Chemistry of building materials

Martin Keppert Department of materials engineering and chemistry

224 35 45 63

martin.keppert@fsv.cvut.cz

Lectures

7. aggregates, air binders

8. Hydraulic binders – Portland cement

9. ceramics, glass

10. metals

11. Natural and synthetic polymers

12. Deterioration of building materials, analytical chemistry fundamentals

7.A Earth, rocks, aggregates

Earth crust 5-100 km

Kůra

Plášť

Vnější jádro

Vnitřní jádro

Core (Fe+Ni, dense metals)

Mantle (silicates, light metals)

Litosphere (crust + upper mantle 100-180 km)

„floating“ tectonic plates (mm/year)

Astenosphere – plastic 100-150 km

Tectonic plates and their relative movement (mm/year)

Tectonic plates

Rift: two plates pull apart, new crust is formed by volcanos; Afraican rift valley (Victoria lake), Mid-ocean ridges

Subduction: oceanic plate moves under a continental (Andes, Japan)

Collision of two oceniac or continental plates: Himalayas, Mariana Trench

Earth crust

continental: 25-100 km Granitic, sediments ocean: 5-10 km Basaltic, sediments

Elementary composition of earth crust: Compounds of Si, O, Al and other elements: quartz (SiO2) Silicates (salts of „siliceous“ acid

Geology cyclus V

olc

an

ic p

ro

cesses:

ingenio

us r

ocks

cry

sta

lize fro

m m

agm

a

Weathering of rocks due to action of surroundings (water, atmosphere, organisms) – finer particles, chemical alterations

Sedimentation of weathered particles, compaction, solidification: Sedimentary rocks

Transport of weathered particles – water, wind

Metamorphosis: action of high temperature and pressure on ingenious and sedimentary rocks – recrystallization to sedimentary rocks

Weathering of rocks

Water: mechanical deterioration solvent bacteria, higher plants Wind: transport of particles

Mechanical – desintegration of rocks to particles Chemical – change of chemical structure of rocks

Rocks and minerals

Rock = mixture of minerals; specific size and orientation of minerals crystals

Mineral = single chemical compound with defined crystal structure

Mineral: calcite CaCO3, trigonal crystal lattice

rock: marlstone

calcite CaCO3

quartz SiO2

Clay minerals

Ingenious rocks

Crystalized (solidified) magma Contain quartz and feldspars (silicates with Al, Ca, Na, K) Hard, strong, chemically stable Production of crushed aggregates

plutonites Slow crystallization - Large grains - High content of SiO2

- „acid“ - High viscosity of melt granite

Effusive ingenious rocks Fast crystallization - - Fine grains - lower content of SiO2

- „base“ basalt

Compounds of silicon and oxygen Quartz, silicates

Silicates –salts of silicic acid

Fundamental structure unit: anion [SiO4]4-

Si O

O

O

O tetrahedrons SiO4 form – usualy with other elements – structure of silicates, feldspars, clay minerals…

Other elements: Si4+, Al3+, H+, Na+, K+

H4SiO4

-

-

- -

Quartz SiO2

SiO4 tetrahedron

many varieties – due to impurities (coloured oxides)

tetrahedrons SiO4 are fully connected

Quartz SiO2

frequently present in many ingenous, sedimentary and metamorphic rocks hard – provides hardness also to the rock – due to strong bond Si-O high chemical stability – high resistance to weathering

aggregates with quartz are not appropriate for thermaly loaded concrete

Thermal instability

α-quartz β-quartz β-tridymite 573º C 870º C

0.378 cm3 g-1 0.395 cm3 g-1 0.442 cm3 g-1

specific volume increase – fracture of material

molten SiO2

1705˚ C

0.48 cm3 g-1

Molten state or glass

Fragment of crystalline structure: start of crystallization or imperfect melting

anisotropic isotropic

raw material for glass and porcelain production

quartz sand (SiO2 > 99 %, Fe2O3, Al2O3) – buildings,

cheaper ceramics, forms for metals casting

Pure quartz SiO2 – sources and utilization

Opal and chalcedony – dangerous forms of SiO2

Dangerous for concrete – alkali-silica reaction

Chalcedony – microcrystalline SiO2

Opal – hydrated amorphous SiO2

SiO2.nH2O

Feldspars

large group of rocks-forming minerals chemicaly: dual silicates (e.g. potassium aluminum silicate)

Formal formula: composition given ”in oxides”

feldspar is not a mixture of oxides!!

sodium Na-feldspar Na2O.Al2O3.6SiO2 mineral albite

calcium Ca-feldspar CaO.Al2O3.2SiO2 mineral anorthite Found in earths crust – mixed feldspars

potassium K-feldspar K2O.Al2O3.6SiO2 mineral orthoclase

Feldspars – sources and utilization

occurence – feldspars are present in most of ingenous rocks

any deposits of pure feldspar – only in mixtures with quartz and other minerals

ingenous rocks with high content of feldspars are used as raw materials in ceramics industry → flux component

melting temperature of feldspars 1100 – 1500˚ C

glass industry – feldspars are cheap source of Al, K, Na, Ca

Clay minerals

laminated alumino silicates product of feldspars weathering contain bound water very fine particles with water – plastic after firing – hard, sintered

kaolinite, illite, montmorilonite..

