Degradation of inorganic building materials
Ing.Martin Keppert, Ph.D.
Department of materials
engineering and chemistry224 35 45 63
web: http://tpm.fsv.cvut.cz/
degradation (corrosion) agentstemperaturewateratmospheresaltsbiodegradation
degradation of important building materialsaggregates, building stone, mortar, gypsum...concrete
Degradation
of building
materials
gradual, spontaneous, slow process in which material losses own characteristic properties due to environmentcorrosion environment – external agents taking effect on the material (water – ground, rain, surface; temperature, chemicals in soil and air)degradation of material: loss of strength and cohesion, dissolution, appearance..corrosion of construction: lifetime of construction, reparation costs, loss of material, costs due to forced outageprevention of corrosion: selection of material (..concrete composition), protection of construction against aggressive environment
Corrosion actionsphysical caused by physical forces, no chemicalreactions(frost damage of concrete)
chemical chemical reactions of material withenvironments components causing degradation of material(sulphate degradation of concrete)
biocorrosion material is damaged by action of animals, plants and microorganisms and theirmetabolic products; (dry rot)
Corrosion
action
Degradation due
to temperature changes
response of material to temperature chnges:very high temperature (fire): thermaldecomposition of the material„common temperature changes“ by cycling day-night, winter-summer and by sun shining (-20 to 40º C)
Thermal
expansion:
response of material
to temperaturechanges
→ tension
on binder+aggregates
interface
→
cracks
winter summer
loss
of strength
and cohesion, water
attack
to
construction
temperature gradient in construction
temperaturegradient
different
expansionof warm
and cold
parts
of construction
Degradation due
to temperature changes
Degradation due
to water actionwater in building constructions
1.
water
vapor:
component
of atmosphere, everywherehigher
temperature
= higher
possible
absolute
air
humidity
warm
air
may contain more vapor
the
the
cold
onerelative
humidity = degree
of saturation
by vapor
at
given temperature
2. equilibrium
dampness: content
of water
in materialdepends
on: air
humidity, temperature, type of material
is
caused
by vapor
condensation
in materiala) bonded
water
–
adsorbed
on surface
non-moveable, not dangerous, does
not freeze
water in building constructions
2. equilibrium
dampness: content
of water
in materialb) free
water: liquid
in porous
systém of material
origin: vapor
condensation, ground
water, rainmovement
in pores:
up – by capillary
action
smaller
pores
= higher
elevationdown – by gravity
equilibrium
of gravity
and capillaryelevation: cm to 2 meters
above
ground
Degradation due
to water action
freezing-thawing action: ice - 10 % higher volume thanliquid
water
ice
in pores
expandes
and acts
by crystallizationpressure on the
pore
walls
10 ºC -10 ºC
Degradation due
to water action
water is solvent and transport medium for othercorrosion
agents
1. anorganic
and organic
salts2. components
of atmosphere
(CO2
, NOX
, SOx
)3. soluble
components
of material: Ca(OH)2
, CaSO4
.2H2
O
→ chemical
corrosion
water is necessary for life of bacteria, fungi and algae
→ biocorrosion
Degradation due
to water action
Degaration
by
atmospherephysical: abrasion of constructions by particles(dust, sand) in wind
aerosol = dust + water drops → visual damage
Degaradation
by atmosphereCorrosion agents in atmosphere
CO2 natural
occurence
in atmosphere
0,03 %carbonic
acid
–
the
weakest
acid, salts
carbonates
2 2 2 3H O CO H CO+ ↔
1. carbonation of lime
mortars
(+) and concrete
(-)
( ) 2 3 22Ca OH CO CaCO H O+ ↔ +
mortar: + hardeningconcrete: -
reinforcement
corrosion, disturbance
of
equilibrium
composition
of cement binder
CO2 :2. dissolution of carbonatescalcite CaCO3
: limestone, marble, marl, lime mortars
23 2 2 3CaCO H O CO Ca 2 HCO+ −+ + ↔ +
insolublecalcite
waterrain, ground
soluble
(1,6 g/l)calcium
hydrogencarbonate
reversible
process
↔
→ calcite
dissolution
(high
CO2
in water)← calcite
precipitation
(low
CO2
in water, water
evaporation)
Degaradation
by atmosphereCorrosion agents in atmosphere
1.
