chemie stavebních materiálů - cvut.czkzei.fsv.cvut.cz/pdf/123_cs01_pr7_2018.pdf · any deposits...
TRANSCRIPT
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Chemistry of building materials
Martin Keppert Department of materials engineering and chemistry
224 35 45 63
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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
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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
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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
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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
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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
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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
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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
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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
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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
-
-
- -
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Quartz SiO2
SiO4 tetrahedron
many varieties – due to impurities (coloured oxides)
tetrahedrons SiO4 are fully connected
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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
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Molten state or glass
Fragment of crystalline structure: start of crystallization or imperfect melting
anisotropic isotropic
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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
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Opal and chalcedony – dangerous forms of SiO2
Dangerous for concrete – alkali-silica reaction
Chalcedony – microcrystalline SiO2
Opal – hydrated amorphous SiO2
SiO2.nH2O
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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
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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
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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
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Laminated structure: layers are sliding → plasticity
Firing destroys the laminated structure high sorptivity for liquids and gases
kaolinite
Clay minerals
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Laminated structure – swelling due to water
incorporation between layers → volume expansion (10x) →
sealing
Clay minerals
Bentonite (mainly mineral montmorilonite)
dam
coarse aggeragtes
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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
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Soil texture classification
Clay: size < 2 um Silt: 2-50 um Sand: 50 um – 2 mm Gravel: > 2 mm
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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
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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)...
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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
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Marble
= recrystallized limestone (CaCO3)
good workability
low chemical resistance
Greece, Italy
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Aggregates
filler in concretes and mortars
natural x artificial x recycled
gravel (sediments) x crushed (compact rocks)
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Production of crushed aggregates
Kuželový drtič
grading
mining
crushing
jaw crusher
cone crusher
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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
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Rotary kiln
Foto M. Vavro, 2007.
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Recycled aggregates Wastes from building industry
recycling of debris – crusing and grading
graded debris – aggregates in concrete, embankments, backfills
risk – ensuring of constant properties
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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
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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. %
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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
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Non-hydraulic binders
• (air) lime
• gypsum
• Sorel cement
• water-glass
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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
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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
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Limestones in Czech Republic
Jirásek, J., Sivek, M.: Ložiska nerostů. Ostrava: MŠMT ČR & Vysoká škola báňská – Technická univerzita Ostrava, 2007.
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vápenka Kotouč Štramberk
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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
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Calcination of limestone shaft furnace with direct heating
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Calcination of limestone shaft furnace with indirect heating
burnt lime (CaO)
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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)
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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
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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
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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
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Lime cycle
CaCO3 → CaO + CO2
CaO+H2O → Ca(OH)2
Ca(OH)2 + CO2 → CaCO3 + H2O
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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
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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
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Historic lime kilns
pile
Shaft kiln
Hoffmann kiln - circular Třemošnice
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Gypsum
Egypt mortar: mixture of gypsum, lime and
limestone aggregates
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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)
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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
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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
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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
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Production of
β-hemihydrate
4 2 4 2 231CaSO .2H O CaSO . H O H O
2 2
110-125º C, hot air
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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
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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
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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
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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
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Gypsum renders
interior renders
+ single layer (fast), regulují klima v místnosti
MS – gypsum, MVS – lime+gypsum
gypasum:lime:sand = 1:1:3
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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
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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
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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
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Hydrophobization
hydrophilic hydrophobic
material's surface
octyl-tri-ethoxy-silan
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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)
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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)
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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
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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
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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
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air binders – raw materials, production, properties, setting and hardening process
Goals