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UNIVERSITY OF NAIROBI
DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING
AN INVESTIGATION ON THE EFFECTS OF PARTIAL REPLACEMENT OF RIVER SAND WITH MASONRY SAND ON THE
PROPERTIES OF CONCRETE
Project Supervisor ENG S. S. MIRINGU
BY
NG`ANG`A KELVIN KARIITHI
F16/36318/2010
A Project submitted in partial fulfillment of the requirement for the award of the degree of
BACHELOR OF SCIENCE IN CIVIL ENGINEERING
APRIL 2015
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DEDICATIONTo my parents Mwaura and Njeri, my brothers and sisters, my colleagues at the University of
Nairobi and all my Lecturers.
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DECLARATIONI, NG`ANG`A KELVIN KARIITHI, do declare that this report is my original work and to
the best of my knowledge, it has not been submitted for any degree award in any University
or Institution.
Signed_______________ Date ____________
CERTIFICATION
I have read this report and approve it for examination.
Signed_______________ Date_____________
Eng S.S MIRINGU (project supervisor)
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ACKNOWLEDGEMENTFirst of all I thank the Almighty God for His love, care guidance and protection. It is by His
Grace and mercy that i have come this far.
Furthermore I thank my supervisor and lecturer Eng S. S. Miringu for his guidance and input
throughout this project period. It is from his knowledge and expertise that made this research
a success. Thank you for allowing me to pick your brain. Also much appreciation is shown to
Mr Muchina of the concrete laboratory for his guidance and advice especially in the
laboratoryworks. I also thank Nicholas (concrete laboratory) and Martin (soils laboratory) for
their helpful input in this project.
In addition I thank my family especially my parents Mwaura and Njeri for their support and
guidance throughout my life. It is with their sacrifice that I have made it this far.
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ABSTRACTConcrete plays a major role in the construction industry and a large volume of concrete is
being used globally. River sand, which is one of the constituent materials used in the
production of conventional concrete, has become expensive due to high transportation costs.
Furthermore it has become very scarce and poses negative impacts to the environment with
its extraction. In view of this, there is a need to identify suitable alternative material from
industrial processes in place of the river sand. Masonry sand which is a residue waste
material after the extraction and processing of rocks to form various sizes of ballast can be
used as an alternative.
In this study the feasibility of the use of masonry sand for concrete class 30 was investigated.
A nominal mix proportion of 1:1:2 for concrete class 30 with a water cement ratio of
0.42wasused. The properties of the concrete made with different ratios of sand to masonry
sand (sand: masonry sand) 100:0, 75:25, 50:50, 25:75 and 0:100 were investigated. The
compressive strength was measured at 7 and 28 days with the tensile strength at 28 days. The
highest strength was achieved at 50% replacement with an average of 35.33N/mm2
compressive strength and 3.46N/mm2 tensile strength.
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TABLE OF CONTENTS
DEDICATION................................................................................................................................... i
DECLARATION.................................................................................................................................... ii
ACKNOWLEDGEMENT................................................................................................................ iii
ABSTRACT......................................................................................................................................... iv
LIST OF FIGURES.................................................................................................................................v
LIST OF TABLES..................................................................................................................................vi
CHAPTER 1.....................................................................................................................1
1.1 Introduction.................................................................................................................................1
1.2 Problem Statement......................................................................................................................2
1.3 Objective......................................................................................................................................2
1.4 Scope of Work.............................................................................................................................3
CHAPTER 2.....................................................................................................................4
2.1 Literature Review.........................................................................................................................4
2.2 Production of masonry sand........................................................................................................5
2.3 Properties of masonry sand.........................................................................................................5
2.4 Impact of masonry sand..............................................................................................................6
2.5 Applications of masonry sand......................................................................................................6
2.6 Obstacles to applications.............................................................................................................7
2.7 Concrete......................................................................................................................................7
2.7.1 Cement.................................................................................................................................7
2.7.2 Water....................................................................................................................................8
2.7.3 Aggregates............................................................................................................................8
2.7.4 Chemical admixtures............................................................................................................9
2.8 Fresh concrete...........................................................................................................................10
2.8.1 Workability.........................................................................................................................10
2.8.2 Concrete Bleeding...............................................................................................................11
2.8.3 Segregation in concrete......................................................................................................12
2.9 Hardened concrete....................................................................................................................13
2.9.1 Properties of hardened concrete........................................................................................13
2.9.2 Compressive strength.........................................................................................................13
2.9.3 Tensile strength..................................................................................................................14
CHAPTER 3...................................................................................................................15
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3.0 METHODOLOGY.........................................................................................................................15
3.1 Particle size distribution.............................................................................................................15
3.2 Fresh concrete slump................................................................................................................15
3.3 Hardened concrete....................................................................................................................17
3.3.1 Determination of compressive strength – cube test to (BS: 1881: PART 16; 1983)............17
3.3.2 Determination of tensile strength using the splitting tensile strength method..................20
CHAPTER 4...................................................................................................................22
4.0 RESULTS AND ANALYSIS.............................................................................................................22
4.1Laboratory test results................................................................................................................22
4.2 Sieve analysis BS 882: 1992.......................................................................................................22
4.3 Concrete analysis.......................................................................................................................24
4.3.1 Fresh concrete analysis workability....................................................................................24
4.3.2 Compressive strength.........................................................................................................25
4.3.3 Tensile strength..................................................................................................................30
4.4 Cost Benefit Analysis..................................................................................................................32
CHAPTER 5...................................................................................................................32
5.0 DISCUSSION...............................................................................................................................32
5.1 Grading......................................................................................................................................32
5.2 Workability................................................................................................................................33
5.3 Compressive strength................................................................................................................34
