Green Brick Making Manual
VERTICAL SHAFT BRICK KILN PROJECTCLEAN BUILDING TECHNOLOGIES FOR NEPALGREENBRICKMAKINGMANUAL
VERTICAL SHAFT BRICK KILN PROJECTCLEAN BUILDING TECHNOLOGIES FOR NEPALGREENBRICKMAKINGMANUAL
About this publicationThis publication has been developed as part of the VSBK technology transfer processin Nepal. It gives the reader a more scientific insight into green brick making. Theneed for it is based on the experience which the VSBK technology transfer has hadin India and Nepal. It is intended for individuals who have established or intend toestablish clay brick firing units. The publication is a practical approach and willprovide the reader with “hands-on” experience to improve the quality of the products.AuthorsHeinrich Mueller, Civil Engineer and Senior Technical Advisor to the VSBK ProgrammeNepal, has been working with the VSBK technology over the past ten years.Dr. Soumen Maithy, PhD in Ceramics, working as Senior Material Technologist atDevelopment Alternatives, India and has been associated for many years not onlywith the VSBK technology but in the green brick making sector specifically.Suyesh Prajapati, Mechanical Engineer and VSBK Coordinator at the VSBKProgramme Nepal, associated with the brick sector for over five years.Anil Datta Bhatta, Mechanical Engineer, Technology Transfer Manager at the VSBKProgramme Nepal.Bijay Lal Shrestha, Mechanical Engineer, Senior Programme Engineer at the VSBKProgramme Nepal.CopyrightsThe VSBK Programme Nepal and its collaborating partners in Nepal and Indiareserves all rights and ownership of the original materials, including photographspresented in this document. The readers are free to cite references or make use ofit for non-commercial purpose in course of development work. However the VSBKProgramme regards it mandatory that due acknowledgement be given wheneverthis document is used/cited, and that a copy of any document prepared with theassistance or reference or original text/information quoted from this document besent for inclusion in our resource center.Additional copies can be obtained at VSBK Programme, PO Box 113, Kathmandu,Nepal. Electronic copy can be downloaded from www.vsbknepal.com, www.skat.chISBN 3-908156-12-2Design and layoutkiirtistudio, KathmanduPrintingHillside Press, KathmanduPublication is supported bySwiss Agency for Development and Cooperation (SDC) Nepal, skat Swiss ResourceCenter and Consultancies for Development, St. Gallen, Switzerland and DevelopmentAlternatives, IndiaNepal, 2008ii
CONTENTSPREFACEV1BASIC SOIL KNOWLEDGE FOR BRICK 51.3.61.3.7Introduction . 1Origin and formation of soil . 1Physical weathering . 2Chemical weathering . 2Types of soil . 2Main horizons of soil occurrences for brick making . 2Grain size . 3Grain size distribution of soil and its technical importance . 5Colours of soil . 7Soils of Nepal . 9Chemical properties of soil . 10Additives . 132SOIL TESTING FOR BRICK .6.12.6.22.6.3Introduction . 17Suitability for brick business . 17Visual test . 17Soil reserve calculation . 18Soil sampling methodology . 20Soil test methods . 21Field tests . 21Laboratory test . 26Chemical analysis . 26Physical analysis . 26Pilot scale test . 27Brick bat production and analysis . 27Small scale test production and analysis . 34Full scale production and analysis . 343ECONOMIZATION IN BRICK PRODUCTION3.13.1.13.1.23.2Introduction . 35Production of hollow green bricks . 35Use of cheap internal fuel . 36Brick quality . 361735iii
3.33.43.53.6Energy economisation . 38Environmental effects . 39Determination of internal fuel to be added . 40Cycle of brick business fine tuning . 424GREEN BRICK PRODUCTION 4.6.44.6.54.6.64.74.7.14.8Introduction . 43Soil excavation . 43Best practices of soil mining . 44Soil storage . 45Functions and importance of raw material storage . 46Methods of raw materials storage . 46Season for soil storage . 47Pugging of raw materials . 48An introduction to pugmill . 49Pugging process . 50Moulding . 52The mould and its design . 53Making a wooden mould . 53Releasing agent . 55Moulding area preparation . 55Accessories for moulding . 56Moulding process . 58Drying and stacking . 60Importance of drying . 60Principles of brick drying . 61Factors affecting brick drying . 62Behaviour of a brick during drying . 63Field based tests for determination of drying stage . 65Stacking patterns and its effect on drying . 66Preparation of drying and stacking yard . 68Preparation of stacking base . 68Storing of green bricks . 68BIBLIOGRAPHYiv4371
