Properties of marble as building veneer

Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. Vol. 33, No. 2, pp. 215-218, 1996

Pergamon

Copyright © 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0148-9062/96 $15.00 + 0.00

0148-9062(95)00050-x

Technical Note Properties o f Marble as Building Veneer E. M. WINKLERt:

INTRODUCTION Logan et al. [1] explain the bowing of thin suspended marble slabs on the AMOCO building in Chicago, 50 East Randolph Street. The anomalous expansioncontraction behavior of crystalline calcite marble combined with the release of locked-in residual stresses may result in considerable strains responsible for bowing by expansion [2]. Laboratory tests with the same Carrara marble support the observations limited to the Amoco Building. Similar cases of warping have been discussed by some other authors. It is thought that moisture is important in the bowing process. In the following, the role of moisture is discussed which is instrumental for both concave (inward) and convex (outward) warping, also warping of granite panels. MOISTURE Bucher [3] in his presidential address in New Orleans in 1956, stresses the need for moisture in the bowing of slabs. "The sagging is dependent primarily on the presence of moisture in the rock, because examples of this bending of marble and limestone slabs under their own weight seem to have been reported only from countries with abundant rainfall, such as western Europe, northern and eastern North America and eastern Texas. The writer has never heard of bent marble slabs seen at classical localities in Greece or Egypt. This suggests that the moisture that gets into limestone at intervals reduces the equivalent viscosity far enough to make bending possible within the short interval of a few decades". Moisture in stone is found as liquid water from rain, rising ground moisture, and condensation of moisture on cold wall surfaces; such moisture freezes in the capillaries, transports soluble salts and slowly dissolves carbonate rocks. Bucher's explanation of gravity deformation in the presence of unspecified moisture does not consider the effect of the release of locked-in stresses, the anisotropic thermal behaviour of calcite, nor the effect of ordered water molecules in narrow capillaries.

Condensation of water vapour from ambient high relative humidity (RH) in capillaries smaller than 0.1/~ m [4] can attract the positive H ÷ of the water molecule to the negatively charged capillary wall, 2-3 layers of molecules oriented on both sides of the capillary wall; such oriented water does not freeze above -40°C. Continuous rows of ordered water molecules cause swelling by elongation and stone disruption, but also damage by greater interaction with sulfate in capillaries smaller than 0.1 #m. CONVEX AND CONCAVE WARPING Both convex and concave warping were observed by workers on the AMOCO building [5]. Concave warping of both kinds are also in evidence on the Greenwood and Metarie cemeteries in moist New Orleans, Louisiana, the stone panels loosely attached with metal pins. Figure 2 illustrates two marble panels with both concave and convex warping. Most slabs on older tombs are Carrara marble closing the cavity of the tomb above the high groundwater table in the Mississippi delta at New Orleans. The granite slabs are of recent date. Continuous exposure to near 100% RH inside the tomb cavity, as well as higher recorded stone temperatures inside the tomb cavity [1] tends to aggravate the inside microenvironment. Consequently, the greater temperature and humidity inside the tomb cavity have expanded the stone slab more inside than outside. The excessive moisture condensation inside the partitioned burial chambers behind the stone panels into an upper and a lower chamber was observed by the author in preparation of a funeral. The center location of the inside partition is visible on both tombs by the moisture bleeding through to the surface of the panels (Fig. 3) which are not warped. ASYMMETRY OF WARPING IN GRAVEYARD STONES

Some bowed graveyard stones appear asymmetric, the warp being strongest near the bottom of the slabs (Fig. 2). The loose suspension with often a single pin in the upper center permits such movement in contrast to the tight anchoring of the thin stone veneers on buildings. Plastic deformation by gravity [4] appears to play a role in humid tUniversity of Notre Dame, Indiana, U.S.A. :~Address for correspondence: 17635 Juday Lake Drive, South Bend, climates often overlapping with the anisotropic heat--cold IN 46635, U.S.A. expansion-contraction cycles of calcite. 215

216

WINKLER: TECHNICAL NOTE Temp *C

roundest grains of the c o m m o n commercial calcite marbles with the least degree of interlock; it is therefore more prone to dilation by heat--cold cycles than Georgia or Vermont marbles [5].

