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MARBLE WEATHERING IN EUROPE -

RESULTS OF THE EUROCARE-EUROMARBLE EXPOSURE PROGRAMME 1992-1994

SIMON, STEFAN

Konservierung und Denkmalpflege Consulting, Olching, Germany

SNETHLAGE, ROLF

Bavarian State Conservation Office, Munich, Germany

KEYWORDS: Colour Measurement, Exposure Programme, Marble, Surface Roughness, Ultrasonic Velocity, Water Absorption, Surface Recession, Conservation

SUMMARY

Within the frame work of the EUREKA project EU 496 EUROCARE-EUROMARBLE, an outdoor exposure programme started at the beginning of '92. The selected marble types are Carrara, Laas (Italy), Pentelic (Greece) and Ekeberg (Sweden). The exposure sites are located at 7 places in Europe (Stockholm, Goteborg, Moscow, Munich, Vienna, Messina and Aries). Test specimens of special design with polished and cut surfaces have been manufactured to monitor the weathering process on marble by non-destructive measurements (ultrasonic velocity, surface roughness, colour change and water absorption). On small Carrara marble drill cores surface annual recession rates have been determined gravimetrically. Two sets of measurements have been recorded in 1992 and 1994.The results obtained vary significantly in dependence on the different exposure sites and marble types. They are discussed in this report with respect to an eventual use of marble as .geo-indicator" for corrosivity. Additionally, with a deeper knowledge of the first steps of marble weathering, better conservation strategies for endangered European marbles can be developed. In 1994 the exposure racks was completed with marble samples which have been subject to test conservation treatments. A first comparison of the treatments is presented.

1. INTRODUCTION

Marble is susceptible to environmental impacts and chemically relatively simple. For comparative investigations on deterioration processes, marble is the most appropriate natural stone material. It has been shown [Viles, 1990) that the initial reaction of calcite surfaces to incident rainfall produces clear morphological alterations even within a short term exposure of two months. There are weathering mechanisms that are restricted to the surface, and others that also affect the bulk. It is generally accepted that physical, chemical and biological processes are interacting.

The aim of this project, within the frame work of EU 496 EUROCARE-EUROMARBLE [Snethlage and Simon, 1992), is to obtain more information about the specific forms of marble weathering developing under different climatic and environmental conditions. In a first report, the preliminary results after short-term exposure of nine months based on the first set of measurements recorded in 1992 have been

presented [Simon and Snethlage, 1993).

2. MATERIALS AND METHODS

2.1 Exposure of Standard Items

Four types of marble were selected for exposure:

Carrara (CM) marble (Italy) of medium (arabescato) quality, saccharoidal, with grey veins. Ekeberg (EM) marble (Sweden), greenish-yellow dolomitic (92%) marble with calcite (4%)

160

and tremolite inclusions. Laas (LM) marble (Italy), medium-coarse grained white calcitic marble. Pentelic (PM) marble (Greece), white saccharoidal, with yellow veins and pyrite

inclusions. Exposure started at the beginning of 1992. The exposure sites are located at 7 places in Europe, in Stockholm, Goteborg, Moscow, Munich, Vienna, Messina and Aries. Test specimens of special design (.Standard Items") with polished and cut surfaces respectively, were manufactured [Snethlage et al., 1991) to monitor the weathering process by non-destructive measuring techniques. The items are mounted on teflon bars on the metal grid of the exposure table in an unsheltered exposition facing the

main wind direction.

Environmental parameters are recorded directly at the exposure site (sites 3,4,8) or nearby. The exposure sites cover the European range of climatic conditions [Table 1).

The following parameters were investigated in situ: ultrasonic velocity, surface roughness, colour and water absorption. The investigation methods and techniques applied have been described previously in detail [Simon and Snethlage, 1993).