PREFACEIn most of the Asian countries the art and science of green brick makingis often the most neglected but most important aspect of achievingsystematically good quality fired bricks and other ceramic products.The art of brick making has been kept informally within families andhas been passed on to generations through traditional knowledge. Therehas been no recorded attempt to transfer the art and science of thisaspect of brick making know-how to “outsiders” in a scientific andsystematic way. Therefore, until today, except the practising moulders,many professional brick making entrepreneurs know very little aboutthe best green brick production practices and the reasons thereof.This green brick production manual has been written by VSBKtechnology related professionals with the aim to transfer the knowhow of best green brick production practices, especially for the newVSBK firing technology, to all professionals and brick makingpractitioners who aspire to know more about the HOW and WHY ofgreen brick making. It also deals with the basic knowledge andunderstanding the science of the entire process, from soil selection tomaking a product ready for firing.This manual is divided into 4 chapters. Chapter 1 deals with the basicsof good quality green brick making, meaning the basic know-how ofsoil. Soil differs from place to place and withhin short distances,therefore, entrepreneurs need to know which soil is good and which isnot for brick production in a VSBK, this is eventually fundamental brickmaking know-how. In chapter 2, soil testing methods is described thatprovides useful information about the characteristics of soils. In chapter3, the economisation and fine tuning methods to select the best possiblesoil for the brick business is described in a very practical manner. Andfinally, in chapter 4, the entire green brick making process is describedstep by step.This manual does not claim to cover all aspects of the vast topic of'Green Brick Production', but focuses on providing the basic and practicalunderstanding of correlation between different parameters which arerequired for making a green brick. It provides the why and the how insuch a way that brick making practitioners and professionals willing totake up this profession will understand.v
The more traditional and improved brick making know-how can bedisseminated to the brick production industry the more awareness willbe created to conserve nature and the entire environment, therebycontributing to reduce CO2 emissions and global warming. It is ourendeavour to see that modern brick practicing entrepreneurs andprofessionals adopt the same and support in conservation of naturalresources i.e. soil and coal.The VSBK programme Nepal would like to acknowledge the contributionof Dr. Soumen Maity, Development Alternatives and the VSBKProgramme Nepal engineers, Mr. Suyesh Prajapati, Mr. Anil DattaBhatta, Mr. Bijay Lal Shrestha and Mr. Heini Müller, Senior VSBKProgramme Advisor for writing this manual. Thanks also go toMr. Keshar Joshi for his creative inputs. Without their practical workingexperience, this publication would not have been possible.Thank you.Urs HagnauerProgramme ManagerVSBK Programme Nepalvi
SOIL KNOWLEDGE1BASIC SOIL KNOWLEDGEFOR BRICK MAKING1.1 INTRODUCTIONSoil is a period in a lengthy process of deterioration of the parent rockand its physico-chemical evolution. Depending on the parent rock andclimatic conditions soil appears in an infinity of forms possessing anendless variety of characteristics.It is essential to be aware of the properties of a soil before using it forfurther processing, especially for VSBK technology brick making. Theseproperties fall into the following categories; grai (particle) size and itsdistribution, colour and other physical as well as chemical properties.Many types of soil have been used for fired brick making, includingclay, loam and even materials from anthills and termite mounds. Goodquality clay ensures a strong and durable brick and