Nasycení
vody CO22.
Rozpouštění
kalcitu
3.
Odpaření
vody v jeskynia krystalizace kalcitu
23 2 2 3CaCO H O CO Ca 2 HCO+ −+ + ↔ +
Sulphur oxides SO2 a SO3Nitrogen oxides NOX (NO, NO2
, N2
O3
....)
origin: industry, transport, energy
productionacid-forming oxides: forms
acid
with
water
(rain, aerosol)
(acid rain): H2
SO3
, H2
SO4
, HNO2
, HNO3
Ca(OH)2 in concrete
and mortars–
is
neutralized
to salts
carbonates CO32- –
salts
of carbonic
acid
(the
weakest
acid)
are dissolved by other acids:
( )3 3 3 2 22CaCO 2 HNO Ca NO CO H O+ → + +
loss
of strength, dissolution
of limestone
and marl
–
statues, historical
buildings
Degaradation
by atmosphereCorrosion agents in atmosphere
Degradation by soluble
salts
Common ions in pore
solution
in building
materials:Ca2+, Na+,NH4
+
SO42-, Cl-, NO3-, CO3
2-
Origin of salts in buildings:materials component (CaSO4.2H2O in gypsum)dissolved in ground water which attacks constructionsproducts of corrosion by acid rains metabolic products of microorganisms and animalswinter maintenance of roads and pavements
Degradation by soluble
salts: mechanism
1. salt dissolves in waterunsaturated
solution
(unsaturated = water can
dissolve even more salt)2. the unsaturated sollution is transported by
pore system (capillary elevation)3. formation of saturated solution
(saturated – solution with the highest possibleconcentration of salt – e.g. NaCl 360 g/l)→saturation
due
to
water evaporation (summer)
4. further
evaporation
→ crystallization of salt fromsaturated
solution
Degradation by soluble
salts:on surface
A) the
saturated
solution
is
formed
on the
surfaceof construction
→
crystals
are vissible
-
eflorescence
aesthetic problem
–
historical
buildings, frescoes...efflorescence
does
not damage
the
construction
Degradation by soluble
salts:
crystallization
in pore
system
B) saturation
is
reached
in pores of material(close
to surface) → crystals
are formed
in the
pores
(subflorescence)growing
crystals
generate
crystallization pressure –
crystals
press
on the
pore
walls
→ up
to 100 MPa –higher
than
the
material´s strength→
→ cracks in construction, flaking of plaster, disintegration of construction
Degradation by soluble
salts: cyclic
hydration
and dehydration
hydrates: crystals
containing
some
molecules
of waterin structure
specific
expansionvolume
1 g Na2
SO4cm3 g-1
crystals volume cm3
Na2
SO4
0,373
0,373 (100 %)Na2
SO4
.10H2
O
0,683
1,549 (415 %)
Hydration
and dehydration
depend
on humidity of air:in winter
are stable
hydrates, in summer
crystals
without
water. Hydration pressure!