Nr site T r.H. sunshin 502 N02 03 prec. (oC) (%) e (h) (µg/m3) (µg/m3) (µg/m3) (mm)

2 Messina 18,9 67,3 2420 20,9 59,2 14, 1 735 3 Goteborg 8,4 77,4 7,9 27,6 39,0 855 4 Moskau 6,0 73,6 1556 27,1 39,1 698 5 Munchen 9,3 77,6 1741 8,6 48,7 37,6 974 6 Wien 11,5 71 ,5 1937 19,3 38,4 536 7 Stockholm 7,2 71 ,6 1604 5,2 25,0 44,0 600 8 Aries 14,6 71,5 2628 14,2 28,4 506

Table 1: General environmental conditions at the exposure sites (r.H. = relative humidity, prec. = precipitation) ~]

2.2 Surface Recession

18 drill core slabs (h=4cm,r=2cm) of Carrara marble (statuario) divided in three sample groups A, B and C were exposed in unsheltered position. Since a retarding effect of surfactant adsorption on the dissolution kinetics of calcite could be shown under laboratory conditions [Simon, Boehm and Snethlage, 1992), the sample groups Band C were subject to a pretreatment with surfactants. A is the label of the reference group. The samples of group B were saturated by capillary rise and full immersion with the cationic silicone surfactant Abil Quat 3270 (c=1.75g/I, 24h). Abil Quat 3270 is a quaternary ammonium polydimethylsiloxane (Th. Goldschmidt AG, FRG). The sample group C was treated in a two step process by an anionic silicone surfactant Abil s 255 (polysiloxane-polyorganothiosulfate) followed by immersion in a solution of butyldiammoniumchloride. Assuming an equal dissolution on the top area and the cylinder jacket of the sample, with the marble density 2.72 g/cm

3, gravimetric surface recession rates were calculated and extrapolated per annum.

Additionally, the ultrasonic velocity was measured.

2.3 Test Application of Conservation Agents

Carrara marble drill cores (statuario quality) were artificially aged by freezing-thawing cycles. The average ultrasonic velocity of the samples, which had initially been 6,4 km/s, was reduced continously during 160 freezing/thawing cycles to approx. 4 km/s. After preconditioning to 20°cn5% r.H. the

4)annual means collected 1991-1995

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samples were treated by capillary rise and subsequent full immersion with the conservation agents presented in Table 2. The exposure of the treated samples on the racks at the seven sites started in autumn 1994.

Abbreviation Agent

B .Bologna Cocktail" [Rossi-Manaresi et al., 1979)

M Water: Methyltrimethoxysifane: Methanol (molar relation 2:1 :2), 48 h prepolymerized

[Wheeler et al. , 1991)

MAM M +AMO (Aminopropyltrimethoxysilane) (1 :1)

MDAM M + DAMO (N-(2-Aminoethyl(-3-Aminopropyl)Trimethoxysilane) 1 :1

MAO M +cationic silicone surfactant Abil Quat 3270 (Goldschmidt) 2% in methanol 1 :1

MNP M +anionic Phosphoric acid ester Marlophor NP 6 (Hi.ils) 2% in methanol 1 :1

w Wax (100 g bleached bee wax, 2 g Kolophonium, 200 ml white spirit) WH Wacker H diluted 1: 1 with methylethylketone

Table 2: Selected conservation agents for marble treatment

3. RESULTS

3.1 Exposure of Standard Items

3.1.1 Colour Change Due to the beginning formation of a patina, colour changes can be observed on the marble surface, which are characterized by a shift to rising B-values in the L,a,b-diagram. This yellow shift can be attributed to the oxidation of Fe(ll) to Fe(lll) in the surface of the marble. At the mediterranean sites Aries and Messina the contribution of dust deposits has also be taken into account. Because of its significant content of tremolite inclusions, the Swedish Ekeberg marble is especially susceptible for the formation of

a yellow patina as a first weathering step.

