Production of different types of unfired clay bricks · flexural strength of bricks is get for the...

I

Production of different types of

unfired clay bricks

Student’s Name:

1- Hussain Ali Abd ul-sada

2- Mohammed Majid Yasser

Supervisor

Assist. Prof. Dr. Abbas Oda dawood

A project report submitted in partial fulfilment of the

Requirements for the award of the degree of

Bachelor of Civil Engineering

Civil Engineering Department

Engineering College

University of Maysan

Iraq

2018-2019

III

DECLARATION

I hereby declare that this project report is based on my original work except for citations and

quotations which have been duly acknowledged.

Signature : _________________________

1- Name : Hussain Ali Abd ul-sada

Date : _________________________

Signature : _________________________

2- Name : Mohammed Majid Yasser

Date : _________________________

IV

APPROVAL FOR SUBMISSION

I certify that this project report

“Production of different types of unfired clay bricks”

was prepared by Hussain Ali Abd ul-sada and Mohammed Majid Yasser has met

the required standard for submission in partial fulfilment of the requirements for the award

of Bachelor of Civil Engineering at University of Maysan.

Approved by,

Signature : _________________________

Supervisor : Assist. Prof. Dr. Abbas Oda dawood

Date : _________________________

V

Dedication

Dedicate this work, to my mother and father

To my family, to my teachers, to candles that burn to light up for others

To everyone who taught me characters I dedicate this humble project to the

Lord Almighty to find acceptance and success

And to all who stand by my side of my professors and colleagues

And in particular, Assist. Prof. Dr. Abbas Oda dawood

VI

ACKNOWLEDGEMENTS

I would like to thank everyone who had contributed to the successful

completion of this project. I would like to express my gratitude to my research

supervisor, Assist. Prof. Dr. Abbas Oda dawood for his

invaluable advice, guidance and his enormous patience throughout the

development of the research.

In addition, I would also like to express my gratitude to my loving parent

and friends who had helped and given me encouragement......

VII

ABSTRACT

The mud is considered one of the oldest construction material in Iraq and

still used in the country regions for farmers houses or animals shelters. In Iraq,

there are different types of mud constructions, included adobe, unfired bricks

and cob, the present study is focused on unfired clay brick masonry

construction. The main material of unfired clay brick used in the present study

is the clay, which obtained from south Amarah from depth of 2 m below natural

ground level to obtain pure and clean clay. The study mainly focused on

production different types of unfired clay bricks according to local procedure

used in the south of Iraq, by addition different materials to the clay to improve

its properties and especially large deformation due to shrinkage. The materials

added classified into three concept, the first additives included natural fibers to

improve tensile strength of brick and reduce the cracking due to shrinkage, the

natural fibers included straw, sawdust and rice husk. The second additives

included added the fine and coarse sand as stabilizer to reduce the volumetric

changes. The third additives is adding cement to increase adhesive and cohesion

of the mud matrix. The measurements included compressive strength of both

brick, mortar and masonry and also the flexural strength of bricks alone. Also

the behaviour of unfired masonry prisms are compared to the traditional fired

clay brick prisms. The results indicated that the higher compressive strength of

bricks is get for the mix that included clay, coarse sand straw and the maximum

flexural strength of bricks is get for the mix that include clay and sawdust, while

for unfired masonry prism the higher compressive strength is obtained with mix

that included clay, coarse sand straw. Finally a proposed formula to obtain the

compressive strength of unfired brick masonry from the compressive strength of

brick and mortar is presented.

VIII

TABLE OF CONTENTS

CHAPTER Page

1 1-1 INTRODUCTION 1

1 -2 -Brick-Making History 4

1-3-Traditional Unfired Clay Bricks 6

1-4- Strength of unfired clay brickwork 9

1-5- Mortars for unfired clay brickwork 9

1-6-Advantages of Unfired Clay-Brick 11

1-7-Disadvantages 11

1-8- Objectives of Project 12

1-9- Project Layout 12

2 2-1 Introduction 13

2-2 Literature Review 13

3 3-1-General 17

3-2-Materials 17

3-3-Method of Mixing 19

3-4- Raw materials proportions 26

3-5- Failed Mixes 30

4 4-1- General 31

4-2 Effect of Natural Fibres 31

4-2-1Comparison among Straw, Husk rice and Sawdust 37

4-3- Effect of Sand 38

4-3-1 Comparison among fine and coarse sands 41

4-4 Effect of Cement 43

4-4-1 Comparison among mixes incorporated cement 47

4-5-Masonry 48

4-5-1: Unfired bricks used for masonry prisms 49

4-5-2: Mud Mortar 50

4-5-3: Unfired Masonry 51

IX

CHAPTER Page

4 4-6-1 Traditional Fired Brick Masonry 57

5 5-1 Conclusions 60

5-2- Recommendations 61

List of Tables

Table (3-4-1): Mix proportions of clay only and different types of fibers 25

Table (3-4-2): Mix proportions of clay with sand 27

Table (3-4-3): Mix proportions of clay with cement 28

Table 4.2: Results of Effect of Natural Fibres 38

Table (4-3) : Result of effect of sand 43

Table (4-4 ): Result of effect of Cement 49

Table (4-5-1): Compressive Strength for Unfired bricks used for masonry prisms 50

Table (4-5-3): The compressive strength for Unfired Masonry 57

Chapter one Introduction

1

CHAPTER ONE

Introduction

1.1 Introduction

Maysan province is located in the eastern south of Iraq. The top soil of Maysan

province is mainly clay soil, and considered one of main sources of clay bricks in

Iraq, therefore a Brick Factories are widely spread through areas of the province.

The spread of these factories leads to pollutants spread in wide areas and

negatively affected the surround villages. According to output gases and smoke

produced by traditional bricks factories the environmental problems could not be

skipped. The Diseases like asthma, lung diseases and other respiratory system

diseases caused by these factories has spread in a scary shape. This fact forces us

to look for another way to product a clay bricks for construction.

Clay bricks are commonly used in construction sector in Iraq. Mud bricks had been

used in the construction of shelters for thousands of years, and approximately 30%

of the world’s present population still live in earthen structures [1].Clay brick had

been used as the earliest building materials since ancient time and still be used yet.

