Stone degradationusing limestone as indicator

Deterioration of stone materials

Chemical Chemical weathering weathering processesprocesses

LeachingLeaching

Chemical Chemical reactionsreactions

Biological Biological activitiesactivities

Physical/Physical/mechanical mechanical weathering weathering processesprocesses

Frost Frost actionaction

Salt Salt crystallizationcrystallization

MoistureMoisture

expansionexpansion

Thermal Thermal expansionexpansion

Biological activityBiological activity

General deterioration forms

unsheltered unsheltered conditionsconditions

1st stage - black 1st stage - black crustscrusts

2nd stage - loss of 2nd stage - loss of materialmaterial

sheltered sheltered conditionsconditions

St. Paul’s Cathedral, London

Bankside power station, London

In use At present modern art gallery

Portland Limestone, St. Paul’s Cathedral, London, fresh and weathered surfaces

0

10

20

30

40

50

60

70

80

90

100

1960 1970 1980 1990 2000

Year

Rec

essi

on

/ µ

m y

ear-1

0

50

100

150

200

250

300

SO

2 /

µg

m-3

Recession fresh surfaceRecession weathered surfaceSO2

Schematic view of memory effect

-30

20

70

120

170

220

0 10 20 30 40 50

Time in years

SO

2 (µ

g m

-3)

0

20

40

60

80

100

120

Rec

essi

on

(µ

m y

r-1)

Sulphur dioxide

Recession

The multi-pollutant programme

• ICP Materials exposure 1997 - 2001

• EU 5FP project MULTI-ASSESS incl. HNO3 and particles 2002 - 2003

• Comparative exposure of different calcareous stone materials

• Assessment of threshold levels for pollution, deterioration and soiling

Limestone - trends in the multi-pollutant situation

0

10

20

30

40

50

60

70

80

90

01 P

ragu

e-Bec

hovic

e

03 K

opist

y

05 Ä

htär

i

07 W

aldho

f Lan

genb

rüge

08 A

scha

ffenb

urg

10 B

ottro

p

13 R

ome

14 C

asac

cia

15 M

ilan

16 V

enice

21 O

slo

23 B

irken

es

24 S

tock

holm

Sou

th

26 A

spvr

eten

27 L

incoln

Cat

hedr

al

31 M

adrid

33 To

ledo

34 M

osco

w

35 L

ahem

aa

36 L

isbon

37 D

orse

t

Su

rfa

ce

re

ce

ss

ion

/ µ

m

1987-19911997-2001

Surface recession (µm-1year exposure)

-25

-20

-15

-10

-5

0

GREECE POLAND UNITEDKINGDOM

LATVIA LATVIA CZECHREPUBLIC

ITALY

SAAREMAA DOLOMITE

BAUMBERGER SANDSTONE

GOTLAND SANDSTONE

PORTLAND LIMESTONE

CARRARA MARBLE

CITY CEMETERY

(GREEN AREA)

CITY CENTER

ATHENS KRAKOW LONDON RIGA1 RIGA2 PRAGUE ROME

Background to Portland Limestone

• The quarries are located on the Isle of Portland in Dorset, England.

• The tablets have been used in all recent UNECE, EU and SIDA programmes

• Portland has been quarried since the Roman period but became popular in the 17th century when Inigo Jones and Sir Christopher Wren used it in many buildings including St.Paul's Cathedral, London. Portland has remained popular with architects and builders because of its fine grain and good durability, and because it weathers very evenly.

Now the demonstration…

General deterioration forms

unsheltered unsheltered conditionsconditions

1st stage - black 1st stage - black crustscrusts

2nd stage - loss of 2nd stage - loss of materialmaterial

sheltered sheltered conditionsconditions

Comparison of surface loss on sheltered (top) and unsheltered (bottom) limestone samples

Exposure in sheltered position

• Weight incerase is presumed to arise from the conversion of calcium carbonate into calcium sulphate (gypsum) that is not dissolved by rain as is the case for open exposure.

• The concentration of sulphates is found to be greatest in the top 1 mm of the tablets but there will still be small increases to a depth of 3 mm in some cases.

• The crust thickness can be estimated by using a gypsum density of 2.5, a weight gain factor of 0.36 from the stoichometry and the face area of the tablets giving

m crust = Weight gain (mg)0.36 x 2.5 x 5

The distribution of soluble material

• A powder sample is obtained by drilling at four places on a 50 x 50 mm surface. Samples are obtained initially at 1 mm depth from the surface at 2 diagonally opposed locations on the tablet.

•

• The concentrations of the major cations (Na+, K+, Ca2+ Mg2+ ) and anions (Cl-, NO3

- SO42-) are obtained by de-ionised water

extraction (20 ml for 30 minutes) and measured by ion chromatography or some other appropriate method.