ABSTRACT

This research was conducted to improve on the quality of the Artisan brick in terms of increased characteristic strength, low water absorption, durability and stability. The artisan clay bricks in Uganda are characterised with low strength, erosion, tiny cracks, lime pop out, warping. Efflorescence occurrence and high-water absorption. The raw clay and artisan burnt clay brick samples were collected from artisan brick making places from Eastern, Central and Northern Uganda. The sampling was done using IS-5454 procedures. Testing was carried out in geology and Material laboratories to ; Classify local artisan brick, relative uniform force made bricks from raw clay and modified ones, investigate mineral percentage existence in natural and purified clay, crushing strengths of the artisan, modified  units  from purified clay,relative uniform force made bricks , effect on purifying clay, know  presence of the alkalis in the clay .From the three regions, raw clay did not satisfy the mineral requirements for manufacturing . It however required substantial refining action on the raw clay for production of stable, strong and durable brick. Refining was done and the raw clay structure was improved and shifted to the positive side of the required mineralogy for stable, higher characteristic strength, slight efflorescence, low water absorption, class one bricks and durability. I therefore recommend that the artisan do include both refining processing of raw clay before making clay bricks and use the method of constant force moulding process.

CHAPTER ONE

INTRODUCTION

1.1 Background

Bricks are the commonly used forms of building materials in the construction of buildings in the world and are one of the oldest known building materials dating back to 700BC. Bricks were used during the time of Ancient Egyptians, the Romans, and the Mesopotamians and the gothic period when they became very common in the northern Europe.   Clay bricks have been widely preferred as building material because of their high compressive strength, durability, fire and   weathering resistance, thermal and sound insulation (Frontiers of Architectural research, 2017). The fundamentals of brick manufacturing since ancient times have not changed (Reston, 2006). Basic principles of manufacturing bricks are fairly the same but individual manufacturers do tailor their manufacturing process to fit their particular clay raw materials. In due course of tailoring the process to fit a particular raw clay material, some manufacturers do make mistakes that can lead to poor quality products. The poor brick products are characterized by lime pops, blistering (tiny holes), cracks, warping, softness or low strength under burning, efflorescence, brick erosion, high rate of water absorption etc.

Bricks in first class when immersed in water, should not absorb more than one sixth of its dry weight, second class should not absorb more than a quarter of its dry weight (Khann, 2001). For brick manufacturing, clay must possess some specific properties and characteristics.  Clay is one of the most abundant natural materials on earth (Reston, 2006).  Clay do occur in three principal forms i.e. Surface clays, shale’s and fire clays of which of these forms have similar chemical compositions (Reston, 2006). The three forms are composed of silica and alumina with varying amounts of metallic oxides. The type and source of clay used in the manufacturing of bricks varies greatly depending on the geographical locations of the manufacturing site (Federico, 2005) The manufacturer minimizes variations in chemical compositions and physical properties by mixing clay from different locations in the pit. During mining it is observed that there is a variation of chemical composition even in the same pit. These variations are compensated for by varying manufacturing processes.  Clay bricks in Uganda are manufactured by Artisans, small and medium scale manufacturers. Around 84% of all Ugandan houses have brick walls compared to the 12% which is built with mud and poles (Suistanability,2015). The artisan clay bricks manufacturers’ products are estimated to be over 80% of the brick products in Uganda and are characterized with defects on the market. Artisan clay bricks are relatively cheaper than medium scale manufacturers in Uganda. Clay bricks manufactured by the artisans in Uganda and Tanzania are more   than 10% wasted during transportation, handling and   construction process on sites (Sustainability, 2015).

To address the issue of the quality in the manufacturing of artisan clay bricks in Uganda, this research focused on the study of the right manufacturing   process, identification   of   the physical properties of raw clay to be used as per geographical location, design of appropriate artisan method of purifying raw clay to meet specific characteristics properties of producing durable, stable and strong   burnt clay brick.

1.2 Statement of the problem

Clay bricks after sintering during firing do gain high strength even up to 100N/mm² (Dhir, 1996). Good clay bricks do have low absorption of water, class one brick does not absorb more than a sixth of its dry weight and class two does not absorb more than a quarter of its dry weight (Khann, 2001).Good bricks do have fine texture, exhibit low variations in sizes, do have either red or yellow colour due to the presence of iron oxide, no efflorescence that appear on built walls, do not exhibit cracks and warping.

The artisan manufactured bricks in Uganda are largely characterized by noticeable defects like lime pop out, warping, cracks, high water absorption, erosion, blistering, low compressive strength, occurrences of efflorescence on built walls which is assign of poor-quality brick. The characterized defects of the artisan  manufactured clay brick in Uganda leads to  low strength of walling units, dump rooms, poor appearance of walls, frequent repainting of walls, lack of trust for structural specification during design process, high projects costs due to high waste generation during handling and construction, less durability of structures and variations in quality of brick products. Basing on the problems identified, this research has introduced artisan methods of refining raw clay and methods of improved moulding of bricks that has yielded better class of bricks.

Figure 1.1 : Efflorescence

Figure 1.2 : Cracks

Figure 1.3 : Erosion

1.3 Objective of the study

1.3.1 Main objective

To assess causes of poor quality of artisan manufactured clay bricks in Uganda and recommend measures for improvement.

1.3.2 Specific objectives

The specific objectives of the study are:

1. Establish the present manufacturing process used by the artisans in the manufacture of local clay bricks.
2. To determine the chemical percentage (Al₂O₃, SiO₂, Fe₂O₃ and CaO) compositions of clay locally used by the artisans, in manufacturing bricks in Uganda.

• To improve on the percentage chemical (Al₂O₃, SiO₂, Fe₂O₃ and CaO) composition ratios as related to the ideal composition for quality

1. Recommend the new methods of manufacturing improved artisan clay brick to meet specific characteristics properties of producing durable, stable and strong burnt clay brick.

1.4 Research questions

The research was aimed at addressing the following research questions:

1. How does the artisan in Uganda process the manufacturing of the local clay bricks?
2. What are the natural percentage chemical (Al₂O₃, SiO₂, Fe₂O₃ and CaO) compositions of artisan brick making clay in specific geographical locations in Uganda?

• To what extent can the natural composition of the percentage chemical (Al₂O₃, SiO₂, Fe₂O₃ and CaO) be improved to produce stable, durable and strong artisan brick?

1. How can the artisan in Uganda improve the brick manufacturing process to produce the stable, durable, strong and reliable clay brick for construction?

1.5 Justification of the study

If this research was not conducted, building projects (that employs artisan local clay bricks), their costs would continue to be high due to high wastes involved because of the weak nature of the artisan bricks during handling, transportation and construction process.

Designers/Consultants would not make use of a reliable artisan local manufactured clay bricks for design specifications.

Artisan improved manufacturing process for production of reliable artisan clay brick would not be in place.

Coldness due to poor class of bricks that absorption high water in the houses built by the use of low-class artisan brick would continue to affect asthmatic patients.

Defects largely characterised with efflorescence would continue to turn houses poor looking because of the migrations of the salts.

1.6 Significance of the study

The study has provided adequate information to consulting engineers a basis of design specification on the grade of artisan clay brick with improved manufacturing process by Ugandan artisans. The research has provided adequate information regarding the purification of the raw clay to get the appropriate percentage chemical composition leading to stable, durable and structural clay artisan brick that is economical for structural works in Uganda. The introduction of the clay purification formula and improved uniform force moulding that lead to production of quality artisan clay brick consequently increase time interval for repainting the houses, high compressive crushing strength, smart looking products, add value to knowledge body and hence value engineering.

1.7 Scope and limitations of the study

1.7.1 Geographical, time and content scope

The research was conducted in Uganda from December 2018 to August 2020. Representative clay samples were obtained from the artisan manufacturing sites in the districts of Mukono, Lira and Kamuli. Districts in Uganda from four major regions i.e. northern, eastern, western and central were written on small papers and were folded for purposes of hiding their names. The folded district names from the four major regions were put in four tins in which each tin was representing a region.  The papers in each tin were shaken and evenly mixed up. Random picking of the papers was done in order to choose the districts in which the study was to be conducted. The research was limited to manufacturing of brick from raw and purified clay, tests for water absorption, compressive crushing strength, efflorescence of the modified & artisan burnt clay brick, percentage chemical analysis of (Al₂O₃, SiO₂, Fe₂O₃ and CaO) for both raw clay and purified clay.

1.7.2 Financial scope

Seven million Ugandan shillings was spent to deliver this research. The total cost of 100% was personal savings that covered allowances for field teams, logistics, transporting and testing of materials, stationery and report production.