it must have specificproperties that confer a high degree of plasticity when mixed with water,so that it can be moulded into a brick. In addition, the clay must havesufficient tensile strength to stay within its moulded shape and its deadweight.1.2 ORIGIN AND FORMATION OF SOILThe ground is the solid part of our planet. At its surface it becomes soil- a loose material of varying thickness, which supports vegetation, andbears humanity and its structures. Soil is the result of the transformationof the underlying parent rock under the influence of a range of physical,chemical and biological processes related to biological and climaticconditions and to animal and plant life.The transformation of rocks into soil is termed as soil formation or soildevelopment. Soil formation starts primarily with the weathering ofrocks. The weathering processes are primarily destructive in natureand help to change the consolidated rocks into unconsolidated soil.Weathering processes are of two types:GREEN BRICK MAKING MANUAL1
1.2.1 PHYSICAL WEATHERINGSOIL KNOWLEDGEThis is a mechanical process, causing disintegration of massive rocksinto smaller particles without any chemical change or formation ofnewer products. Physical weathering is caused by the following factors.TEMPERATUREThe alternate expansion and contraction of rocks due to variation intemperature produces cracks. The number of cracks slowly increasesand the rock gets broken into pieces.WATERIn cold regions, water freezes in rock joints and expands in volume.Due to this tremendous pressure the rock splits into a loose mass ofstones. Rain water falling on the rocks also causes some abrasion.Moving water due to rains in rivers and flood plains has tremendoustransport capacity and by its rolling actions further grinds the stonesinto smaller pieces. Water through its erosion forces removes theweathered parts and deposits as fine sand, silt or clay.WINDWind carrying particles in suspension, like sand from rock fragments,when blowing constantly over a rock at great speed exerts a grindingaction whereby the rock gets disintegrated.1.2.2 CHEMICAL WEATHERINGEssentially the origin ofa soil is largely determined by the nature ofthe parent rock, the climate, the vegetationand the topography.Chemical weathering takes place mainly at the surface of rocks withthe dissolution of soluble minerals and formation of secondary products.This is called chemical transformation. No chemical weathering ispossible without the presence of water. The rate of chemical reactionsincreases with dissolved carbon dioxide and other solvents in water.Higher temperatures and humid climates also greatly aid in chemicalweathering. This is the reason for finding a high amount of soil in tropicalclimates.1.3 TYPES OF SOILThe most suitable soilfor brick making comesfrom the subsoil layers.A typical soil profile can be divided into three parts: top soil containinglarge quantities of organic matter; subsoil containing little or no organicmatter; and bedrock, which may or may not be broken down into lumps.1.3.1 MAIN HORIZONS OF SOIL OCCURRENCES FOR BRICKMAKINGA cross section of the ground makes it possible to observe the varioussoil layers.2GREEN BRICK MAKING MANUA L
SOIL KNOWLEDGETop soil : No sampleTop SoilSub-soil : Sample 1Sub-soil : Sample 2Sub-soilSub-soil : Sample 3Bed Rock : No sampleThe subsoil layer is called an Impure Clay Layer containing variousamounts of iron, calcium, magnesium and other ingredients, which areessentially referred to as brick clay. Indeed, the main chemicalcomposition of brick clays are minerals like silica (SiO2), alumina (Al2O3),iron oxide (Fe2O3), lime (CaO2), magnesia (MgO) and alkalis (K2O,Na2O, etc.). Although there are no definitions of ideal composition,changes in the amount of chemicals affects the quality of the fired bricksin a VSBK firing system. Further the presence of some harmfulconstituents like iron nodules (hard reddish to dark brown sphericallumps), stone particles, soluble salts and limestone in the soil has adetrimental effect on the quality of the fired brick.Though the constituents of the soil are necessary for obtaining highquality bricks, practically it seems to be an ideal case because it is verydifficult to get such quality