asbestos case studies 1: water pipes made of asbestos...

Asbestos case studies 1:Water pipes made of asbestos cement

Erzsébet Tóth (Eötvös L. University, Budapest)

31. 08. 2007

Asbestos-cement water pipe production: Selyp (Hungary, 2000)

Final products

Raw material: chrysotileasbestos from Canada

Production waste

Fibre-cement production: Technology is more or less independent of the fibre type used: asbestos is now replaced by cellulose and synthetic fibres.

After forming the pipe/roofing tile/corrugated sheet etc., the product is kept for a while in warm and steamy environment to enhance the fastening and hydration of the cement.

Fibre-cement production: binding of the cement

Slurry is made up of fibers, portland cement and water

discussed next 60–90%wet process

Concrete - cement Definitions

‘ Cement is a hydraulic binder, i.e. a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes and which after hardening, retains its strenght and stability even under water ’ ENV 197-1: CEM cement

‘ Portland cement is a hydraulic cement produced by pulverizing portland-cement clinker ‘ ASTM C 219-94

‘ Concrete is a composite material produced by using cement to bind fine and coarse aggregate (sand and gravel) into a dense coherent mass’.

Mortar: use of only fine aggregates (sand)

Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006

Ettringite

Alite

Cement chemical nomenclature


Cement mineralogy

The microscopical study of Portland cement clinker to determine the mineralogy started at the end of the 19th century.

Törnebohm gave the names alite, belite, celite and felite to four distinctive crystalline components + isotropic residue.

Later:

•Alite = tricalcium silicate C3S

•Belite and felite = dicalcium silicate C2S

•Celite = Calcium Alumino Ferrite – mainly C4AF

•Isotropic residue = Calcium Aluminates – mainly C3A


Cement mineralogy

Actually Portland cement contains four major mineral phases:

•Alite = tricalcium silicate C3S 50-70 %

•Belite = dicalcium silicate C2S 15-30 %

•Aluminate phase = mainly tricalcium aluminate C3A 5-10%

•Ferrite phase = mainly C4AF 5-15 %

(brownmillerite)

For asbestos (and fiber) cement: high C3S and low C3A is the best


Cement mineralogy - Alite – C3S

- Orthosilicate – monoclinic (M1 or M3)

- Biaxial Negative with 2V ~ 20-60°

- Low birefringence 0.002-0.010 ~ first order gray int. Color

- colourless with // polars – high positive relief

- 3 triclinic - 3 monoclinic and 1 rhombohedral polymorphs exist

- First crystal structure determination by Jeffery (1952)


Alite - Mineral formula: Ca3SiO5- Chemical formula: 3CaO.SiO2 (C3S)


Alite – crossed polarsJan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006

Cement mineralogy - Belite

Larnite Ca2SiO3 is the natural analogue of belite

- Five polymorps exist at ordinary pressures the β – C2S polymorph is most common.

- Monoclinic - Space group P21/n

- Biaxial Negative with 2V ~ 64-69°

- second order interference colors

- colourless – (amber) yellow with // polars – high positive relief

- First cristal structure determination by Midgley (1952)


- Mineral formula: Ca2SiO4- Chemical fomula: 2CaO.SiO2 (C2S)Belite


Belite- crossed polars


Cement mineralogy - Aluminate Phase

- Cubic

- Typically fills interstices between crystals of belite and ferrite.

- light-brown color

Cement mineralogy - ferrite phase

- Orthorombic – biaxial negative - Composition ranges from C5A2F to C6AF2

- Typically fills interstices between crystals.

- light-brown – yellow color

- brownmillerite is a rare natural analogue.


Hydration of cement minerals

Belite + water

C2S + 2H CSH + CH

Ca(OH)2 ; Portlandite

Calcium Silicate Hydrate


Cement mineralogy - portlandite Ca(OH)2

– Hexagonal - Uniaxial Negative

- first-order red and second –order blue int. colors

- colourless , forming minute hexagonal plates

- Crystal structure is identical to the Mg(OH)2 structure

Layered structure – with Ca octahedrally and O tetrahedrally coordinated. Interlayers forces are weak giving good (0001) cleavage ; P-3m1 spage group


Portlandite - Ca(OH)2


CSH - Calcium Silicate Hydrate

SEM - BSE image Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006

Fundamental details about the most important cement hydrates, the calcium silicate hydrates or CSH-phases (structure, hydration kinetics, bonding mechanism etc.) are still unknown. This is due to their small particle size (~20 nm), low ordering, heterogeneity and low stability.