Biodegradation
Biodegradation: bacteria
unicellular microorganismsboth auto and heterothrophicwide range of environments
sulphur and nitrifying bacteria: are everywhere
(water, soil, cattle sheds)
normal
temperature, feed, neutral
pH...acquire
energy
by oxidation
of S and N compounds
→
„produce“
sulphates
SO42-
and nitrates
NO3
-
→ source of soluble salts →
salt degradation
prevention: cleanness, dry, light
heterotrophic organisms → acquire energy by oxidation of organic substances: wood, dust, fabric, paperenvironment: feed, damp, normal temperaturedamages: sap rot – damage wooden construcions
mycelium fibers
grow
in walls
– mechanical damage
metabolic production of organic acids → dissolve
calcite
prevention: fungicides, dry, cleanness – no dust
Biodegradation: fungi
Fungi
Fungi consuming cellulose-
oxidize cellulose and hemicelluloses in wood, textile,
paper etc.dark rot of wood –
wood is darkening; cubic
disintegration, loss of strengthSerpula lacrymans – dry rot fungus
mycelium fruiting
body
Fungi consuming lignin- oxidize ligninwhite rot –
fibrous disintegration –
fibers of cellulose
Trametes
versicolor
Fungi
Biodegradation: algae
autotrophic organisms → production of CO2 → supportdissolution
of calcite
CaCO3
(limestone, mortars)production of organic acid → dissolution of CaCO3
form colour slimy coatings – water structuresalgae growing in pores → expansion and mechanical
damage
Biodegradation: plants
and animals
mechanical damage: growing roots, animals actionin walls
(insects, rats)
animals excrements: hosts bacteria → productionof acids
and salts
→ salt corrosion, dissolution
of calcite
Biodegradation
prevention of all kinds of biodegradation:
dry and light environmentcleannessproper construction – insulation, water drainagemaintenance of building – reduction of groundwater attack, rain in, presence of animals and plants…
Chemical, physical and biological action often works simultaneously and promote each other
Chemical reaction causes physical force(expansion
of its
products)
Bacteria produce aggresive chemicals
Mechanicaly damaged wall is easily chemicaly attacked
The degradation protection has to be complex, againstall corrosion actions
Degradation of building materials
Degradation of building
materials
freezing-thawing and water action – affect allporous building materialschemical degradation – depends on chemicalcomposition of he materialbiodegradation – wood is most sensitive, othermaterials are attacked by biodegradation in damp environment
Degradation of concrete
Physical
degradation of concrete
mechanical damage: flowing water, plants..freezing-thawing damage: depends on porosity
higher water/cement ratio → higher porosity → higher freezing-thawing damage
thermal degradation of concrete:1. decomposition
of hydration
products
(CSH, CAH) (from
200 C)2. dehydration
of Ca(OH)2 (from
500˚C)
→
loss of strengthdifferent thermal expansion of binder and aggregates: cracks
on interface between
bider
and aggregates
Chemical
degradation of concrete
1. kind: dissolution
and leaching
of binder2. kind: chemical
reactions
of binder
with
environment
resulting
to non-binding products (frequently
followed
by efflorescence)
3. kind: chemical
reactions
with
formation
of voluminous products → expansion
All
chemical
corrosion
processes
cause loss
of strength and cohesion
Extreme
cases: disintegration
of concrete4. corrosion of steel reinforcement
Concrete: 1. kind dissolution
and leaching
dissolution of Ca(OH)2 from cement binder in porewater and consequent leaching out of Ca(OH)2
dangerous water: „hungry water“ (soft) – with lowcontent of Ca2+ and other minerals (rain and riverwater)