1.8 Conceptual framework

The strength, stability and durability of clay bricks depends on the chemical composition of clay and on the manufacturing process which includes mixing, proportionating of clay constituents, drying and firing.

The independent variables which are indicators of quality for classifications of bricks are compressive strength, water absorption and efflorescence.

The dependant variables are the manufacturing processing used by the artisan and the chemical structure of the clay used.

. Figure 1.4 shows slurry clay fractionating of clay

A

B

Figure 1.4 : Slurry Fractionation A & B

Figure 1. 5 : Conceptual Frame Work

CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction

This chapter presents the already available materials in the occurrence and chemical composition of brick making clay, percentage mineral compositions of clay for optimum quality manufacturing of clay brick, particle sizes required of clay for optimum quality, firing of clay bricks, densities of common encountered soils and physical properties of clay bricks on firing, methods of refining clay, and analysis of clay properties and field testing of the clay brick.

2.2 Occurrence and chemical composition of brick making clay.

Clay occur in three principal forms i.e. surface clays, shale and fire clays, all of which have similar chemical compositions but different physical characteristics (Reston, 2006). The surface clays may be the up thrusts of older deposits or of more recent sedimentary formations. They are found near the surface of the earth. Shales are the ones that have been subjected to high pressures until they have nearly hardened into slates and fired clays are usually mined at deeper levels than other clays and have refractory quantities (Reston, 2006). The type and source of clay used in the production of bricks varies greatly depending on the geographical location of the production site. .In a study titled the use of Waste Material in the Manufacture of Clay Brick revealed that the chemical composition of common types of brick making clay and shale was  SiO₂,AL₂O₃,Fe₂O₃,TiO₂,CaO, MgO, Na₂O, k₂O and LOI ( Banff,2005) . The main difference between clay body types is silicon dioxide (SiO₂), Aluminium oxide (Al₂O₃) and iron oxide (Fe₂O₃) and CaO contents (Federico, 2005). Silicon dioxide and the aluminate are major composition of the clay that makes a brick and the rest are regarded as impurities.

In a study titled  Mineralogical  and  Chemical  Composition  and  Distribution  of Rare Earth Elements  in  Clay–Rich  Sediments  from  Central  Uganda also revealed that when an opening is made with in the clay zone it exhibits layers ranging from  uppermost dark grey layer that is rich in organic matter under which a grey layer exits and then a brown layer, which becomes more brown near the top of the water table and in the same study  the clay sediments exhibited the major and minor elements of the clay rock as:SiO₂, TiO₃, Al₂0₃, Fe₂O₃, MgO, CaO, Na₂O, k₂O,P₂O₃,LIo (Nyakairu,2001). In mineralogy of clay, most particle sizes are of dimensions of 2µm and less which are responsible for the cohesion and plasticity of moist clay (Dhir, 1996).

2.3 Optimum composition of clay for quality manufacturing of clay bricks

Clay is the principal raw material in the traditional ceramic manufacturing industries.

The features that most industries mostly look for in clay are mainly the composition and particle size which determine the feasibility of that clay to be processed (Mousharraf,2011). Composition and particle size of the clay to be used for brick manufacturing are subject to distinction based on origin of clay. Clays found in the origin is called Residual clays. These clays are typically deposited along the igneous rocks from which they are formed and are obtained in relatively pure state. These are found to be coarser particles sizes with wide particle sizes distribution and show lower plasticity.

Another type of clay is sedimentary clays that are deposited by transportation from their origin by natural agencies like water, wind etc. The grading action of clay particles in water, wind and ice results in very fine particles sizes giving the sedimentary clay very high plasticity (Mousharraf, 2011) .In a study conducted by  the Department of Materials and Metallurgical Engineering, BUET, revealed that Quartz lowers the plasticity of the green body and leads to micro cracks formation in the fired body. It also revealed that white clay has high silicon content and at the same time has substantial amount of aluminate and fairly low impurity content in it and it possesses the greatest potential to be turned into industrial suitable raw materials for the traditional ceramic manufacturing (Mousharraf, 2011). When the raw clay is much higher in silicon dioxide, ferric oxide and Titanium oxide and falling short in aluminate content makes the raw material un suitable for ceramic manufacturing. The strength, durability and absorption of the resulting ceramic products are dependent on the state and nature of sintering within the brick.

Melted mineral to fill

The gaps of the particles

Figure 2. 1 : Sintering on Firing

For purposes of producing fired clay brick, a silicon dioxide content of between 55-70% is ideal (Federico, Chidiac, 2005).The total percentage coverage for the silica and aluminate ranges from 75% to 84% by weight of the raw clay materials and the rest of the impurities would take up the rest of the portion for quality product.

2.4 Ideal mineral percentage requirement for earth soils for quality brick manufacturing

2.4.1 Alumina (Al₂O₃)

Alumina is required in the range of 20-30% (Civil seek,2019). All clays are basically hydrous aluminium silicates. Clays are responsible for plastic character of mud.  During manufacture of bricks, if alumina is present in higher proportions the brick products do shrink and develop cracks on drying and if they are in smaller proportions brick would not be moulded easily and nicely. The use of the range of the percentage (20-30%) proportion is for imparting the bricks with sufficient plasticity.

2.4.2 Silica (SiO₂)

Silica (50-60) % (Civil seek,2019). Silica is present in two forms. One as combined as constituent of clay (Kaolinite) and free silica (sand or quartz) The total silica proportion required is in the range of 50-60% (Civil seek,2019) however Federico recommends range of 55-70%. Silica takes the biggest percentage of the portion of the clay brick and silica is responsible for strength, hardness, resistance to shrinkage and shape of the brick and also to a great extent for the bricks’ durability or long life. Too much of the silica in the brick earth making material results in brittleness and porous structure of the brick and may not sinter easily.

2.4.3 Lime (CaO)

The maximum required for brick making is 4% (CIVIL SEEK,2019), this component makes burning and hardening of bricks quicker and is considered desirable with the following conditions: –

• Not more than 4 % because in that case, it may cause excessive softening of bricks on heating (lime and magnesia acts as fluxes)
• Must be present only in finely powdered and thoroughly dispersed form and if present in small grains or nodules the lime itself will get slaked(heated) and once the brick made with this kind of lime is used, lime in it will easily get hydrated and cause disintegration of brick. Magnesia which is easily associated with lime has a similar effect. It is their total percentage which must be considered while determining the composition of the brick earth (Civilseek,2019).

2.4.4 Iron oxide

Iron oxide (4-6) % (Civil seek,2019) is required in the brick earth and it also work like oxides of calcium and magnesium as a flux i.e. lowers down the softening temperature of the silica. The iron oxide in addition to work as flux, it imparts the red colour to the brick. Shortage of iron oxide in the earth soil will lead to yellow colour or light red. Yellow colour may also show the incomplete sintering of bricks.

2.5 Firing of clay bricks

 2.5.1 Engineering properties of clay bricks on firing

(a) Compressive strength

Compressive strength of brick is remarkably improved by firing at high temperatures (Karaman, 2006).  Increase in the compressive strength is due to the decrease in the porosity and increase in bulky density with increasing temperature. Increase in firing time does no big effect on the compressive strength according to experiment done by Karaman when the firing time of from 120 minutes to 148 minutes resulted in small increase of 7% in the compressive strength of clay brick. Increasing firing time does not improve on the quality of brick and result in waste of energy and time (Karaman, 2006).

Table 2.1 Effect of Firing Time and Temperature on Compressive Strength of Clay bricks

(Karaman, 2006)

Table 2.2 Effects of Firing Temperature on Compressive Strength of Clay Brick

(Johari, 2010)

Figure 2. 2 : Effects of Firing Temp. on Compressive Strength of Clay Brick (Johari,2010)

(b)  Density

Density of brick depends on specific gravity of clay, methods of           manufacture, and degree of burning. Density of burned bricks made with clay usually exceeds1.6g/cm3 and is averagely 2.0g/cm³. When density of a brick decreases, its strength and heat conductance decrease and water absorption increases. Firing time longevity has no effect on density of clay brick (Karaman, 2006)

Table 2.3. Effect of Firing Time and Temperature on Density of Clay Bricks)

(Karaman,2006)

• Water absorption

Table 2.4 Effect of Firing Time and Temperature on Water Absorption of Clay Bricks

(Karaman,2006)

 (d)Bending strength

Table 2.5 Effect of Firing Time and Temp. on Bending of Clay Brick

(Karaman, 2006)

The brick structure formed at lower temperatures (840-960 ^oC) remained essentially the same until temperatures of over 1080oC are reached. The porosity of brick shows an increment of 1.4% and 0.1% from 800^oC to 900^oC and 900^oC to 1000^oC, respectively (Fig. 2.4).

