Durability is the ability to last a long time without signifcant
deteriorationFactors Related to Concrete Durability1. concrete
cracks2. High Humidity and Rain3. Freezing and Thawing.
Carbonation!. "ul#ate $ttack%. $cids attack &. "eawater
'()osure*. Chloride and "teel Corrosion+. $lkali,"ilica Reaction
-$"R.1/.$brasionconcrete cracksConcrete, like most materials, will
shrink slightly when it dries out. Common shrinkage is about 1/16th
of an inch in a 10-foot length of concrete. The reason contractors
lace !oints in concrete a"ements and #oors is to allow the concrete
to crack in a neat, straight line at the !oint, where concrete
cracks due to shrinkage are e$ected to occur. Control or
construction !oints are also laced in concrete walls and other
structuresHigh Humidity and Rain0high humidity only don&t a'ect
on concrete durability butwith carbon dio$ide or another acid
content will induce concrete erosion or/and ()T corrosion Freezing
and Thawing0The most otentially destructi"e weathering factor is
free*ing and thawing while the concrete is wet, articularly in the
resence of deicing chemicals. +eterioration is caused by the
free*ing of water and subse,uent e$ansion in the aste, the
aggregate articles, or both.Carbonation by Contact with 2ater-aters
with a . greater than 6./ may be aggressi"e if they contain
bicarbonates, also contains free carbon dio$ide. -ater with this
aggressi"e carbon dio$ide acts by acid reaction and can attack
concrete."ul#ate $ttack0.igh amounts of sulfates in soil or water
can attack and destroy a concrete that is not roerly designed.
0ewage and sea water both contain dangerous amounts of sulfate will
enetrate hardened concrete and attack it by con"erting calcium
aluminates C12 and sulhoaluminates into calcium sulhoaluminates.
The e'ect on the concrete is e$ansion which tears the concrete
aart.3 0ulfate attack is more se"ere at locations where the
concrete is e$osed to wetting and drying cycles, than continuously
wet cycles.3 "ul)hates in the en3ironment4 sulhates can arise from
two main sources in the en"ironment 5 seawater and soil and
groundwater6icroscoic "iew of sulhate attack3 $cids attack concrete
by dissol"ing both hydrated and unhydrated cement comounds as well
as calcareous aggregate. 7n most cases, the chemical reaction forms
water-soluble calcium comounds, which are then leached away.
0iliceous aggregates are resistant to most acids and other
chemicals and are sometimes secifed to imro"e the chemical
resistance of concrete3 Concrete deterioration increases as the .
of the acid decreases from 6./. 7n fact, no hydraulic cement
concrete, regardless of its comosition, will hold u for long if
e$osed to a solution with a . of 1 or lower. To rotect concrete
from such se"erely acidic en"ironments, surface treatments are
often used. Fig. 2: Concrete surfaces with diferent depths of
erosionThere are essentially three ways to im)ro3e concrete4s
resistance to acids1. choosing the right concrete comosition to
make it as imermeable as ossible8. isolating it from the
en"ironment by using a suitable coating1. modifying the en"ironment
to make it less aggressi"e to the concrete.3 "eawater '()osure4
Concrete has been used in seawater e$osures for decades with
e$cellent erformance. .owe"er, secial care in mi$ design and
material selection is necessary for these se"ere en"ironments. 2
structure e$osed to seawater is most "ulnerable in the tidal or
slash *one where there are reeated cycles of wetting and drying.
0ulfates and chlorides in seawater re,uire the use of low
ermeability concrete to minimi*e steel corrosion and sulfate
attack. 2 cement resistant to sulfate e$osure is helful. 9roer
concrete co"er o"er reinforcing steel must be ade,uate, and the
water-cementitious ratio should be lower "alueChloride Resistance
and "teel Corrosion0Chlorides resent in lain concrete :that which
does not contain reinforcing steel; is generally not a durability
concern. 7n reinforced, the aste rotects embedded steel from
corrosion through its highly alkaline nature. The high .
en"ironment in concrete :usually :greater than 18./; causes a
assi"e rotecti"e o$ide flm to form on steel. .owe"er, the resence
of chloride ions from deicers or seawater can destroy or enetrate
the flm.