This is due to their simplicity, low cost, good thermal isolation, acoustic isolation

properties, simple manufacturability and long building's life. The clay material can

be easily reused or resumed to the ground without any negative impaction the

environment [2 - 4]


2

Fig. (1.1): pollution due to Bricks factories in Maysan Province

The conventional method of bricks production has brought undeniable

shortcomings. The consumption of earth-based materials as clay, shale and sand in

brick production resulted in resource depletion, environmental degradation, and

energy consumption. Virgin resources mined from riverbeds and hillsides to

service brick industry leaving mines areas un-reclaimed. Environmental

degradation accompanies such mining activities with air pollution and remains

after the mines cease operations, leaves scars on the landscape. The brick was

anciently produced by mixing the virgin resources, forming the bricks, drying them

and then firing them [5 - 7]


3

Most of the researches went through enhancing the clay brick quality and

properties by mixing the clay with various recycled wastes as foundry sand, granite

sawing waste, harbor sediments, perlite, fly ash, clay waste and fine waste of

boron, sewage sludge, waste glass from structural wall and other different wastes

[8]

What we really need is to find another way to product a clay brick which will be

friendlier with the Environment and which will lead to decrease the pollution, so in

our experiments we decided to focus on producing Unfired Clay Bricks (UCB).

Unfired clay materials provide a sustainable and healthy alternative as a

replacement to conventional masonry materials, such as fired clay and concrete

block, in both non-load bearing and low rise load-bearing applications .Unfired

clay materials offer potential health benefits to internal built environments,

primarily through passive regulation of relative humidity. Though traditional clay

masonry materials, such as adobe, clay lump and cob blocks, as well as more

recently developed compressed earth blocks have been used successfully in a

variety projects, more and more interest has been shown in using unfired clay

bricks produced by high volume industrial brick manufacturers. The tensile

strength of unfired clay materials is low and the bond between unfired clay units

and traditional clay mortars is poor, therefore walls have relied on their bulk mass

to ensure lateral load resistance and resilience [9]

Traditional forms of unfired clay bricks (cob blocks, adobe and mud bricks) are

generally made by hand and as a result, have variable dimensions and other

properties. Traditional earth masonry has thick walls (often over 300mm thick) as

the mortar provides low bond strength and the thick walls have sufficient mass to

keep themselves stable against lateral loads in dwellings Because of the

environmental and financial cost of using materials in construction, it is preferable


4

to reduce the wall thickness to approximately 100mm for internal partitions (the

standard thickness for fired clay bricks and concrete block work). Thinner walls

also reduce the structural weight loading and increase available space inside

buildings.

Modern unfired clay brickwork uses units manufactured to accurate tolerances

using a commercial extrusion or pressing system to provide a consistent, high

quality product. This enables rapid, cost effective, 100mm thick walls with low

environmental impact to be constructed. In most cases, modern unfired clay bricks

are produced in commercial fired brick manufacturing plants using similar

materials to fired bricks, but without putting the bricks through the firing process.

This significantly reduces the energy used in manufacture and previous research

has indicated unfired bricks have 14% of the embodied energy of fired bricks and

25% of the embodied energy of concrete blocks. In Germany, some fired brick

plants have moved to making only modern earth masonry and associated products.

[10]

1-2 -Brick-Making History

One of the oldest building materials were mud bricks, which molded by hand and

dried in the sun for days. Later, bricks were made of clay and fired in kilns to

create a strong. The raw materials that were required to make bricks were widely

available, and brick-making quickly became a trade. Bricks are commonly made of

a combination of clay and sand. The mineral content of the brick determines what

color the brick will be. For instance, red bricks contain more iron, while whiter

bricks have little iron content. Throughout history, bricks have been used in every

culture, from the Ancient Chinese to the Romans. People viewed brick as a

stronger material than wood, in term of good resistance to fire, rot, and pests. Brick

has been used to build most structures from homes to barriers to tombs. In modern


5

times, bricks have been used to create outdoor living spaces like patios and bars, as

well as for decorative uses, including flowerpots, mailboxes.

The Middle East has a rich history of brick-making structures. Bricks that date

back almost 10,000 years made from excess mud from flooded rivers have been

discovered throughout the Middle East, Fig(1-2). The oldest testament to the use of

brick was recorded in the Bible, which recounts the Israelite slaves building

pyramids for the Egyptians. Bricks were made by combining clay with straw,

which better allowed them to withstand the elements and the test of time. These

become known as adobe bricks, qualified by their composition of straw and clay,

and being dried only by the sun. While adobe construction is often linked to

Mexican peoples, adobe bricks can be found across the globe including in the

Middle East, West Asia, and Africa [10 - 12]

Figure (1-2) : Brick-Making History


6

1-3-Traditional Unfired Clay Bricks

Unfired Clay Bricks still used in some villages in Iraq and there are many

buildings are still extant for a long years. Fig(1-3). The traditional way industry

Unfired Clay Bricks is by mixing soil with straws and water. The ratios of

materials are determined manually using expertise without any kind of

calculations. After the materials have set, they started mixing the soil with the

straw until it mix together perfectly they added the water to the mix. Then, they

mixed the materials together using their feet. After that, they left the mix for 1 day.

In the next day, they started casting the bricks using wooden mold.

The mold is open from its both upper sides. They started molding the mix in the

mold and compressing it using their hands bonding together perfectly, then the

uplifted the mold and the mix still in its place taking the mold shape. The repeated

this process until they have the enough number of bricks. The bricks have a perfect

shape with sharp corners without any kind of irregular shapes Fig (1 – 4 ).

After end the molding, they left the bricks to drying in the sun for several days (it

takes approximately 3 days in the summer in Iraq), Fig(1 – 5 ).

In some places they use a rice husk instead of a straw but in same industry way.

After the bricks dried, they use it for building houses. The mortar they used also

made from a clay mixed with straw. The houses are faced inappropriate weathers

like rains and winds but they still extant and it will still extant for lot of years.