5.4 Tensile strength.........................................................................................................................34
CHAPTER 6...................................................................................................................34
6.1 CONCLUSION.............................................................................................................................34
6.2 Recommendations.....................................................................................................................35
REFERENCES...............................................................................................................36
REPORTS......................................................................................................................37
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LIST OF FIGURES.Figure 1 Masonry sand..........................................................................................................................4Figure 2 Masonry sand..........................................................................................................................4Figure 3 Typical quarry..........................................................................................................................5Figure 4 Slump test apparatus.............................................................................................................16Figure 5 Preparation of slump test......................................................................................................17Figure 6 Measuring of slump...............................................................................................................17Figure 7 Casting of cubes.....................................................................................................................18Figure 8 Curing of cubes......................................................................................................................18Figure 9 Loading of cubes....................................................................................................................19Figure 10 Manual compression machine.............................................................................................19Figure 11 Crushing of cubes.................................................................................................................20Figure 12 Loading of a cylinder............................................................................................................20Figure 13 Splitting of a cylinder...........................................................................................................21Figure 14 Grading for river sand..........................................................................................................23Figure 15 Grading for masonry sand....................................................................................................24Figure 16Bar chart representing varying slump values for different masonry sand percentages........25Figure 17Bar chart showing variation of compressive strength at 7 days for different replacements.27Figure 18bar chart showing variation in compressive strengths at 28 days for different replacements of masonry sand..................................................................................................................................29Figure 19combined line graph showing compressive strength at 7 and 28 days.................................29Figure 20 Bar chart showing tensile strength variations with different proportions of masonry sand 31
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LIST OF TABLES.Table 1 Sand grading...........................................................................................................................23Table 2 Sand grading...........................................................................................................................23Table 3minimum and maximum limits according to BS 882:1992.......................................................24Table 4 Masonry sand grading.............................................................................................................25Table 5 Masonry sand grading.............................................................................................................25Table 6 Showing slump values.............................................................................................................26Table 7 Showing cube crushing forces at 7 days..................................................................................27Table 8 Showing compressive strength values at 7 days.....................................................................27Table 9 Showing cube crushing forces at 28 days................................................................................28Table 10 Showing compressive strength values at 28 days.................................................................29Table 11showing cylinder splitting values at 28 days..........................................................................31Table 12 Showing tensile strength values at 28 days...........................................................................32
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CHAPTER 1
1.1 IntroductionConcrete is the most widely used construction material which consists of coarse aggregates,
fine aggregates, binder(cement) and water. Coarse aggregates consists of particles which are
more than 5mm in diameter while fine aggregates are materials passing 5mm BS sieve as
defined by BS 882: 1983. The aggregates should have good mechanical properties in terms
shape, density, grading, hardness and purity to achieve the required strength and durability.
The mixture of these materials results in a chemical reaction called hydration and a change in
the mixture from liquid-plastic state to a solid state occurs over a period of time aided by the
cement which bonds them together. The fine aggregates in this mixture function to assist in
producing workability and uniformity in the mixture, filling spaces created by the coarse
aggregates. Fine aggregates are normally sand which is sourced from river banks or dug from
pits. The coarse aggregate is usually ballast which is produced mechanically by crushers from
quarried rock. There are some areas in Kenya where people crush stones to make ballast in
small scale to supplement their income.
The demand for sand continues to increase day by day as construction of new infrastructural
projects and expansion of existing ones is continuous thereby placing immense pressure on
the supply of the sand and hence mining activities are going on legally and illegally without
any restrictions. Lack of proper planning and sand management causes disturbance of marine
ecosystem and also upset the ability of natural marine processes to replenish the sand. Also
the quality of natural river sand is decreasing as deposits diminish. BS 882:1983 defines
impurities as those fine materials passing BS test sieve 150um which are composed mainly of
clay and silt. These impurities cause detrimental effects on the properties of concrete made.
In view of this there is a need in developing countries to identify alternative materials to
lessen or eliminate the demand for natural sand.
Masonry sand could be used as an alternative of natural sand. It is a byproduct generated
from quarrying activities involved in the production of crushed coarse aggregates. Masonry
sand is generally considered as a waste material after the extraction and processing of rocks
to make ballast. It causes an environmental load due to disposal problem. Hence, the use of
masonry sand to make concrete will not only reduce the demand for natural sand but also the
environmental burden caused by its disposal (Manassehet al2010). Moreover, the
incorporation of masonry sand will offset the production cost of concrete since such costs as
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for transportation of natural sand from their deposits will be reduced. Waste management cost
will also be reduced as well as augmenting the quality of concrete.
In this study the possibility of the use of masonry sand as full or partial replacement of
natural river sand was conducted. The main aim was to replace the natural river sand with
masonry sand without compromising on the required properties of the concrete like strength.
The main problem observed was with the reduction in workability as the percentage of
masonry sand increased (Neville et al 1995).
1.2 Problem StatementIn line with the Kenyan vision 2030, there has been increased development in Kenya. This
has led to increased demand for concrete and therefore aggregates and cement. Kenya is a
largely agricultural country with the highest population involved in farming. This loosens the
soil and when it rains soil erosion occurs leading to high deposits of silt and clay being
deposited in river beds. Although natural river sand is formed in the same way the presence
of the other organic materials such as silt and clay leads to diminished quality of the fine
aggregate.
Presence of these impurities in the sand leads to production of concrete of low workability
and low strength which is an undesirable characteristic. Although the sand can be washed it
would be very costly especially in large scale. The sand deposits are located far from the
construction sites and so there is high transportation costs which make acquisition of the sand
more costly.
Due to the high cost and diminishing quality of sand there is need for the alternative material
to replace sand. The masonry sand manufactured from crushers does not have as much
impurities and there are lesser transportation costs as compared to sand and thus it is a more
favorable replacement and therefore justified the feasibility of this experiment.
1.3 ObjectiveThe main aim of the project was to investigate the variation in concrete strengths after
replacement of sand with masonry sand from 0%, in 25% intervals up to 100%.The effect of
the masonry sand on the workability was investigated too. A cost analysis was done in
comparison with the natural river sand.
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1.4 Scope of WorkIn this study, the effect of masonry sand in concrete in terms of compressive strength and
tensile strength was investigated. There were 30 number of cubes with dimensions 150 x 150
x 150 mm and 15 cylinders with dimensions 150mm diameter and 300mm length. Samples
with 0% (no masonry sand), 25%, 50%, 75% and 100% of masonry sand were cast.