Table 2.6: Effect of Firing Temp. on Porosity of Clay Brick

(Johari,2010)

Figure 2. 3 : Effect of Firing Temperature on Porosity of Clay Brick

(Johari,2010)

The increasing in porosity is the result of diffusion at relatively low temperature without significant shrinkage. The shrinkage value for temperature 800oC, 900oC and 1000^oC is 0.31%, 0.50% and 1.04%, respectively. The surface also looks rough and a bit dusty. The bricks that are sintered until 1000^oC are considered as having a porous structure since their water absorption rates are higher than 25%, as shown in Figure 2.3.

Table 2.7: Effect of Firing Temp. on Water Absorption of Clay Brick

(Johari,2010)

Figure 2. 4 : Effects of Firing on Water Absorption on Clay Brick

(Johari, 2010)

Between 1000^oC to 1100^oC, the solid-state sintering becomes very significant since the clay body been fully sintered. Very few pores can be seen in the microstructure. Brick porosity value reduces significantly from 39.33% to 27.06% and it was 31% reduction. The purpose of the solid-state sintering process is to develop atomic bonding between particles by a diffusion mechanism. This diffusion followed by grain growth will create a dense structure with significant shrinkage. The shrinkage value increases to 74% causing the reduction in volume for brick sintered from temperature 1000⁰C to 1100⁰C. A progressive gain in strength can be observed on brick sintered at 1100⁰C where the compressive strength increased from 25.4N/mm2 to 71.8 N/mm2. This is also the temperature at which vitrification is first detected by SEM Starting from 1100⁰C, the liquid phase sintering becomes a very important sintering mechanism. During this process, the reduction of pores becomes more significant as the compacted structure starts to increase its performances, such as strength and water permeability. The fired-clay brick sintered at 1100^oC begins to diffuse and shrink as the liquid phase starts to form and fill up the pores, creating smaller pores. The brick shrinks 37% when sintered from 11000C to 12000C causing the porosity to reduce 47.5%. The effect of firing also causes the water absorption value to reduce 42% lower than the value for brick sintered at 1000oC. The internal surface of pores in bricks sintered at 1200⁰C and 1250⁰C has a “glazed” view Figure. 2.5.

Figure 2. 5 : SEM Micrographs for the Clay Fired at Different Temperatures

(Johari, 2010)

The sintering process reaches the optimum temperature at 1200⁰C, whereby its microstructure contains minimum pores with porosity value 14.2 % and produces the highest strength, 89.5 MPa, as shown in Fig. 2.2. However, at 1250⁰C, the microstructure shows larger pore sizes and lower porosity value which is 5.87% with brittle fracture behaviour. The brick becomes more brittle due to a larger portion of glassy phase in the microstructure. Therefore, the strength of the sample becomes lower (83N/mm²). Even though the porosity value is lower than the brick sintered at 1200⁰C, this only effect on the water absorption properties where the value of water absorption for brick sintered at 1200⁰C and 1250⁰C is 6.63% and 2.71%, respectively.

Firing has a positive influence on the microstructure of brick promoting a dense structure with low permeability. At temperatures of 1000⁰C or above, the technical quality and durability of bricks is generally superior. It displays high in compressive strength, lower porosity and water absorption value. The findings indicate that the physical and mechanical properties of bricks can be controlled to a significant extent by varying the firing temperature. The best firing temperature for fired-clay bricks with good performance of mechanical properties was discovered to be 1200⁰C. There is no doubt about its potential in the construction industry, not only as filler in walling systems, but also as load bearing structures. However, due to economic reasons, the firing temperature can be reduced to between 1050°C to 1100ºC. The fired-clay brick can still achieve strength around 40-70 N/mm2, porosity below 29% and obtain water absorption value below 25%.

2.6 Separation of silica from local clay

Separation of silica from local clay can be separated by various methods i.e. by washing and wet sieving.

Silica occurs in three main crystalline forms. The principal occurrence is as the mineral quartz but it also occurs in other rarer mineral forms known as tridymite and cristobalite. It is a very durable mineral resistant to heat and chemical attack and it is these properties that have made it industrially interesting to man. The first industrial uses of crystalline silica were probably related to metallurgical and glass making activities a few thousand years BC. It has continued to support human development throughout history, being a key raw material in the industrial revolution especially in the glass, foundry and ceramics industries. Silica contributes to today’s information technology revolution being used in the plastics of computer mouse and providing the raw material for silicon chips(Hosne,2013).

For industrial use, pure deposits of silica sand capable of yielding products of at least 95 percent silica are required. Often much higher purity values are needed. Washing is the most common separation process. Clay may contain quartz, feldspar, mica, coloured minerals, sometimes soluble salts and occasionally organic matter. Washing process is so adjusted to separate clay and silica particles as far as possible. Washing process may, however, need some adjustment depending upon the individual characteristics of the clay under washing. The washing schedule has to be worked out taking into consideration the peculiarity of the clay to be washed and the impurities present. Most sieve analyses are carried out dry. But there are some applications which can only be carried out by wet sieving. This is the case when the sample which has to be analysed is e.g. a suspension which must not be dried; or when the sample is a very fine powder which tends to agglomerate (mostly < 45 µm) – in a dry sieving process this tendency would lead to a clogging of the sieve meshes and this would make a further sieving process impossible. A wet sieving process is set up like a dry process: the sieve stack is clamped onto the sieve shaker and the sample is placed on the top sieve. Above the top sieve a water-spray nozzle is placed which supports the sieving process additionally to the sieving motion. The rinsing is carried out until the liquid which is discharged through the receiver is clear (Hosne,2013)

2.6.1 Separation of silica by washing method

Around 4 grams of sample were mixed with 500 ml water. The mixture was stirred with the help of a stirring machine at a fixed speed (1000 rpm). After stirring, a settling time was given for the mixture. The settling time allowed the silica particles to settle down while the clay particles remained in the suspension. Then the silica and clay particles were separated. The silica particles were dried and after drying weight were measured. During the separation 0.3grams of an electrolyte [(0.1gram Na₂CO₃ + 0.2-gram Na₂SiO₃.9H2O) +100 ml water] was added in the mixture. It aided the separation process (Hosne,2013).

2.6.2 SEM (scanning electron microscope) analysis

Finally, the separated silica particles were taken for SEM analysis. Silica samples were mounted on specimen stub and as silica is not electrically conductive, it was made electrically conductive by gold sputtering.

Chemical analysis

Figure 2. 6 : Separation of Silica from Local Clay by Washing Method

(Hosne, 2013)

2.6.3 Separation of silica by wet sieving

At first sample was placed on a sieve having smallest opening, then distilled water was poured on it. Distilled water was used to avoid iron or some other impurities coming into the sample through water. The mixture was allowed to pass through sieve openings. Sand particles remained at the upper portion of the sieve. Washing continued until sand particle become free from clay. Obtained silica was then dried in the oven

2.6.4 Microscopic analysis

  After the separation of clay, silica samples were observed under optical and polarizing light microscope respectively.

2.6.5 Optical mineralogy

Finally, Optical mineralogy was done on the basis of polarizing micrograph. Some mineral other than quartz was identified by thi

Figure 2. 7 : Separation of Silica from Local Clay by Wet Sieving Method

(Hosne, 2013)

2.6.6 Result and discussions

Effect of stirring and settling time Tables 2.6 and 2.7 shows the experimental data of obtained silica during washing method at different parameters. First, the stirring time was varied and the effect was observed. There was no significant change during this operation.

Table 2.8 Data of Silica Obtained with Different Stirring Time

(Hosne,2013)

Then, the settling time was varied to observe the change of silica content.  The amount of silica was increased with increasing the settling time.

Table 2.9 Data of Silica Obtained with Different Settling Time

(Hosne,2013)

2.6.7 Effect of electrolyte addition

Table 2.10 shows the effect of electrolyte addition on separation process. The effect was significant. As the amount of electrolyte increased the amount of separated silica also increased. But settling time had higher effect than electrolyte in this work.

Table 2.10 Data of silica obtained during electrolyte addition

(Hosne,2013)

2.6.8 Chemical analysis

Chemical analysis of the separated clay was done to know the percentage of silica. Around 58 percent silica was present in the separated clay. It was clear from the analysis that most of the silica particles retained with clay. Washing method could not separate all the silica particles. So wet sieving was carried out. It gave higher percentage of separated silica than washing method.