7

Figure(1 – 5 ) :drying in the sun Figure (1 – 4 ) :casting the bricks


8

Figure (1 – 3 ): some picture for houses in south of Iraq


9

1-4- Strength of unfired clay brickwork

The compressive strength of unfired clay brickwork is much more complicated

than for block work or fired clay bricks and no single strength value can be

assigned. The strength of unfired brickwork is dependent on the material

properties, the dimensions of the wall and the water content. The material property

that influences the masonry strength more than any other is the clay content in the

masonry.

As the water content in the masonry units is increased, the strength decreases and it

is therefore important to keep the masonry dry once constructed through

appropriate detailing, such as provision of a fired masonry or block work plinth to

prevent accidental wetting from spills. The water content will normally be highest

during construction (from application of wet mortar and render), and will then

stabilize to a lower level (stronger masonry) during use.

The strength of unfired brickwork is normally lower than fired clay bricks or

concrete block work, and 100mm thick unfired clay brick walls are currently not

recommended for high load structural applications. Increasing the wall thickness

will open the possibility for structural use of unfired brickwork.

1-5- Mortars for unfired clay brickwork

As the wall thickness decreases, the mortar must bond more to the masonry units to

provide sufficient structural strength against lateral loads (pushing horizontally

against the wall). The effect of wall thickness on required bond strength can be

determined by a structural engineer, but it can be calculated that a 300mm thick

wall with almost no bond strength (traditional earth masonry) can support the same

load as a 100mm thick wall with a bond strength of approximately 0.2N/mm2. The


10

bond strength of different mortars with modern earth masonry is shown in the

figure below. This figure includes clay/sand and lime mortars used for traditional

earth masonry and a cement/sand mortar used with fired bricks.

As shown, the mortars used for traditional earth masonry do not provide the bond

strength required to construct 100mm thin walls using modern earth masonry. The

use of a preformulated sodium silicate/clay/sand mix does, however, provide the

required strength and provides a bond strength similar to cement mortars with fired

bricks. The preformulated sodium silicate mortar has less than 10% of the

embodied CO2 than typical cement based mortars but does not perform as well at

high water contents. These high water contents can be avoided through appropriate

detailing. An alternative to a sodium silicate based mortars is to tie 100mm thick

modern earth masonry to a timber or other frame to provide the required lateral

load capacity. This will provide the environmental benefits of earth masonry

(thermal mass and humidity buffering) to a timber framed building.[10]


11

1-6-Advantages of Unfired Clay-Brick

1- Minimizing the environmental pollution caused by the gases emitted from

the brick production factories.

2- There is no need for fuel as that required in burning fried bricks, which

reduces the cost of production.

3- The availability of raw materials and low of the prices of the materials to be

added to the mix.

4- The community accepts this type of material as well as its historical

importance.

5- The possibility of using it to strengthen and restore historic sites such as

shrines and pyramids.

6- Low-cost and great thermal behavior.

1-7-Disadvantages

1- The tensile strength of unfired clay bricks is low and the bond between

unfired clay units and traditional clay mortars is poor, and therefore walls

have relied on their self’s weight to ensure lateral load resistance.

2- The compressive strength of unfired clay bricks is weak compared with fired

clay bricks that make it unsuitable for loaded walls.

3- It has a high absorption ratio compared with fired clay bricks so it would be

unsuitable to use in exposed places.


12

4- To produce unfired clay bricks we need use the Sun heat to make it dry so

we will be able to produce it in the summer only which the temperature will

be suitable, but even in summer it will need a lot of days to make it usable.

1-8- Objectives of Project :

Although mud brick is considered one of the oldest construction materials,

engineers and builders do not have enough information about its mechanical

properties. Also there is no accurate design code to follow before construction.

The research aims to produce building blocks that can be used as an alternative to

burnt mud bricks in which their manufacturing process accompanied toxic gases as

side effect, that have a significant impact on the health side.

Different materials are added to clay to produce the unfired clays. The comparison

among different types of produced unfired clays is restricted to compressive

strength of bricks as main structural characteristics in additional to volumetric

change.

1-9- Project Layout

The present project consisted of five chapters:

1- Chapter One: General Introduction and Historical abstract about Producing

Unfired Clay Bricks.

2- Chapter Two: Literature Review.

3- Chapter Three: Experimental Work.

4- Chapter Fourth: Result and Discussion

5- Chapter Five: Conclusions and recommendations

Chapter two Literature Review

13

CHAPTER TWO

Literature Review

2.1 Introduction

The present chapter presented the available studies related to unfired clay

bricks. In general there are limited researches available in the literature related

to production of unfired clay bricks.

2.2 Literature Review

Oti and kinuthia [14], 2009, used Lower Oxford Clay (LOC), two different

types of lime (L1 and L2), GGBS and Portland cement (PC) in production

unfired clay bricks. They found that the performance of using lime-activated

GGBS for both laboratory and industrial-scale unfired clay masonry brick

production is better than that of the PC-activated GGBS bricks.

Maheri, [15] et al , 2011, studied the improving of the durability of straw-

reinforced clay plaster cladding for earthen buildings. Four different tests were

conducted to investigate the effects of crusher dust and clay contents on the

strength and durability. The material used was clay soil, crusher dust, lime and

straw. When 5% lime is added to the mix, the compressive strength increases by

more than 5, which indicates the effectiveness of lime in increasing the strength

of the dried plaster. By comparing the results of samples of mix types it appears

that addition of 10% crusher dust, corresponding to a reduction of

approximately 5% in clay content, improves the compressive strength by 26%.

The increase in strength due to addition of crusher dust seems to be as a result


14

of improved consistency of the mix. However, as the crusher dust content

increases to 20% and higher, resulting in a reduction in clay content beyond

40%, a marked reduction in the strength of the plaster.

Miqueleiz et al [16], 2013, investigated the using of alumina filler wastes and

coal ash waste for unfired brick production. Mechanical test and durability

assessment were carried out on unfired brick test specimens made using marl

clay soil and alumina filler waste as a target material, and 70% mix of coal ash

waste were used as commercials additive (Portland cement and Lime)

replacement. They concluded that the compressive strength resistance of the

unfired bricks reduced as the clay replacement level increased .Also, the unfired

brick test specimens made with the blended mixtures containing coal ash waste

and lime tended to achieve higher strength values when compared with the coal

ash waste and Portland cement blends. The unfired brick test specimens were

able to withstand the repeated 48-hour freezing/thawing cycles.

