Chemistry of inorganic bonding compounds II

AggregatesIng. Milena Pavlíková, Ph.D.

K123, D1045224 354 688,

milena.pavlikova@fsv.cvut.czhttp://tpm.fsv.cvut.cz

Inorganic binding compounds IIHydraulic binders

Hydraulic limes

Cement

Others

ConcretePortland cement

Aggregates

Fillers

Water

Geopolymers

Hydraulic

binderssetting and hardening at highrelative humidity or underwater„hydraulicity“ - the ability of biner to set under waterVicat´s (1818) Hydraulicity Index (HI):

Eckel´s (2005)CementationIndex (CI):

CASHI +

=

MCFASCI

×+×+×+×

=4.1

7.01.18.2

Assuptions

of

using

cementation

index1. all available SiO2 combines with CaO to form C3 S

2. all Al2 O3 combines to form C3 A

3. MgO is considered equivalent to CaO

4. Fe2 O3 is considered equivalent to Al2 O3

→ oversimplification, since the mineralogy of hydraulic binders is different and more complex than assumed here

The properties of hydraulic binders are not only dependant on

their composition (read CI), but also:

1. on the conditions of their manufacture

2. indirectly related to the burning temperature and time

Types

of

hydraulicity

Natural – cement

Latent – vitreous siliceous materials which react with calcium hydroxide to formhydraulic mixture

first was used on a large scale by the Romans – pozzolana = a volcanic ash, eg. Pantheon

natural pozzolans – trass, pumice

artificial pozzolans - ground brick, pottery, silica fume, fly ash, metakaolin, blast furnaceslag

The pozzolanic reaction may be slower than the rest of the reactions which occurduring cement hydration, and thus the short-term strength of concrete made withpozzolans may not be as high as concrete made with purely cementitious materials.

On the other hand, highly reactive pozzolans, such as silica fume and high reactivitymetakaolin can produce "high early strength" concrete that increase the rate at whichconcrete gains strength.

Pozzolanic

reaction

at pH=12,45 nad 25°C

( )[ ]( )[ ] ( )[ ]−−−

−−

+→+≡−−≡

+→+≡−−≡

43

23

7

28

OHAlOHSiOOHAlOSi

OHOHSiOOHSiOSi

−+ +→ OHCaOHCa 2)( 22

CSH and CAH gels

Hydraulic bindersOverview

Hydraulic lime

Natural cement

Artificial cement

Others

Hydraulic

limes

Produced by heating (calcining) limestone that contains clay and other impurities (75-80% CaCO3) at 1100-1200°C.

Calcium reacts in the kiln with the clay minerals to produce silicates that enable the lime to set without exposure to air. Any unreacted calcium is slaked to calcium hydroxide.

Hydraulic lime is used for providing a faster initial set than ordinary lime in more extreme conditions (including under water).

Natural - used for a certain period of time.

Artificial - with pozzolana active materials admixture sincethe early 19th century.

Hydraulic

limes

Division according to their hydraulicity:Low hydraulic with 10-15 %Strong hydraulic with more than 15 % of hydraulic oxides

Hydraulic lime is a useful building material for the following reasons:

It has a low modulus of elasticity,

There is no need for movement joints,

It allows buildings to "breathe",

It has a lower firing temperature than Portland cement, and produces less CO2

than ordinary lime, and so is less polluting,

Brickwork bonded with lime is easier to re-use,

It is less dense than cement, thus less cold bridging,

Lime re-absorbs CO2, thus partially offsetting the large amount emitted during its manufacture.

Natural

cement

Parker – calcination of septaria from clay deposits on theIsle of Sheppey (UK) → hydraulic binder „Roman (Parker´s) cement“, patent in 1796

Setting times of 5 to 10 minutes

Kilns – intermittent or continuous, 1000 -1100°C

Residence time up to 10 or 15 days

Calcined product is reduced to powder by mechanicalmeans.

Powder is stored in silos.