All samples were cured in the water curing tank at the University of Nairobi concrete
laboratory. The cube samples were used as compression test specimens to determine the
compressive strength at the age of 7and 28 days. The cylindrical samples underwent the
tensile splitting test at the age of 28 days to determine the tensile strength.
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CHAPTER 2 LITERATURE REVIEW
2.1 INTRODUCTIONMasonry sand can be defined as residue, tailing or other non-voluble waste material after the
extraction and processing of rocks to form fine particles less than 5 mm. Usually, Masonry
sand is used in large scale in the highways as a surface finishing material and also used for
manufacturing of hollow blocks and lightweight concrete prefabricated elements.
Figure 1 Masonry sand
Figure 2 Masonry sand
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2.2 Production of masonry sand Quarry is produced during the crushing, milling and screening of quarried rock to produce
coarse aggregate (ranging from 20 mm to 5 mm) (ballast) and other products.
Crushing of quarried rock is carried out in stages, with the primary crushing stage typically
carried out using jaw crushers or gyratory crushers and subsequent (secondary and tertiary)
stages by cone or impact crushers. Fines production increases with an increase in the number
of crushing stages. The proportion of fines produced varies with the type of rock and also the
type of crusher used (Hudson et al 1997).
Figure 3 Typical quarry
2.3 Properties of masonry sandDifferent quarries according to their production process may generate a full range of masonry
sands in relation to their particle size and composition of the mother rock. For instance,
masonry sand produced from primary screening may have higher or lower clay content
than those produced through tertiary crushing and screening. Masonry sand is composed of
the same mineral substances as the soil and solid rock from which it is derived, even
though changes to its physical and chemical characteristics may have occurred. Masonry
sand by its nature, is usually inert or non-hazardous.
Disaggregation, mixing and moving to different locations, exposure to atmospheric
conditions and to surface or groundwater, as well as segregation and the increase of surface
area due to particle size reduction, may cause physical and chemical transformations
with detrimental effects to the environment (BGS, 2003). Masonry sand is considered as a
more consistent material in relation to its composition and particle size.
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Commonly, the decision making criteria upon which the suitability of masonry sand is
determined, is based on technical specifications and standards or on characterization
procedures developed by the end users, such as construction product manufacturers.
Therefore, it is end users that define whether masonry sands comprise a valuable material.
Parameters such as rock type, extraction technique and processing route, affect the
generation of quarry dust as well as their end properties.
2.4 Impact of masonry sandEnvironmental protection and social responsibility is of vital importance to the quarrying
sector to reduce any adverse consequences (for example, in health and safety) and costs
associated with the production of masonry sand (for example, storage, dealing with arising
transport, and handling). The generation of masonry sand may cause adverse impacts on the
environment (such as the local air, land, water, flora and fauna) and human healthand the
mitigation of potential impacts is mandatory. Commonly, various dust control practices
(conventional or alternative) are employed to minimize the impact of masonry sand
generated by quarry activities (Petavratzi 2005).
Health issues and the protection of fauna and flora are addressed through the management
and protection of air quality. The utilization of masonry sand is seen as a way to minimize the
accumulation of unwanted material and at the same time to maximize resource use and
efficiency.
2.5 Applications of masonry sand The end use of masonry sand may require some degree of processing to be undertaken in
order to comply with technical specifications. End applications may be of high or low
value, or may require a small or a large volume of masonry sand.
These uses include:
Manufactured sand (sand replacement in concrete) Soil mineralization, compost, artificial soils and remediation. Site restoration and landscaping. Road pavements Embankment construction. Landfill capping.
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2.6 Obstacles to applicationsMasonry sand can be suitable a material for a variety of end applications, however, currently
their utilization is not widespread to the level it would have been expected mainly due to
reasons related to quantities available and awareness as to its importance.
A major obstacle to utilization is the limited knowledge of exact quantities of masonry sand.
It is recommended that figures on quantities of dust produced, marketed and stockpiled
should be calculated in order to properly evaluate the quantities of masonry sand currently
available, and information that present the geographical distribution of masonry sand
should be compiled to enable the identification of potential end markets. Furthermore, the
limited awareness of potential markets by aggregate producers, the limited knowledge
about masonry sands, their characteristics and the absence of fully developed fit for-use
specifications for a wide range of end products have limited its use.
2.7 ConcreteConcrete is a construction material composed of cement (commonly Portland cement) as
well as other cementitious materials such as fly ash and slag cement, coarse aggregate
(such as gravel, limestone, or granite, and a fine aggregate such as sand), water, and
chemical admixtures. Concrete solidifies and hardens after mixing with water and
placement due to a chemical process known as hydration. The water reacts with the cement,
which bonds the other components together, eventually hardening to a strong material.
Concrete is used to make pavements, architectural structures, foundations, and
motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for
gates, fences and poles. Concrete is used more than any other man-made material in the
world.( http://en.wikipedia.org/wiki/Concrete)
2.7.1 Cement
Cement is the most important ingredient in concrete. One of the important criteria for the
selection of cement is its ability to produce improved microstructure in concrete. The cement
commonly used in Kenya is categorized as Portland Pozollana 32.5N or ordinary
Portland 42.5N also referred to as power plus (Manguriu et al., 2013).The cement used
in this experiment was Portland Pozollana Cement 32.5N. Cement properties critical in
production of concrete are specified in BS 4550 of which some are its fineness and setting
time of not less than 45 min and not more than 10 hours.
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2.7.2 Water
Combining water with a cementitious material forms a cement paste by the process of
hydration. The cement paste glues the aggregate together, fills voids within it, and allows it to
flow more easily (workability). Less water in the cement paste will yield a stronger, more
durable concrete; more water will give an easier-flowing concrete with a higher slump.
Impure water used to make concrete can cause problems when setting or in causing
premature failure of the structure. Water fit for drinking is acceptable for mixing concrete
(BS 1480:1980). Hydration involves many different reactions, often occurring at the same
time. As the reactions proceed, the products of the cement hydration process gradually bond
together the individual sand and gravel particles, and other components of the concrete, to
form a solid mass.
2.7.3 Aggregates
Aggregates are important constituents in concrete. They give the body to the concrete, reduce
shrinkage and effect economy. Aggregates occupy 70 to 80% of the volume of the concrete.