Smeu et al.[17],2014, studied the unfired clay bricks as building materials made

from clay mixed with cement (C), lime (L), sand (S) and sawdust (SD). They

tried to stabilize the mixtures with clay using cement and lime as binder. The

cement (C) was 10% and 5%, lime (L) was 15% and 5%, sand (S) was 10% and

sawdust (SD) was 2.5% and 5%. Bending tensile strengths and the compressive

strengths are increasing from 7 days age to 28 days age. Also see that using lime

as a binder instead of cement; the compressive strengths will increase

significantly at 28 days age compared when using only cement.Used only lime

as a binder had a significantly and visible shrinkage of the dimensions of the

batches. Added sand, the compressive strength and also the bending tensile

strength are lower at 28 days age.


15

Al-Ajmi et al [18] , 2016, studied the using of earth construction as energy

efficient housing. They used mud bricks consist of clay, water, and binding

material such as rice husks or straw. They found that although mud brick is

considered one of the oldest construction materials, engineers and builders do

not have enough information about its mechanical properties, also there is no

accurate design code to follow before construction. Their study is devoted to

enhance the low compressive strength of mud brick without sacrificing its low

thermal conductivity properties. The experimental program in this research

includes the use of different admixtures to increase the compressive strength of

the basic mud mix. The experimental results show that the increase of cement

ratio, as ingredient to a certain limits, can lead to an optimum compressive

strength of the brick.

Saravanakumar et al. [19] 2018, investigated experimentally the replacement of

clay by metal powder and sawdust in unfired bricks. The specimens were made

using 10% cement,8% sand, 2% sawdust and different percentage of steel slag.

Mechanical test were carried out on unfired brick. there is potential in using

steel slag as a strengthening material for unfired brick production. the ideal ratio

for steel slag was 32% where it gave the highest compression strength. When

increasing or decreasing the ratio, the compression resistance decreases with it.

Water absorption percentages are in the range of high class bricks. The strength

resistance and water absorption values were within the acceptable limits for

masonry unit.

El-Mahllawy et al [20] 2018, evaluated the feasibility of stabilizing clay bricks

with marble cutting waste (MCW). This waste currently discarded in huge

quantities as a sludge resulted from sawing the marble blocks to slabs, grinding

and polishing of marble processes to the landfills located around the marble


16

processing factories located in the Shaq El-Thoban industrial zone, Cairo

governorate, Egypt causing negative impacts on the environment, health and

sustainable development. Experimental investigations were carried out to

explore the effect of addition of the MCW in different clay-base mixes at

different percentages up to 25% at the expense of the hydrated lime. Cement,

hydrated lime and MCW are the three types of solidification agents used, clay

and sand were also added in the formulations of the unfired clay brick

specimens. Laboratory cylindrical stabilized and compressed specimens were

made, and then they were cured in a humidity chamber for 2 and 4 weeks, then

after were air dried, tested and evaluated according to the Egyptian code for the

building by the stabilized and compressed earth soil (ECBS, 2016). To enhance

the durability of the cured specimens, transparent silicon – based paint was used

for this purpose. The laboratory results demonstrate high potential usage of

MCW based additives up to 15% incorporating HL. In addition, the used paint

could be an effective treatment way for the use of stabilized bricks in a wet

environment. The use of eco-friendly building materials will be a great

contribution for the environmental advantages and suggest a remarkable

economical alternative to the fired building units.

Chapter Three Experimental Work

17

CHAPTER three

Experimental Work

3-1-General

The experimental program was accomplished in the laboratories of the college

of Engineering, University of Maysan. The objective of this project was to

produce different types Unfired Clay Bricks (UCB) with regular size using

different materials like soil, straw, sawdust, rice husk, cement etc…

3-2-Materials

The materials used in this investigation were commercially available materials,

which include soil, straw, sawdust, rice husk, cement, sand.

1- Soil: In our experiments, we used south Amarah soil from depth of 2 m

below natural ground level, which is used by most local factories in the

production of bricks, the liquid limit of this soil was 37%, and plastic

limit was 21%.

2- Cement: Ordinary Portland cement was used throughout this

investigation. The full quantity required was brought to the laboratory

and stored in a dry place.

3- Coarse Sand: The retained sand on sieve No. 4 was added to the mix to

increase the compressive strength of the unfired bricks.


18

4- Fine Sand: Also fine sand that pass through sieve No. 4 and retained on

sieve No. 19 was used to increase the compressive strength and

homogeneity of the mixture as well.

5- Straw: Straw is main part of adobe or unfired bricks traditionally used in

the south of Iraq .The length of straw ranges between (2 – 6) cm,

therefore it is considered as main part in the present study, Fig(3-1).

Sawdust used in this investigation was collected from local farms in

Maysan province .The major contribution of the sawdust admixture is

the reduction in the dry density and increasing the bonding strength.

6- Sawdust: The coarse sawdust is used in the present experimental study

passing from sieve No. 12 mm , sawdust was collected from the carpentry

shops scattered throughout the region . Fig(3-2)

Figure (3-1) : Straw Figure(3-2): Sawdust


19

7- Rice husk: The rice husk, also called rice hull, is the coating on a seed or

grain of rice. It consists of hard materials, including silica and lignin .In

the present study sawdust are used it as an alternative to straw in the mix.

Passing from sieve No. 4.75 mm, Fig (3-3).

Figure (3-3) : Rise husk

3-3-Method of Mixing

1- The mixing procedures for clay to make unfired bricks are different for

country to other. In the present work two mixing procedures are used:

First Method- Traditional Method: In this method or procedure, the

traditional work method used by local Iraqi builders for adobe contraction is

used with the following steps:

2- Preparation of the soil fermentation area by enclosing a floor area (1 )

with concrete and Wrapping of floors and ends with thin nylonlayer.Fig

(3-4)


20

Figure (3-4): Soil fermentation

3- Weighing a quantity of the soil and placing it in the fermentation place

And Spray it with water ratio of 25% from dry weight of soil and leave

for 24 hours.