2.6.9 Sedimentation/Dispersion

This test is done by shaking a portion of the sample into a jar of water and allowing the material to settle.  The material will settle in layers.  The gravel and coarse sand will settle almost immediately, the fine sand within about a minute, the silt requiring as much as about an hour, and the clay remaining in suspension indefinitely.  The percentage of each component is estimated by comparing the relative thickness of each of the layers in the bottom of the jar, keeping in mind that the larger sized particles will typically settle into a denser mass than the fines (Geotechnical engineering manual,2017)

Table 2.11 Visual Grain Size Identification

(Geotechnical Engineering Manual,2017)

2.7 Analysis of clay properties

A number of researches have been carried out so far on clays from various region across the country in order to identify the compositional variation. Such analysis is usually performed with the X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) methods. Table 2.12 lists the XRF analysis of some locally available clay types.

In reference to the data in Table 2.12, a comparison of local clay to imported material (standard compositions) would make obvious that the indigenous material is much higher in SiO2, Fe2O3 and TiO2 content and falling short in Al2O3 content. Typically, majority of Silica stay in free form as Quartz. Rest of the Silica content are associated with Alumina in bonded form, which forms phases like Kaolinite, Halloysite etc (Table2.14). Moreover, amount of impurities like Fe₂O₃ and TiO₂ are also high in most of the local clay types

Table 2.12 XRF Analysis of Local and Imported Clay

(Adnan, 2011)

Although Bijoypur Clay (White Clay) has high SiO₂ content, but at the same time it has substantial amount of Al₂O₃ and fairly low impurity content in it. Hence this clay possesses the greatest potential to be turned into industrially suitable raw material for traditional-ceramic manufacturing.

Table 2.13shows another XRF analysis, where the compositions of various locally available clay are compared. The data show that % Silica of the local clay are in the range of 65-73, % Alumina in 22-27, % Iron (III) Oxide in 1-9 and % Titanium Oxide within 1%, which present the challenges of dealing with local clay for the suitability of industrial application due to high Silica content.

Table 2.13 XRF Analysis of Various Locally Available Clays

(Adnan, 2011)

Table 2.14 shows the compositional analysis done by XRD of some locally available clay which strongly indicates the presence of Quartz, in all of them. In general, the presence of excess amount of Quartz lowers the plasticity of the green body and also leads to micro crack formation in the fired body. Moreover, long exposure to silica dust causes significant health hazard.

Table 2.14 Summary of XRD Analysis of Local Clays

(Adnan,2011)

In the analysis of the local clays in china, shows the X-Ray diffraction pattern for three types of clay i.e a pattern for standard China Clay and the existence of Quartz and Kaolinite in the composition, pattern for locally available Mymensingh White Clay and Bijoypur Clay respectively. The XRD patterns indicate the presence of higher amount of Quartz or free Silica and relatively lower Kaolinite (bonded Silica) content in locally available clay in comparison to those in China Clay. Hence, substantial refining action is necessary to make the indigenous material suitable for industrial manufacturing.

Another important factor for clay to be used as raw material is the particle size. Particle size has a significant role on the plasticity of clay. Generally, the smaller the particle size the better is the plasticity of clay. However, there is a lower limit of particle size below which the property starts to deteriorate. China Clay due to its large particle size shows poor plasticity. Thus, plasticity of green clay body is usually improved by adding other clay like Ball Clay which has very fine particle size. Ideally, the average particle size required for green body mixture is around 45 microns.

In case, the mixture has particle size below that, then the green body fails to hold its shape. Table 2.15 shows the particle size distribution of local clay which indicates that local clay has larger particle size. Bijoypur Clay, Mymensingh White Clay and Yellowish Gray Clay have particle size larger than 100 microns, whereas Mymensingh Yellowish Gray and Black Clay have particle size just below 100 microns. In general, local clays have larger particle size.

Table 2.15 Particle sizes distribution and analysis of % residue through sever analyser

(Adnan, 2011)

Atterberg limits of clays when plotted as a plasticity chart i.e.  Plasticity index against plastic limit, aids in identification of clay types and physical properties of clay (Bain, 1971). Plasticity index equals to difference between the liquid limit and that of plasticity limit.

The plasticity index gives an indication of the ‘degree’ of plasticity shown by a clay body and May often be correlated with properties such as specific surface area, dry strength, and rheological behaviour. The plastic limit gives an estimate of the sorptive properties of clays (in this case for water) and may be correlated with other characteristics such as shrinkage on drying (Bain, 1971).

Figure 2. 8 : Clay Identification

(Brain,1971)

2.8 Chapter Summary

This chapter has given brief literature on the existence, occurrence and formation of clay. It has highlighted the types of clay in nature and given the chemical compounds present in raw clay and the ideal percentage of the chemical compounds required of the earth soils to manufacture a stable, strong and durable burnt clay brick. It has also highlighted the benefits of firing of clay bricks as gain in high atomic bondage that leads to high compressive strength, high density, low water absorption, low efflorescence effect. It has given the methods of refining clay to improve on the structure of the raw clay chemically.

CHAPTER THREE:

METHODOLOGY

3.1 Introduction

This chapter provides the methodology that was adopted in order to achieve the objectives. It describes the scope and conditioning of clay in its natural state, process of purifying the natural clay to yield the level of mineral percentage proportionality required for high quality production of clay brick, process of manufacturing bricks.

It further describes the methods of determining the compressive crushing strengths, water absorption, efflorescence ability and classification of bricks in various quality types per regions of Uganda.

 3.2 Study area

Districts in Uganda were divided into four major regions i.e. northern, eastern, western and central. Random sampling was carried out of the districts in each region.  Results were that Mukono was picked for central, Lira for northern, Kamuli for eastern and Kisoro for western. However, Kisoro was later eliminated because it was found to be using stones for construction while the bricks in the area are imported from other places and yet funds had been spent in traversing the place in search for artisan brick making sites.

3.3 Sampling techniques, size and instruments

The choice of burnt clay brick making area depended on getting a brick maker who also had a heap of clay from which he had used partly to make the already burnt clay brick. Such places were identified in Mukono and lira. Unfortunately, there was no brick maker who had clay and bricks in Kamuli. Therefore, there was no basis of comparison however, clay was picked from Kamuli for percentage chemical analysis of aluminium oxide (Al₂0₃), silicon dioxide (SiO₂), iron three oxide (Fe₂O₃) and calcium oxide (Cao) for raw clay.

Three representative samples of burnt clay bricks from each selected brick artisan making areas were obtained following procedures provided in IS- 5454 which states that for lot of 2002 to 10,000 bricks sample size for compressive strength, breaking load, transverse strength, bulk density, water absorption and efflorescence is taken as 5 pieces. However, 50 bricks were picked from each site to cater for possible damages in transit, handling and any eventualities. The burnt artisan local clay bricks were handpicked from artisan brick making places of Mukono and Lira

The clay samples from Mukono, Lira and Kamuli were loaded in sacks for easy transportation. The samples of natural clay and that of burnt clay bricks were durably and clearly labelled and delivered for storage. From the storage the natural wet clay was given two months to dry. After drying, lamped clay was broken into smaller particles and got packed in plastic bottles and delivered to Geology Laboratory of the Department of Geology and Petroleum studies of Makerere University for testing. Artisan clay bricks were packed and delivered to Materials Laboratory of Kyambogo University for testing. Water absorption and efflorescence were carried out on the bricks.

3.4 Artisan brick manufacturing process in Uganda

. The following are the stages in which the Ugandan brick artisans do manufacture the clay bricks: –

1. Visual identification of clay deposits in the area of operation
2. Mining of clay from clay deposits areas and heaping the mined clay.

• Tempering of clay

1. Molding of brick units
2. Drying of molded brick
3. Burning of bricks and cooling

3.4.1 Visual clay identification

They do normally identify clay in lower plain areas of the swamp places as fine grained and sticky soils that get stuck in clothes and difficult to remove when wet but can be scraped when dry.

3.4.2 Clay mining

The selected area for clay mining is first cleaned or un soiled at the top to remove most of the un desirable top soils which is always rich in pebbles and organic matters .Clay is mined by use of hand tools like spades, shovels, hoes and is placed in heaps for some days for it to dissipate the excess water it is mined with. Usually the time allowed is between 3 to 7 days depending on the water content in the clay.