The aggregates combine with the cement and water to produce concrete. Basically there are
two types of aggregates, the fine aggregate and the coarse aggregate. The sand obtained from
river beds or quarry is used as fine aggregate. The fine aggregate along with the hydrated
cement paste fill the space between the coarse aggregate. The important properties of
aggregate are
1) Shape and texture
2) Size gradation
3) Moisture content
4) Specific gravity
5) Unit weight
6) Durability and absence of deleterious materials.
The masonry sand, river sand and ballast used in this experiment were sourced from Ruai
area in Nairobi county. The BS 812: Part 102 describes the tests carried out to determine the
physical characteristics of the aggregates. The grading of aggregates defines the proportion of
particles of different size in the aggregates.
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Sieve analysis was used to determine the particle size distribution of aggregates according to
BS 882:Part 103.
2.7.4 Chemical admixtures
Chemical admixtures are materials in the form of powder or fluids that are added to the
concrete to give it certain characteristics not obtainable with plain concrete mixes. In
normal use, admixture dosages are less than 5% by mass of cement, and are added to the
concrete at the time of batching/mixing. The most common types of admixture are:
• Accelerators speed up the hydration (hardening) of the concrete.
• Retarders slow the hydration of concrete, and are used in large or difficult pours where
partial setting before the pour is complete is undesirable.
• Air entrainments add and distribute tiny air bubbles in the concrete, which will reduce
damage during freeze-thaw cycles thereby increasing the concrete's durability. However,
entrained air is a trade-off with strength, as each1% of air may result in 5% decrease in
compressive strength.
• Plasticizers (water-reducing admixtures) increase the workability of plastic or "fresh"
concrete, allowing it to be placed more easily, with less consolidating effort.
Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers which
have fewer deleterious effects when used to significantly increase workability.
Alternatively, plasticizers can be used to reduce the water content of a concrete (and have
been called water reducers due to this application)while maintaining workability. This
improves its strength and durability characteristics.
• Pigments can be used to change the color of concrete, for aesthetics.
• Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
• Bonding agents are used to create a bond between old and new concrete.
• Pumping aids improve pumpability, thicken the paste, and reduce dewatering – the
tendency for the water to separate out of the paste.
http://en.wikipedia.org/wiki/Concrete
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2.8 Fresh concreteFresh concrete is that stage of concrete in which concrete can be moulded and it is in plastic
state. This is also called "Green Concrete". Another term used to describe the state of fresh
concrete is consistence, which is the ease with which concrete will flow.
2.8.1 Workability
Workability is often referred to as the ease with which a concrete can be transported, placed
and consolidated without excessive bleeding or segregation. Consistence in concrete means
the degree of wetness; within limits, wet concretes are more workable than dry concrete, but
concrete of same consistence may vary in workability. Due to the fact the strength of concrete
is adversely and significantly affected by the presence of voids in the compacted mass, it is
vital to achieve a maximum possible density. This requires sufficient workability for virtually
full compaction to be possible using a reasonable amount of work under the given conditions.
Presence of voids in concrete reduces the density and greatly reduces the strength.
The cement used in this study was portland pozollana 32.5 N which has a high content of fine
materials such as fly ash, calcined clay and volcanic ash .This causes it to take up alot of
water to wet due to the high surface area thus causing the concrete mix to have a low
workability.
Workability is measured by slump test, compacting factor test and vebe time test (BS 1881:
Parts 102,103 and 104).Workability in concrete is affected by water cement ratio and
aggregates size distribution.
Water content or Water Cement Ratio
The more the water cement ratio the more the workability of concrete. Since by simply
adding water the inter particle lubrication is increased. High water content results in a higher
fluidity and greater workability. Increased water content also results in bleeding. Another
effect of increased water content can also be that cement slurry will escape through joints of
formwork.
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Amount and type of Aggregate
Using smooth and round aggregate increases the workability. Workability reduces if angular and rough aggregate is used. For a greater size of aggregate- less water is required to lubricate it, the extra water is available for workability
Angular aggregates increases flakiness or elongation thus reducing workability. Round smooth aggregates require less water and less lubrication and have greater workability in a given water-cement ratio.
Porous aggregates require more water compared to non-absorbent aggregates for achieving
same degree of workability.
2.8.2 Concrete Bleeding
Bleeding in concrete is sometimes referred as water gain. It is a particular form of
segregation, in which some of the water from the concrete comes out to the surface of the
concrete, being of the lowest specific gravity among all the ingredients of concrete. Bleeding
is predominantly observed in a highly wet mix, badly proportioned and insufficiently mixed
concrete. In thin members like roof slab or road slab and when concrete is placed in sunny
weather shows excessive bleeding.
Due to bleeding, water comes up and accumulates at the surface. Sometimes, along with this
water, certain quantity of cement also comes to the surface. When the surface is worked up
with the trowel, the aggregate goes down and the cement and water come up to the top
surface. This formation of cement paste at the surface is known as laitance. In such a case, the
top surface of slab and pavements will not have a good wearing quality.
Water while traversing from bottom to top, makes continuous channels. If the water cement
ratio used is more than 0.7, the bleeding channels will remain continuous and un-segmented.
These continuous bleeding channels are often responsible for causing permeability of the
concrete structures. While the mixing water is in the process of coming up, it may be
intercepted by aggregates. The bleeding water is likely to accumulate below the
aggregate. This accumulation of water creates water voids and reduces the bond between the
aggregates and the paste.
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The poor bond between the aggregate and the paste or the reinforcement and the paste due
to bleeding can be remedied by re-vibration of concrete. The formation of laitance and the
consequent bad effect can be reduced by delayed finishing operations.
Bleeding rate increases with time up to about one hour or so and thereafter the rate decreases
but continues more or less till the final setting time of cement.
The bleeding is not completely harmful if the rate of evaporation of water from the surface is
equal to the rate of bleeding. Removal of water, after it had played its role in providing
workability, from the body of concrete by way of bleeding will do good to the concrete.
Early bleeding when the concrete mass is fully plastic, may not cause much harm, because
concrete being in a fully plastic condition at that stage, will get subsided and compacted. It is
the delayed bleeding, when the concrete has lost its plasticity, which causes undue harm to
the concrete. Controlled re vibration may be adopted to overcome the bad effect of bleeding.