4- After 24 hours, we mix the clay mixture with one of the materials

according to the ratios in table (3-1) until the homogenization matrix is

obtained.

5- A sample of the mixture is then taken and placed in the oven to verify the

water content used in the mixture. Fig.(3-5)


21

Figure (3-5): mix mud with one of materials

6- Preparing the brick mold with dimensions (240 mm x 110 mm x 75 mm)

by cleaning it and grease from the inside. Fig (3-6)

Figure (3-6): Molds


22

7- Fill the mold on three layers with compaction. After that we settle and lift

the mold and then clean it and paint it and return the process again.Fig(3-

7)

Figure (3-7): Fill the mold

8- After 24 of casting the bricks, samples are taken and placed in the oven at

65 ° C for drying purposes due to poor natural temperature in the winter

season and also leaving samples to dry naturally. Fig(3-8)

Figure (3-8): Bricks after casting


23

Second Method: Due to the fact that the cement granules are very soft and

difficult to mix with the clay, and also the hardening speed of the cement, we

had to use another method to mix it.

1- Take dry soil and grind it with a grinding machine to get soft soil. Fig(3-

9)

Figure (3-9) : Soil grinding

2- Weighing a quantity of grinding soil and place it in the mixing vessel.

3- Weighting the amount of cement or sand according to the mixing

percentages in Table (3-4-1) and put them in the mixing vessel.

4- A 25% water content of dry soil weight and 50% of the weight of the

cement shall be taken and gradually added to the mixture

5- Mix the mixture well to get a homogeneous mix. Fig (3-10)


24

Figure (3-10) : mixing of materials

6- Preparing the brick mold with dimensions (240 mm x 110 mm x 75 mm)

by cleaning it and grease from the inside.

7- Fill the mold on three layers with compaction and settle the surface.

8- Leave the bricks in the mold for 24 hours after that, lift the mold and

leave the block under the sun to dry. Fig(3-11)


25

Figure (3-11) :Mud with mold

3-4- Raw materials proportions

The mix proportions of deferent mixtures are listed in Tables (3-4-1) to (3-4-3).

Tables (3-4-1) showed the mix proportions for clay unfired clays with different

binders fibers namely straw, sawdust and husk rice. Tables (3-4-2) showed the

traditional mix proportions of abode in the south of Iraq which consisted of clay

and straw by modified with different percentages of sand. Tables (3-4-3)

showed mixes included cement and sand.

Table (3-4-1): Mix proportions of clay only and different types of fibers

Group Clay

(%)

Straw

(%)

Sawdust

(%)

Rise

husk

(%)

Water

(%)

G1 100 - - - 27

G2 95 5 - - 28

G3 95 - 5 - 28

G4 95 - - 5 27


26

Figure (3-12): Some images while working


27

Table (3-4-2): Mix proportions of clay with sand


Group Soil

(%) Fine

sand (%) Coarse

sand (%)

Straw

(%) Water

(%)

G5 87.5 10 - 2.5 28

G6 82.5 15 - 2.5 28

G7 87.5 - 10 2.5 29

G8 82.5 - 15 2.5 27


28

Table (3-4-3): Mix proportions of clay with cement

Group Soil

(%) Cement

(%)

Sand

(%) Straw

(%)

W.C % for

Cement

%

Water

(%)

G9 90 10 - - 50 26

G10 80 10 10 - 50 26

G11 77.5 10 10 2.5 50 26


29



30

3-5- Failed Mixes

In additional to above materials, its tried to used plastic wastes fibers instead of

straw but the process is failed. Fig (3-15)

Figure(3-15) : plastic wastes fibers

CHAPTER FOUR RESULTS and DISCUSSION

31

CHAPTER FOUR

RESULTS and DISCUSSION

4-1- General

In the present chapter the results are listed and discussed. The results included

compressive strength, flexural strength and description of volumetric changes

during pressing of unfired bricks. Then the behavior of unfired brick masonry

prisms are presented and compared with that of fired clay brick masonry

prisms. A proposed formula are presented for evaluation the compressive

strength of unfired masonry from the compressive strength of unfired brick and

mortar based on Euro Code procedure.

4-2 - Effect of Natural Fibers

In the present study three types of natural fibers are used into mud matrix to

produce unfired clay bricks, namely straw, rice husk and sawdust, in which

straw are the traditional fibers in the south of Iraq in mud matrix for structural

applications like adobe construction. In additional to these natural fibers its

tried to use the recycled plastic fibers PET fibers but its failed may be due to

smooth surface of PET fibers which is failed in bonding stresses before develop

the required tensile strength. The effect of the three natural fiber types is listed

below.

1- Clay only: When the soil is only used to produce mud bricks, we notice

that during the drying period, cracking on the surface and sides of the bricks

occurs due to the shrinkage tensile stresses. The weak tensile strength of


32

mud as weak brittle material and also the absence of an additive that helps to

increase the cohesion of the matrix, led to early failure of these samples. The

maximum cracked compressive strength is 1.1 MPa. While the flexural

strength is 0.55 MPa. The proposed formula for the flexural strength of

unfired clay bricks consisted on clay only is:

√ ́

ft = flexural tensile strength of unfired brick

fb = compressive strength of unfired brick

2- Soil with Straw: Using straw as an admixture for the mud mix increased

the performance of clay bricks compared with samples included clay only.