3.4.3 Tempering of clay

Is the converting of the mined clay into homogeneous mix of the desired plasticity by mixing it thoroughly with proper quantities of water? This process is done manually using men. Clay is thoroughly kneaded under feet of men with gradual addition of water till desired homogeneity and plasticity is obtained

3.4.4 Molding of bricks

Molding is the process of making properly shaped bricks units from thoroughly tempered clay. In Uganda molding is done using hand molding. The quality of the tempered clay is made soft so that it can be molded into the required shapes conveniently. The bricks are shaped from tempered clay on a table and then transferred to a leveled prepared ground using a wooden mold to make up green bricks

Figure 3.1: Artisan Method of Brick Molding

3.4.5 Drying of molded brick (green bricks)

On removal from the mold the brick is rested on the largest plane for about 3 days and then changed to the smallest plane for about 4 days there after the bricks are stacked in an orderly format under a shade leaving gaps for aeration. In the shade, is where the green bricks gain strength before they become ready for firing or burning. After gain of strength and drying under the shade, the green bricks are stack in clamp style as shown in the field kiln for burning.

Figure 3.2: Field Kiln Burning of Bricks and Cooling

After stacking the green bricks in a field kiln as shown in figure 3.2, the fuel in foam of firewood or agriculture waste e.g. coffee husks, rice husks, wood dust etc. are fed in the openings created in the field kiln.

The field kilns are either rectangular or square. The sizes of the kiln around Kampala are between 2.1 to 3.0 meters in width and 3.5 to 6.0metres in length. After feeding in either the husks or the fire wood then energized the fire for the firing to take place. At the beginning of firing, the wet grass is placed at the top of the field kiln. The firing time is prolonged until the wet grass at the top is burnt to ash. After the grass has got burnt, the opening in the field kiln are closed by use of mud mortar and the broken bricks, the sides of the field kiln also are covered by the mud mortar to avoid the loss of the heat.

 3.5 Testing procedure

Testing commenced with mineral content analysis of the natural clay from the areas of Mukono, Lira and Kamuli to confirm the percentage natural mineral existence of Al₂O₃, Fe₂O₃, SiO₂ and CaO. The natural clay was there after purified using slurry fractionating method taking advantage of different densities of the natural clay constituents in the slurry.  After clay purification, the purified clay was analysed on the effect that had occurred on its mineral content rearrangement in the clay structure.  Clay units were made from the purified clay using artisan method of moulding and bricks made from raw clay using relative uniform force mould, dried, baked and tested of compressive crushing strength, water absorption and efflorescence. The artisan bricks were also tested for compressive crushing strength, water absorption and efflorescence. Testing was done at Makerere University Department of Geology and Petroleum Studies Laboratory Uganda, Kyambogo University Civil Engineering Material Laboratory Uganda.

3.6 Data presentation

Test results were presented on Standard Test Forms and summarised accordingly as shown in Appendix 1 to give a quicker overview in interpreting results. Further presentations were made in form of figures with representative graphs showing the overall behaviour of the materials.

 3.7 Data analysis

The test results obtained were analysed using Microsoft excel.

3.8 Research approach and design

This research was experimental since different types of clay and baked clay brick samples from different regions of Uganda were taken for laboratory testing to: –

(i). Confirm and analyse percentage of natural mineral existence of Al₂O₃, Fe₂O₃, SiO₂ and CaO and effect of purifying clay on the percentage existence of Al₂O₃, Fe₂O₃, SiO₂ and CaO.

(ii). Know the compressive strength, absorption and efflorescence effects of the artisan bricks and new manufactured building clay units from purified clay to obtain the relationship between the artisan method of manufacturing, and the manufacturing method that involved clay purification.

(iii). Know the purity level /response of clay from different regions of Uganda.

3.9 Analysis for natural and purified clay of the percentage existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO

Samples were tested for percentage existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO in its natural and purified state to determine its conformity to the percentage required to produce the required product for engineering standards that make the brick stable, durable and strong.

3.9.1 Objective

Aluminate (Al₂O₃₎, silicate (SiO₂₎, iron three oxide (Fe₂O₃) and lime (CaO) are the major constituents of the earth that support good making earth brick material. These constituents must be in certain proportionality for safe brick making.  The major objective of the test was to measure the proportionality of the constituents of both in the natural and purified state to ensure the right range of the proportionality of the earth constituents before getting into safe manufacturing of the required product that can stand the test of strength, stability and durability.

3.9.2 Significance

The importance of carrying out the analysis for natural and purified clay of the percentage existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO was to know if the constituents of the clay in the regions selected were complying in the right proportions of the earth that produce the brick that is strong, stable and durable.

3.9.3 Apparatus;

• Grinding machine
• Digester
• Automatic absorption spectrophotometer (Agilent 240FS AA)

Figure 3.3: Automatic Absorption Spectrophotometer (Agilent 240FS AA)

3.9.4 Procedure

(i) The clay sample was put in grinding machine and grounded to the powder form.

(ii) The clay powder was then mixed with aqua regia (mixture of hydrochloric acid and nitric acid) for digest.

Figure 3.4 Aqua Regia (mixture of hydrochloric acid and nitric acid)

(iii) The resultant solution/digest was then fixed to the chambers of the Absorption spectrophotometer (Agilent 240FS AA) for analysis.

3.9.5 Observations

Readings were recorded in standard form and results were expressed in parts per million (ppm) for both natural state and purified state and percentage were obtained as presented in appendix.

3.10 Clay purification

The clay purification was to remove the free sand, coarse particles, organic materials and silt from natural clay and remain with bonded silicon dioxide and have significant increase in the aluminate in the composition of the clay samples after sand, coarse particles, organic matter and silt separated from the clay structure.

3.10.1 Significance

The significance of the purification process was to confirm the clay structure that is good enough for manufacturing engineering products and separate the impurities of clay from pure clay.

3.10.2 Test apparatus;

• Transparent 20 litre bucket
• Closely weaved cloth
• Stop Watch with accuracy of 0.1s and
• Mingling pad (stick)

3.10.3 Test procedure

1. Three transparent buckets labelled A, B and C were used in each test.
2. In bucket B and C natural sample of the same type of clay was placed to approximately occupy 25% of each transparent bucket by volume.

• Water was then topped on the natural clay to approximately filling to 90% of each bucket by volume.

1. The mingling pad was used to stir the clay to mix with water to make uniform clay slurry. Mingling took approximately 30 minutes for brown clay and light grey clay. For dark grey clay it took less than 30 minutes.
2. A third transparent bucket A in each experiment was covered on top with a closely weaved cloth and secured firm with rubber band.
3. The clay slurry in bucket B was poured on top of the secured firm closely weaved cloth on top of Bucket A and the clay trapped on top of the cloth and left to settle and water drip through for 72 hours (3 days).

• The slurry in bucket C was left to settle for 72 hours (3 days) to ensure that the clay structure separates from coarse particles, sand, organic materials and silt. The water on top was siphoned/ sucked off using a clear horse pipe. Data was recorded in a standard form for analysis

Figure 3.5: Slurry Fractionating

3.10.4 Observations

1. The clay that was in bucket C, was left settling and observed to have developed into layers.
2. The top most layer was clear water with floating organic materials

• The second layer from top was smooth on touching and sticky

1. The third layer from top was smooth but not sticky on touching
2. The fourth layer from the top was coarse on touching and rough.
3. The smooth and sticky layer was scooped using hands from bucket C after siphoning/sucking off the clear water and is from which new building units were manufactured and referred as modified units.

• The clay that was poured on top of the closely weaved cloth on bucket A was seen to allow slow dripping of water through the cloth and after three days a suspension was seen as a filtrate and at processes of pouring the slurry on the cloth ,when the coarse materials started appearing onto the cloth ,the pouring stop because the coarse materials are not found to be good.
• The methods used for bucket B and that of C , bucket C method was found to be more perfect because it ensures total separation compared to pouring which can led to mix silt and sticky clay in the process of pouring since the  silt is close to sticky clay in the slurry settling fractioning.

1. The yield of the sticky layer was seen more in brown clay, seconded by light grey clay and was list in dark grey clay.

3.11 Compressive crushing strength test

3.11.1 Objective

Compressive strength test is a mechanical test measuring the maximum amount of compressive load a material can bear before fracturing. The major objective of the test was to measure the maximum amount of load that the materials can carry/bear before fracturing i.e. the artisan brick, made brick from raw clay, modified brick from purified clay and compare their results of bearing capacity/characteristics strengths to see if the purification of the clay increases value in terms of  strength ,stability and durability.