2.8.3 Segregation in concrete
Segregation can be defined as the separation of the constituent materials of concrete. A good
concrete is one in which all the ingredients are properly distributed to make a homogeneous
mixture. There are considerable differences in the sizes and specific gravities of the
constituent ingredients of concrete. Therefore, it is natural that the materials show a tendency
to fall apart.
A well made concrete, taking into consideration various parameters such as grading, size,
shape and surface texture of aggregate with optimum quantity of water makes a cohesive
mix. Such concrete will not exhibit any tendency for segregation. The cohesive and fatty
characteristics of the matrix do not allow the aggregate to fall apart, at the same time; the
matrix itself is sufficiently contained by the aggregate. Similarly, water also does not find it
easy to move out freely from the rest of the ingredients.
The conditions leading to segregation are:
Badly proportioned mix where sufficient matrix is not there to bind and contain the aggregates.
Insufficiently mixed concrete with excess water content.
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Dropping of concrete from heights as in the case of placing concrete in column concreting.
When concrete is discharged from a badly designed mixer, or from a mixer with worn out blades.
Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by dumper, long lift by skip and hoist are the other situations promoting segregation of concrete.
Vibration of concrete is one of the important methods of compaction. It should be
remembered that only comparatively dry mix should be vibrated. If too wet a mix is
excessively vibrated; it is likely that the concrete gets segregated. It should also be
remembered that vibration is continued just for required time for optimum results. If the
vibration is continued for a long time, particularly, in too wet a mix, it is likely to result in
segregation of concrete due to settlement of coarse aggregate in the matrix.
2.9 Hardened concrete
This is a state in which the concrete attains after setting. It becomes hard like a rock with the
most important property being compressive strength.
2.9.1 Properties of hardened concrete
The most important properties of hardened concrete are compressive strength, tensile
strength, flexural strength, creep and shrinkage. In this experiment the compressive and
tensile strength were studied.
2.9.2 Compressive strength
The compressive strength of concrete is the most common measure for judging not only the
ability of the concrete to withstand load, but also the quality of the hardened concrete. Test
results obtained from compressive strength tests have proved to be sensitive to changing mix
materials and mix proportions as well as to differences in curing and compaction of test
specimens.
Compressive strength is defined as: ƒc, N/mm2 or MPa = P/ A where: P = load to failure in
Newtons and A = cross-sectional area, mm2
Concrete cubes of 150mmx150mmx150mm dimension are normally used to determine
compressive strength (BS1881: Part 116).Compressive strength is used to evaluate concrete
22
strength development over a period of time. Compressive strength is normally determined at
age of 7 and 28 days and compared with set standards to give assurance on capability of
concrete to carry subjected loads in its life span of use
The most significant factor influencing compressive strength is the amount of cement in the
mix, relating to water-cement ratio (W/C). The lower the W/C, the higher the strength.
2.9.3 Tensile strength
Indirect tensile strength is normally determined by cylinder splitting test (BS 1881: Part 117)
and entails diametrically loading cylinder in compression along its entire length. It is
evaluated as;
ft=2 Fπld where l and d are the cylinder length and diameter. F represents the crushing force,
This varies from 5 to 13 percent of cube compressive strength. Indirect tensile strength of a
concrete is affect by water-cement ratio and aggregates bond development (Munday and Dhir
1984).
23
CHAPTER 3 METHODOLOGY
3.0 EXPERIMENTAL WORKThe methodology involved collection of the materials necessary which were provided by the
University of Nairobi concrete laboratory. The aggregates were sourced from Ruai area in
Nairobi county. The cement used was portland pozollana Savannah cement 32.5N. The mix
design carried out by University of Nairobi concrete laboratory provided a nominal mix
proportion of 1;1;2:0.45 for concrete grade 30. Trial mixes were cast and tested. Particle size
distribution grading and sieve analysis were carried out on the aggregates with the slump test
carried out on the fresh concrete. On the hardened concrete the compressive strength test and
split tensile strength test were carried out.
3.1 Particle size distribution This was done in accordance with the process stipulated in BS 812 part 1 1975. The masonry
sand and river sand were dried in the oven. Sieves were arranged in order of decreasing
aperture sizes between 5 mm to 0.15 mm. The aggregates were passed through the sieves by
shaking them manually while ensuring that no material was lost. The retained material was
weighed and recorded. The passing material was returned to the column and sieved with the
remaining sieves in order of decreasing aperture sizes.Mass retained on each sieve was
calculated as a percentage of the original dry mass.The cumulative percentage of the original
dry mass passing each sieve down to the smallest aperture sieve was also calculated. The
grading curve: percentage (%) passing was plotted against the particle diameter on a standard
semi log graph together with the upper and lower limits of the adopted fine aggregate
grading curve envelope.
The objective was to determine the particle size distribution of specified aggregates and to
draw grading curves for the aggregates specified.
3.2 Fresh concrete slumpAfter the concrete was prepared in accordance with the BS procedures given in laboratory
guidelines, the slump test was measured. This test was carried out using the standard
procedure as outlined in BS 812.
24
Apparatus used
Truncated conical mould 100 mm diameters at the top, 200mm diameter at the bottom and 300mmm high.
Steel tamping rod 16mm diameter and 600mm long with ends hemispherical.
Figure 4 Slump test apparatus
The inside of the mould was cleaned and oiled before the test and the mould made to stand on
a smooth hard surface. The mould was held down using the feet rested on the foot rests, and
the mould filled in three layers of approximately equal sizes. Each layer was then tamped
with 25 strokes using the tamping rod and the strokes being uniformly distributed over the
cross-section of the layer. The surface was smoothened using the trowel, and the surface of
the cone and base plate wiped clean. The cone was then lifted vertically upright and the
slump measured for each sample design. The slump was measured as the difference between
the height of the mould and that of the highest point of the specimen.