-Merlino S, Bonacorssi E, Armbruster T Am Mineral., 1999, 84:1613–1621

-Merlino S, Bonaccorsi E, Armbruster T Eur J Mineral., 2001, 13 :577-590

-E. Bonaccorsi, S. Merlino, H. F. W. Taylor, Cem. Conc. Res., 2004, 34, 1481.

Tobermorite1.4 nm

80-100°C

Tobermorite1.1 nm

300°C

Tobermorite0.9 nm

Occurs as a natural mineral


hydrated Alite GrainJan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006

Asbestos cement water pipes –following decades of use

VT: water-pipe (17th district Budapest, age unknown)

VR: water-pipe operating for 44 years (1028 Budapest, between 1956–2000)

Strong internal alteration: stronger interaction with potable water than with soil humidity

potable water is typically hard water in the region

CarbonationConcrete will carbonate if CO2 from air or from water enters the concrete according to:

- Ca(OH)2 + CO2 --> CaCO3 + H2O

- Calcium Silicate hydrates + CO2 -> various intermediate mineral phases

Various intermediate mineral phases -> CaCO3 + H2O + SiO2.nH2O

- Ferrite hydrates + CO2 --> CaCO3 + hydrated alumina + iron oxides

The carbonation process requires the presence of water because CO2 dissolves in water forming H2CO3. -If the concrete is too dry (RH <40%) CO2 cannot dissolve and no carbonation occurs. - If the concrete is too wet (RH >90%) CO2 cannot enter the concrete and the concrete will not carbonate. Optimal conditions for carbonation occur at a RH of 50% (range 40-90%).


CarbonationConcrete surface

Carbonated zone


Carbonation combined with leaching

Natural water can leach carbonates, formation of soluble calcium bicarbonate, the only remaining product is a gelatinous silica product.

Diagram illustrating the zones of soft water attack (St John et al. 1998)


Free asbestos web on the inner surface of the water pipe, in direct contact with the potable water

Mg, Si, O – serpentine asbestos

Ca – cement material

VR red alteration zone, thin section

XPD of the VR water pipe

B: brownmillerite; C: calcite; CHR: chrysotile; G: gypsum; K: kaolinite; L: larnite; P: portlandite; Q: quartz; V: vaterite; 10Å: TOT layer silicatered rectangle indicates the region of the main clinker phases

Strong internal alteration: stronger interaction with potable water than with soil humidity

potable water is typically hard water in the region

XPD of the VR water pipe

B: brownmillerite; C: calcite; CHR: chrysotile; G: gypsum; K: kaolinite; L: larnite; P: portlandite; Q: quartz; V: vaterite; 10Å: TOT layer silicatered rectangle indicates the region of main clinker phases

Alteration zonation in water pipes1. Free web of asbestos fibres (thickness: 1–2 mm) with a dark

brown crust (thickness ~0.1 mm)Crust composition: Fe-Mn-(oxy)-hydroxides (inferred from dark brown colour), quartz, calcite, gypsum, organic material(?)

2. Red alteration zone (thickness: 1–2 mm)Composition: vaterite, calcite, chrysotile, (quartz)

3. Pale grey alteration zone (thickness: 3 mm)Composition: calcite, vaterite, brownmillerite, chrysotile

4. Dark grey (unaltered) zone (thickness: 6–10 mm)Composition: portlandite, brownmillerite, larnite (tricalcium-silicate?, mayenite?), chrysotile

5. Yellow outer mineral crust (thickness: 1 mm)Composition: calcite, gypsum, quartz, kaolinite?, 10Å-layer silicate

Conclusions1. Asbestos cement water pipes are corrobated both by drinking water

(inside) and soil humidity (outside). The inside interaction is much more pronounced than the outside one.

2. Interaction with drinking water: cement material (and partly also serpentine asbestos) is replaced by CaCO3 polymorphs, calcite and vaterite. Alteration zonation develops outwards.

3. As a consequence of cement consumption, a free web of asbestos fibers develops on the inner surface of the pipe, which is a potential contaminant of drinking water. The associated health risk has to be assessed in the future (water pipes laid down in the 1960-1980-ies may serve till 2020-2030!!!!!).

4. Interaction with soil humidity (outer pipe surface): cement is only a little bit attacked, and a protective mineral layer – made of calcite and gypsum – develops on the outer surface of the pipe. No real alteration zonation inwards.

5. The observed effects will be the same for other fibre-cement pipes as well, therefore the replacing fibres need to be tested for their possible health effects.

asbestos case studies 1: water pipes made of asbestos...

Documents