.c

o reference

01992

!;?!! 1994 ----------- 14 ,00:r

11 1 ~0 -- IJ . l: nC10 00'1-...... ~· o. o r:i. n o~0

El 0 ~ G'U a . cl D 0 ~ -- 0

~ o cfl ,00 °-o 0 1

0 0 2 ,00 -

0

0

----(J,t}-e--' - -------

-3 ,00 -2 ,00 -1 ,00 0 ,00 1 ,00 2 ,00

a

Fig. 1: Development of B-value on the exposed faces of Ekeberg Marble (average of all

exposure sites)

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3.1.2 Surface Roughness Chemically, the dolomitic Ekeberg marble is more resistant to dissolution than the other marble types. In the order Ekeberg, Pentelic, Laas and Carrara marble the surface roughness seems to be increasing.

There is a direct and linear correlation between the roughness and the annual sum of precipitation at the

exposure sites

3 -

2,5 -E' 2 -:::l. -~ 1 ,5 -)( Q.)

ro 1 -cc 0,5 -

0 ---·------·---

400 600 800 1000

precipitation (mm) annual mean

Fig. 2: Correlation bet\\·een the Ra \'alue and the average annual sum of precipitation at the seven exposure sites

This result is accordance with the NAPAP study (Baedecker et al., 1990), which came to the conclusion that dry deposition of S02 and nitric acid amount 7-26% and wet deposition (acid rain) ca. 10% of the

chemical weathering of carbonate stone. The remaining part could be attributed to natural, karstic dissolution caused by the C02 content of the rainwater. For this reason in Munich, the exposure site with the highest annual precipitation, the standard items show the highest surface roughness, followed by Goteborg. In Stockholm and Aries, however, the surface roughness proceeds significantly slowlier.

3.1.3 Ultrasonic Velocity and Capillary Water Uptake

As a bulk parameter the ultrasonic velocity is determined by the internal grain and pore structure.

Therefore it is not supposed to be affected by environmental influences as fast as the morphological surface features roughness and colour. Nevertheless, it could be proved, that the ultrasonic velocity of the bulk marble material responds sensibly to the environmental conditions already after a few months.

In the case of Carrara marble [fig 3) the measured decrease of the ultrasonic velocity is 0,2 km/s*a which could cause the complete structural disintegration of the marble within 50 years! However, field observations prove that the linearity of this process is not very likely.

Similarly as the Carrara marble (initial velocity 5,2 km/s) the Pentelic marble (PM, initial velocity 5,7 km/s) is affected. A slight decrease could also be measured with the samples of Ekeberg marble.

However, the coarse-grained Laas marble, which showed the lowest ultrasonic velocity at the beginning of the exposure suffered almost no reduction of the ultrasonic velocityWhether the coarser grain and

pore structure of the Laas marble could explain its different behaviour must still be experimentally proved.

The capillary water uptake shows a similar development as the ultrasonic velocity. Except for the Ekeberg marble the coefficient W of capilary water uptake increased. The highest values were recorded

for the Carrara marble samples. There is a good correlation between the coefficient W of capillary water uptake and the ultrasonic velocity.

163

6.5

6.0

5.5

···················· ··· ···· · · · ··· ······· ··· · ····· · · · · · · · ··· ·· ·············~· ··· · ... ....... . .

u 5.0 .................................... A

u G 4:5

4.0

'

. x

.• x ••• ... . . . . .. .. •... . ... ...... . ..... ........ ...... •. .. . . . . ... .. .... ..... . .• .. ... x

.. .. ······· ~· .. ......... ... ...................... .. ...... : .... .. ...... .. .. ..... ... -~·-· ........ .

3.5 ............. . . ····x·········· · ·· . . .. ..... ... .. ........... .. ..... . ......... .. . . . .. .......... . .. .

3.0 CHIO CHI! CHl3 EHIO EHll EHl3 LHIO LHll LHl3 PHIO PHI! PHl3

Fig. 3: The change of the average ultrasonic velocity Va, 2 in comparison with the zero-measurements (0), 1992 ( 1) and 1994 (3) for the four marble types CM, EM, LM and PM.

6.5

- 6.0 U1

"E 5.5 ::.1.