Production – in France, Switzerland, Belgium, Italie, Austria, Russia

Slow

and

half

–

slow

setting

natural

cement

Produced by calcining a naturally occuringargillaceous/siliceous limestone

Burned at higher temperatures below the state ofsintering– completely vitrified

Black, hard and dense parts → slow setting binder

Less hard and less dense yellow lumps → quick settingbinder

Setting time – 15 minutes to 2 hours

Artificial

cement

Apsdin (1824) – described production of Portland cement

Method involves double kilning

Calcined limestone, then mixed with clay, finally burning

Probably used a low temperature – product resembled more to a quicksetting natural cement

Johnson (1880) – recognized omportance of clinker formation withcomplete vitrification, fast cooling and finer grinding using of ballmills

The first artificial cements manufactured in intermittent kilns

Around 1900 – rotary kilns replaced them with double kilning

Nowdays - intermittent kilns for production of lime, rotary kilns forsintering mixture of lime and clay

Others

Pozzolanic lime - mixture of hydraulic or non hydraulic lime with pozzolana

Selenitic lime (Scott’s cement) - non or feebly hydraulic limes to which a small percentage of SO3 has been added

Mixed cement - combination of natural cement and grappiercement produced from grappiers of hydraulic lime

Mixed portland (double portland) - combination of two types or natural cement

Pozzolanic cement - mixture of pozzolana and hydraulic lime, natural cement or artificial cement

‘Ciment fondu’ - complete fusion of bauxite and limestone whereby mainly calcium aluminates are formed

ConcretePortland cement

Aggregates

Fillers

Water

Portland cementthe most common type of cement

a basic ingredient of concrete, mortar, stucco and most etc.

a fine powder produced by grinding Portland cement clinker, calcium sulfate, and minor constituents

Clinker:made by heating in a kiln, quickly cooled at 100°C

a homogeneous mixture of raw materials to a sintering temperature (1450 °C)

aggregated into lumps or nodules, diameter 1-10 mm

Low Heat (LH) and Sulfate Resistant (SR) types - limited amount of C3Aformation

raw materials:limestone (CaCO3), or chalk

clay, or shale

sand, iron ore, bauxite

fly ash and slag

Cement kiln

used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement

calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates

As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture → improvement of their efficiency has been the central concern of cement manufacturing technology.

The manufacture of cement clinker

1. grinding a mixture of limestone and clay to make a fine "rawmix"

2. heating the rawmix to sintering temperature in a cement kiln:

70 to 110 °C free water is evaporated

110 to 450 °C adsorbed water evaporated

450 to 600 °C clay-like minerals decomposition

600 to 900 °C calcium carbonate reacts with SiO2 to form belite (C2 S).

900 to 1050 °C calcium carbonate decomposes to calcium oxide and CO2 .

1050 to 1300 °C formation of belite (C2 S), C4 AF and C2 A

1300 to 1450 °C partial (20–30%) melting takes place, and belite reacts with calcium oxide to form alite (C3 S).

3. grinding the resulting cooled clinker to make cement

Methods

of

rawmix

preparation:

1. dry-ground to form a flour-like powder

it is very difficult to keep the fine powder rawmix in the kiln, because the fast-flowing combustion gases tend to blow it back out again. It became a practice to spray water into dry kilns in order to "damp down" the dry mix, and thus, for many years there was little difference in efficiency between the two processes, and the overwhelming majority of kilns used the wet process.

2. wet-ground with added water to produce a fine slurry with the consistency of paint, and with a typical water content of 40–45%

obvious disadvantage that, when the slurry was introduced into the kiln, a large amount of extra fuel was used in evaporating the water

a larger kiln was needed for a given clinker output, because much of the kiln's length was used up for the drying process.

☺

wet grinding of hard minerals is usually much more efficient than dry grinding. When slurry is dried in the kiln, it forms a granular crumble that is ideal for subsequent heating in the kiln

Cement

1400-1450 °C - required to complete the reaction

hot clinker falls into a cooler which recovers most of its heat, and cools the clinker to around 100 °C

cement kiln system is designed to accomplish these processes efficiently

clinker is mixed with gypsum to retard the initioal setting of cement andthen ground to a very fine powder, partical size of 5 to 50 μm

interground with other active ingredients to produce:blastfurnace slag cement

pozzolanic cement

silica fume cement

if stored in dry conditions - can be kept for several months without appreciable loss of quality

Clinker

composition

In 1897, Törnebohm, identified the principal components of portland cement:

Four types of crystal

Alite

Belite

Celit

Felit

Amorphous substance

After 35 years – establishing of their chemical composition.

