Building Technology & Materials 1

 A roof is part of a buildingenvelope.It is the coveringon the uppermost part of
a buildingor shelter .
The word also denotes the framing or structure whichsupports that covering.
 The characteristics of a roof are dependent upon the purpose of the buildingthat it covers.
 In mostcountries a roof protectsprimarilyagainst rain.A verandamay be roofedwith
material thatprotectsagainst sunlight.
 Theroof of a gardenconservatoryprotectsplantsfromcold, wind,and rain, but admits
light.
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Roofingmaterial is the outermost layer on the roof of a building, sometimes self-
supporting, but generallysupported by an underlyingstructure. The outerlayer
of a roof shows great variation dependent upon availabilityof material, and the
nature of the supporting structure.
 Thatch
 Shingle
 Asbestos
 GI sheets
 Metal roofing
 Concrete , etc.
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 Introduction
 The name fibro is short for "fibrous (or fibre) cement sheet", more commonly
called"asbestos cement sheet"or "AC sheet".
 It is a building material in whichasbestos fibres are usedto reinforce thin rigid
cement sheets.
 Althoughfibrowasused in a numberof countries, it wasin Australiawhere its
use was the most widespread.
 Fibroin all its forms was a verypopular building material, largelydueto its
durability. The reinforcingfibres involvedwere almost alwaysasbestos.
Asbestos
cement.

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GENERALCHARACTERISTICSOFASBESTOS-CEMENTPRODUCTS*
Group Use Gradeor Type
Processof
Manufacture
Shingles Roofingor Siding Plain, veneered& texturedsurface
Wetmachine, semi-
drymachine
Clapboards Siding Plain& texturedsurface
Wetmachine, wet-
press
FlatSheets
Walls, sheathing,
industrial& residential
construction,industrial
equipment,insulation
Plain, impregnated, integrally
waterproofed
Wetmachie,wet
process
Corrugated
sheets
Roofing,siding,
ornamenal
Plaingraywithdifferentsized
corrugations
Wetmachine, wet
press
Pipe
Waterworks, drainage,
sewage,industrial
processing
3-36-in.diameterup to 13 ft.long Wetmachine
Molded
Products
Industrialpurposes Plain, impregnated Molding

 Chrysotile
 Alsoknownas whiteasbestos chrysotileis a memberof theSerpentinegroup.
 Most flexibleof allasbestosfibres; they can withstandthe fiercest heat but are so softand
flexible
 can be spunand wovenas easily as cotton.
 Crocidolite
 Crocidoliteis knowncolloquiallyas blueasbestos and is a member of theAmphibole group.
 Theneedle-likefibresare the strongest of all asbestosfibresand have a highresistanceto
acids.
 Amosite
 Amositeis alsoknownas brownasbestosand is, like crocidolite, a memberof theAmphibole
group.
 Its harsh, spikyfibreshave good tensilestrengthand resistanceto heat.
 In buildings,amositewas usedforanti-condensation and acoustic purposes; on structural
steelit was usedfor fire protection
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 Man-made rock-likematerial producedby asbestos,
cement and watermixture hardening and further
polymeric overcoating.
 Asbestoscement sheets have higher tensile, bending
and impact strengththan hardened cement pasteor
mortar.
 Asbestoscement sheets are characterized by lower
water permeabilityand higherleaching resistance and
mineralized water resistance than concreteand
Portland cement mortars.
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Characteristics of
asbestos cement flat
sheet
Asbestos cement sheets are
Durable
weatherproof,
freezeresistant
Fireproof
waterproof
Theyseldomneeda repair andthey
are of considerable rigidity.
.
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PhysiotechnicalCharacteristics:
Length, mm 
1750(+15)(-15)
Width, mm 1130(+10)(-5)
Thickness, mm 5,8 (+1,0)(-0,3)
Heightof an average corrugation,
mm
40 (+4,0)(-4,0)
Pitchof corrugation, mm 
150
Bendingstrength, MPa 
notlessthan16,0

Density(volume weight), gcm3

not lessthan1,6
Impactstrength, kJm2 notlessthan1,50
Polymericcoatingadhesionto
asbestoscementsheets, MPa

notlessthan1,0
Surface appearance 
withoutcracks, blisters,exfoliations
Heatresistanceof polymeric
coating
100%within2 hours