leaching is dangerous for water and underground structuresprevention – proper waterproofing
reduction of Ca(OH)2 concentration in concrete causesdisruption of equilibrium between components of cement binder → results to decomposition of CSH and CAH hydrates → decrease of strengthdecrease of pH due to lower Ca(OH)2 → damage of steelreinforcementcalcite efflorescence is formed on the surface
Concrete: 1. kind dissolution
and leaching
acid corrosion: reaction of Ca(OH)2 from cement binder with acid components of environment: acids of sulphur and nitrogen (H2SO4, H2SO3, HNO3) from acidrain and biocorrosionCa2+ salts are formed from Ca(OH)2– no binding abilitydecrease of Ca(OH)2 concentration results to disruptionof equilibrium in cement binder and consequentdecomposition of CSH and CAH binderformed salt may be soluble → efflorescence
( ) ( ) ( )odpareni a krystalizace3 3 2 3 22 2 2
Ca OH 2 HNO Ca NO 2 H O Ca NO .2 4H O+ → + ⎯⎯⎯⎯⎯⎯⎯⎯→ −
efflorescence
Concrete: 2. kind formation
of
non-binding
products
carbonation of concrete: reaction of Ca(OH)2 frombinder with CO2 from air or water (water structures)
calcite CaCO3 is formed
decrease of Ca(OH)2 causes:decrease
of pH → corrosion of steel reinforcement
disruption
of binder
equilibriumin extrme cases may start carbonation of CSH
and CAH hydrates
to SiO2
, Al2
O3
→ decrease
of strength
( ) 2 3 22Ca OH CO CaCO H O+ → +
Concrete: 2. kind non-binding
products
concrete
cube
observation of concrete carbonation by phenolphtaleinu: colour change at pH 8-10
no.colour:pH ≈
8
carbonated
concreteno Ca(OH)2reinforcementis
damaged
violet:pH >
10
high
Ca(OH)2OK
Concrete: 2. kind non-binding
products
chemical reactions having voluminous products → are formed and crystallized in concrete and generatedcrysallization pressure – products expansion damagesstructure of concrete: decrease of strength, disintegration
SO42- voluminous
product
on grains
boundariesexpansion
of binder
Concrete: 3. kind expansive
products
sulphate attack
sulphate expansion (gypsum expansion)sulphate attack
on concrete:
ground
water
sea
watersulphates
from
aggregates
sulphides: may by found in aggregates, are spontaneously oxidized to sulphates
test of aggregates on presence of sulphides and sulphates:1. HCl decomposes sulphides to H2 S (smells)2. sulphates are precipitated by BaCl2 as insoluble BaSO4
Concrete: 3. kind expansive
products
sulphate expansionmechanism:
1. formation of gypsum
( ) 24 2 4 22
Ca OH SO 2 H O CaSO .2H O 2OH− −+ + → +
in concrete gypsumvolume + 17 %
( ) 2 2 2 4 221Ca OH SO O H O CaSO .2H O2+ + + →
formation
of gypsum
from
SO2
from
air:
Concrete: 3. kind expansive
products
sulphate expansionmechanism:
2. formation of ettringite
( )2 3 2 4 2 2 2 3 4 23CaO.Al O .6H O 3 CaSO .2H O 19 H O 3CaO.Al O .CaSO .32 H O+ + →
hydrate
C3
AH6from
concrete
gypsum ettringiteexpansion
2,65x
Concrete: 3. kind expansive
products
protection of concrete against sulphate expansion:
prevent from contact of concrete with high-sulpahte watersea structures:
-
cement with
low
C3
A (max 5 %)
-
low
porosity of concrete
(low
w/c)-
adding
of pozzolana (slag) → it
reacts
with
Ca(OH)2
instead
of gypsum
formation
Concrete: 3. kind expansive
products
magnesium expansion1. kind reaction
of soluble
Mg2+
salts
(ground
and sea
water)
with
Ca(OH)2
in concrete
2. kind reaction
of MgO
(v cementu) with water:
slow
process: takes
place
in settled
concrete
( ) ( )+ + → +4 2 4 22 2MgSO Ca OH 2 H O Mg OH CaSO .2H O
voluminous
product
( )2 2MgO H O Mg OH+ →
Concrete: 3. kind expansive
products
chloride corrosionorigin
of chlorides: winter
maintenance
salt, sea
water
CAH hydrates
react
with
chlorides
(NaCl, CaCl2
) toFriedel‘s salt 3CaO.Al2
O3
.CaCl2
.10H2
O (non-binding)1. expansion