Alite

Tricalcium Silicate C3S, 3CaO.SiO2

formula: Ca2.90Mg0.06Na0.01Fe0.03Al0.04Si0.95P0.01O5

the major, and characteristic, mineral in Portland cement, it constitutes about half of the total cement volume, setting and development of "early" strength

Thermodynamically unstable below 1250°C – fastcooling → high reactivity and hydration heat X on slow cooling it tends to revert to belit and CaO

Hydration:

2Ca3 SiO5 + 6H2 O →

3CaO.2SiO2 .3H2 O + 3Ca(OH)2

hydrate is referred to as the "C-S-H" phase

It grows as a mass of interlocking needles thatprovide the strength of the hydrated cement system.

BeliteDicalcium Silicate β- C2S, 2CaO.SiO2

Formula: Ca1.94Mg0.02Na0.01K0.03Fe0.02Al0.07Si0.90P0.01O3.93

Rarely occurs naturally (larnite)

solid solution, contributes "late" strength, due to its lowerreactivity, hzdrates slowly, responsible for the long-term gain in strength, called ageing

Thermodynamically stable, prepared at 300°C

Hydration:

2Ca2 SiO4 + 4H2 O →

3CaO.2SiO2 .3H2 O + Ca(OH)2

hydrate is referred to as the "C-S-H" phase

grows as a mass of interlocking needles that provide the strength of the hydrated cement system

Tricalcium

aluminateTricalcium aluminate C3A, 3CaO. Al2O3

the most basic of the calcium aluminates, does not occur in nature

pure C3A formed when the appropriate proportions of finely-divided calcium oxide and aluminium oxide are heated together above 1300°C, mineral is cubic, with unit cell dimension 1.5263 nm and has density 3064 kg.m-3, it melts with decomposition at 1542°C

occurs as an "interstitial phase", crystallizing from the melt

forms an impure solid solution phase, with 15-20% of the aluminium atoms replaced by silicon and iron, and with variable amounts of alkali metal atoms replacing calcium, depending upon the availability of alkali oxides in the melt

Effect on cement properties:

high basicity → reacts most strongly with water

the most reactive of the Portland clinker phases

Hydrated phases Ca2AlO3(OH).nH2O leads to the phenomenon of "flash set" (instantaneous set), and a large amount of heat is generated → Portland-type cements include a small addition of calcium sulfate (typically 4-8%)

3CaO. Al2 O3 +3 CaSO4 .2H2 O+26 H2 O →

3CaO. Al2 O3 .3 CaSO4 .32H2 O

ettringite (3CaO.Al2O3.3CaSO4.32H2O) passivating aluminate crystals

aluminate reacts slowly to form the AFm phase 3CaO.Al2O3.CaSO4.12H2O.

These hydrates contribute little to strength development.

Tricalcium aluminate is associated with three important effects that can reduce the durability of concrete:

heat release, which can cause spontaneous over-heating in large masses of concrete

sulfate attack

Tetracalcium

alumino-ferrite phaseC4 AF, 4CaO.Al2 O3 .Fe2 O3 (brownmillerit)

Hydration in the absence of gypsum:

reaction between the aluminate and ferrite phases and water is fast and highly exothermic

The reaction produces hexagonal calcium alumino-hydrates, C2AH8 and C4AH13.

At ambient tempera-ture these hydrates are unstable and transform into

cubic and thermally-stable calcium alumino-hydrates, C3AH6:

2 C3 A + 21 H2 O →

C2 AH8 + C4 AH13 →

2C3 AH6 + 9 H2 O

Gypsum is interground with clinker to regulate the setting process of cement:

C3 A + 3 CaSO4 .2H2 O + 26 H2 O →

C3 A.3CaSO4 .32 H2 O,

ettringite, tri-sulphoaluminate (TSA)

The C4AF is believed to react in the same way as C3A to produce a type of ettringite with iron content, tri-sulpho-alumino-ferrite (TSAF).

Detection of clinker mineralsobserved and quantified by petrographic microscopy:

clinker nodules are cut and ground to a flat, polished surface

exposed minerals are made visible and identifiable by etching thesurface (using hydrogen fluoride vapour)

surface can be observed by:

optical microscopy in reflected light → colour phases

alite – brown

belite – blue

melt phases – white

electron microscopy - minerals may be identified by microprobeanalysis

X-ray diffraction - on the powdered clinker, to quantify the mineralsaccurately using the Rietveld analysis technique.