everywhere. For example while examiningthe soil of a brick making site if the required constituents are achievedin one particular soil sample, it may vary with the other sample in thesame area. The different constituents affect the working properties ofclays and can greatly vary even within a distance of metres.Bed RockTo be suitable for brickmaking in a VSBK firingsystem, the basic constituents of soil musthave around 60-70%finer materials i.e. clayand silt and lesser than30% coarser materialsuch as sand.A high plastic clay issuitable for pottery usebut unsuitable for making bricks. Similarly anon-plastic clay is unsuitable for makingfired bricks.The only sure way to determine the feasibility of a particular clay forbrick making is to make the desired product on a trial basis and analyzethe results after firing.1.3.2 GRAIN SIZEThe grain size and its distribution of a soil have a decisive influence onits moulding properties and the resultant fired brick quality. Grain sizerefers to the mean or effective diameter of individual mineral grains orparticles. Grain size is classified as:GREEN BRICK MAKING MANUAL3
SOIL KNOWLEDGESoil that contains particles greater than 2mmis not suitable for goodquality brick making inVSBK technology.CLAYGrain sizes of clay are smaller than 2μm i.e; (0.002 mm).SILTGrain sizes of silt ranges from 2 to 63μm.SANDGrain sizes of sand are greater than 63μm.Niesper (1958) and Winkler (1954); rawmaterial classification diagram showingclay, silt and sand distribution.ABBASuitable for makingtiles or potteriesUnsuitable for qualitybricks in any brick kilnClayPercentclayPercentsiltSilty claySandy clayCMedium suitabilityfor VSBK bricksDCClay loamClaySilty Cclay loamSiltSandy clay loamCDHighly suitable forbricks fired in VSBKBLoamySandsandLoamSandy loamSilt loamSiltBSandPercent sandCLAYClay content in greenbrick increases theworkability and firedstrength, however toomuch ( 70%) deteriorates both the greenand fired brick quality.Clay grains are always smaller than 2μm. They differ from other grainsin their chemical composition and physical properties. In chemical termsthey are hydrated alumina-silicates formed by the leaching processacting on the primary minerals in rock. Physically speaking, clay veryoften assume a platy elongated shape. Their specific surface is infinitelygreater than that of rougher round or angular particles.Presence of a recommended amount of clay is a must in any brickmaking activity. It imparts the workability and green strength in bricks.It also helps in binding the coarser particles with each other during thevitrification process and contributes to achieve the fired brick strength.However too much clay content in any soil reduces the workabilityduring brick moulding and increases the shrinkage rate thus formingcracks during drying of green bricks.4GREEN BRICK MAKING MANUA L
SILTSOIL KNOWLEDGEThe grain size of silt ranges from 0.002 to 0.063 mm. From the physicaland chemical point of view the silt component is virtually identical tothe sand component, the only difference being one of size. Silt givessoil the stability by increasing its internal friction. The films of waterbetween the particles grant a certain degree of cohesion to silty soil.Presence of silt is of utmost importance in brick making. It acts as amediator between sand and clay by reducing the plasticity content andpreventing high shrinkage cracks during drying process. Although itdoes not aid in binding activity, but fills up the gaps between coarsersand and finer clay thus providing a homogenous structure resulting inhigh fired strength.SANDThe grain size of sand is greater than 0.063 mm (63μm). However forgood quality brick making in the VSBK firing system, sand particlescoarser than 2 mm are not suitable. Sand is often made up of particlesof free silica (SiO2) or quartz (polymorphic transformation of silica).The open structure and permeability are typical of sand. Hence waterretentivity of sand is very poor.Sand (lesser than 30%) is also essential in brick making, since it helpsin opening up the fine-clay structure and making it workable for manualmoulding so that the brick making soil does not stick to the hand orto the mould during the molding process. During the firing of a