of Friedel‘s salt
2. decrease
of strength
due
to decrease
of CAH concentration
salt corrosion: efflorescence and crystallization pressure
Concrete: salt corrosion
sea water corrosionleaching
out
of Ca(OH)2 and decomposition
of CSH
and CAH hydratesreaction
of CAH to Friedel‘s salt
sulphate expansionmagnesium expansioncrystalization
and cyclic
hydration-dehydration
of
salts
in pores
of concrete
prevention of salt corrosion of concretelow
porosity (low
w/c)
low
C3
A in concretelow
Ca(OH)2
in concrete
–
use of blended
cements with
pozzolana content
Concrete: salt corrosion
Concrete: corrosion
of steel
reinforcement
fresh concrete: very high pH (alkaline ≈ 12)steel
is
passivated – layer of Fe(OH)3
protects steel
against
corrosion
carbonated concrete: pH slowly decreases → thepassive layer is destroyed when pH decreases app. to 9,5 → corrosion of reinforcement takes place
loss of contact betweenconcrete and reinforcement
aggregates with high content of amorphousSiO2 (opal, chalcedony) → causes Alkali-silicareaction - ASR
amorphous
SiO2
+ NaOH (KOH)
gel of sodium
silicate
absorbs water→
expansion
Aggregates, stone-cutted products
prevention of alkali-silica reaction1. no amorphous SiO2 in aggregates
maximum content
–
few
percenthighest
content
in river
sediments
(USA, China)
2. reduce alkali content (Na2 O, K2 O) in cement
Aggregates, stone-cutted products
reinforcement protectiongood
concrete
–
no cracks
–
carbonation
starts
in cracksstainless
steel
reinforcement
–
expensive
cathodic protection
of reinforcement
Concrete: corrosion
of steel
reinforcement
Aggregates, stone-cutted
products
aggregates made from magmatic rocks (dominant in Czech Republic):
dense
–
no pores
= no damage
by ice
and waterhigh
chemical
resistance
limestone aggregatescalcite
CaCO3 : attacked
by acid
rains
and by
CO2
dissolution
sandstoneporous
–
sensitive to freezing-thawing
and
water
actionusually
contains
some
calcite
CaCO3
– attacked
by acid
rains
and biocorrosion
Aggregates, stone-cutted products
crust on sandstone: calcite in sandstonereacts with SO2 – in poluted air (cities) →product is gypsum CaSO4.2H2O
dark
colour
-
dust
Aggregates, stone-cutted products
Degradation of materials
based
on calcium
carbonate
CaCO3
calcite CaCO3 is dominant component of lime mortarsand plasters, limestone, marlstoneCaCO3 is dissolved by all acids – both inorganic and organic (acid rains, biodegradation)
mortars with cement – higher corroion resistance
( )3 3 3 2 22
3 2 3 2 2 4 2 2
CaCO 2 HNO Ca NO CO H O
1CaCO H SO O H O CaSO .2H O CO2
+ → + +
+ + + → +
soluble
Degradation of gypsumgypsum = typical air bindersolubility of CaSO4.2H2O: 2,4 g/ldissolves mainly in flowing watersolution of CaSO4.2H2O is acid → steel corrosion
gypsum
can
not be
reinforcedgypsum in wet environment: hydrofobization
(hydrofobized gypsum repels water)thermal stability of gypsum: very lowgypsum
decomposes
from
60 °C, from
120 °C
decomposes
rapidly
to hemihydrate CaSO4
.1/2 H2
O
Degradation of ceramicsceramics: high resistance to thermal and chemical action (dissolves only in HF)physical corrosion: degradation by freezing-thawing action and by salts
resistance depends ongranulometry of raw materials(Winkler diagram)
unfired bricks: sensitiveto flood
Fort Jefferson, Florida
Degradation of glass
weak point - brittlenes
chemical corrosion: glass dissolves in HFand in highly alkaline solutions(cheap
or
old
glass
in dishwasher)
increase of resistivity to alkalies: boiling
of glass
in water
or
acid
–
surface
layer
in enriched
by
SiO2
–
more resistant
to alkalies
Wood