25
Figure 5 Preparation of slump test
Figure 6 Measuring of slump
3.3 Hardened concrete
3.3.1 Determination of compressive strength – cube test to (BS: 1881: PART 16; 1983)
The specimens were cast in steel moulds of 150 by 150 by 150 mm cubes which conforms to
the specifications of BS 1881. The moulds surfaces were first cleaned and oiled on their
inside surfaces in order to prevent development of bond between the mould and the concrete.
The moulds were then assembled and bolts and nuts tightened to prevent leakage of cement
paste. The moulds were filled with concrete in three layers, each layer being compacted using
26
the table vibrator at the University of Nairobi concrete laboratory to remove as much
entrapped air as possible and to produce full compaction of concrete without segregation. The
moulds were filled and overflowing concrete removed by a trowel. Surface finishing was also
done by the trowel. The test specimens were then left in the moulds undisturbed for 24 hours
and protected against shock, vibration and dehydration at room temperature.
Figure 7 Casting of cubes
The cubes and cylinders were then cured in a curing tank for 7 and 28 days.
Figure 8 Curing of cubes
After the cubes and cylinders were cured, they were dried and tested. In the manual compression machine the load was applied on the smooth surface and increased continuously until the failure of the specimen. The maximum load withstood by the specimens was noted, mean compressive strength was determined. For each percentage replacement 3 cubes were cast and tested after 7 and 28 days.
27
Figure 9 Loading of cubes
Figure 10 Manual compression machine
28
Figure 11 Crushing of cubes
The compressive strength is determined by the following formula
fc=F/Acfc =is the compressive strength in N/mm2
F = is the maximum load at failure in NewtonA =is the cross sectional area of the specimen
3.3.2 Determination of tensile strength using the splitting tensile strength method
This is an indirect test to determine the tensile strength of cylindrical specimens. Splitting tensile strength tests were carried out on cylinder specimens of size 150 mm diameter and 300 mm length at the age of 28 days curing, using compression testing machine according to BS 1881-118 at University of Nairobi concrete laboratory. To avoid the direct load on the specimen the cylindrical specimens were kept below the wooden strips. The load was applied gradually till the specimens split and readings were noted.
Figure 12 Loading of a cylinder
29
Figure 13 Splitting of a cylinder
The splitting tensile strength was calculated using the following formula:
ft=2 Fπld
Where
ft= splitting tensile strength of the specimen in MPa
F = maximum load in N applied to the specimen
d = measured diameter of the specimen in mm, and
l= measured length of the specimen in mm
30
CHAPTER 4
4.0 RESULTS AND ANALYSIS
4.1Laboratory test results
4.2 Sieve analysis BS 882: 1992The sieve analysis was important in order to determine whether the grading of the aggregates
lay within the limits as provided by BS 882:1992. If they failed there would have been a need
to blend them with other sizes in order for them to meet the criterion. A graph is drawn of the
cumulative percentage passing against the sieves aperture sizes and compared with the limits
Fine aggregates; Sand
Table 1 Sand grading
Pan mass (g) 134Initial dry sample mass + pan (g) 536Initial dry sample mass (g) 402Washed dry sample mass + pan (g) 530Washed dry sample mass (g) 396
Table 2 Sand grading
Sieve size (mm) Retained mass (gm) % Retained (%) Cumulative passed
percentage (%)14 0 0.0 100.010 0 0.0 100.04.76 7 1.7 98.32.36 18 4.5 93.81.18 53 13.2 80.60.6 117 29.1 51.50.3 131 32.6 18.90.15 55 13.7 3.90.075 15 3.7 0.2<0.075 3.7 0 0 396
31
Table 3minimum and maximum limits according to BS 882:1992
Acceptance CriteriaMin(%) Max (%) 100 10089 10060 10030 10015 1005 700 15
Blue represents the minimum limit while green represents the maximum limit
0.01 0.1 1 10 1000
102030405060708090
100
Sieves (mm)
Pass
ing
(%)
Figure 14 Grading for river sand
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Fine aggregates :Masonry sand
Table 4 Masonry sand grading
Pan mass (gm) 122Initial dry sample mass + pan (gm) 570Initial dry sample mass (gm) 448Washed dry sample mass + pan (gm) 515Washed dry sample mass (gm) 393
Table 5 Masonry sand grading
Sieve size (mm) Retained mass (gm) % Retained (%) Cumulative passed
percentage (%)14 0 0.0 100.010 0 0.0 100.04.76 23.6 6.0 94.02.36 125.8 31.9 62.11.18 104.2 26.4 35.70.6 65.2 16.5 19.20.3 40.4 10.2 9.00.15 23.48 6.0 3.90.075 12.2 3.1 0.8<0.075 3.1 0 0 395
0.01 0.1 1 10 1000
102030405060708090
100
Sieves (mm)
Pass
ing
(%)
Figure 15 Grading for masonry sand
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4.3 Concrete analysis
4.3.1 Fresh concrete analysis workability
Slump results
Table 6 Showing slump values
Percentage replacement of sand with masonry sand in concrete Class 30 with nominal mix ratio of 1:1:2:0.42
% replacement of sand Workability
0 36mm
25 24mm
50 17mm
75 11mm
100 6mm
0% 25% 50% 75% 100%0
5
10
15
20
25
30
35
40
Figure 16Bar chart representing varying slump values for different masonry sand percentages
This shows that workability decreases as more masonry sand is used.
34
4.3.2 Compressive strength
After using the manual compression machine at University of Nairobi concrete laboratory to
crush the cubes the following forces were obtained
Table 7 Showing cube crushing forces at 7 days
% replacement of sand with masonry sand
Cube failure load at 7 days in KN
Cube 1 cube 2 cube 3
0% control 460 460 480
25% 465 470 470
50% 490 490 490
75% 480 460 475
100% 460 455 465
Stresses resisted by the cubes were thus calculated from the formula
fc = F / AC
Where
fc is the compressive strength in Newtons per square mm
F is the maximum load at failure in Newton’s
AC is the cross sectional area of the specimen on which the compressive force acts (150
x150) mm2
35
Table 8 Showing compressive strength values at 7 days
% replacement of sand with masonry sand
Stress calculated at failure for 7 day cubes in kN/mm2 Average stress kN/mm 2 Cube 1 cube 2 cube 3
0% control 20.44 20.44 21.33 20.74
25% 20.66 20.88 20.88 20.8
50% 21.77 21.77 21.77 21.77
75% 21.33 20.44 21.11 20.96
100% 20.44 20.22 20.67 20.44
0% 25% 50% 75% 100%19.5
20
20.5
21
21.5
22
compressive strength at 7 days
Figure 17 Bar chart showing variation of compressive strength at 7 days for different replacements.