The straw worked as links or natural fibers which led to increase the tensile

resistance of the samples for shrinkage and prevent the cracks due to tensile

stresses, which was clear during the drying period where no cracks appeared

in the resulting bricks which happened in the first mix (Clay only). The

addition of straw also increased the compressive strength of the bricks as

well as its compressibility. In spite of the Deformations, the cracks did not

appear even after the brick depth pressed to about half of the centimeter,

after increasing the strength of compression, the sides of the block were

crushed and there was no longitudinal or transverse cracks, Fig. (4-1). The

maximum cracked compressive strength is 2.4 MPa . While the flexural

strength is 0.5 MPa. . The proposed formula for the flexural strength of

unfired clay bricks consisted on clay only is:

√ ́


33



a- Brick before test

b- Brick after test

Figure (4-1) : compressive for brick


34

3- Soil with Rice Husk: As a result of the small size of rice husk, the

bonding strength has been lower than in straw, which was longer. The rice

husk added an extra compressive force in the bricks, preventing severe

deformation of the brick (the thickness of the brick and the lack of

significant descent) which obtained in the straw mix with the clay. However

,rice husk is increased the stability of the brick and reduced its

compressibility and led to the appearance of cracks along the surface of the

brick, Fig. (4-2). The maximum cracked compressive strength is 2.4 MPa

and the compressive strength at failure is obtained for clay only bricks is

2.64 MPa. While the flexural strength is 0.6 MPa.

√ ́





35

b- Brick after test


4- Soil with Sawdust: The sawdust was the best additive for the bricks as

the sawdust was not as hollow as in the straw and it were longer than the rice

husk. It was also more flexible than straw and lighter as well. These

differences were evident during its use in the mixture. The mixing process

was easier and the shrinkage was less than in the rest of the mixtures. The

test showed that the compressive strength was higher than the previous

mixtures and also the deformations were significantly lower. When the

compressive strength increased, the failure appeared in the form of capillary

cracks on the surface of the block as well as a collapse on its sides.Fig. (4-3).

The maximum cracked compressive strength is 2.85 MPa and the

compressive strength at failure is obtained for clay only bricks is 3.9 MPa.

While the flexural strength is 0.85 MPa.

√ ́




36


b- Brick after test

Figure (4-3): compressive for brick


37

4.2.1 Comparison among Straw, Husk rice and Sawdust

As mentioned above the straw, rice husk and sawdust play the same role in mud

matrix, namely as natural fibers that increased the tensile stresses and general

cohesion of brick body.

Figure( 4-1) : (4-3) and Table (4-2) showed the comparison among these three

fibers on the compressive strength of unfired clay brick in which straw fibers are

considered as reference brick due to straw is the traditional fibers in unfired clay

brick in the south of Iraq. The sawdust fibers yielded the higher compressive

strength with about 118.75% larger than straw fibers, also rice husk presented

higher compressive strength than straw fiber by about 110%. For flexural strength,

the sawdust presented a higher tensile strength than the straw by about 170%, also

rice husk presented higher compressive strength than straw fiber by about 120%.

Table 4.2: Results of Effect of Natural Fibers

Group

Description Specimens Compressive strength (MPa)

Flexural

strength

(MPa)

Flexural

strength

% straw Cracked

strength

Failure

strength

Comparison

per straw

(%)

G1

Clay only A1

1.1 -

45

0.4

80

B1 0.95 -

G2

Clay + straw

A2 2.4 -

1

0.5

1 B2 2.1 -

G3

Clay +

Sawdust

A3 2.4 2.8

118.75

0.85

170 B3 2.85 3.9

G4

Clay + Rice

Husk

A4 2.2 2.6

110

0.6

120 B4 2.4 2.64


38

Figure(4-4) : The compressive strength of Natural Fibers

4-3- Effect of Sand

In this phase, the traditional mud matrix that consisted of straw and clay is

modified by adding sand. The addition of sand to mud matrix play the role of

stabilizer to reduce the volumetric change of unfired bricks. Both fine and

coarse sands are used in the mud matrix that consisted of both clay and straw.

1- Soil, Fine sand and Straw: When the straw was used with the Fine sand,

the Fine sand increased the compressive strength of the brick and the

straw added the elasticity to it as well as the bond strength and reduced

the cracks during the drying period. The increased compression strength

of the brick is due to sand resistance to compressibility,In addition, the

addition of sand and reduce the proportion of straw in the mixture, which

led to the reduction of deformation of the brick during the test while

maintaining flexibility. We noticed that increasing the proportion of sand

0

0.5

1

1.5

2

2.5

3

1G 2G 3G 4G

Compressive strength



39

in the mixture to some extent improves the properties of the resulting

bricks, such as its resistance to pressure, as well as its elasticity. Fig(4-5).

The maximum cracked compressive strength is 2.75 MPa and the

compressive strength at failure is obtained for clay only bricks is 5.2

MPa. While the flexural strength is 0.64 MPa.

√ ́





40

b- Brick after test


2- Soil, Coarse Sand and Straw: The addition of coarse sand instead of

fine sand was not a significant change in the resistance of the brick to

compression, where the values were close to different mixing ratios of

the mixtures.fig(4-6). The maximum cracked compressive strength is

2.87 MPa and the compressive strength at failure is obtained for clay

only bricks is 4.1MPa. While the flexural strength is 0.52 MPa.

√ ́




41


b- Brick after test


4.3.1 Comparison among fine and coarse sands

As mentioned above the straw, Fine sand and Coarse sand play the same role in

mud matrix, namely as natural fibers that increased the tensile stresses and general

cohesion of brick body.


42

Figure (4-5) : (4-6) and Table (4-3) showed the comparison among these two fibers

on the compressive strength of unfired clay brick in which straw fibers are

considered as reference brick due to straw is the traditional fibers in unfired clay

brick in the south of Iraq. The Fine sand yielded the higher compressive strength

with about 112.5% larger than straw fibers, also Coarse sand presented higher

compressive strength than straw fiber by about 120%. For flexural strength, the

sawdust presented a higher tensile strength than the straw by about 110%, also rice

husk presented higher compressive strength than straw fiber by about 150%.

Table (4-3) : Result of effect of sand

Grou

p

Descripti

on

Specim

ens

Compressive strength (MPa)

Flexur

al

strengt

h

(MPa)

Flexur

al

strengt

h %

straw

Cracked

strength(MPa)

Failur

e

strengt

h

(MPa)

Comparis

on per

straw (%)

G5

Clay +

10% Fine

Sand +

Straw

A5 2.7 3.74

112.5

0.55

110 B5 2.33 3.81

G6

Clay +

15% Fine

Sand +

Straw

A6 2.64 5.5

114.6

0.64

128 B6 2.75 5.2

G7

Clay +

10%

Coarse

Sand +

Straw

A7 2.7 3.8

120

0.52

104 B7 2.87 4.1

G8

Clay +

15%

Coarse

Sand +

Straw

A8 2.4 4.1

100

0.75

150 B8 2.42 4.22


43

Figure(4-7) : The compressive strength of effect of sand

4-4 Effect of Cement

The effect of cement on unfired clay brick is investigated. Firstly the cement is

added to the clay only, secondly cement is added for clay and sand mix and

finally cement is added for the mix that included clay, straw and sand mix.