Setting

and

hardeningwater is mixed with Portland cement → product sets in a few hours and hardens over a period of weeks.

typical concrete sets in about 6 hours, and develops a compressive strength of 8~ MPa in 24 hours.

strength rises, continues to rise slowly as long as water is available for continued hydration, but concrete is usually allowed to dry out after a few weeks, and this causes strength growth to stop.

caused by the formation of water-containing compounds, forming as a result of reactions between cement components and water.

water/cement ratios between 0.25 and 0.75

stiffening can be observed which is very small in the beginning, but which increases with time.

The point in time at which it reaches a certain level is called the start of setting.

The consecutive further consolidation is called setting, after which the phase of hardening begins.

Stiffening, setting and hardening - caused by the formation of a microstructure of hydration products of varying rigidity which fills the water-filled interstitial spaces between the solid particles of the cement paste, mortar or concrete.

The behaviour with time of the stiffening, setting and hardening therefore depends to a very great extent on the size of the interstitial spaces, i. e. on the water/cement ratio.

The hydration products primarily affecting the strength are calcium silicate hydrates ("C-S-H phases").

Further hydration products are calcium hydroxide, sulfatic hydrates (AFm and AFt phases), and related compounds, hydrogarnet, and gehlenite hydrate.

Calcium silicate hydrates contain less CaO than the calcium silicates in cement clinker, so calcium hydroxide is formed during the hydration of Portland cement. This is available for reaction with supplementary cementitious materials such as ground granulated blast furnace slag and pozzolans.

Hydrationalite

2Ca3 OSiO4 + 6H2 O →

3CaO.2SiO2 .3H2 O + 3Ca(OH)2

This is a relatively fast reaction, causing setting and strength development in the first few weeks.

belite

2Ca2 SiO4 + 4H2 O →

3CaO.2SiO2 .3H2 O + Ca(OH)2

This reaction is relatively slow, and is mainly responsible for strength growth after one week.

Tricalcium aluminate hydration is controlled by the added calcium sulfate, which immediately goes into solution when water is added. Firstly, ettringite is rapidly formed, causing a slowing of the hydration (see tricalcium aluminate):

Ca3 (AlO3 )2 + 3CaSO4 + 32H2 O →

Ca6 (AlO3 )2 (SO4 )3 .32H2 O

The ettringite subsequently reacts slowly with further tricalcium aluminate to form "monosulfate" - an "AFm phase":

Ca6 (AlO3 )2 (SO4 )3 .32H2 O + Ca3 (AlO3 )2 + 4H2 O →

3Ca4 (AlO3 )2 (SO4 ).12H2 O

This reaction is complete after 1-2 days.

The calcium aluminoferrite reacts slowly due to precipitation of hydrated iron oxide:

2Ca2 AlFeO5 + CaSO4 + 16H2 O →

Ca4 (AlO3 )2 (SO4 ).12H2 O + Ca(OH)2 + 2Fe(OH)3

high pH-value of the pore solution important for most of the hydration reactions

Hydration

periods

1. pre-induction hydration: starts after Portland cement is mixed with water, a brief and intense

Calcium sulfates dissolve completely and alkali sulfates almost completely, short, hexagonal needle-like ettringite crystals form at the surface of the clinker particles, first calcium silicate hydrates (C-S-H) in colloidal shape can be observed.

The first hydration products are too small to bridge the gap between the clinker particles and do not form a consolidated microstructure, consistency of the cement paste turns only slightly thicker.

2. induction period - setting starts after approximately one to three hours, when first calcium silicate hydrates form on the surface of the clinker particles, which are very fine-grained in the beginning.

3. accelerated period - further intense hydration of clinker phases takes place, starts after approximately four hours and ends after 12 to 24 hours.

During this period a basic microstructure forms, consisting of C-S-H needles and C-S-H leafs, platy calcium hydroxide and ettringite crystals growing in longitudinal shape. Due to growing crystals, the gap between the cement particles is increasingly bridged. During further hydration, the hardening steadily increases, but with decreasing speed.

The density of the microstructure rises and the pores fill: the filling of pores causes strength gain.

Usage

of

PC in the production of concrete

as a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element.

in the factory production of pre-cast units, such as panels, beams, road furniture, or may make cast-in-situ concrete such as building superstructures, roads, dams.