36
After 28 days the remaining cubes were crushed and values recorded
Table 9 Showing cube crushing forces at 28 days
% replacement of sand with masonry sand
Cube failure load at 28 days kN
Cube 1 cube 2 cube 3
0% control 620 610 625
25% 680 670 660
50% 810 790 785
75% 760 760 755
100% 730 720 730
Using the same formula as above the compressive strengths at 28 days were calculated and recorded as shown below.
Table 10 Showing compressive strength values at 28 days
% replacement of sand with masonry sand
Stress calculated at failure for 7 day cubes in kN/mm2
Average stress kN/mm 2
Cube 1 cube 2 cube 3
0% control 27.55 27.11 27.77 27.47
25% 30.22 29.77 29.33 29.77
50% 36 35.11 34.88 35.33
75% 33.77 33.77 33.55 33.69
100% 32.44 32 32.44 32.29
37
0% 25% 50% 75% 100%0
5
10
15
20
25
30
35
40
compressive strength at 28 days
Figure 18bar chart showing variation in compressive strengths at 28 days for different replacements of masonry sand
0% 25% 50% 75% 100%0
5
10
15
20
25
30
35
40
compressive strength at 7 dayscompressive strength at 28 days
Figure 19combined line graph showing compressive strength at 7 and 28 days
38
4.3.3 Tensile strength
The cylinders were crushed at 28 days with the splitting tensile method. Forces obtained were recorded as shown below.
Table 11showing cylinder splitting values at 28 days
% replacement of sand with masonry sand
Cylinder splitting value at 28 days in kN
Cylinder 1 Cylinder 2 Cylinder 3
0% control 160 155 160
25% 200 190 205
50% 260 240 235
75% 200 210 220
100% 210 210 220
The tensile strength was then calculated from the following formula
ft=2 Fπld
Where
ft = splitting tensile strength of the specimen in MPa
F = maximum load in N applied to the specimen
d = measured diameter of the specimen in mm
l= measured length of cylinder
The following values were obtained
39
Table 12 Showing tensile strength values at 28 days
% replacement of sand with masonry sand
Stress calculated at failure for 7 day cubes in Kn/mm2
Average values kN/mm 2
Cylinder 1 Cylinder 2 Cylinder 3
0% control 2.26 2.18 2.26 2.23
25% 2.82 2.62 2.9 2.78
50% 3.68 3.39 3.32 3.46
75% 2.82 2.96 3.1 2.96
100% 2.96 2.96 3.1 3.00
0% 25% 50% 75% 100%0
0.5
1
1.5
2
2.5
3
3.5
4
tensile strength values at 28 days
Figure 20 Bar chart showing tensile strength variations with different proportions of masonry sand
40
4.4 Cost Benefit AnalysisIn this study the project considered was the rehabilitation of the Yatta canal in Kituicounty
near Matuu. Information obtained from Engel Engineering services a crushing plant just 10
kilometers from Matuu town was that a tonne of washed masonry sand would cost Ksh 600.
On further investigation a supplier to Toddy Civil Engineering Company delivered 20 tonnes
of natural river sand at a cost of Ksh20000 per delivery. Toddy Civil Engineering Company
Limited is the construction company doing the rehabilitation of Lot II of the Yatta canal. This
shows that a tonne was going for ksh 1000 inclusive of the transport costs.
Therefore 20 tonnes of masonry sand would cost 12000 plus a transport cost of around ksh
4000 which is still less than Ksh 20000 for the delivered river sand. This shows that masonry
sand if used would be cheaper than the natural river sand which is located far from the
construction sites. The river sand brought by the supplier is sourced from the Athiriver which
is about thirty kilometers from Matuu town.
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CHAPTER 5
5.0 DISCUSSION
5.1 GradingThe grading of the masonry sand fell within the limits provided by BS 882:1992.Grading is
of importance as it affects the workability of concrete. The development of strength
corresponding to a given water/cement ratio requires full compaction and this can only be
achieved with a sufficiently workable mix. It is necessary to produce a mix that can be
compacted to a maximum density with a reasonable amount of work.
A smooth gradation curve decreases the voids between the aggregate particles in a
homogeneous concrete mix, and, because the voids must be filled with a mixture of cement
and water, it therefore decreases the amount of cement required. (The paste portion of the
concrete can also be increased by adding water, but this increases the water-cement ratio and
decreases strength.) Cement is usually the most expensive component in concrete, so
minimizing the amount needed makes the mix more economical.
In order to see the effects of gradation on concrete cost, pack a beaker with 1-inch-diameter
rock and measure the amount of water needed to fill up the beaker. This water represents the
volume of the voids in the beaker. Then, take the same beaker, packing it with a
homogeneous mixture of 1-inch-diameter and ⅜-inch-diameter rock and again measure the
quantity of water needed to fill the beaker.
Less water will be needed to fill the beaker with the two sizes of stone. Every time another
size is added to the mix, the void content in the beaker will decrease. This is what happens in
a cubic yard of concrete, as well, except that the voids are filled with cement and water.
Another factor that can affect the economy of a concrete is the fineness of the aggregate.
Because all surfaces of all particles in the mix must be covered with cement paste, the more
surface area present in the concrete, the more cement and water needed to do the job.( Ref 9)
42
5.2 WorkabilityThe variation of workability of fresh concrete for various proportion mixesof masonry sand
with river sand was measured in terms of slump. Degree of workability for river sand and
masonry sand were low as shown in table 4.6 with the highest being 36 mm which consisted
of natural river sand only. Concrete with 100% masonry sand had a very low slump of 6mm.