1- Soil and Cement: When cement is added to the soil alone, it makes the

bricks fragile, brittle and weak. The maximum cracked compressive

strength is 0.9. While the flexural strength is 0.7 MPa.

√ ́



0

0.5

1

1.5

2

2.5

3

3.5

G5 G6 G7 G8




44

2- Soil, Sand and Cement: When sand was used with cement as a clay

additive, we did not notice a change in the properties of the brick, where

it remained fragile and weak.fig(4-8).The maximum cracked compressive

strength is 1.1. While the flexural strength is 0.63 MPa.

√ ́





45

b- Brick after test


3- Soil, Sand, Straw and Cement: The addition of straw, along with the

presence of sand and cement to the clay mix, increased the strength of the

bonding between the mixing elements, and also increased the bearing of

the bricks for compressing, even if it less than the cement-free mixtures,

where the cement makes the mix brittle.The presence of straw has

increased the elasticity of the brick and the lack of cracks.fig(4-8). The

maximum cracked compressive strength is 2.4 MPa and the compressive


46

strength at failure is obtained for clay only bricks is 2.9 MPa. While the

flexural strength is 0.85 MPa.

√ ́





47

b- Brick after test


4.4.1 Comparison among mixes incorporated cement

As mentioned above the straw, (Cement+ Sand)and (Cement + Sand + Straw) play

the same role in mud matrix, namely as natural fibers that increased the tensile

stresses and general cohesion of brick body.

Figure( 4-8) : (4-9) and Table (4-4) showed the comparison among these two

Materials on the compressive strength of unfired clay brick in which straw fibers

are considered as reference brick due to straw is the traditional fibers in unfired

clay brick in the south of Iraq. The Cement & Sand yielded the lower compressive

strength with about 46 % larger than straw fibers, also Cement, Sand & Straw

presented equal compressive strength for straw fiber by about 100%. For flexural

strength, The Cement & Sand presented a higher tensile strength than the straw by

about 140%, also Cement; Sand & Straw presented higher compressive strength

than straw fiber by about 170%.


48

Table (4-4 ): Result of effect of Cement

Figure(4-10): The compressive strength effect of Cement

4-5-Masonry:

Generally, the masonry units represent the units that consisted of bricks and

mortars. The behavior of masonry units are different from the behavior of

bricks or mortar alone. Generally the compressive strength of masonry is

0

0.5

1

1.5

2

2.5

3

G9 G10 G11



Grou

p

Descripti

on

Specimen

s

Compressive strength (MPa)

Flexural

strength

(MPa)

Flexura

l

strengt

h %

straw

Cracked

strength

Failure

strengt

h

Compariso

n per straw

(%)

G9

Soil +

Cement

A9 0.9 -

37.5

0.7

140 B9 0.8 -

G10

Soil +

Cement

+ Sand

A10 1.1 -

46

0.63

126 B10 0.92 -

G11

Soil +

Cement

+ Sand

+Straw

A11 2.2 2.6

100

0.85

170 B11 2.4 2.9


49

less than the compressive strength of bricks and mortar due to weak bonding

between them which failed before reaching the strength of bricks or mortars.

In the present study the prisms of masonry are investigated which consisted

of three unfired bricks and mortars from similar materials of that used to

manufactured the unfired bricks. Also the present study incorporated the

testing of traditionally fired clay bricks masonry in order to compared the

behavior of fired bricks with unfired bricks masonry.

4-5-1: Unfired bricks used for masonry prisms

Six types of unfired bricks are considered for masonry assemblage as

following:

1- Clay and Straw

2- Clay and Sawdust

3- Clay with 10% Fine Sand and Straw

4- Clay with 10% Coarse Sand and Straw

5- Clay with cement and sand

6- Clay with cement and sand in additional to straw

The compressive strength of each type of unfired bricks is listed in Table

(4-5-1).


50

Table (4-5-1): Compressive Strength for Unfired bricks used for masonry

prisms

Group Description Compressive Strength

(MPa)

G2 Clay + Straw 2.4

G3 Clay + Sawdust 2.85

G5 Clay + 10% Fine Sand + Straw 2.7

G7 Clay + 10% Coarse Sand + Straw 2.87

G10 Clay + Cement + Sand 1.1

G11 Clay + Cement + Sand + Straw 2.4

4-5-2: Mud Mortar

The mortar used for unfired masonry brick was produced by mixing clay and 5%

straw with water content was equal to 40% from the dry weight of clay. The mortar

compressive strength was 1.5 MPa which was used by testing a cube with

dimensions of (10x10x10) cm. fig (4-10)

a- cube during test


51

b- Cube after test

Figure (4-11) : Cube Mud Mortar

4-5-3: Unfired Masonry

The unfired masonry behavior is studied by using prisms consisted of three

bricks and mortar. Six mixes are considered

1. Clay and Straw

2. Clay and Sawdust

3. Clay with 10% Fine Sand and Straw

4. Clay with 10% Coarse Sand and Straw

5. Clay with cement and sand

6. Clay with cement and sand in additional to straw

The compressive strength of each mix is listed in Table (4-5-2).


52

1- Clay with Straw

Figure (4-12) : masonry brick( Clay + Straw )


53

2- Clay with Sawdust:

Figure (4-13) : masonry brick( Clay + Sawdust )


54

3- Clay, 10% Fine sand and Straw:

Figure (4-14) : masonry brick( Clay +Fine sand + Straw )


55

4- Clay,10% Coarse Sand and Straw:

Figure (4-15) : masonry brick( Clay +Coarse sand + Straw )


56

5- Clay, Sand, Straw and Cement

Figure (4-16) : masonry brick( Clay + Cement +Sand + Straw )


57

Table (4-5-2): The compressive strength for Unfired Masonry

4-6-1- Traditional Fired Brick Masonry

The compressive strength of fired clay brick was 10 MPa and the compressive

strength of mortar with mixing ratio of 1:3 was 20 MPa. The masonry compressive

strength was 4.5 MPa. The compressive strength of masonry fired brick was more

lower than the compressive strength of fired and mortar. The decreasing ratio was

equal to 45% of compression strength of fired clay brick and equal to 22.5% of

compression strength of the mortar. The cause of decreasing of compressive

strength of masonry was because of the deference in thermal expansion coefficient

between the fired clay brick and the mortar.