degradationbiodegradation – rot, insectsoscilation of temperature and humidity: causescontraction and swelling → crackschemical degradation: wood is attacked by oxidisingagents, acids and bases → depolymeration and oxidation of cellulose, change of color and mechanicalpropertieswood of coniferous trees is more chemically stablethan wood of deciduouswood protection: fungicides, biocides, fire protection
Degradation of synthetic
polymers
depends on composition of the polymergeneraly: high chemical stability
low
thermal
stability:
softening, melting, burning, thermal
decomposition
UV radiation
(sun) causes
photochemical reactions in polymer –
decomposition
of polymer chain
(embrittlement)
biocorrosion of polymers: organic compoounds serve as nutrient for fungi (rot) and bacteria
Goalsdescribe principals of physical corrosion of building materialsdegradation by water actiondegradation by agressive gassesbehaviour of salt in porous materialsbiodegradationchemical degradation of concrete
6B. Analytical
chemistry
Analytical chemistry in civil engineering
analysis of materialscomposition of cement, lime etc., content of sulfates
in aggregatesenvironmental analysis composition of water: drinking, mixing water for concrete, ground water –
contains dangerous
components for building materialscomposition of soil: contamination by toxics
waste analysis before land fillingrubble composition, contaminated soils (oil, heavy metals Hg, Cu, Pb, Cd…)
Samplingrepresentative sample contains all components of the material in the same ratio as are present in the sampled material
sampling of liquids and gasses: usually homogeny –no problemsampling of solids: the material is crushed, homogenized, quartered
sampler
for
solids
and powders quartering
Chemical
analysisqualitative: composition of sample (elements, ions, molecules)quantitative: determination of concentration of components
conventional: volumetry and gravimetry instrumental: by help of instruments
Volumetry
-
titrationfor determination of concentration of a compound in liquid solutionunknown solution = analytereagent = standard solution of a compound (titrant)principle: analyte reacts with equivalent amount of reagentaccording known chemical reactionendpoint of titration – by visual indicator(point of equivalence)
Volumetry
-
titrationacid-base titration:
for determination of acid concentration by help of KOH reagentacid reacts with a baseendpoint indicated by pH measurement (colourchange of a chemical indicator, pH meter)
2 4 2 4 2H SO 2 KOH K SO 2 H O+ ↔ +
analyte reagent
ACID
KOH
ACID KOH
ACID ACID KOH KOH
KOH KOHACID
ACID
n 12n
1n n21c V c V2
1 c V2cV
=
= ⋅
⋅ = ⋅ ⋅
⋅ ⋅=
Volumetry
-
titration
2 4 2 4 2H SO 2 KOH K SO 2 H O+ ↔ +
Gravimetryanalyte is precipitated by a chemical reaction in form of a known and insoluble productFe3+ ions are precipitated in alkaline environment as insoluble Fe(OH)3
( )33
Fe 3 OH Fe OH+ −+ →filtration, drying,weighing
( )
( )
Fe OH 3
Fe OH 3FeFe
mMnc
V V= =
Instrumental
analysisvarious methods = lot of devicesfast, cheapbased on: a) interaction of species with „light“
b) electrochemistryInteraction of elements (molecules, solid phases) with electromagnetic waves of different wavelengths
VISible
UV IR
Turbidimetrymeasurement of intensity of light passing through a studiedsystem – dust in air, concentration of suspensions
determination of SO42- precipitated as BaSO4
calibration – series of suspensions of known concentrations
Turbidance: I/I0
lightsource detector
Atomic emission spectroscopyEach element can absorb and emit „light“ – energy featuring a characteristic wavelength (UV, VIS)
Wavelength of emitted radiation = identification of elementIts intensity = proportional to concentration
Plasma torch(up to 10 000 K)excitation of atoms decomposition of
emitted light to particular wave-lengths