~ 5.0

rs 4.5 5 4.0

ll

3.5 +-----+----f-tl---1

0 0.5 1.5

W-Value (kg/m2"h0 .5)

Fig. 4: Con-elation between capillary water uptake and ultrasonic velocity

3.2 Surface Recession

Estimates of carbonate stone recession rates ranges from 4 to 34 µm/a for marble under various environmental conditions (Lipfert, 1989). Physical recession rates calculated by the recent NAPAP study average 15-30 µm/a for marble. (Baedecker et al., 1990). In this study, the recession rates, based on the cumulated exposure time (1991-1996) range from 14 µm/a for Vienna to 25,1 µm/a for Goteborg.

The recession rates differ from site to site .

The highest rates were measured in Goteborg (3) and Munich (5), in accordance with the highest Ra-

values. Relatively low are the recession rates in Vienna (6), Moskau (4) and Aries (1). In this respect it is interesting to know that Moscow and Vienna are suffering from the highest S02 levels of all exposure

sites within the project.

164

The sample group B, which has been treated with a cationic silicon surfactant shows slightly lower

recession rates. for instance in Munich (5) the adsorption of the surfactants reduced the recession rates for 10-20%. The efficiency is now, two years after the application, decreasing. The fact that the adsorption of surfactants lowers the dissolution rate confirms a surface controlled dissolution reaction (Plummer et al., 1978).

x x

x x 30 .... .. . . . . ........ ... ...... .. ... .... . ... .. .. ... .. ..... .. .. . . . · ···· ··· · ···· ·· ··· · · ················

x x R

E

c K

·· · · ·· ·· · · · ··· · ·;(··· ····· ·· .. . . · ······· ·· ···

~ 20 . . ··· ·· · · . . ..... y ~ 0 15 . . . . .. . . . . .. ...... .. . .. . . ~ .

Fig. 5: Maximal physical recession rates (µm/a) ot the standard items at the exposure sites 2-8 and of the pretreated sample groups A, B, C

3.3 Test Application of Conservation Agents

The influence of the selected conservation agents on the white colour of marble is shown inThe Methyltrimethoxysilane compounds modified with aminofunctional adhesive coupling agents cause a significant yellow-shift (higher 8-values) and darkening (lower L-values) compared to the reference (indicated by the box). Also beewax brings about a yellowing of the marble surface. The other agents do not change the aspect particularly.

The ultrasonic velocity shows the highest consolidation efficiency for the two modified Methyltrimethoxysilane compounds MAM, MDAM and for the ,,Bologna Cocktail •. The superficial wax layer had no influence on the ultrasonic velocity.

One set of samples was exposed to microbiological simulation chamber at Hamburg University. After two months of incubation at 28°C and humid atmosphere, the two samples treated with wax and with the Bologna Cocktail were covered by microorganisms. The lowest contamination rate for bacteria and funghi was found for the MAQ treated sample [Wilimzig, 1995).

D

165

ST D

I

41 D

• M ' II CJ •

I ~- Reference -3 ·r· a B

111 - e- ..-ia- •i1.,5-__ •-EJ- -~ o o o 2 : I ~~ ll ll•ct..ifla• • Ill a l!I 1 .,. CJ AM

• El • o. • CJ -n:i D 13 D • ~ El I I MD • • L-tJ : El l!l • Ill I • MNP

-- -- -- -- =-=- ri _ J!!.:. ~-~-·'Sm ~-o _______ 1f -~~---· ---o-l 1• W -8 -7 --6 -5 -4 -3 D -2 -1 b Lll __ W_H __

I

m -1 -

-2 -

a

Fig. 6: Correlation between B- and L- value for the treated test samples before exposure in august 1994

G.o -I vto (km/s) 1--

5,5

5,0

0 w

21.0S. 1~~f;, 23:20·10

·- 1- .. -- ·

. - - - -~ . -1

1

8 M MAO MNP MAM MDAM \/\IH

conservation agent

Fig. 7: Box & \\'hi sker diagram of ultrasonic velocities of the marble samples as a function of the conservation agent

166

4. CONCLUSIONS

During the first three years of exposure most of the selected stone parameters underwent significant changes which were different for the four marble types and the seven exposure sites. On the basis of

ultrasonic velocity, surface recession, surface roughness and colour change measurements a sequence of corrosivity for marble could be derived: Corrosivity increases in the order Stockholm, Vienna, Aries,

Moscow, Messina, Munich, Goteborg.

