ECM 206 CHAPTER 5 Bricks and Masonry Concrete Bricks

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    Types of clay bricks

    Solid

    If holes passing through @ nearly through

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    Properties of clay bricks

    1. Water absorption, Porosity and Suction.2. Density.3. Compressive Strength.4. Efflorescence and Soluble Salt.5. Moisture Expansion.6.

    Thermal Properties.

    7. Resistance to chemical attack.8. Behavior under fire conditions.

    1. Water absorption, Porosity and Suction Water absorption of a clay brick is the percentage of the increase

    in weight of a clay brick when it has been saturated.

    Water absorption of the brick used: in a wall affects the mode of rain penetration through the

    outer leaf of a cavity wall to define the flexural strength used in lateral load design.

    Porosity, water absorption and suction depend on claycomposition, duration and temperature of curing.

    2. Density Solid density depend on clay composition. It varies from 2250 to 2800 kg/m3. Commonly close to 2600 kg/m3. With perforation and frog standard bricks varies from 1.8 kg to

    3.8 kg in weight.3. Compressive Strength

    Compressive strength decrease with increasing porosity and isinfluenced by clay composition and firing.

    It is subjected to creep at normal temperature. Youngs Modulus lies between 5 and 30 N/mm2, Compressive strength is limited by brittle fracture and sensitive to

    flaws associated to:

    a) Large particlesb)

    Fissured formed during shaping

    c) Shrinkage crack

    4. Efflorescence and Soluble Salt Brickwork develop efflorescence of white salt brought to

    the surface by water and deposited by evaporation.

    The soluble salts which may be present in the bricks aresulphates of sodium, potassium magnesium and calcium.

    It is not harmful to bricks and disappears after certainperiod.

    Efflorescence should always be dry brushed away beforerendering or plastering a wall.

    The risk of efflorescence may be reduced by using bricks oflow soluble salts content.

    5. Moisture Expansion Fired brick ceramic exhibit long-term expansion on

    exposure to moist air. Expansion is progressive and continues indefinitely at

    diminishing rate.

    Brick expand on being warmed and shrink when cooled.6. Thermal Properties

    Thermal conductivity is controlled by proportions ofcrystalline and glassy constituents and porosity.

    Higher bulk density has higher conductivity. Rises sharply with increasing moisture content. Coefficient of thermal expansion lies between 5 to 7 x 10-6

    peroC

    7. Resistance to chemical attack Brick ceramic is very resistant to alkalis acids and can

    counter chemicals under extreme conditions.

    Useful in chemical plants e.g. clay pipes for acid affluent

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    8. Behavior under fire conditions It is fired material, the performance under fire generally

    excellent.

    Thermal stresses may produce small spalling in certaintypes.

    Severe fires may cause slight of fusion of exposed faces.

    Perforated has lower resistant.

    Calcium silicate bricks

    Calcium silicates bricks constitute a well established class of buildingmaterial, distinct both from clay bricks or blocks, and concrete

    bricks or blocks.

    The term calcium silicate brick or more correctly known as autoclaved calcium silicate-bonded brick includes sandlime and

    flintlime bricks are produced in a high pressure steam-hardening

    process. Raw material siliceous aggregates, high calcium lime and water. Sandlime described bricks in which only natural sand is used with

    the lime

    Flintlime bricks contain a substantial proportion of crushed f lint.Application Calcium Silicate Brick

    Being substantially similar in application to clay bricks, calciumsilicates bricks are used for an equally wide range of loadbearing

    and non-load bearing structures. All calcium silicate bricks except those that should not used in wet

    condition are resistant to attack by most sulphate salts in soil

    ground water.

    Principles of the process Use of steam under pressure. Principle as the domestic pressure cooker autoclaving. Silica (constituent sand/flint) reacts slowly with hydrated lime

    (Calcium hydroxide) + water Calcium hydrosilicates.

    All the autoclaving time is used up by this reactionresultantcalcium, hydrosilicates envelop each grain of sand more @ less

    completely & form bridges between them.

    An excess of binder would lower the strength.Method of manufacturing

    Sand-cement bricks

    Main material Portland cement and sand. BS 1180:Nov.:1972 specified sand-cement brick according to its

    compressive strength.

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    Engineering bricks

    Very hard, dense and true in shape. Normally impervious and absorb very little moisture and usually

    used for load bearing members.

    In order to qualify as Engineering Bricks, both the required strengthand absorption properties must be obtained and also it must

    attained the standard durability. Engineering bricks was developed in respond to the demand for

    structural material with very high load bearing capacity.

    Dimensions

    Brick sizes may be specified in either or both of two ways. The work size which is the actual size of the brick with allowances

    for manufacturing tolerances.

    Theformat sizes which is the actual sizes + the thickness of themortar joints.

    The standard size used at present are:-

    Work size 215 x 102.5 x 65 mm

    Format size 225 x 112.5 x 75 mm

    (i.e. assuming a 10mm joint)

    Many manufacturers are also able to supply alternative sizes andspecial shapes.

