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Impacts on materials fall into four categories;
1. Discoloration
2. Material loss3. Structural failure
4. Soiling
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Surface discoloration is the non-uniformity of
colour or hue on the surface of a single concrete
placement. There are no valuation studies or material
inventories from which estimates of the costs of
discoloration can be estimated
However, such costs are probably very small
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A material loss; acid rain is leaving its mark on
buildings, statues and other man-made structures.
Limestone and marble are particularly vulnerable
because acids attack their principal constituent, calcium
carbonate. These reactions produce water-soluble
substances that easily leach out and weaken the
structure.
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Structural failure refers to loss of the load-carrying
capacity of a component or member within a structure
or of the structure itself.
Structural failure is initiated when the material is
stressed to its strength limit, thus causing fracture or
excessive deformations.
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In a well-designed system, a localized failure
should not cause immediate or even progressive
collapse of the entire structure.
Ultimate failure strength is one of the limit
states that must be accounted for in structural
engineering and structural design.
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Soiling is an optical effect (a darkening of reflectance) and
results primarily from the deposition of airborne particulate
matter to external building surfaces
The soiling on the brick consists of a thin but tenacious layer
and follows a fairly regular pattern.
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Material Sensitivity to air
pollution
Stock-at-risk
Brick very low Very large
Mortar moderate to high very large
Concrete low very large
limestone, marble)
atural stone
(sandstone
high (severely affected by SO2) large (especiallyculturally
valuable objects)
Unalloyed steel high (severely
affected by SO2)
very small
Stainless steel very low medium
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Aluminium very low medium
Copper low low
Lead very low low
Nickel and nickel-
plated
high (especially in
SO2 polluted
environment)
very low
Zinc and galvanised
steel
high (especially in
SO2 polluted
environment)
medium
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Acid Rain Since the beginning of the Industrial Revolution soiling and
degradation of buildings in urban areas has been noticeable.
The cause of this has often been attributed to the effects of air
pollution.
The pollutants that form acid rain are principally sulphur
dioxide and nitrogen oxides; both of these are released fromthe combustion of fossil fuels like coal and oil. Since the
Industrial Revolution emissions of both have increased.
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Most structures and buildings are affected by acid
deposition to some degree because few materials are
safe from these effects.
In addition to atmospheric attack structures that are
submerged in acidified waters such as foundations
and pipes can also be corroded.
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It mainly refers to loud and irritating
sound which disturbs the peaceful life.
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Industries
Traffic
Electrical generators
Construction activities
Explosions
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Damages structures by developing
cracks.
High intensity sound can break window
panels.
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These types of stones are commonly used forbuildings and monuments- include granite,
sandstone,limestone, marble and slate.
Reviews have concluded that acid deposition damage
to siliceous stones is negligible, and therefore attention
is confined here to calcareous stones, i.e. limestone,
marble and calcareous sandstones. These have been
extensively used as building materials in Europe.
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The current opinion is that brick is unaffected bysulphur dioxide attack. However, the mortar
component of brickwork is not. Mortar consists of
sand, calcium hydroxide and other carbonate phases.
The primary agent of mortar erosion is acid attack on
the calcareous cement binder
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Portland cement, the major binding agent in mostconcrete, is an alkaline material which is susceptible toacid attack. Potential impacts to concrete includesoiling/discoloration, surface erosion, spalling and
enhanced corrosion of embedded steel. However, for all these impacts (with the exception of
surface erosion) damages are more likely to occur as aresult of natural carbonation and ingress of chloride
ions, rather than interaction with pollutants such as SO2 The main factor influencing the durability of concrete
is the corrosion of embedded steel reinforcement.
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In new concrete, these bars are protected from acidcorrosion by the alkaline characteristics of the
cementitious component of the concrete.
As surface erosion does not affect structural integrity it
has no impact on concrete durability. However, in badly
prepared concrete, when carbonation has already led to
steel corrosion, cracks will develop rendering the
system more accessible to attack by SO2, as thecorrosion products of steel occupy a greater volume
than the steel.
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SHAHAARBAN.P
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