brickit prevents high firing shrinkage thus avoiding firing cracks, warpageand abrupt achievement of vitrification. Since in a VSBK the greenbricks are stacked vertically, the compressive strength of the bricksduring vitrification are vital to avoid any sagging and hence anydeformation of fired bricks during the firing process. An appropriateamount of sand evenly distributed within the green brick providesthis essential strength to withstand the load of brick stacks duringthe vitrification stage.1.3.3 GRAIN SIZE DISTRIBUTION OF SOIL AND ITSTECHNICAL IMPORTANCEThe soil distribution refers to the relative proportion of sand, silt andclay, irrespective of chemical or mineralogical composition. They havea decisive quality influence depending on the selected firing technology.Sandy soils are called coarse-textured, and clay-rich soils are calledfine-textured. Loam is a commonly used terminology defining thetextural class representing about one-fifth clay, with sand and siltsharing the remainder equally. However loam is considered not feasiblefor good quality VSBK brick making since it does not conform to therecommended (30% clay, 70% silt and sand) grain size distribution.Traditional brick making uses the open atmosphere (sun and wind)for drying of greenbricks. Use of sandprevents faster dryingespecially during summer months therebyreducing chances ofshrinkage cracks anddeformation.GREEN BRICK MAKING MANUAL5
SOIL KNOWLEDGEWorkability and drying behaviour of the clay body are especiallydetermined by the content of fractions of less than 2μm. Fine grainedclays generally have high drying shrinkage rates. However, even withineach type of clay the drying parameters varies, depending on the grainsize distribution and mineralogical association.The extent of linear drying shrinkage also depends on the amount ofwater added for homogenization and workability. A freshly mouldedgreen brick shrinks until the added water is evaporated and the particlesof clay body have formed as a stable framework. The addition of sandalone does not result in such a gradation or spread in particle sizes.Raw materials should be added therefore which complements theexisting grain size distribution, e.g. silty loams.If the unfavorable drying properties of clay are corrected merely byhigh sand additions the workability of the clay body will also be adverselyaffected. Therefore, to solve the problem of high shrinkage rates, it isrecommended to add a mixture of various clays or silts, if necessarywith sand additives, to obtain a body with uniformly good properties.The increase in finer fraction grain size distribution on fired bricks shouldalso be noted. An increase in grain fraction of less than 2μm (clayfraction) often produces at the same time higher firing shrinkage therebycreating greater chances of warpage and distortion.As well as the vitrification behavior, the grain size distribution alsoinfluences the strength of products and their frost resistance. Bricksand tiles produced from coarse clays possess lower frost resistanceand lower strength. The properties of clays for brick product, (whichare dependent on grain sizes) are significantly affected by the mixingprocess. Mixing in a pug mill results in a partial homogenization anddensification of clay mineral aggregates and hence an improvement inproperties (compressive strength, water absorption, shape and size,ring, etc.) of the green and resultant fired brick.In general for achieving a good quality of fired bricks, the idealdistribution of grain size in a soil should be as given in the 'Table 1'. Thevalues given in the table below are plotted into the Niesper (1958) andWinkler (1954) raw material classification diagram shown overleaf.TABLE 1. IDEAL DISTRIBUTION OF GRAIN SIZE FOR VSBK BRICKS6S.N.Elements1.Sand2.Silt3.ClayGREEN BRICK MAKING MANUA LSizeRecommended Value2 mm – 0.063 mm20-45%0.063 mm – 0.002 mm25-45% 0.002 mm20-35%