These may be supplied with concrete mixed on site, or may be provided with "ready-mixed" concrete made at permanent mixing sites.

in mortarsfor plasters and screeds

in grouts

squeezed into gaps to consolidate foundations, road-beds

Types

of

PC

There are different standards for classification of Portland cement. The two major standards are the ASTM C150 used primarily in the U.S. and European EN-197. EN 197 cement types CEM I, II, III, IV, and V do not correspond to the similarly-named cement types in ASTM C 150.

EN 197-1 defines 5 classes of common cement that comprise Portland cement as a main constituent:

I Portland cement - comprising Portland cement and up to 5% of minor additional constituents

II Portland-composite cement - Portland cement and up to 35% of other single constituents

III Blastfurnace cement - Portland cement and higher percentages of blastfurnace slag

IV Pozzolanic cement - Portland cement and up to 55% of pozzolanic constituents

V Composite cement - Portland cement, blastfurnace slag and pozzolana or fly ash

White

Portland cement

White Portland cement differs physically from thegray form only in its color, and as such can fallinto many of the above categories

its manufacture is significantly different from thatof the gray product, and is treated separately

In combinationwith white aggregates to produce whitee concreteforprestige construction projects and decarative work

with pigments to produce brightly colored concretes andmortars

Safety

When cement is mixed with water a highly alkali solution(pH ~13) is produced by the dissolution of calcium, sodiumand potassium hydroxides.

Gloves, goggles and a filter mask should be used forprotection.

Hands should be washed after contact. Cement can cause serious burns if contact is prolonged or if skin is not washedpromptly.

Once the cement hydrates, the hardened mass can besafely touched without gloves.

Environmental

effects

emissions of airborne pollution in the form of dust, gases

noise and vibration when operating machinery and during blasting in quarries

consumption of large quantities of fuel during manufacture

release of CO2 from the raw materials during manufacture

damage to countryside from quarrying.

burning fuel containing sulfur, should be aware of the acute and chroniceffects of exposure to SO2

The CO2 associated with Portland cement manufacture falls into 3 categories:

1. derived from decarbonation of limestone,

2. from kiln fuel combustion

3. produced by vehicles in cement plants and distribution.

AggregatesMaterial consisting of uncrushed and/or crushed natural and/or artificialmineral substances suitable for use in concrete.

Coars:

Fraction 4 to 63 mm

Natural - gravel limestone or granite, sandstone, dolerit, basalt

Artificial – crushed concrete, brocks, blast-furnace slag

Fine:

Fraction 0 to 4 mm

sand from a pit, rivers or sea

Necesary to wash – removing of salt, organic materials or clay perticles

Cover about 75-80% of concrete volume.

Aggregate serves as reinforcement to add strength to the overall composite material.

Problematic

aggregates

Various types of aggregate undergo chemical reactions in concrete, leading to damaging expansive phenomena.

The most common are those containing reactive silica, that can react (in the presence of water) with the alkalis in concrete.

reactive mineral components of some aggregates are opal, chalcedony, flint and strained quartz.

Alkali Silica Reaction or ASR - an expansive gel forms, that creates extensive cracks and damage on structural members.

aggregates containing dolomite - dedolomitization reaction occurs where the magnesium carbonate compound reacts with hydroxyl ions and yields magnesium hydroxide and a carbonate ion. The resulting expansion may cause destruction of the material.

presence of pyrite, an iron sulfide - generates expansion by forming iron oxide and ettringite.

Other reactions and recrystallizations, e.g. hydration of clay minerals in some aggregates, may lead to destructive expansion as well.

Water

Combined with a cementitious material, this forms a cement paste.

The cement paste glues the aggregate together, fills voids within it, and allows it to flow more easily.

Less water in the cement paste will yield a stronger more durable concrete; more water will give an easier flowing concrete with a higher slump.

Impure water (organic residues, sulphates, salts) used to make concrete can cause problems, either when setting, or later on.

Water-cement ratio is the ratio of weight of water to the weight of cement used in a concrete mix. It has an important influence on the quality of concrete produced.

A lower water-cement ratio leads to higher strength and durability, but may make the mix more difficult to place. Placement difficulties can be resolved by using plasticizer. The water-cement ratio is independent of the total cement content (and the total water content) of a concrete mix.

Too much water will result in settling and segregation of the sand/stone components mix with too much water will experience more shrinkage as the excess water leaves, resulting in internal cracks and visible fractures (particularly around inside corners) which again will reduce the final strength.

