝑚𝑎𝑠𝑠/𝑣𝑜𝑙𝑢𝑚𝑒

Figure. 3.11: Flowchart representing work in the laboratory
*As determined by the Mix design
Water
Batching.
Test on the Hardened
Concrete
Antensil
Curing
Workability Test
Moulding Concrete Mix
Mixing
Cement
Aggregat
es see
es
Coffee husk

CHAPTER FOUR
RESULTS AND ANALYSIS
4.0 Sieve analysis
Sieve analysis for fine and the coarse aggregates is based to BS 882:1992. The weight of
aggregate percentages passing the sieves is measured and the percentages determined. The values
were weighed for aggregates passing the sieves, expressed in percentage and recorded in the
table as shown below. A plot of the cumulative percentage passing against the sieves sizes done
on a graph containing the sieve envelop, showed that the curve lied within the limits. This meant
that the aggregates were good for use and no blending of the different sizes was needed.
Fine aggregate
Initial weight=740gms
Table 4.1 Particle size distribution of the fine aggregates
Sieve sizes
(mm)
Weight
retained (g)
% retained Cumulative
% retained
Weight
passing (g)
% passing
5.00 20 2.70 2.70 720.00 97.3
2.36 40 5.41 8.11 680.00 89.13
1.18 100 13.51 21.62 580.00 78.38
0.60 220 29.73 51.35 360.00 48.65
0.30 280 37.84 89.19 80.00 10.81
0.15 60 8.11 97.30 20.00 2.70
0.075 20 2.70 100.00 0.00 0 .00

Figure 4.1 A graph showing the grading of sand
0
20
40
60
80
100
120
-1.5 -1 -0.5 0 0.5 1
percentagepassing
log sieve sizes
Percentage passing

Course aggregate
Initial weight of coarse aggregates =6260.00gms
Table 4.2 Particle size distribution of the Course aggregates
Sieve size Weight retained Weight passing % passing
50.00 1005.00 5255.00 83.95
38.10 1250.00 4005.00 63.98
20.00 1525.00 2480.00 39.62
15.00 1265.00 1215.00 19.41
10.00 650.00 565.00 9.03
5.00 520.00 45.00 0.72
2.36 45.00 0.00 0.00

Figure 4.2: Particle Size Distribution Curve for course Aggregates
Discussion
Sieve analysis was done using the standard test sieves conforming to diameters and mesh
apertures given in BS 410:1976. The results of sieve analysis were represented graphically in
grading curves. From the curves, fine aggregates were found to lie within the limits. Normal
aggregates were within the limits of the coarse aggregates given in BS 882:1992. Grading is of
importance in concrete mix design in the determination of the proportion of fine aggregates and
thus the calculation of course aggregate content. Grading also affects workability of concrete
mixes. The results of the sieve analysis for fine and coarse aggregates are presented in Figures 4.
0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
cummulative%weightpassing
logarithmic scale of sieve analysis
% passing
% passing

1 and 4.2 respectively. It could be observed from Figure 4.2 that the coefficient of uniformity
(Cu) and coefficient of curvature (Cc) for fine aggregates are 4.95 and 1.24 respectively. Thus,
the sand can be said to be well graded (Smith and Smith, 1998). Similarly, the Cu and Cc for
coarse aggregates are 0.89 and 1.75 respectively as obtained from Figure 4.2. This shows that the
granite is uniformly graded (Smith and Smith, 1998). It can be concluded that the fine and coarse
aggregates are suitable for making good concrete. Sieve analysis of fine aggregate when
determined in accordance with BS 812-103.1, using test sieves of the sizes given in Table 4
complying with BS 410, full tolerance, the grading of the sand should comply with the overall
limits given in Table 4. Additionally, not more than one in ten consecutive samples shall have a
grading outside the limits for any one of the grading C, M or F, given in Table 4 (CL 5.2.1).
4.1 Results of slump test on fresh concrete samples
The slump test results were essential in determining the workability of the concrete design. The
design mix chosen was a very low slump concrete mix with a water/cement ratio of 0.6. The
water/cement ratio was chosen so as to clearly see the effects of CHA on concrete workability.
Table 4.3 showing slump test values
Percentage replacement ofCHA
%
SLUMP
0 60
5 59
10 55
15 50
20 45
25 35

