Degradation of inorganic building materials

Ing.Martin Keppert, Ph.D.

Department of materials

engineering and chemistry224 35 45 63

keppert@fsv.cvut.cz

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