3.11.2 Significance

The test was important in determining the level at which the purification of clay and relative uniform force moulding affects the bearing strength of the products manufactured from purified clay using artisan moulding methods and raw clay using relative uniform force moulding as compared to artisan brick.

3.11.3 Sample preparation

The artisan clay brick samples were obtained from parent source and were ready for testing. The clay units from purified clay were moulded using artisan moulding style; bricks from raw clay moulded using relative uniform force method, dried, and baked before tested.

Figure 3.6: Relative Uniform Applied Force Metal Mould.

Figure 3.7: Relative Uniform Applied Force Metal Mould.

3.11.4 Apparatus;

• Hydraulic compressive testing machine
• Steel measuring tape
• Calculator
• Note book
• Pen

3.11.5 Procedure

1. All the prepared material was assembled in the laboratory.
2. The dimensions of each brick in contact with the bearing surface were taken for each brick.

• The bricks were placed on the bearing plate of the compression testing machine one at a time then the upper plate was lowered by the screw until it touched the brick. All the nobs that allow hydraulic force to be generated were closed and the pumping of the machine was then done to exert force on the brick which was placed between the bearing plate and the upper screwed plate. As the pumping continued a force in kilo newton’s was registered on face plate. The force stopped being generated automatically when the fracture occurred in the brick and a reading was taken.

1. All contact surfaces and crushing forces for each brick were recorded in a standard form to allow calculation of crushing force for each brick.
2. Average crushing force for each type from different regions, manufactured bricks from purified & raw clay and artisan was got for comparison.

Figure 3.1 : Hydraulic Compressive Testing Machine

3.11.6 Reporting

Contact surfaces of each brick to the bearing plates were recorded with corresponding forces readings that caused a fracture.

3.12 Absorption tests

3.12.1 Objective

To determine the classification of the bricks (quality) produced by the artisans and modified bricks from purified clay and the effects of the extent to the bricks undergo during wet conditions (durability) and (weathering).

3.12.2 Significance

• To determine the durability of the artisan modified as related to the standard brick.
• To classify the quality of the artisan, modified as related to the standard brick.
•  To show the input of purifying the raw clay.

.3.12.3 Apparatus;

• Electronic compact scale to accuracy of 0.01gram
• Transparent water container
• Alarm clock
• Note book
• Pen

3.12.4 Procedure;

1. Five bricks from artisan sites, five relative uniform molded bricks and modified made clay units were selected from Mukono and Lira.
2. Each dry baked brick was cleaned of loose sand /clay and were marked 1,2,3,4 and 5.

• Each cleaned dry brick was weighed and the dry weight recorded as M1.

2. After recording the dry weight, all bricks were immersed in clean water for 24 hours After 24 hours of immersion all the bricks were wiped of water and immediately weighed and recorded M2.
3. Average weight for the dry and that of the wet were calculated.
4. From the averages the dry values and the wet values of the bricks, absorption was calculated as :

Absorption= (M2-M1/M1) x100

Figure 3.2 : Electronic Compact Scale to Accuracy of 0.01gram

Figure 3.3 : Dry Brick Being Weighed

3.12.5 Reporting of results

The absorption of the bricks was recorded that lead to the classification of the bricks.

3.13 Efflorescence

3.13.1 Objective

Efflorescence is the migration of salt in a solution form from inner part to the surface of porous material, where it forms a coating.The major objective was to determine the presence of the alkalis in the bricks and the earth material that was used to manufacture the brick.

3.13.2 Significance

The test provided the knowledge of the detection of the alkalis that are dangerous to the building units as they affect the walls and construction at large. This test was important as it measures the resistance of the building materials’ ability to absorb water that would bring dampness in the house and make the plastering of the walls peel off.

3.13.3Apparatus;

• Transparent buckets
• Alarm clock

3.13.4 Procedure

1. Five bricks were selected from each sample and the bricks were labelled bearing the name of their origin.
2. All the bricks were totally immersed in clean water for 24 hours

• After 24 hours all were removed and placed under shade where there was enough air circulation.

1. After two weeks the brick surfaces were observed, to monitor salt migration that had occurred on their surfaces.

Figure 3.4 : Efflorescence Test

3.13.5 Reporting

Appearances of salts on the surface of the on the brick surface were reported.

3.14 Chapter summary

This chapter has given a brief methodology that was adopted to achieve the objective of the study. It has described the scope of work, testing procedures of the mine logy of clay in raw and purified states, methods of refining clay to achieve the objectives, methods of testing for compressive strength, water absorption & efflorescence and manufacturing process of the artisan man in Uganda.

CHAPTER FOUR

PRESENTATION, ANALYSIS AND DISCUSSION OF TEST RESULTS

4.1 Introduction

In this Chapter, the test results obtained through the testing processes were presented in Tables and Figures. Test results analysis was carried out to give the relationship between the findings and the standard construction/material requirements. Explanations have been deduced to give a qualitative understanding between the findings and standard requirements, their impact on the process of purifying natural clay and thus leading to conclusions and recommendations.

4.2 Analysis for Natural Clay of the Percentage Existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO

Table 4.1 presents the results from analysis for natural clay of the percentage existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO with an aim of confirming the natural availability of the required constituents for the adequate formula of the earth soils for the manufacture of quality bricks.

Table4.1 : Results of Percentage Existence of Al₂O₃, Fe₂O₃, SiO₂ and CaO in Natural State

Table 4.2 Percentage sum of Aluminate and Silicon dioxide in Natural Sample

4.3 Analysis and Discussion of Natural Clay of the Percentage Existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO.

A suitable earth for brick making should have various constituents in the following proportions

(i) Alumina

Alimina-Al₂O₃ (20-30) % (Civil seek,2019). If the percentage of alumina is higher than 30 % the brick will shrink on drying and develop cracks. If the percentage is smaller the brick will not be moulded easily and nicely.

The test results as observed from Table 4.1, for alumina is between 0.3 to 1.7% for clay from Lira, between 0.7 to 1.1% for clay from Mukono and between 0.6 to 1.2 % for clay from Kamuli indicating non-compliance for the ideal range of the clay that is mined and used directly for manufacture of bricks

(ii) Silica

Silica- SiO₂ (50-60) % (civil Seek,2019).   However, Federico recommends a silicon dioxide content of between 55-70% as ideal. The total percentage coverage for the silica and aluminate ranges from 75% to 84% by weight of the raw clay materials (Federico, 2005).  Silica exist in two forms that is combined (bonded) as constituent of clay and that exists as free silica (sand or quartz). Silicate is responsible for strength, hardness and resistance to shrinkage and shape of the brick and to a great extent for its durability or long life (Civil Seek,2019). Too much free sand in the brick making earth raises the proportion of silica that makes the resulting manufactured brick brittle and porous.

The test results as observed from Table 4.1 for silica is between 90 to 92.5% for clay from Lira, between 86.1 to 91.2% for clay from Mukono and between 68.4 to 98.7 % for clay from Kamuli indicating non-compliance for the ideal range of the clay that is mined and directly used for manufacture of bricks.

(iii) Lime

Lime-CaO (4) % maximum (Civil seek,2019). Lime makes burning and hardening of bricks quicker and therefore is considered desirable. Lime is not required  to be more than 4% because it causes excessive softening of bricks on heating. Lime and magnesium acts as fluxes. During brick making lime must be present in finely powdered and thoroughly dispersed form. If lime is present in nodules or grains it gets slaked (heated) (civil seek,2019). If a brick is with this kind of lime is used, it gets easily hydrated and causes disintegration of the brick.

The test results as observed from Table 4.1 for lime is between .09 to 1.3% for clay from Lira, between 0.2 to 1.9 % for clay from Mukono and between 0.1 to 0.9 % for clay from Kamuli indicating compliance for the ideal range of the clay that is mined and directly used for manufacture of bricks

(iv) Iron oxide- Fe₂O₃

Iron oxide- Fe₂O₃ (4-6) % (Civil seek,2019). Iron oxide also acts as flux i.e. it lowers down the softening temperature of silica. Iron oxide has an additional function of imparting colour to the brick. The excess of this iron makes the brick too soft during burning imposing a risk of deformation in shape. Lack of iron oxide in the earth affect the final colour of the brick instead the brick may be yellow or light red.

The test results as observed from Table 4.1 for Fe₂O₃ is between 0.5 to 1.5% for clay from Lira, between 0. 6 to 1.8% for clay from Mukono and between 0.4 to 0.9 % for clay from Kamuli indicating non-compliance for the ideal range of the clay that is mined and directly used for manufacture of bricks.

