Alte Gemmi

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?

1

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).

2

Tory Island

Granitic rocks at the sea shore are weathered to rounded shapes. This phenomenon is called boulder weathering.

3

Martinstobel

A sandstone cliff is weathered to tafoni like shapes in sheltered parts.

4

Maderanertal

A limestone is weathered by dissolution. Rain water is a hydrocarbonic acid which dissolves Calcium carbonate. Such traces are called karst.

5

Villnachern

The result of weathering are e.g. deposited sands and gravels.

6

Salar de Uyuni (Bolivia)

Another result of weathering are evaporites. Salts are the most soluble products of rocks.

7

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)

8

9

ExogenicProcess

EndogenicProcess

10

“Weathering”=

Decomposition of materials byexogenic processes

“Weather“ = Energy of the Atmosphere

Processes: physical + chemical + biogenic

11

damaged cultural values

decomposedrocks

of buildingseffects

of rocks

DeteriorationWeathering

12

justnatural?

Ruine Belfort, Brienz/Brinzauls

A ruin – the result not just of weathering but also of destruction on purpose, fire etc....

13

nearby Saint-Ursanne

Weathering is non-uniform – local – specific - deterioration is accordingly differentiated

14

Zürich, Central

A closer look at any wall shows an astonishing variety of weathering traces.

15

Tour de Moron 2004(2006)

Weathering may be intensely and proceed rapidly...

16

Tour de Moron (2006)

17

Tour de Moron (2006)

18

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)

19

Cartatscha (2005)

20

Endingen, Jüdischer Friedhof – Grabsteine aus dem 18./19. Jahrhundert

Jewish cemetery, with 200 to 300 years old tombstones

21

Luzern, Löwendenkmal 1821 (2006)

22

Luzern, Löwendenkmal 1821 (2006)

23

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.

24

Conservation of Löwendenkmal – Andreas Küng pointing to traces of crabs (2006)

25

Abandoned quarry of Bernese Sandstone,

Krauchtal near Burgdorf

Foto: Rainer Kündig

26

Sandsteinabbau

Traces of ...

27

Sandsteinabbau

... Pickaxes Fotos: Rainer Kündig

28

The same stone – butdifferent weathering!

Why?What‘s the difference?

29

http://www.tripadvisor.de (25.3.2010)

30

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?

31

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.

32

33

Key factor no. 1

Exposure!to exogenic forces

34

Basel, Münster

The same exposure – but different weathering patterns because of different stone properties.

35

Key factor no. 2

Resistance!Sensitivity

to exogenic forces

36

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?

37 38

� 3 : 4

39

� 1 : 7

40

� 17 : 1

41

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).

42

43

Types of weathering (1)

Physical actions– Thermal expansion / contraction

– Frost disintegration

– Salt crystallization

– Hygric swelling / shrinking

– Biogenic physical impact

44

Types of weathering (2)

Chemical actions– Dissolution

– Hydration

– Oxidation, Carbonation, ...

– Biogenic chemical impact

45

Types of weathering (3)

Synergetic actionschemical...

+ physical...+ biological...

46

Falkenstein (Elsass)

Salt weathering

Salts are very important in the breakdown of rocks and the weathering of buildings.

47

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

48

Cracking of materialsby salt crystalsgrowing in pores

Nitronatrite (NaNO3) on ceramics- Laboratory experiment)

49

Fissures extend by crystalsgrowing from bulky to columnar shapes

Nitronatrite (NaNO3)on ceramics – Laboratory experiment

50

Isometric crystalsgrow at the beginning and develop into whiskers

Nitronatrite (NaNO3)on mortar – Laboratory experiment

51

The power ofgrowing plants

52

ClifdenLichens – good or ill?

Are lichens damaging or not?

53

„Micropitting“by lichen(Biofilms) onlimestone

a symbiosisaimed atlongevity

54

Response to (unwanted) weathering

Protection!Maintenance!

55

Pirghebuli (Georgien 2002)

...and the leck of maintenance

56

Pirg

hebu

li 20

06ht

tp://

ww

w.m

cs.g

ov.g

e/up

load

s/fil

es/a

fishe

bi/p

irgeb

uli(

25.3

.201

0)

57