This is as a result of the finer particles present in masonry sand. The smaller the size of the
aggregate, the high is the surface area and hence more amount of water is required for
wetting the surface. Hence, the very low workability as compared to that of concrete made
with natural river sand only. The class of concrete was class 30 which is a high strength
concrete. The cement used was portland pozollana 32.5N which also has a lot of fine
materials such as fly ash which also contributes to the low workability since more water is
required to wet it. Ordinary portland cement would have been more suitable for concrete
class 30. The workability results are plotted in the form of graph and are shown figure 4.3.
Manufacturers of masonry sand should produce masonry sand with better grading in order to
improve workability
5.3 Compressive strengthCompression test is the most common test conducted on hardened concrete because it is an
easy test to perform, and also because most of the desirable characteristic properties of
concrete are qualitatively related to its compressive strength. The compressive strength of
conventional concrete at the 7th day was found to be 20.74N/mm2 which is less as compared
to 50% masonry sand replacement which was found to be 21.77 N/mm2.This is a 5% increase
in strength . At 28 days compressive strength greatly increased as shown in figure
4.6.Conventional concrete had a value of 27.47 N/mm2compressive strength while at 50%
replacement it had a value of 35.33N/mm2 which is a 28% increase in strength. Generally
concrete made with a mixture of masonry sand and sand produced concrete with a higher
strength than conventional concrete. The optimum ratio for highest strength was found to be
at 50% masonry sand and 50% river sand.
5.4 Tensile strengthThe test results of split tensile strength at 28 days are shown in table 4.11.Conventional
concrete had a value of 2.23 N/mm2 as compared with that of 50% sand replacement which
had a value of 3.46 Nmm2 . This is a 55% increase in tensile strength. Figure 4.5 shows the
variation of tensile strength values for the different mix proportions.
43
CHAPTER 6
6.1 CONCLUSIONThe study revealed that masonry sand can be used as a partial or complete replacement of
natural river sand in the manufacture of concrete. Highest concrete strength can be achieved
at 50% replacement of sand. The highest strength in this experiment was achieved at 50%
replacement with a compressive strength of 35.33N/mm2 and a tensile strength of
3.46N/mm2. Generally the masonry sand improved the properties of the concrete.
The increase of the physical and mechanical properties can be attributed to the high content
of fine materials in the masonry sand. The high fine material content makes the concrete
more cohesive (Aitcin, 1990). The weight of the specimens created was found to increase
from 7.9kg of a cube made with conventional concrete to 8.2kg of masonry sand concrete a
3.8% increase in mass. Increase in mass leads to increase in density and therefore increase in
compressive strength.
It was noted that the workability reduced as more masonry sand was added as reflected by the
decreasing slump values from 36mm to 6mm with a water cement ratio of 0.42. This can also
be attributed to the high fine material content. They have a high surface area which require
more water to wet.
Masonry sand is considered as a waste material and therefore it is available at a lower price
when washed than the river sand. Its use will therefore lead to lower cost of construction
which is greatly needed in a developing country like Kenya. To achieve vision 2030 such
materials should be utilized. In consideration to the environment the use of the masonry sand
will reduce the waste overload by its use (Manasseh et al 2010). Environmental degradation
will be reduced by its use since negative effects of sand mining will be reduced.
Alkali aggregate reaction affects concrete leading to stiffness, loss of strength and
impermeability. This reaction reduces the durability and destroys the appearance of concrete
structures. One of the measures against it is to reduce the access of moisture to the concrete in
order to maintain the concrete in a sufficiently dry state. Masonry sand requires more water to
wet and would therefore be sufficiently better than sand in combating the effects of alkali
aggregate reaction.
44
6.2 RecommendationsFrom this study it is recommended to use of masonry sand in the manufacture of concrete
especially for high strength concrete. It has been found that it increases the properties of the
concrete. I recommend the replacement of 50% river sand in concrete for optimum strength
of the concrete.
The main problem experienced was the decrease in workability as more masonry sand was
added. It is recommended that a proper mix design be carried out to achieve a more workable
concrete mix without affecting the properties of the concrete made. The use of super
plasticizers and plasticizers should be studied to investigate their influence on workability
and strength of concrete made with masonry sand.
In this study beams were not tested since most of the tension is carried by the reinforcing bars
in reinforced concrete. Further studies on the influence of masonry sand in reinforced
concrete.
This study also recommends additional studies on the chemical properties of the masonry
sand. The alkali aggregate reaction should be put into focus.
In conclusion further studies on the cost to benefit ratios should be done on the suitability of
using the masonry sand.
REFERENCES1. Aitcin, D. C. & Mehta, P. K., (1990). Effect of Coarse Aggregate
Characteristics on Mechanical Properties of High Performance Concrete, ACI,
45
materials Journal, 87(2), 103-107.
2. B.S 1881: part 116: 1983, Method for Determination of Compressive Strength of
Concrete Cubes, Testing Concrete; British Standards Institution, London.
3. BS 1881: Part 108:1983, Methods for Making Test Cubes from Fresh
Concrete, London; British Standard Institution.
4. Manasseh, J.O.E.L. (2010): Use of Crushed Granite Fine as Replacement to
River Sand in Concrete Production, Leonardo Electronic Journal of Practices and
Technologies, Iss.17, pp.85-96.
5. Celik, T. and Marar, K., (1996). Effects of Crushed Stone Dust on some
Properties of Concrete, Cement and Concrete Research 26(7), 1121-1130.
6. Jain, M. E. M, Safiuddin, M. and Yousuf, K.M., (1999). A Study on the Properties of
Freshly Mixed High Performance Concrete, Cement and Concrete Research, 29(9),
1427-1432.
7. A.M.Neville, Properties of Concrete: Fourth and Final Edition, Pearson Education
Limited, Essex, 2002
8. BS 812: Part 1:1975,Sampling, Shape, Size and Classification, Testing Aggregates;
British Standard Institution.
9. http://www.lafarge-na.com/wps/portal/na/en/3_A_11_12-
The_Effect_of_Aggregate_Gradation_and_Fineness_on_Concrete_Properties
REPORTSManguriu, G.N., Karugu, C.K., Oyawa, W.O., Abuodha, S.O. and Mulu, P.U. 2013 Partial
Replacement of Natural River Sand with Crushed Rock Sand in Concrete Products.
46