    Frog ... A depression in one (or sometimes both) of the bedsurfaces of a pressed back.

    Arris ... The sharp edge formed by any two surfaces meeting at anangle.

    Head ... The short surface of a brick which may or may not beexposed in a wall.

    Face ... The long surface of an exposed brick, or the exposedsurface of a wall.

    Stretcher brick laid horizontally, flat with the long side of thebrick exposed on the outer face of a wall.

    Header brick laid flat with the short end of the brick exposed. Soldier brick laid vertically with the narrow ("stretcher") side

    exposed.

    Sailor brick laid vertically with the broad side exposed. Rowlock brick laid on the long, narrow side with the small or

    "header" side exposed.

    Shiner brick laid on the long narrow side with the broad sideexposed

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    Applications of engineering bricks

    Internal and external load bearing walls. Load bearing piers and column. Partition walls. Cladding and facings. Foundations

    Perimeter and garden walls. Paving and floorings.

    Manufacturing process

    There are five basic stages in brick manufacture, though many of theoperations are interdependent - a particular brick will follow through

    these stages in a way designed specifically to suit the raw material

    used and the final product:

    1. Winning and storage2. Preparation3. Forming4. Drying5. Firing and cooling

    1. Winning and storage Wining means obtaining the raw material for the brick

    production.

    Clays are mainly composed by silica and alumina. Alumina is the soft and plastic part of the clay. This will readily

    absorbs water, and makes the clay plastic, and melts when

    burned. There 3 types of clay, namely:

    i. Surface clayii. Shaleiii. Fire clays

    The most suitable material for brick making is the clay with30% sand and silt.

    The presence of sand will reduce the shrinkage occurringduring the burning.

    Besides that, the clay also should have sufficient plasticity(after adding water), in order to ease the molding and shaping

    process.

    2. Preparation The clay is crushed to break up large chunks and remove

    stones and ground prior to mixing the raw material.

    Most plants then screen the clay, passing it through inclinedvibrating screens to control particle sizes.

    Bricks Production and Process

    1. .Steam Method Adjust the autoclaving time and steam pressure get the

    performance characteristics.

    2. Pressing Method Used for producing solid and hollow bricks Press in mould using dynamic presshead.

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    3. Forming Tempering, the first step in the forming process, produces a

    homogeneous, plastic mass ready for molding.

    It is most commonly achieved by adding water to the clay ina pug mill (a mixing chamber with one or more revolving

    shafts with blades).

    After pugging, the plastic clay mass is ready to go to theforming step.

    There are three principal processes for forming brick: Stiff-mud process Soft-mud process Dry press process

    Stiff-mud process Also known as EXTRUSION PROCESS or WIRE-CUT PROCESS

    The clay is mixed with just enough water to produce plasticity(usually about 12 - 15% water by weight)

    The clay is extruded through a "die", producing a horizontalcolumn of clay which passes through an automatic cutter

    Cutter-wire spaces and die sizes are precisely calculated tocompensate for shrinkage during drying and firing

    Textures can be applied by die attachments that cut, scratch,roll, brush, or roughen the surface as the column leaves the

    die

    The green bricks are then stacked by hand

    Bricks are stacked with care to allow sufficient airspacebetween them to create even coloring and uniform strength

    during drying and firing

    Most of the bricks and structural clay t iles are manufacturedusing this process, and they are THE HARDEST AND MOST

    DENSE

    Soft-mud process Also called as molded brick or hand made bricks. The clay contains too much water to be extruded (about 20

    - 30% water by weight)

    Instead of extrusion, individual molds (often wood) areutilized, and are lubricated with either oil, water ( it iscalled water-struck bricks) or sand (it is called sand-struck

    bricks) to prevent the clay from sticking.

    If sand is used, grains with a maximum diameter of .5mmare sprinkled on the mold surfaces after being immersed in

    water

    If oil is used, it will be absorbed by the brick and burnedduring firing

    The soft-mud process can be done by hand and bymachine. The hand-made bricks have more specialized,"architectural" shapes.

    There will be three person working together in producingthe hand made bricks. One lumps the processed material

    to a brick-sized volume, another molds and applies sand to

    the clay, and the third washes and prepares the mold for

    re-use.

    In the machine-driven soft-mud process, the bricks don'thave to be touched until they are dried. The bricks are

    more standard and are produced in mass quantities Both soft-mud bricks go into the same dryer, but different

    from the dryer for extrusion (stiff-mud process).

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    Dry press process The DRY-PRESS PROCESS is adaptable for clays of very low

    plasticity (not more than 10% water by weight).

    Instead of wooden molds, the clay is formed with steelmolds and is put under high pressure to create a very

    compact, dense brick. Hydraulic or compressed air-rams generate pressures

    ranging from 3 - 10 N/mm2.

    This process is not as common as the soft-mud and stiff-mud.