SOIL KNOWLEDGEBClayClaySiltPercentclayPercentsiltSilty claySandy clayCClay loamSandSiltyclay loamSandy clay loamSandLoamysandLoamSandy loamSilt loamPercent sandSiltSuitable areaof clay for VSBKbrick productionASTEP 1Plot the percentage of sand 20-45% on the diagram as shown by lines A.STEP 2Plot the percentage of silt 25-45% on the diagram as shown by lines B.STEP 3Plot the percentage of clay 20-35% on the diagram as shown by lines C.Thus the compositionof 30% sand, 40% siltand 30% clay is at thecross point of line A, Band C. This compositionis ideal for VSBK brickproduction.1.3.4 COLOURS OF SOILSoil colour is a result of various chemical processes acting on soil. Theseprocesses include the weathering of geological material, the chemistryof oxidation-reduction actions upon the various minerals of soil,especially iron (Fe2O3), calcium (CaO) and manganese (MnO2), andthe biochemistry of the decomposition of organic matter. Other aspectsof earth science such as climate, physical geography, and geology allinfluence the rates and conditions under which these chemical reactionsoccur. Soils tend to have distinct variations in color both horizontal andvertical layers. Iron (Fe2O3), gives a characteristic red colour to thesoil, whereas calcium (CaO) gives a whitish colour and manganese(MnO2) provides a black colour to the soil. The characteristic colour ofa soil depends on the amount of mineral present. However, sometimesalso the colour of an individual mineral is masked due to the presenceof high percentage of another mineral. For example a soil with 6% ironcan give a dark yellow colour instead of characteristic red if the calciumcontent is more than 2%.GREEN BRICK MAKING MANUAL7
INTERPRETING SOIL COLOURSOIL KNOWLEDGEColour is also a sign of the mineralogical content of a soil. Iron minerals,by far, provide the most and the greatest variety of pigments in earthand soil (see Table 2). By identifying the possible minerals present in asoil through observing the colour, it is possible to predict the behaviourof the soil during the firing process and the resultant colour andproperties of the fired brick. However only very experienced brickmaking professionals are able to interpret the fired brick quality andbehaviour according to the colour of the soil.TABLE 2. PROPERTIES OF MINERAL AND ITS COLOUR HematiteFe2O3MagnetiteFe3O4FerrihydriteFe (OH)3Iron sulfideFeSSizeColour(1-2 mm)yellow, brownyellow( 0.4 mm)redblackdark redblackHumusblackCalciteCaCO3whiteDolomiteCaMg (CO3)2whiteMagnesiumMnO2blackQuartzSiO2light grayEFFECTS OF COLOUR IN BRICK QUALITYGenerally, in Kathmandu valley, black coloured and pale yellow type ofsoil are found and used for brick making. Black coloured soil has highorganic matter content hence while firing lower energy input is needed.Black soil has a high degree of shrinkage and is likely to crack duringthe drying process if not properly protected. On the other hand yellowsoil requires higher energy input since there is very less organic matterpresent. The drying shrinkage with yellow soil is less compared to black.Therefore, bricks with yellow soil have uniform shape and size.Quality of fired bricks cannot be linked only to the colour of the soil. Italso depends on various factors such as firing process and temperature,grain size, chemical content of the soil etc. Due to its high plasticity,black soil has higher water absorption rate i.e; higher moisture contentthan the yellow soil. Thus bricks with black soil (containing humus1 )will need longer time for drying than the yellow one. Generalizing, onecan say that fired bricks made out of black soil have better colour (cherry8GREEN BRICK MAKING MANUA L
SOIL KNOWLEDGEred) than fired bricks made out of yellow soil. Colour of soil does nothave direct impact on the ring or strength of fired product. But generallyit has been observed that fired bricks made out of black colour soiltend to give better ring than the yellow one. Dark black soil is not verysuitable for brick making, because it contains a high degree of humusand is difficult to mix with water during the clay preparation processdue to its high plasticity and occurrence as hard lumps. They have avery high degree of shrinkage so are more susceptible to cracks duringdrying and even firing process. Red soil colour is du
'Green Brick Production', but focuses on providing the basic and practical understanding of correlation between different parameters which are required for making a green brick. It provides the why and the how in such a way that brick
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