10 μm

kaolinite Al2O3.2SiO2.2H2O

Laminated structure: layers are sliding → plasticity

Firing destroys the laminated structure high sorptivity for liquids and gases

kaolinite

Clay minerals

Laminated structure – swelling due to water

incorporation between layers → volume expansion (10x) →

sealing

Clay minerals

Bentonite (mainly mineral montmorilonite)

dam

coarse aggeragtes

Sedimentary rocks

Clasification according origin: clastic, biochemical, chemical

Clastic sediments – sedimentation of fragments of weathered rocks transported by water or wind to a new place (e.g. seabed)

consolidated clastic sediments: sandstone, conglumerates grains consolidated by a matrix – clay, quartz, carbonates used as decorative rocks, earlier as construction material

Non-consolidated mixtures of clay minerals and coarser particles: clay, soil, sand – according to particles size

Highly diversified group

Soil texture classification

Clay: size < 2 um Silt: 2-50 um Sand: 50 um – 2 mm Gravel: > 2 mm

Sedimentary rocks

biochemical sediments – sedimentation and alteration of organismsm limestone main components CaCO3, usually white-gray

sedimentation of mollusc shells Production of lime, metalurgy, aggregates Sensitive to acid action and CO2 - dissolution

Cement stone – limestone impured by quartz and clay – cement Coal, crude oil organic sediments – energy phosphorites sedeiments with high content of phosphates – bones, teeths and birds and bats guano

Chemical sedimentary rocks (evaporites)

salts (oxides) precipitate on the seabed during evaporation (concentration) of sea water magnesite: MgCO3 refractories gypsum: CaSO4.2H2O production of gypsum-based binders iron ore, halite (NaCl)...

Metamorphous rocks

recrystallized ingenous and sedimentary rocks

gneiss variable group of metamorphous ingenous rocks (quartz and silicates)

slate metamorphous clay minerals – laminated structure

platy parting – roofing

Marble

= recrystallized limestone (CaCO3)

good workability

low chemical resistance

Greece, Italy

Aggregates

filler in concretes and mortars

natural x artificial x recycled

gravel (sediments) x crushed (compact rocks)

Production of crushed aggregates

Kuželový drtič

grading

mining

crushing

jaw crusher

cone crusher

Ligth artificial aggregates

thermally expanded clay

clay with small coal particles – firing – coal burns – flue gas causes foaming – low bulk density

ceramics..

1. clay mining 2. pilling 3. clay granulation 4. firing at 1100˚ C

5. Product: porous particles (low bulk density → thermal insulation)

sintered surface

clay

aggregates

fuel

rotation

Rotary kiln

Foto M. Vavro, 2007.

Recycled aggregates Wastes from building industry

recycling of debris – crusing and grading

graded debris – aggregates in concrete, embankments, backfills

risk – ensuring of constant properties

7B. Binders (cements)

binder: matter which – after mixing with water – provides paste with binding and setting ability

fast setting and hardening

non-hydraulic (air) binders: set only in contact with air work and keep properties (strength, cohesion) only in dry environment

lime gypsum Sorel cement

hydraulic binder: works also in wet environment and in water

portland cement, mixed cements, hydraulic lime

Chemical composition of matters

Elementary composition CaCO3 = Ca + C + 3 O

wCa= 40 hm. % wC= 12 hm. % wO= 48 hm %

”in oxides” CaCO3 = CaO.CO2

wCaO = 56 hm. % wCO2 = 44 hm. %

Phase compositions

CaCO3 calcite

wcalcite= 100 hm. %

Cement notation

Symbols of oxides present in inorganic binders:

C CaO S SiO2

A Al2O3

F Fe2O3 H H2O

M MgO T TiO2

N Na2O

K K2O

SO3 S

C CO2

CaCO3 CC CaO.CO2

CH Ca(OH)2

Non-hydraulic binders

• (air) lime

• gypsum

• Sorel cement

• water-glass

Lime...

