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Importance of fired bond in determining the pore qualities of structural…
Importance of fired bond in determining the pore qualities of structural clay products
[HEATING]
Clay dehydrates & eliminating hydrating water
[VITRIFICATION]
Structural clay powder melt
--->
Molten
[DIFFUSION]
Molten particle in powder diffuse with each other
--->
Fused phase
flow around the remaining unmelted parties & fill in the pores
[COOLING]
Particles stick together
--->
Glassy bond
[SOLIDIFICATION]
Clay will solidify
--->
Fired bond
Important properties that should be consider in fabricating facing materials
TEXTURE
Produce during shaping step in manufacture
Extrusion
Produce smooth texture (by die-slickened surface)
Produce rough texture (by cutting off thin layer)
Produce distinctive texture (by applying sand
Molding
Produce sand-struck brick texture (by coating mould interior with sand)
Produce water-struck brick texture (by wetting mould interior with water)
Pressing
Lower water content / stiffer consistency
More regular in shaper & sharper in outline
COLOUR
Factors affecting the colours of brick:
selection of raw material of blend
changing maturing temperature
time at maturing temperature
kiln atmosphere (exposure time)
controlled blending
COATINGS
Continuous coating
Sand, coloured salts, clay/sand mixture are spray / rolled onto column surface
Engobes
Mature to semivitreous / vitreous state
Glaze
Matures to glass-like substance
Must resist thermal dimension movement & moisture expansion (by exposing to steam at 1035 kPa), otherwise will form crazed cracks
DURABILITY
Failure
Spalling
Craze cracks
Crumbling & disintegration
Salt crystallization
Poor design practice
Mismatch in movement
Exposure of place in the structure
Saturation coefficient
Ratio of cold absorption to boiling water absorption
Room water absorption = Amount of water brick can pick up
Boiling water absorption = Pores can be intruded only upon force
Lower saturation coefficient = better way to predict durability
Max permissible saturation coefficient = 0.78
Min compressive strength = 21 Mpa
May be errors
Pressure relief concept need qualification
Water absorption
Percentage weight increase after immersing dry sample in water
Two soaking procedures (cold absorption, boiling absorption)
Below 8% => High probability of success
Above 14% => Perform adequately
EFFLORESCENCE
Surface discolouration of brick, occurs during storage of finished brick / after placing in construction
Due to exterior sources
Salt formed by soluble constituents entering the masonry & evaporation of water
Required careful& aggressive cleaning procedures
MOISTURE EXPANSION
Reaction with water vapour
Occurs rapidly in first month
Show reversal on heating 110˚C
CHIPPING
During packaging & transportation to job site
ASTM C216 => allowable no. of chips & extent of chipping
THERMAL EXPANSION
Adequate expansion joints causing breakage of bricks
Value: 4.5 - 9.0 μm/m.K.