    This is because; the bricks achieves more or less the sameresults with the other previous method, but with more

    technology and more money.

    4. Drying

    When wet clay units comes out of mold or cutting machines,they contain about 7 to 30 percent moisture (depending on the

    forming method).

    Before the firing process begins, most of this water isevaporated in dryer chambers at temperatures ranging from

    about 380C to 204

    0C.

    The drying time, which varies with different clays, is usuallyfrom 24 to 48 hr.

    Although heat may be generated specifically for dryerchambers, it is more commonly supplied as exhaust heat fromfiring kilns.

    Heat and humidity must be carefully regulated to avoidexcessive cracking in the ware.

    5. Firing Firing (burning), is one of the most specialized steps in the

    manufacture of brick, requires from 40 to 150 hours,

    depending upon kiln type and other variables.

    Several kilns are in use, the chief types being tunnel andperiodic kilns and the fuel may be natural gas, coal, oil,

    sawdust, propane or combinations of these fuels.

    A periodic kiln is one that is loaded, fired, allowed to cool andunloaded, after which the same processes are repeated.

    In a tunnel kiln, units are similarly loaded on special cars whichpass through various temperature zones as they travel throughthe tunnel.

    The heat conditions in each zone are carefully controlled andthe kiln operates continuously.

    Firing may be divided into six general stages:1. water-smoking (evaporating free water),2. dehydration,3. oxidation,4. vitrification,5.

    flashing, and

    6. cooling. The actual temperatures will differ with the clay or shale.

    However, in general the temperature are:

    water-smoking takes place at temp. up to about 2040C dehydration from about 1490C to 9820C), oxidation from 5380C to 9820C vitrification from 8710C to 13160C

    6. Cooling After the temperature has reached the maximum and is

    maintained for a prescribed time, the cooling process begins.

    For periodic kilns: the cooling period is 48 to 72 hours. For tunnel kilns: the cooling period is more than 48 hours. The rate of cooling has a direct effect on color and besides that

    the excessively rapid cooling will cause cracking

    Therefore, cooling is an important

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    Types of kiln

    There are four basic types of kiln:1. Clamps2. Intermittent Kilns3. Continuous Kilns4. Tunnel Kilns

    Clamps

    Is the centuries old firing method still used for some stock &hand-made bricks

    Formed by building up green bricks, in special close, stackedformations on a layers of fuel @ rough breeze laid on a base of

    burned bricks

    The fuel or breeze is ignited by small fires started in the fuel mixedin the green bricks.

    The clamp is usually left to burn itself out and cool down. Control is dependenton amount of fuel added bricks may vary

    considerably in quality.

    Intermittent kilns

    Are still used for the firing of special bricks and other requirementswhich do not justify large-scale production.

    They are heated by fires in grates in the outer walls the bricksbeing set when the kiln is cold, and temperature gradually raised to

    cover each stage of the firing cycle in succession.

    The kiln then is allowed to cool slowly until the bricks can behandled and withdrawn.

    Continuous kilns

    Consists of a number of chambers connected in such a way that firecan be led from one to another stationary bricks are heated,

    fired and cooled.

    All stages of firing from setting & drying to cooling & drawing cantake place concurrently and continuously in different parts of thesame kiln.

    Fire is made to progress around the kiln by feeding fuel usually coal,oil, or gas to zones via equi-distant openings in the crown.

    The kiln usually consist of 2 parallel sections connected at the ends the chambers form a continuous tunnel.

    When large output is required, OR when even closer control overthe firing is needed, the chambers are built as a series of arched

    structures arched are arrange transversely to the main direction

    of gas flow. Inter-chamber openings are provided to maintain the continuity of

    the system.

    The modern continuous kiln is a highly efficient unit which combinesexcellent quality and large output with economy operation.

    Tunnel Kiln

    Are more recent innovation kiln

    In tunnel kilns it is bricks that move while the fire stay still. The brick will be carried on kiln car, pass along a tunnel through

    preheating, firing and cooling zones.

    The temperatures and track speed are controlled to provideoptimum conditions in each zone and may varied to produce a

    specific functional and appearance quality.

    Are mostly gas or oil fired, although some utilize solid fuel which isnormally fed to the mouths at the top or side.

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    Concrete blocks

    Made of several material but the most common is concrete. Due to the high compressive strength and ease to handling

    individual blocks.

    Assorted in sizes and shapes. The size of a concrete block is specified by nominal dimensions

    Solid concrete block must have at least 75% of its cross sectionmade up of concrete.

    Block having over 25% of its cross sectional area empty is classifiedas hollow block.

    The usual hollow concrete block has a core area making up to 40 to505 cm

    2of its cross section.

    The most common nominal size of standard block is 8 x 8 x 16 in (20x 20 x 40 cm).

    Available as either heavyweight or lightweight block depending onthe type of aggregates used.

    Types of mortar joint

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    Types of brick tie Special shape bricks

    Squint brick

    Radial brick

    Bullnose brick