Group Description Compressive

strength (MPa)

G2 Clay + Straw 1.65

G3 Clay + Sawdust 1.6

G5 Clay + 10% Fine Sand + Straw 1.3

G7 Clay + 10% Coarse Sand + Straw 1.9

G10 Clay + Cement + Sand 1.5

G11 Clay + Cement + Sand + Straw 1.2


58

4-6-2- Unfired Brick Masonry

The highest decrease in the resistance of masonry bricks was equal to 52%

comparing it with the compressive strength of unfired clay brick and mortar, while

The highest decrease was 30%. This decreasing of the compression strength is low

comparing it with decreasing of the compression strength in masonry fired brick.

The reason that compressive strength of unfired masonry brick was close to unfired

bricks were because the bricks and mortar were made of the same material and

have the same Poisson ratio.

Proposed Formula for Compressive Strength of Unfired Clay Bricks

Due to difficulty and time consuming to measure the compressive strength of

masonry units which is needed for numerical analysis or design calculations the

codes of practice presented different formula to obtain the compressive strength of

masonry units from the compressive strength of mortar and bricks which could be

obtained easily.

The three compressive strengths of mortar, bricks, and masonry can be

conveniently related as done in Euro code6 as (Kaushik et al, 2007):

)(ffKf mbM 2

where fb : compressive strength of bricks, MPa; fm: compressive strength

of mortar, MPa;f'M : compressive prism strength of masonry, MPa; K:

constant depending upon brick properties and brick-mortar joint

configuration; α, β: constants representing contribution of bricks and mortar

compressive strengths on f'M


59

According to above results of bricks compressive strength, masonry

compressive strength, and masonry compressive strength, the following

equations are proposed to estimate the masonry prism compressive strength

from the compressive strengths of unfired bricks and mortar obtained

experimentally.

1- soil with straw

)3(685.0 55.075.0

mbM fff

2- soil with sawdust

)4(66.0 5.065.0

mbM fff

3- Soil, Fine sand & Straw

)5(69.0 35.05.0

mbM fff

4- Soil, Coarse sand & Straw

)6(761.0 49.068.0

mbM fff

5- Clay ,Cement & Sand

)7(96.0 74.087.0

mbM fff

6- Clay , Cement , Sand & Straw

)8(57.0 42.066.0

mbM fff

CHAPTER FIVE Conclusions and Recommendations

60

CHAPTER Five

Conclusions and recommendations

5-1 Conclusions

1- Use of clay alone is not appropriate as masonry unit where it considered a

brittle and fast-cracking material. Additional materials should be added to

the mix to increase its strength and flexibility of the brick. The maximum

compressive strength for this mixture was 1.1 MPa and the flexural

strength was 0.4 MPa.

2- Adding straw increased the strength and plasticity of the brick. Increased

plasticity of the bricks by adding straw is important thing. Despite the

great deformations that have happen to it, the cracks were not shown on

its surface as well as not get collapse. We can benefit from this property

in areas where earthquakes get. The maximum compressive strength for

this mixture was 2.4 MPa and the flexural strength was 0.5 MPa.

3- Adding rice husk somewhat increased the strength of the bricks but its

small size did not give a high bonding strength to the bricks. The

maximum compressive strength for this mixture was 2.4 MPa and the

flexural strength was 0.6 MPa.

4- The Sawdust considered as one of the best additive materials that we used

in this research as being thick, long and not hollow as in straw increased

brick compressive and bonding strength when adding it to the mix. Also

it decrease the cracks occurred during drying period. The maximum



5- Using the sand in production of bricks is considered as a good addition,

whether the sand is fine or coarse, it increased its strength and decreased


61

the deformation that occurred to it during test. The maximum



6- Using the cement in production of bricks is considered as a bad addition

because the cement made the mixture brittle, weak and fast-cracking

material. The maximum compressive strength for this mixture was 0.9

MPa and the flexural strength was 0.7 MPa.

7- The maximum compressive strength o masonry unfired brick was 1.9

MPa which was made of clay, coarse sand and straw. The compressive

strength of masonry bricks was close to compressive strength of unfired

bricks and mortar. This was because the bricks and mortar were made of

the same material and have the same Poisson ratio.

5-2- Recommendations

1- Use of high compressive materials such as steel slag as an additive to

increase the compressive strength.

2- Use of plasticized materials and reduce water content in the mix which

will facilitate the production industry, increase its strength and will

reduce the pores in it. Also reduce water content will reduce the salts that

cause efflorescence in the bricks.

3- Increase the brick dimensions which will increase its bonding and

compressive strength.

4- Use a high-mechanical pressure for the bricks during the production

process to increase its bonding strength and reduce the pores in it which

will increase its density.


62

5- Use additional materials as an addition to the bricks and check the

possibility of increasing its strength.

6- Study another type of mud construction like adobe and cob.

References

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[7] Jeorge J. Venta, P.Eng. “Life cycle analysis of brick and mortar products”,

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http://www.greenspec.co.uk/building-design/unfired-clay-bricks/


64

[18] Farraj Al-Ajmi*, Hany Abdalla, Magdi Abdelghaffar, Jamal Almatawah,

Civil Engineering Department, College of Technological Studies, The Public

Authority for Applied Education & Training, Kuwait

[19] R. Saravanakumar1, Ramesh. K2 & Vinothkumar. S3Assistant Professor,

Department of Civil Engineering, St. Joseph’s College of Engineering Chennai,

India ,2018

[20] Medhat S. El-Mahllawy1,*, Ayman M. Kandeel1, Mahmoud L. Abdel

Latif 1 and Abdeen M. El Nagar1 Raw Building Materials and Processing

Technology Research Institute, Housing and Building National Research Center

(HBRC), Egypt

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