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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
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