It is also observed in Table 4.2 that the total sum of aluminate and silicon dioxide for eight samples are above the required maximum total sum of 84% and one sample is below the required minimum total sum of 75%. It confirms that the raw clay is impure for use in the making of bricks that is required for stability, durability and strength due to high amounts of silicon in them.

Table 4.3 : Results of Percentage Existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO in Purified Clay

Table 4.4 : Percentage sum of Aluminate and Silicon dioxide in Purified Samples

Table 4.5 : Comparison of Percentage Existence of Al₂O₃, Fe₂O₃ SiO₂ and CaO in Natural and Purified State of Clays of Lira and Mukono

Figure 4.1 Effects of Purifying Clay on Aluminate (Lira clay) in Percentage

Figure 4.2 Effects of Purifying Clay on Fe₂O₃ (Lira clay) in Percentage

Figure 4.3 Effects of Purifying Clay on SiO₂ (Lira clay) in Percentage

Figure 4.4 Effects of Purifying Clay on CaO (Lira clay) in Percentage

Comparison of % Mineral Availability in Natural and Purified Lira light Grey Clay

Figure 4.5: Comparison of % Mineral availability in natural and purified state of Lira light grey clay

Comparison of % Mineral Availability in Natural and Purified Lira Dark Grey Clay

 Figure 4.6: Comparison Availability in Natural and Purified State of Lira Dark Grey Clay of % Mineral

Figure 4.7 Comparison of % Mineral Available in Natural and Purified state of Lira

Brown Clay

Figure 4.8 Effects of Purifying Clay on Aluminate (Lira clay) in Percentage

Figure 4.9 Effects of Purifying Clay on Fe₂O₃ (Mukono clay) in Percentage

Figure 4.10 Effects of Purifying Clay on SiO₂ (Mukono clay) in Percentage

Figure 4.11 Effects of Purifying clay on CaO (Mukono clay) in Percentage

Figure 4.12: Comparison of % Mineral Availability in Natural and Purified State of Mukono Light Grey Clay

Figure 4.13: Comparison of % Mineral Availability in Natural and Purified State of Mukono Dark Grey Clay

Figure 4.14: Comparison of % Mineral Availability in Natural and Purified State of Mukono Brown Clay

In Table 4.3, 4.5 and Figures 4.1, 4.2,4.5,4.6,4.7,4.8.4.9,4.12,4.13and 4.14 it was observed that after purification process, Al₂O₃ and Fe₂O₃ increased in percentage as compared to what existed in its natural state. It was found that the purification process tends to shift the clay to better line state of its alumina and iron oxide as regards the brick manufacturing requirement compared to its state in raw form.

It was also observed that SiO₂ and CaO decreased in percentage as compared to what existed in its natural form. Purification tends to remove the un bonded or free sand (SiO₂)/quartz and CaO tends to disassociate after dissolving and remain as Ca(OH)₂ in the water. This process shifts the high levels of both SiO₂ and that of CaO to low levels which are good in the brick manufacturing. The purification process did not exactly match the constituents as is required for an ideal clay for manufacture of ideal brick but it shifted the  clay to better direction than the raw clay i.e. reducing free sand that would impart to the manufactured brick brittleness and porousness, that calcium oxide that would render the brick easily hydrated and cause disintegration and it made the aluminate increase for better plasticity and increased Iron oxide for lowering down the softening temperature and impart a good red colour.

.

4.4 Presentation, Analysis and Discussion for Compressive Crushing Strength Tests

Table 4.6: Compressive Crushing Tests Results for Artisan Common Clay Brick from Lira

Characteristic strength of artisan clay brick from Lira is 0.63N/mm² as calculated in appendix II

Table 4. 7: Compressive Crushing Tests Results for Relative Uniform Force Applied Made Brick from Raw Clay Lira

Characteristic strength of relative uniform applied force made brick from raw clay Lira is 3.3N/mm² as calculated in appendix II.

Table 4.8: Compressive Crushing Tests Results for Artisan Common Clay Brick from Mukono

Characteristic strength of artisan clay brick from Mukono is 0.38N/mm² as calculated in appendix II

Table 4. 9: Compressive Crushing Tests Results for Relative Uniform Applied Force Made Brick from Raw Clay Mukono

Characteristic strength of relative uniform applied force made brick from raw clay Mukono is 2.62N/mm² as calculated in appendix II

Table 4.10: Compressive Crushing Tests Results for Modified Clay Unit from Purified Lira light Grey Clay

Characteristic strength of modified clay unit from purified Lira light grey clay is 2.0N/mm² as calculated in appendix II.

Table 4.11 Compressive Crushing Tests Results for Modified Clay Unit from Purified Lira Dark Grey Clay

Table 4.12: Compressive Crushing Tests Results for Modified Clay Unit from Purified Lira Brown Clay

Table 4.13: Compressive Crushing Tests Results for Modified Clay Unit from Purified Mukono Light Grey Clay

Table 4.14: compressive Crushing Tests Results for Modified Clay Unit from Purified Mukono Dark Grey Clay

Table 4.15: Compressive Crushing Tests Results for Modified Clay Unit from Purified Mukono Brown Clay

Table 4.16: Comparison of Characteristic Strengths of Lira Bricks.

Figure 4.15: Characteristic Strength Comparison of Bricks from Lira

Table 4.17 Comparison of Characteristic Strengths of Bricks from Mukono

Figure 4.16 Characteristic Strength Comparisons of Bricks from Mukono

Comparisons of the characteristics strengths of both the Lira and Mukono bricks shows that the method of purifying clay and use of relative uniform force applied moulding of bricks increases the characteristic values of the  artisan brick.

It therefore requires purifying clay and use the relative uniform force applied moulding, for maximum characteristic strength production of the artisan clay brick.

If both operations were used sequentially i.e. purify clay then make use of relative uniform force applied moulding, the Lira artisan brick would yield as follows;

(2/0.63)X (3.3/0.63)X0.63=10.5N/mm²

Mukono would yield as follows:-

(5.12/0.38)x(2.62/0.38)x0.38=35N/mm2

4.5 Presentation, Analysis and Discussion for Water Absorption Tests

When clay bricks are subjected to water absorption for classification, class one brick does not absorb more than a sixth (1/6) of its dry weight and class two does not absorb more than a quarter (1/4) of its dry weight (Khann, 2001)

Table 4.18 Water Absorption Test Results for Artisan Bricks from Mukono

(M2-M1)/M1                                          = (3758.76-3337.1)/3337.1

= 0.1264 x100

Water absorbed by the brick                  = 12.64%

First class condition 1/6 of dry weight    =1/6×3337.1

=556.18g

556.18/3337.1                                          =0.1666

=0.1666×100

=16.66%

Water absorbed by the brick is 12.64% less than (16.66%) ,hence the artisan brick from Mukono is classified as class one

Table 4.19: Water Absorption Test Results for Artisan Bricks from Lira

(M2-M1)/M1                                          = (3754.3-3217.4)/3217.4

= 0.1669 x100

Water absorbed by the brick                    = 16.69. %

First class condition1/6 of dry weight      =1/6×3217.4

=536.23g

536.23/3217.4                                         =0.1667

=0.1667×100

=16.67%

Water absorbed by the brick is 16.69 greater than 1/6(16.67) %, hence artisan brick from Lira not classified as class one.

Comparing it with the class two which is ¼ of its dry weight i.e.

1/4×3217.4                          =804.35g

804.35/3217.4                      =0.25

=.25×100

=25%

Water absorbed by the brick is 16.69% less than (25%, hence the artisan brick from Lira is classified as class two.

Table 4.20: Water Absorption Test Results for Clay Unit Manufactured from Purified Lira Light Grey Clay

(M2-M1)/M1                        = 388.6-334.4/334.4=54.2g

=54.2/334.4=0.162

Water absorbed                      =0.162×100=16.2%

First class condition 1/6 of dry weight=334.4/6=55.7

=55.7/334,4×100

=16.66%

Water absorbed 16.2% less than 16.66% hence first-class and shows an improvement compared from the artisan brick.

Table 4.21: Water Absorption Test Results for Clay Unit Manufactured from Purified Lira Brown Clay

(M2-M1)/M1                      =421.54-368.34/368.34

=53.2/368.34=0.144

Water absorbed                  =0.144×100

=14.4%

First class condition 1/6 of dry weight=368.34/6=61.39

=61.39/368.34×100

=16.6%

Water absorbed 14.4% less than 16.6% hence first-class brick an improvement compared from the artisan brick.