EN 459 Building lime

(Air) lime Hydraulic lime

Hydraulic lime (with

added pozzolana)

Natural hydraulic

lime

(white) lime

Dolomitic lime

quicklime (burnt)

CaO

slaked Ca(OH)2

quicklime CaO+MgO

slaked Ca(OH)2

Mg(OH)2

Lime – raw materials

Various ”limestones” – sedimentary rock (shells) with high content of CaCO3 limestone 80 – 100 % of calcit (CaCO3)

production of lime, chemical industry, metalurgy, paper cementstone contains 75-80 % CaCO3 and 20 % of clay minerals Portland cement production dolomite limestone 50 – 90 % CaCO3 10 – 50 % CaMg(CO3)2 production of dolomitic lime

Limestones in Czech Republic

Jirásek, J., Sivek, M.: Ložiska nerostů. Ostrava: MŠMT ČR & Vysoká škola báňská – Technická univerzita Ostrava, 2007.

vápenka Kotouč Štramberk

continuous process

1. limestone crushing (15 cm)

2. mixing of limestone and coke

3. calcination

4. cooling of CaO

3 2CaCO CaO CO CaCO3+coke (coal)

900-1

250

º C

CaO

CO2

coke oxidation: C+O2→CO2

air

Calcination of limestone shaft furnace with direct heating

Calcination of limestone shaft furnace with direct heating

Calcination of limestone shaft furnace with indirect heating

burnt lime (CaO)

Influence of calcination temperature

< 1050 ºC burnt lime: high porosity

high specific surface

fast rection with water

binder in mortars and plasters

>1050 ºC overburnt (dead lime)

lower porosity slow reaction with water production of AAC (autoclaved aerated concrete)

Slaking of CaO to Ca(OH)2 (binder)

slaking = exothermic process

2 2CaO H O Ca OH 65 kJ / mol

1.wet slaking – water surplus; slury of Ca(OH)2 in its saturated solution past, directly at building site

100 kg CaO+300 l water

2. dry slaking – by stechiometric amount of water (1:1)

product – dry powder Ca(OH)2

reaction heat evaporates the surplus water performed directly after calcination lime slurry is prepared

from Ca(OH)2 at building site - production of dry ready-mix mortars and plasters

Dry slaking of CaO to Ca(OH)2

CaO H2O

Ca(OH)2 powder

Lime – setting and hardening

1. start: slurry of Ca(OH)2

2. setting: part of water is dried and absorbed by masonry

3. hardening: carbonation of Ca(OH)2 to calcite

2 3 22Ca OH CO CaCO H O

setting accelerators: proteins – cottage chees, eggs setting retarders: sugar

Lime cycle

CaCO3 → CaO + CO2

CaO+H2O → Ca(OH)2

Ca(OH)2 + CO2 → CaCO3 + H2O

Application forms of slaked lime

dry powder – easy to handle and transport, for ready-mix mortars lime slurry – slurry of Ca(OH)2 in water (1:1) –

time improves the plasticity whitewash – very watery slurry (5-10%) – sugar

production, water treatment, facade painting limewater – clear saturated solution of Ca(OH)2 in

water – 0,2 g/100 g water (0,2% solution) – consolidation of hisorical plasters

Lime - utilization

lime slurry

lime plasters and mortars (+aggregates), stucco

+plasticity

- air binder→lower resistance to water action

Purely lime mortars – historical buildings Nowadays plasters and mortars: Lime + Portland cement

Historic lime kilns

pile

Shaft kiln

Hoffmann kiln - circular Třemošnice

Gypsum

Egypt mortar: mixture of gypsum, lime and

limestone aggregates

Gypsum – raw materials

natural gypsum-dihydrate CaSO4.2H2O

mining

CaSO4.2H2O → CaSO4.1/2H2O + 3/2 H2O

production – dehydration (calcination)

hydration - setting

FGD gypsum flue gas desulfurization – from coal power plants by-product of some chemical procsses (e.g. phosphorus fertilizers, titanium white TiO2)

Flue gas desulfurization gypsum

2 3 2 2 4 2 21SO CaCO O 2 H O CaSO .2H O CO2

Sub-bituminous (brown) coal, lignite: cca 1 % of sulfur

Production of gypusm-hemihydrate

Dehydration of dihydrate:

4 2 4 2 231CaSO .2H O CaSO . H O H O

2 2

a) to hemihydrate: 110-150º C

hemihydrate

b) to anhydrite: over 180º C

4 2 4 2CaSO .2H O CaSO 2 H O

anhydrite

α and β-hemihydrate

α-hemihydrate

-dehydration in a closed vessel (115-125º C) -evolving steam creates overpressure -large crystals