 Asbestos Cement Molding Process
This process resembles the method used for formingasbestos
plastic molded products. It is usedfor the manufacture of
shapes and forms whichwouldnot be otherwise possible to
manufacture. Manufacture by this process is limitedto
specialties; it represents only a very small part of the total
output of asbestos-cement products.
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Asbestos Dry Process
 Raw materialsare mixeddry, and spread in an evenlayeron an endless canvas
belt.
 The thickness of the dry stock sheet is greater than the final thickness desired.
 Sprinkled withwaterand compressed between pressure rollersto make it dense.
 The amount of waterused at this point is critical, because insufficient water can
leadto breakage
 The product is removed fromthe belt; and excessive water result in the material
stickingto the roller.
 The lower of these rollers is generallysmooth; the upper roller may be texturedor
contoured to produce a pattern on the finished product.
 Cutterscan be fittedon the rollers andsimultaneously.
 the sheet can be trimmed to its final size and shape.
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 The product is thenremovedfrom the belt,either mechanicallyor by hand, and
stacked on pallets or frames for setting and curing.
 color is applied as a veneeron the exposedsurface. Thismay be done as a dry
addition before or afterwetting the spreadlayer, or it can be sprayedon afterthe
first pressure rolling operation.
 The product tends to have a lower unit strengththanthe wet process products;
onlyrelativelythin products can be made if the operation is to be practical.
 Unless the dry stock is spread evenlywithuniformcontrol, there are apt to be low
densityspots or nonuniformthickness.
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Asbestos Cement Wet Process.
 The raw materialsare usuallyblendeddry, usingany of several common types of
mechanical mixer, andtransferred in weighedbatches to wet mixingtanks
located higher thanthe press.
 Eachweighed batchis sufficient for just one sheet,and its quantitydepends upon
the size, thickness, and densitydesiredfor the product to be made.
 Weighing may be either manual or automatic; the number of wet mixingtanks
required depends upon the mixingtime relativeto the pressingcycle.
 Sufficient water is addedto the batch to form a slurry that will flowreadily; after
it hasbeen properlymixed, it is passedby gravityto the mold chamber of the
press.
 The consistencyof the slurry, particularlyfor large sheets, frequentlyrequires a
quick hoeingin the mold, to aid in the distribution across thechamber.
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 It is compressed to a dense, hard, and homogeneous sheet. The excess water is
filteredout under the pressuressupplied, and a dwell time at these pressures is
required to permit escape of all of the excess water.
 The formed sheetsare usuallyplaced on steel plates and allowed to set and
hardenfor a periodof 24 to 48 hr. Theyare thencured in accordwiththe
standard practice,prior to final trimmingand shipment.
 This process permits some variations in the formand shape of the manufactured
products;e.g., corrugated sheets maybe made directly.
 Their strengthtends to be equal in all directions; theyare not likelyto havesoft or
low-densityareas. The operation can be shut down without loss of rawmaterials;
however, some material lossesoccur throughfiltering.
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Wet sheetof asbestos-cementis cut fromtheaccumulator drumof a
Hatschekmachine prior to continuing on a conveyor to be made into
building boards, etc.
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ADVANTAGES DISADVANTAGES
Longerlife if properlyfitted .
Less noise fromheavyrain and thermal
movements.
More attractive
Better thermal insulatingproperties.
Rigid& Durable
Non corrosive, fireproof.
Leak proof.
Acoustic insulation
Theyareheavier,thusit ismoreexpensiveto
transportandrequiresa strongerroofstructure.
Brittlenesscausesa highrateof wastedueto
breakageduringtransportandinstallation..
Labourintensivedueto weightandbrittleness.
Thecornersof thesheetsmustbe mitredpriorto
fittingandholesforthefixingscrewsmustbe
drilled.
Easilydiscolorswithdustandalgae.
Themanufacture, processing& discardingof
asbestosproductspresentshazardsto health.
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WIDTH SIZE(MM) COVERINGWIDTH METRIC
WIDTH
OVERALLWIDTH 1.05M 1 1.05
COVERWIDTH 1.01M 2 2.06
COVERINGEFFICIENCY: 3 3.07
(ALLOWINGENDANDSIDELAPS)3.0M LONGSHEETS 91% 4 4.08
ACTUALCOVEROF SHEETLAID: 5 5.09
(ALLOWINGENDSIDELAPS)3.0M LONGSHEETS 2.88SQ. M 6 6.1
20 SQ. M OF LAYINGAREAREQUIRESSHEETING 7 7.11
(ALLOWINGSIDEANDENDLAPS) 8 8.12
WITHSHEETOF 3.0M LENGTH 10.77SQ. M 9 9.13
MAXIMUMPURLINSPACINGFOR ROOFING: 1.4 M FOR 6M 10 10.14
MAXIMUMOVERHANGAT EAVES 0.3M FOR 6 MM 20 20.24
MAXIMUMRAILSPACINGFORSIDECLADDING 1.7 M FOR6 MM 30 30.33
HORIZONTALLAP AT PURLIN 150MM 40 30.33
SIDELAP 44MM 50 50.53
COLORAVAILABLE NATURALGREY

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Building Technology & Materials

 What is asbestos made up of?
 What canasbestos be usedfor?
 What are the properties of asbestos?
What is asbestos sheet?
 Is the asbestos flammable?
DrawFixing details of Asbestos sheet
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 B.C. PUNMIA
 HTTPS://EN.WIKIPEDIA.ORG/WIKI/ASBESTOS_CEMENT
 WWW.VARDHMANROOFING.IN/
 WWW.EVERESTBUILDINGSOLUTIONS.COM/ROOFINGSOLUTIONS.PHP
 WWW.ANANDSALES.IN/ASBESTOS-CEMENT-SHEETS.HTML
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