Table 4.22 Water Absorption Test Results for Clay Unit Manufactured from Purified Lira Dark Grey Clay

(M2-M1)/M1                                     = 409.58-348.12/348.12

=61.46/348.12=0.177

Water absorbed                                 =0.177×100=17.7%

First class condition 1/6 of dry weight=348.12/6=58.02

=58.02/348.12×100

=16.6%

Water absorbed 17.7 greater than 16.6% hence not first class

Second class condition 1/4 of dry weight= 348.12/4 =87.93

=87.93/348.12×100

=25.25%

Water absorbed 17.7 less than 25.5% hence class two no improvement as compared to the artisan brick.

Table 4.23: Water Absorption Test Results for Clay Units that was Manufactured from Purified Light Grey Clay, Mukono

(M2-M1)/M1                                     =   253.06-223.18/223.18

=29.88/223.18=0.134

Water absorbed                                  =0.134×100=13.4%

First class condition 1/6 of dry weight=223.18/6=37.2

=37.2/223.18×100

=16.6%

Water absorbed 13.4% less than 16.6% hence first-class brick

Table 4.24: Water Absorption Test Results for Clay Units that was Manufactured from purified Brown Clay from, Mukono

(M2-M1)/M1                                       =   318.92-281.72/281.72

=37.2/281.72=0.132

Water absorbed                                       =0.132×100=13.2%

First class condition 1/6 of dry weight      =281.72/6=46.95

=46.95/281.72×100

=16.6%

Water absorbed 13.2% less than 16.6% hence first-class brick.

Table 4.25Water Absorption Test Results for Clay Units that was Manufactured from Purified Mukono Dark Grey Clay

(M2-M1)/M1                                      =   293.76-229.37/229.37

=64.39/229.37=0.281

Water absorbed                                   =0.289×100=28.1%

First class condition 1/6 of dry weight=229.37/6=38.23

=38.23/229.37×100

=16.6%

Water absorbed 28.1% greater than 16.6% hence less compared to the artisan brick

Second class conditions of ¼ of the dry weight 229.37=57.34g

=57.34/229.37×100=25.03%

Water absorbed 28.1% greater than 25.035% the brick cannot be used in construction.

Purification of grey and brown clays improves products made out of them to first class.

4.6 Presentation, Analysis and Discussion for Efflorescence Tests

After 24 hours of immersion in water the bricks were placed in a well-ventilated room in which the monitoring was done for eight weeks. After 8 weeks it was seen as follows: –

Table 4.26 Efflorescence Results on Artisan, Modified and Relative Uniform Applied Force Made Bricks of Mukono and Lira

The efflorescence test results gave an indication that the alkalis present in all the three brick types is not serous and dangerous.

For efflorescence regarded as nil is when there are no noticeable deposits of efflorescence. For area to be less than 10% of exposed area of brick when covered by a thin layer of salt is taken as slight. When the deposits are between 10 to 50% is moderate, when area is 50% or more of the exposed surface but not accompanied by powdering and flaking is heavy but raked serious when 50% and more are powdered and flaked surface is seen.

Observation was made on the units on the artisan and modified and seen that the modified has less coverage of the salt migrations. This is an indication that purification does the disassociation of the alkalis and remains in the water as hydroxides which is good for brick manufacturing since alkalis when incorporated in the earth brick making, results in absorbing Water leading to easy disintegration of bricks.

CHAPTER FIVE:

CONCLUSION AND RECOMMENDATIONS

5.1 CONCLUSION

The objective of this research; to assess causes of poor quality of artisan manufactured clay bricks in Uganda and recommend measures for improvement was accomplished;

• Establish the present manufacturing process used by the artisans in the manufacture of local clay bricks was done satisfactory
• Determine the chemical percentage (Al2O3, SiO2, Fe2O3 and CaO) compositions of clay locally used by the artisans, in manufacturing bricks in Uganda been done well.
• Improve on the percentage chemical (Al₂O₃, SiO₂, Fe₂O₃ and CaO) composition ratios as related to the ideal composition for quality done well through slurry fractionationation
• Recommend the new methods of manufacturing improved artisan clay brick to meet specific characteristics properties of producing durable, stable and strong burnt clay brick been done.

Based on Geological laboratory tests of clay samples in three regions of Uganda, Literature available on the industrial requirement of clay for good ceramic  products, physical tests and laboratory analysis done on the artisan ,modified and relative uniform applied force made bricks ,I deduced the following;

• The chemical percentage for the artisans clay in the three regions are as follows;

Mukono area

Lira area

Kamuli area

• Percentage chemicals can be improved by the Ugandan brick artisan through use of clay slurry fractionation.

Clay slurry fractionation is phenomena in which 25% clay occupies space of vertically placed contained and exposed to air at the top most part of the container. Water of 65% by volume of the container is added and mixed with clay to form slurry and allowed to settle for three days to give deposits of layers of the constituents of clay. From these layer deposits give raise to the second layer from top as chemically improved clay structure compared to the raw clay.

• Established that the artisan method of manufacturing processing of clay bricks do require an intervention of refining clay and moulding using method that employ uniform force application for the artisan to produce the dependable ,durable, stable and strong clay bricks in Uganda.

;

5.2 RECOMMENDATION

• Historical methods of brick artisan manufacturing processes were obtained from three regions of Uganda. It is recommended for clay brick artisans to include raw clay refining before moulding of clay brick for purposes of improving on the clay chemical structure to avoid unbounded sand ,much alkalis little aluminate and iron oxide.
• Change the type of mould used to a mould that impart uniform compaction during manufacturing.
• Ugandan government through its agents to emphasize on artisan clay refining process during clay brick manufacturing and change the moulding style to adopt uniform force applied made style so as to produce good quality clay brick of at least 3.5N/mm² to enable the structure engineers take use of artisan bricks for structural specifications/design..

;

REFERENCES

APPENDIX I:

SUMARRY RESULTS OF LABORATORY CLAY CHEMICAL ANALYSIS

Results for Natural Clay Occurring Minerals

Results for Purified Clay Occurring Minerals

APPENDIX II:

SUMARRY RESULTS FOR LABORATORY COMPRESSIVE CRUSHING TESTS

APPENDIX III:

Calculations for Characteristic Strengths of Bricks

Characteristic Strength of Artisan Clay Brick from Lira

Mean=∑f/n=6.52/5=1.304

Standard deviation (Ϭ)=√(∑(f-f_m)²/n) = √.87212/5=0.42

X-teristic strength=f_m-1.6Ϭ={1.304- (1.6×0.42)}=  0.63N/mm²

Characteristic strength=0.63N/mm²

Characteristic Strength of Relative Uniform Applied Force Made Brick from Raw Clay Lira

Mean=∑f/n=17.3/4=4.3

Standard deviation (Ϭ) =√ (∑ (f-f_m)²/n) = √(1.56/4)=0.62

X-teristic strength=f_m-1.6Ϭ=4.3-1.6×0.62=3.3

Characteristic strength=3.3N/mm²

Characteristic Strength of Artisan Clay Brick from Mukono

Mean=∑f/n=8.07/5=1.614

Standard deviation (Ϭ) = √(∑(f-f_m)²/n)=√( 2.95492/5)=0.769

X-teristics strength=  f_m-1.6(Ϭ ) =1.614-1.6×0.769=0.38N/mm²

Characteristic Strength of Relative Uniform Applied Force Made Brick from Raw Clay Mukono

Mean=∑f/n=16.07/3=5.4

Standard deviation (Ϭ) =√ (∑ (f-f_m)²/n) =√( 9.12/3)=1.74

X-teristic strength=f_m-1.6Ϭ=5.4-1.6×1.74=2.62

Characteristic strength=2.62

Characteristic Strength of Clay Unit from Purified Light Grey Clay of Lira

Mean (f_m) =∑f/n=10.98/4=2.745

Standard deviation (Ϭ ) = √(∑(f-f_m)²/n) = √(∑(f-f_m)²/n)= 0.9173/4 =0.48

X-teristic strength= F_m-1.6Ϭ=2.745-1.6×0.48=2.745-1.6×0.48=2.0N/mm²

Characteristic Strength of Clay Unit from Purified Brown Clay  Mukono

Mean (f_m) =∑f/n=38.25/5= 7.65

Standard deviation (Ϭ )= √(∑(f-f_m)²/n)=   √(12.4676/5)=1.58

X-teristic strength of clay unit from from purified brown clay Mukono=  f_m-1.6 Ϭ

=7.65-1.6×1.58=5.122N/mm²

REFERENCES