Figure 4.3 graph of slump test
4.2 Results of compacting factor test on fresh concrete samples
The results obtained from the compacting factor test on fresh concrete samples are given in table
I.
Table 4.4: Compacting factor values of CHA concrete
Percentage replacement of CHA
(%)
Compacting Factor values
0 0.91
5 0.89
10 0.88
15 0.87
20 0.86
25 0.86
0
10
20
30
40
50
60
70
0 5 10 15 20 25
slump(mm)
CHA percentages replacement
SLUMP
SLUMP

Figure 4.4 graph of compaction factor test
Discussion
Method used to determine workability were the slump test and compaction factor test. Slump
test does not measure directly workability is used in site work to detect variations in the
uniformity of mix of given proportions. Slump test is sensitive to consistency of fresh concrete.
Slump was maintained at a constant range of 3050mm for all the replacement. The values
obtained vary as amount of water each sample required to achieve consistency varied.
0.85
0.86
0.87
0.88
0.89
0.9
0.91
0.92
0 5 10 15 20 25 30
COMPACTIONFACTOR
CHA % REPLACEMENT
Compacting Factor values

Table 5.1 showing slump test values
Percentage replacement ofCHA
%
SLUMP
0 60
5 59
10 55
15 50
20 45
25 35
The table indicates that the compacting factor values reduce as the CHA content increases. The
compacting factor values reduced from 0.91 to 0.85 as the percentage CHA replacement
increased from 0% to 25%. These results indicate that the concrete becomes less workable (stiff)
as the CHA percentage increases meaning that more water is required to make the mixes more
workable. The high demand for water as the CHA content increases is due to increased amount
of silica in the mixture. This is typical of pozzolan cement concrete as the silica-lime reaction
requires more water in addition to water required during hydration of cement.
4.3 Results of Compressive Strength Tests on Concrete Cubes
The effect of curing ages on the compressive strength of CHA concrete is presented in Figure 4.6
The figure indicates that compressive strength generally increases with curing period and
decreases with increased amount of CHA.

The results of the compressive strength tests on concrete cubes are shown in Table 4.5 and
Figure 4.6.
Table 4.5: Compressive Strength of Concrete Cubes with various percentages of CHA
Coffee husk Ash
Replacement
(%)
Compressive Strength
(N/mm2)
7 days 14 days 28 days
0 17.51 21.60 29.15
5 17.23 17.85 21.02
10 16.89 16.96 20.64
15 14.38 15.87 19.05
20 10.59 11.63 13.56
25 9.35 9.83 12.42
Figure 4.5: Effect of CHA content on Compressive Strength of concrete at different curing
age.
0
5
10
15
20
25
30
35
0 5 10 15 20 25
COMPRESSIVESTRENGHT
CHA REPLACEMENT %
Compressive Strength (N/mm2) 7 days

Discussion
The results of the compressive strength of concrete cubes show that the compressive strengths
reduced as the percentage CHA increased. However, the compressive strengths increased as the
number of days of curing increased for each percentage CHA replacement. It is seen from Table
4.6 that for the control cube, the compressive strength increased from 17.51 N/mm2 at 7 days to
29.15 N/mm2 at 28 days (i.e. about 66% increment). The 28 days’ strength was above the
specified value of 25N/mm2 for grade 25 concrete (BS 8110, 1997) as shown in Table 4 on the
appendices. The strength of the 5% replacement by coffee husk ash showed increase in
compressive strength from 17.23 N/mm2 at 7 days to 21.02 N/mm2 at 28 days (22% increment).
The 28 days’ strength was above the specified value of 20N/mm2 for grade 20 concrete (BS
8110, 1997) as shown in Table 4. The strength of the 10% replacement by coffee husk ash
showed increase in compressive strength from 16.89 N/mm2 at 7 days to 20.64 N/mm2 at 28
days (22% increment). The 28-day strength was above the specified value of 20N/mm2 for grade
20 concrete (BS 8110, 1997) as shown in Table 4 in the appendixes. The strength of the 15%
replacement by coffee husks ash showed increase in compressive strength from 14.38 N/mm2 at
7 days to 19.05 N/mm2 at 28 days (32% increment). Increase in compressive strength can be
attributed to the reaction of CHA with calcium hydroxide liberated during the hydration of
cement. (Balendran and Martin Buades, 2000; Adesanya and Raheem, 2009).
Figure 4.6 showed the effect of CHA percentage replacement on the compressive strength of
concrete. As could be observed from the figure, there is a general decrease in compressive
strength as the CHA content increases. Since all the specimens meet the minimum strength of
6N/mm2 after 28 days of curing recommended by BS 5224 (1976) for masonry cement, CHA

