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Water Pipes Made of Asbestos Cement

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Water Pipes Made of Asbestos Cement 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: chrysotile asbestos 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 Cement chemical nomenclature Alite Ettringite Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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 Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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 Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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) Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 - Mineral formula: Ca3SiO5 Alite - Chemical formula: 3CaO.SiO2 (C3S) Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Alite – crossed polars Jan 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) Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 - Mineral formula: Ca2SiO4 Belite - Chemical fomula: 2CaO.SiO2 (C2S) Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Belite- crossed polars Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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. Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Hydration of cement minerals Belite + water C2S + 2H Î CSH + CH Ca(OH)2 ; Portlandite Calcium Silicate Hydrate Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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 Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Portlandite - Ca(OH)2 Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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. Occurs as a natural mineral 80-100°C 300°C Tobermorite Tobermorite Tobermorite 1.1 nm 0.9 nm 1.4 nm Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 hydrated Alite Grain Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Asbestos cement water pipes – following decades of use VT: water-pipe (17th district VR: water-pipe operating for 44 years Budapest, age unknown) (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 Carbonation Concrete 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%). Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 Carbonation Concrete surface Carbonated zone Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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) Jan Elsen, EMU School and ERASMUS IP on Technical Mineralogy, 2006 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 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 silicate red 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 silicate red rectangle indicates the region of main clinker phases Alteration zonation in water pipes 1. 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 Conclusions 1. 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..
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