Therefore the results of the EUROMARBLE exposure programme can provide a basis to use crystalline marble as a "geological indicator'' for the environment. The correlation between the monitored

parameters and the environmental data will be a future task in order to establish dose-response

functions.

ACKNOWLEDGEMENT

The project EU 496 is supported by different public and private institutions in each member country. We are very much obliged to Marmorwerke Laas (Italy), Borghamn Company (Sweden), Acropolis Committee (Greece) and the BMFT (Germany) for their generous contributions to EU 496. The authors

wish to thank especially I. Giunta, Ch. Gruber, H.-E. Hansson, S. Holmgren, L. Kennerstedt, A.-M. Lind, R. Lovfendahl, M. Mach, R. Mangio, A. Michailov, E. Osterlund, B. Sizov, C. Urzf, V. Verges-Belmin, J. Weber, M. Willimzig and M. Zagari for their help in the second measurement cycle 1994.

REFERENCES

Baedecker, P.A. et al. (1990): Effects of Acidic Deposition on Carbonate Stone.- NAPAP, Report 19, Section 3,

Washington D.C., 414 pp.

Lipfert, F.W. (1989): Atmospheric Damage to Calcareous Stones: Comparison and Reconciliation of Recent

Experimental Findings.-Atmosph. Environment, 23(2), 415-428.

Plummer, L.N.; W igley, T.M.L. ; Parkhurst, D.L. (1978): The Kinetics of Calcite Dissolution in C02-Water Systems

at 5° to 60°C and O. o to 1. o Atm. C02. - Amer. J. Sci., 278, 179-216. Rossi-Manaresi, R; Alessandrini, G; Fuzzi, S.; Peruzzi, R. (1979): Assessment for the Effectiveness of Some

Preservatives for Marble and Limestones.- 3rd International Congress on the Deterioration and

Preservation of Stone, 24-27.10.1979, Venice, 357-376.

Simon, S; Boehm, H.-P.; Snethlage, R. (1992): A Surface-Chemical Approach to Marble Conservation.- Proc. of the

7th Intern. Congr. on Deterioration and Conservation of Stone, Lisbon, 851-859.

Simon, S.; Snethlage, R. (1993): The First Stages of Marble Weathering, Preliminary Results after Short-Term

Exposure of Nine Months.- Proc. of the Intern. RI LEM/UNESCO Congress on the Conservation of Stone

and other Materials, 29.06.-01 .07.1993, Paris, M.-J. Thiel (ed.), 51-58.

Snethlage, R. ; Dahmen, W. ; Klare, B.; Simon, S. (1991): EUREKA-Projekt EU 496 EUROCARE-EUROMARBLE,

Jahresber. 3 Steinzerfall-Steinkonservierung 1991 , Verl. Ernst & Sohn, Berlin, 263-269.

Snethlage, R.; Simon, S. (1992): EUREKA Project EU 496 EUROCARE-EUROMARBLE.- Proc. of the 7th Intern.

Congr. on Deterioration and Conservation of Stone, Lisbon, p. 21-27.

Viles, HA (1990): The Early Stages of Building Stone Decay in an Urban Environment.- Atmosph. Environment, 24

A, 229-232, 1990.

Wheeler, G.S.; Fleming, S.; Ebersole, S. (1991 ): Evaluation of Some Current Treatments for Marble.- Proc. of the

2nd International Symposium, Geneva, 1991 , p. 439-434.

Wilimzig, M. (1995): pers. comm.