concrete could be used for general concrete works where strength is of less importance such as
in mass concrete, floor screed and mortar.
CHA gain strength slowly at early curing age. This is in line with previous findings that
concrete containing pozzolanic materials gained strength slowly at early curing ages (Hossain,
2005; Adesanya and Raheem, 2009).
The 28-day strength was above the specified value of 15N/mm2 for light weight concrete (BS
8110, 1997) as shown in Table 4.
4.5 Tensile strength of the samples
The following loads in table 4.6 were obtained at failure for the specimen
Table 4.6 loads at failure
Sample
28 days strength
Cylinder 1
(N)
Cylinder
2
(N)
Cylinder
3
(N)
Average
(N)
0%CHA 200 160 180 180.00
5%CHA 235 165 175 191.60
10%CHA 210 195 175 193.33
15%CHA 180 185 200 195.00
20%CHA 195 240 240 225.00
25 %CHA 260 220 190 223.33

Table 4.7 Table showing cylinder splitting value at 28 days for everymix
Sample Average value
(N)
fc
(N/mm2)
0% CHA 180.00 2.56
5%CHA 191.60 2.70
10%CHA 193.60 2.73
15%CHA 195.00 2.76
20%CHA 225.00 3.20
25%CHA 223.33 3.16

Fig 4.6 Graph showing the variation in tensile strengths for various mixes used
Discussion
The analysis of the tensile strengths at 28 days of curing showed that the concrete made from
CHA gain strength from 2.56 N/mm2(control experiment) to 3.2 N/mm2(20% replacement of
cement with CHA). The tensile strength then generally decreased at 25% replacement of cement
with coffee husk).
4.6 Bulk densities of concrete cubes
The Bulk Densities of the Concrete Cubes cast at various days of curing are shown in Table 4.8
and Figure 4.9.
0
0.5
1
1.5
2
2.5
3
3.5
0 20 40 60 80 100
Ten
sile
Stre
ngt
h
N/
mm
2
Percentage of CHA
Graph showing variation of tensile
strength for each mix
Graph showing
variation of tensile
strength for each mix

Table 4.8. Bulk Densities of Concrete Cubes with various percentages of CHA
Coffee Husk Ash Replacement
(%)
Bulk density (g/cm3)
7 days 14 days 28 days
0 2.32 2.37 2.43
5 2.27 2.29 2.31
10 2.21 2.22 2.25
15 2.19 2.20 2.22
20 2.19 2.20 2.20
25 2.18 2.18 2.19
Figure 4.7: Effect of CHA content on Bulk Density of Concrete at different curing
age
2.05
2.1
2.15
2.2
2.25
2.3
2.35
2.4
2.45
0 5 10 15 20 25
bulkdensityg/cm3
CHA replacement %
BulkDensity(g/cm3) 7 days

Discussion
The results of the bulk densities show that the bulk density reduces as the percentage CHA
increases. This could be attributed to the increase in voids in the concrete cubes as the percentage
CHA increases. However, the bulk densities increase as the number of days of curing increase as
the concrete cubes become denser.
Summary
 As the replacement of cement with coffee husk ash increases, the workability
of the concrete is decreasing due to the absorption of the water by the coffee
husk ash.
 The results from the table show the decrease in the workability of concrete when the
percentage of the replacement is increasing. The workability is very less at the standard
water-cement ratio and the water that is required for making the concrete to form a slump
with a partial replacement requires more water. The test conducted at 25% replacement
showed that the water- cement ratio increased to 0.65.

CHAPTER SIX
CONCLUSION AND RECOMMENDATION
6.0 CONCLUSIONS
From the investigations carried out, the following conclusions can be made:
The optimum addition of CHA as partial replacement for cement is in the range 5%.
The compacting factor values of the concrete reduced as the percentage of CHA increased.
The Bulk Densities of concrete reduced as the percentage CHA replacement increased.
The Compressive Strengths of concrete reduced as the percentage CHA replacement increased.
From the results of the various tests performed, the following conclusions can be drawn:
 CHA is a suitable material for use as a pozzolan, since it satisfied the requirement for such
a material by having a combined (SiO2 +Al2O3 +Fe2O3) of more than 70%.
 Concrete becomes less workable as the CHA percentage increases meaning that more
water is required to make the mixes more workable. This means that CHA concrete has
higher water demand.
 The compressive strength generally increases with curing period and decreases with
increased amount of CHA. Only 5% CHA substitution is adequate to enjoy maximum
benefit of strength gain.
 The analysis of the tensile strengths at 28 days of curing showed that the concrete made
from CHA gain strength.

