stone weathering konrad zehnder applied mineralogy … · effects of rocks weathering deterioration...
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Stone WEATHERING Konrad ZehnderApplied mineralogy and non-metallic ressources II 29.3.2010 Schweizerische Geotechnische Kommission
This is an introduction to stone weathering. First, weathering is seen as a phenomenon and part of the big geologic transformation cycle. Then we focus on some characteristics of weathering processes, such as: 1) Where does weathering occur, and where not? 2) What are key factors of weathering? 3) How fast does weathering proceed?
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Urnäschtobel
Weathering is a phenomenon and process we relate primarily to nature. Typical traces of weathering are ridges formed by hard rock (sandstone layers) between eroded soft rock (marls).
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Tory Island
Granitic rocks at the sea shore are weathered to rounded shapes. This phenomenon is called boulder weathering.
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Martinstobel
A sandstone cliff is weathered to tafoni like shapes in sheltered parts.
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Maderanertal
A limestone is weathered by dissolution. Rain water is a hydrocarbonic acid which dissolves Calcium carbonate. Such traces are called karst.
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Villnachern
The result of weathering are e.g. deposited sands and gravels.
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Salar de Uyuni (Bolivia)
Another result of weathering are evaporites. Salts are the most soluble products of rocks.
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Bahamas Platform with active limestone formation. _________________ 100 km http://geology.com (25.5.2010)
A NASA satellite image of the Bahamas Platform where active limestone formation occurs today. The main platformis over 100 miles wide and a great thickness of calcium carbonate sediments have accumulated there. In this imagethe dark blue areas are deep ocean waters. The shallow Bahamas Platform appears as light blue. - http://geology.com (25.5.2010)
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ExogenicProcess
EndogenicProcess
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“Weathering”=
Decomposition of materials byexogenic processes
“Weather“ = Energy of the Atmosphere
Processes: physical + chemical + biogenic
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damaged cultural values
decomposedrocks
of buildingseffects
of rocks
DeteriorationWeathering
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justnatural?
Ruine Belfort, Brienz/Brinzauls
A ruin – the result not just of weathering but also of destruction on purpose, fire etc....
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nearby Saint-Ursanne
Weathering is non-uniform – local – specific - deterioration is accordingly differentiated
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Zürich, Central
A closer look at any wall shows an astonishing variety of weathering traces.
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Tour de Moron 2004(2006)
Weathering may be intensely and proceed rapidly...
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Tour de Moron (2006)
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Tour de Moron (2006)
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Ruin of Cartatscha nearby Trun, 11th c. (2005)
But weathering may also be very slow: medieval tower of Cartatscha castle near Trun, 11th century (2005)
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Cartatscha (2005)
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Endingen, Jüdischer Friedhof – Grabsteine aus dem 18./19. Jahrhundert
Jewish cemetery, with 200 to 300 years old tombstones
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Luzern, Löwendenkmal 1821 (2006)
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Luzern, Löwendenkmal 1821 (2006)
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Luzern, Löwendenkmal
ETH-Professor Ludwig von Tetmajer liess um 1900 einen Entwässerungsstollen um das Denkmal herum graben
(aus: ETH Life 17.5.06)
There hs been a problem with weathering of this monument since long. Chanels to drain water off have been contructed 110 years ago. However, damages continued to evolve.
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Conservation of Löwendenkmal – Andreas Küng pointing to traces of crabs (2006)
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Abandoned quarry of Bernese Sandstone,
Krauchtal near Burgdorf
Foto: Rainer Kündig
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Sandsteinabbau
Traces of ...
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Sandsteinabbau
... Pickaxes Fotos: Rainer Kündig
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The same stone – butdifferent weathering!
Why?What‘s the difference?
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http://www.tripadvisor.de (25.3.2010)
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Weathering is intense in sheltered parts which are reached by leaking water: What impacts may waters have that are leaking from the rock and wetting dry areas?
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Black gypsum crustsoriginating from airpollution
Zürich CH, Stampfenbachstrasse
Running water transports dissolved salts and deposits them at the rims of the wetted zones. In this example, black gypsum crusts are deposited in shelteres areas but washed off in areas of leaking water.
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Key factor no. 1
Exposure!to exogenic forces
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Basel, Münster
The same exposure – but different weathering patterns because of different stone properties.
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Key factor no. 2
Resistance!Sensitivity
to exogenic forces
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External conditions(Exposure)
Internal conditions(Material properties)
Weathering is an interplay of exgenic forces and the material. Materials react according to their properties differently to (the same) weathering influences. –Which stone properties trigger the weathering process?
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� 3 : 4
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� 1 : 7
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� 17 : 1
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This comparison might suggest that porous rocks are generally more sensitive to weathering. However, it is not that simple, since there are very porous and at the same time very wethering resistant stones, such as e.g. calcareous tuff (travertine).
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Types of weathering (1)
Physical actions– Thermal expansion / contraction
– Frost disintegration
– Salt crystallization
– Hygric swelling / shrinking
– Biogenic physical impact
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Types of weathering (2)
Chemical actions– Dissolution
– Hydration
– Oxidation, Carbonation, ...
– Biogenic chemical impact
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Types of weathering (3)
Synergetic actionschemical...
+ physical...+ biological...
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Falkenstein (Elsass)
Salt weathering
Salts are very important in the breakdown of rocks and the weathering of buildings.
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Salt crystallization at and beneath the surface
Paint layer on a wall painting pushed off byby Mirabilite (Na2SO4.10H2O) – Lavin, church
Paint layer on porous ceramics pushed offby Halite (NaCl) – Laboratory experiment
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Cracking of materialsby salt crystalsgrowing in pores
Nitronatrite (NaNO3) on ceramics- Laboratory experiment)
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Fissures extend by crystalsgrowing from bulky to columnar shapes
Nitronatrite (NaNO3)on ceramics – Laboratory experiment
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Isometric crystalsgrow at the beginning and develop into whiskers
Nitronatrite (NaNO3)on mortar – Laboratory experiment
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The power ofgrowing plants
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ClifdenLichens – good or ill?
Are lichens damaging or not?
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„Micropitting“by lichen(Biofilms) onlimestone
a symbiosisaimed atlongevity
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Response to (unwanted) weathering
Protection!Maintenance!
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Pirghebuli (Georgien 2002)
...and the leck of maintenance
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