4 2 4 2 231CaSO .2H O CaSO . H O H O

2 2

β-hemihydrate

-dehydration at atospheric pressure (110-125º C) -irregular, porous crystals

Production of

β-hemihydrate

4 2 4 2 231CaSO .2H O CaSO . H O H O

2 2

110-125º C, hot air

Gypsum setting

hydration of hemihydrate to dihydrate:

4 2 2 4 231CaSO . H O H O CaSO .2 H O

2 2

1. hemihydrate dissolves in mixing water 2. crystallization of dihydrate from solution 3. growing crystals are creating a „mesh“→ setting

4. drying out of surplus water - hardening

8 min 24 min 60 min

α and β-hemihydrate

α-hemihydrate: higher strength, slower setting

β-hemihydrate: lower strength, faster setting

Gregerová, M.: Petrografie technických hmot. Brno: skripta PřF MU v Brně, 1996. 139 s.

9,6 MPa

7,0 MPa

Degree of hydration Compressive strength

w/g=1

Gypsum binders

fast setting gypsum

initial setting time 2 min, final 15 min

mixture of α and β-hemihydrate

calcination 110-150˚ C

1. construction gypsum: more β (dry wall, electrical wiring)

2. stucco: α + β hemihydrate

3. moulding gypsum – α hemihydrate – ceramic moulds

Production of gypsum plaster boards (dry wall)

1. production of hemihydrate

2. mixing of hemihydrate α and β, cellulose fibers (higher toughness), starch (better adhesion between paper and gypsum)

Mělník

Gypsum renders

interior renders

+ single layer (fast), regulují klima v místnosti

MS – gypsum, MVS – lime+gypsum

gypasum:lime:sand = 1:1:3

slow setting gypsum - anhydrit

initial setting 20 min, final 10 – 40 hours

calcination 800 – 1000 ˚C

80 % anhydrite, rest CaO and hemihydrate

application: lité podlahy, omítky

Gypsum flooring

selfleveling flooring

4 2 4 2CaSO 2H O CaSO .2 H O

Anhydrite CaSO4 (slow-setting gypsum)

production - calcination 200-800˚ C

higher calcination → slower setting

setting – hydration to dihydrate – very slow

4 2 4 2CaSO 2H O CaSO .2 H O

selfleveling flooring

Gypsum drawback: small resistivity to moisture

due to relatively high solubility - 2,4 g/l

suitable only for dry interiors

hydrophobization of building materials: inorganic materials are hydrophilic (concrete, bricks, gypsum, stone…) hydrophobization = decrease of wettability by organosilans

octyl-tri-ethoxy-silan

hydrophylic part hydrophobic part

Hydrophobization

hydrophilic hydrophobic

material's surface

octyl-tri-ethoxy-silan

Sorel cement (magnesium cement)

1867 Sorel: mixture of MgO and solution of MgCl2

raw materials:

caustic magnesia: MgO thermal decomposition of MgCO3 (magnesite)

700 800 C

3 2MgCO MgO CO

solution of MgCl2 (15-30 %) from sea water or mineral carnallite (KCl.MgCl2.6H2O)

MgO + MgCl2 2:1 to 8:1 + up to 18 shares of water

setting:

2 2 2 22xMgO MgCl y x H O xMg OH .MgCl .yH O

x=3-5 y=7-8

high binding ability fast increase of strength (60-100 MPa) filler: wood particles (saw-dust, chips), sand

non-hydraulic binder – soluble in water

Sorel cement (magnesium cement)

heraklith – old thermal insulation – wooden chips in Sorel cement inflammable

xylolite – flooring based on Sorel cement saw-dust s filler, impregnation by oil

protect wood against rotting

Sorel cement (magnesium cement) -

utilization

Water-glass

production:

1. as a „normal“ glass – melting of soda ash Na2CO3 or

potash K2CO3 with glass sand (SiO2) at 1200-1400˚ C and dissolving of prepared glass in water (high temperature and pressure)

2. disolution of glass sand in boiling concentrated solution of NaOH(KOH)

2 3 2 2 2 2Na CO n SiO Na O.nSiO CO n=2-3,3

2NaOH + n SiO2 = Na2O.nSiO2 + H2O

Water-glass

Soluble sodium or potassium silicate (Na2O.nSiO2, K2O.nSiO2) hardening: by an acid action (e.g. CO2 from air) – gel of H4SiO4 → binder

utilization: consolidation of historical masonry, refractory concrete, eggs conservation

Na2O.nSiO2+H2O+CO2 = nSiO2.H2O + Na2CO3

air binders – raw materials, production, properties, setting and hardening process

Goals