6.2 Recommendations
The following are recommended from this study:
 The use of local materials like CHA as pozzolans should be encouraged in concrete
production.
 Similar studies are recommended for concrete beams and slab sections to ascertain the
flexural behaviour of lightweight concrete made with this material.
 Durability studies of concrete cubes made with CHA as partial
replacement for cement should be carried out.

References
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Limited, Essex, 2002.
2. ASTM C88-90,”Test for Soundness of aggregates by use of sodium sulphate or
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3. BS 812: Part 110:1990,”Methods of determination of aggregates crushing value (ACV)”,
Testing Aggregates, British standards Institution, London, 1990.
4. BS 812: Part 1:1975,”Sampling, shape, size and classification”, Testing Aggregates, British
Standards Institution, London, 1975.
5. BS 812: Part 2:1975: Methods for determination of physical properties”, Testing
Aggregates, British Standards Institution, London, 1975.
6. BS 1881: Part 116:1983,: Methods tor determination of compressive strength of concrete
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7. DOI 10.5592/otmcj.2012.2.3 research paper
8. International journal of Engineering and Applied Sciences 20012-2015 EAAS & ARF
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APPENDICES
Appendix tables and figures
Table IV: Recommended grade of concrete (BS 8110, 1997)
Grade Characteristic strength Concrete class
7
10
7.0
10.0
Plain concrete
15 15.0 Reinforced concrete with lightweight
aggregate
20
25
20.0
25.0
Reinforced concrete with dense aggregate
30 30.0 Concrete with post tensioned tendons
40
50
60
40.0
50.0
60.0
Concrete with pre tensioned tendons

Table 1: Strength classes ofcements to European Standard BS EN 197-1: 2000.
StrengthClass Compressive Strength(N/mm2
)
Early Strength StandardStrength
2 dayminimum 7 dayminimum 28 day minimum 28 day maximum
32.5N 16.0 32.5 52.5
32.5R 10 32.5 52.5
42.5N 10 42.5 62.5
42.5R 20 42.5 62.5
52.5N 20 52.5
52.5R 30 52.5
The code lettersinthe Standardsare: N- Ordinaryearlystrengthdevelopment. R- Highearlystrength
development.

Table 2: Approximate Compressive Strength (N/mm2
) ofConcrete Mixes Made with a FreeWater /
Cement Ratio 0.6
Type of Cement Type of
Aggregate
Coarse Compressive strength(N/mm2
)
Age (days)
3 7 14 28
OrdinaryPortland(OPC) orSulphate
ResistingPortland(SRPC)
Uncrushed 22 30 42 49
Crushed 27 36 49 56
RapidHardeningPortland(RHPC) Uncrushed 29 37 48 54
Crushed 34 43 55 61
PortlandPozzolanaCement(PPC)
1 N/mm2 = 1 MN/ m = 1 MPa SSD = basedon a saturatedsurface-drybasis
The statistical constant k isderivedfromthe mathematicsof thenormaldistributionspecifiedinBS5328
and increasesasthe proportionofdefectivesisdecreased,thus:
k for10% defectives=1.28 k
for 5% defectives=1.64 k for
2.5% defectives=1.96 k for
1% defectives=2.33

Figure 3 Relationship between
standard deviation and
characteristic strength
Figure 4 Relationship
between compressive
strength and free

Table 4.4 (c) Approximate free-water contents (kg/m3
) required to give various levels ofworkability
Slump(mm) 0-10 10-30 30-60 60-180
Maximumsize of aggregate (mm) Type of aggregate
10 Uncrushed 150 180 205 225
Crushed 180 205 230 260
20 Uncrushed 135 160 180 195
Crushed 170 190 210 225
40 Uncrushed 115 140 160 175
Crushed 155 175 190 205
When coarse and fine aggregates of different types are used, the free-water content is estimated
by the expression: 2⁄3 Wf+ 1⁄3 Wc. Where Wf = free-water content appropriate to type of fine
aggregate and Wc = free-water content appropriate to type of coarse aggregate.

Figure 5 Estimated wetdensity offully compacted concrete
Figure 6 Recommended proportions of fine aggregate according to percentage passing a
600 μm (0.6mm) sieve

Figure 6. Recommended proportions of fine aggregate according to percentage
passing 600 μm (0.6mm) sieve.

Figure 6 (continued). Recommended proportions of fine aggregate according to
percentage passing a 600 μm (0.6mm) sieve.
Figure 6 (continued)

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