Fillersinorganic materials with pozzolanic or latent hydraulic properties

very fine-grained materials added to the concrete mix to improve the properties of concrete (mineral admixtures),or as a replacement for Portland cement (blended cements)

Fly ash: by product of coal fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, silicious fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties

Ground granulated blast furnace slag (GGBFS or GGBS): by product of steel production, is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties

Silica fume: by product of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability

High Reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume, bright white in color, making it the preferred choice for architectural concrete where appearance is important.

Plasticizers

and

superplasticizersPlasticizers:

commonly manufactured from lignosulfonates, a by-product from the paper industry.

lignosulfonate based

Superplasticizers or High Range Water Reducers or Dispersants:chemical admixtures that can be added to concrete mixtures to improve workability.

often used when pozzolanic ash is added to concrete to improve strength.

Adding 2% superplasticizer per unit weight of cement is usually sufficient.

manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, although new generation products based on polycarboxylic ethers

Polycarboxylate Ethers (PCE) or just Polycarboxylate (PC) - the new generation of superplasticisers giving cement dispersion by steric stabilisation, instead of electrostatic repulsion. This form of dispersion is more powerful in its effect and gives improved workability retention to the cementitious mix. Furthermore, the chemical structure of PCE allows for a greater degree of chemical modification than the older generation products, offering a range of performance that can be tailored to meet specific needs.

In ancient times, the Romans used blood as a superplasticizer for their concrete mixes.

Household washing up liquid may also be used as a simple plasticizer.

Geopolymerssynthetic aluminosilicate materials

replacement for Portland cement

Named by Davidovits (1970)

lower carbon dioxide emissions, greater chemical and thermal resistance and better mechanical properties at both atmospheric and extreme conditions

The majority of the Earth’s crust is made up of Si-Al compounds.

Davidovits proposed in 1978 that a single aluminium and silicon-containing compound, most likely geological in origin, could react in a polymerisationprocess with an alkaline solution.

The binders created were termed "geopolymers" but, now, the majority of aluminosilicate sources are by-products from organic combustion, such as fly ash from coal burning. These inorganic polymers have a chemical composition somewhat similar to zeolitic materials but exist as amorphous solids.

Long-time

stability of

geopolymers

Egypt – pyramides (> 6000 y.)

Ancient Rome – Pantheon (2000 y.)

Davidovits has combined his expertise in alumino-silicate chemistry with a long-standing interest in archeology, particularly the archeology of ancient Egypt, and his examination of the building blocks of the major pyramids have led him to the conclusion that, rather than being blocks of solid limestone hauled into position, they are composed of geopolymers, cast in their final positions in the structure. He also considers that roman cement and the small artifacts, previously thought to be stone, of the Tiahuanaco civilisation were made using knowledge of geopolymer techniques.

Production

formed by reaction of an aluminosilicate powder with an alkaline silicate solution at roughly ambient conditions under 100°C in highly alkaline environment → polymeric Si-O-Al bonds

Metakaolin is a commonly used starting material for laboratory synthesis of geopolymers, and is generated by thermal activation of kaolinite clay.

Geopolymers can also be made from natural sources of pozzolanicmaterials, such as lava or fly ash from coal.

Most studies have been carried out using natural or industrial waste sources of metakaolin and other aluminosilicates.

Structure

The chemical reaction that takes place to form geopolymersfollows a multi-step process:

1. Dissolution of Si and Al atoms from the source material due to hydroxide ions in solution

2. Reorientation of precursor ions in solution

3. Setting via polycondensation reactions into an inorganic polymer.

The inorganic polymer network is in general a highly-coordinated 3-dimensional aluminosilicate gel, with the negative charges on tetrahedral Al(III) sites charge-balanced by alkali metal cations.

Empiric geopolymer formula

(Mn{-(Si-O)Z-Al-O}n .wH2O)

Geopolymer

propertiesFrom amorphous to crystaline structure → huge amount of differentproperties

Similar to organic thermoplasts → production and formation under lowtemperatures

Similar to minerals → hard, resistant, refractory (formation at 1 000- 1 200°C)

Long-time properties keeping

Usage:In exchange of zeolites – adsorbent of toxic waste

water purification

catalysts in petrochemical industry

laundry detergents

Production of instruments and formes in plastic industry

and metalurgy

Waste materials recycling

LiteratureVIMMROVÁ, A. and

VÝBORNÝ, J. : Building Materials 10, ČVUT, Prague, 2002.

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