8O

,,~

- ~ ' u , ' / ~ ~' THE BOWING OF GRANITES

I Residual Strain

--

(lockedin) I

0

0.01

o.oe

o.oa

0.04

Thermal Strain,

o.os

0.06

0.07

%

Fig. 1. Thermal strain paths for heating cycles from 23 to near 70°C. Most residual strain is released at the first heating cycle [2]. STONE

FABRIC

The rate of bowing is also influenced by the stone fabric, the degree of cogwheel-like interlock of the grains with one another [6]. The Carrara marble has the

Granites m a y also warp like crystalline marbles. Granitic rocks are microcracked by differential contraction during cooling of the magma. Cracks have developed both around and across the quartz grains by unequal contraction, 4½% of the quartzes vs 2% of the feldspars and hornblende [7]. The microcrack porosity depends on the quartz content in granites, the basis for further expansion by oriented water molecules combined with stress relief. A slightly warped medium grained Swedish red granite at the Greenwood cemetery is visibly bowed 4 m m over a total length of 1.3m, 0.31%, contrasting the bow of marble slabs of up to 3 % of the same length at 2 c m thickness. Other grey granites measured on the Greenwood cemetery only showed

Fig. 2. Pair of bowed slabs of Carrara marble bowed both outward and inward. The slabs are closing the burial chamber loosely suspended with a pin near the top of the panel. Some plastic flow appears to be present. Greenwood Cemetery, New Orleans.

WINKLER:

TECHNICAL NOTE

Fig. 3. Moisture partly discolors the grey polished granite panel on both tombs. The continuous exposure to 100% RH of the closing slab inside the tomb appears to be influenced by the inside concrete partition which splits the interior chamber in the middle. The continuous high water table in the Mississippi delta provides the moisture inside the tombs. Greenwood Cemetery, New Orleans, Louisiana.

217

218

WINKLER: TECHNICAL NOTE

Fig. 4. Surface of Mount Airy granite quarry. Thin sheets have separated, with "tenting" of large sheet in front of persons. Mount Airy, N.C. Picture taken in 1969 [7].

2 m m concave bow. All granite slabs on the G r e e n w o o d cemetery were installed less than 20 yr ago. The question arises whether such m i n o r deflection could have happened in the quarry or mill during cutting or machining. Bowing o f this granite should not be a surprise. Granite is not as readily attacked by acid rain as marble, nor is it affected by anisotropic thermal dilation. Stress relief aided by hygric action are the only factors contributing to expansion and warping.

hind the panels in a closed cavity where the R H can remain near 100%. (5) The capillaries have widened enough to permit entry o f ordinary water substance: frost action and the effect o f transported salts m a y lead to further disruption with visible cracking and crumbling o f the slabs.

Accepted for publication 28 March 1995

SEQUENCE OF EVENTS LEADING TO BOWING OF MARBLE

REFERENCES (1) Anisotropic thermal e x p a n s i o n - c o n t r a c t i o n cycles o f marbles dilates the stone fabric opening up micropores along the grain boundaries. (2) Oriented water molecules enter and expand the stone capillaries when still smaller than 0.1 # m in near 100% R H ambient atmosphere. (3) C o n t i n u o u s chemical surface attack by acid rain and acid fog has dissolved along the grain b o u n d aries. It is unclear if dissolution can start such cracks aided by e x p a n s i o n - c o n t r a c t i o n cycles or did it only accelerate the process o f dilation. (4) The rock strength has diminished by dilation o f the fabric; the panels start to bow; o u t w a r d if the sun and high humidity exposes the slabs f r o m the outside only; inward if moisture is available be-

1. Logan J. M., Hatedt M., Lehnert D. & Denton M. A case study of the properties of marble as building veneer. Int. J. Rock. Mech. Min. Sci. & Geomech. Abstr. 30, 1531-1537 (1993). 2. Sage I. D. Thermal microfracturing of marble. In Engineering Geology o f Ancient Works and Historical Sites (Edited by Marinos and Koukis), pp. 1013-1018 (1988). 3. Bucher W. Role of gravity in orogenesis. Bull. Geol. Soc. Am. 67, 1295-1318 (1956). 4. Snethlage R. Zum Kenntnisstand yon Verwitterungsvorgaengen an Natursteinen, Natursteinkonservierung. Internatl. Colloquium, Munich, 21-22 May 1984, Arbeitsheft 31, Bayer. Landesamt f. Denkmalpflege, pp. 20-27 (1985). 5. Cohen J. M. and Monteiro P. J. M. Durability and integrity of marble cladding: a state-of-the-art review. J. Performance Constr. Facilities 5, 113-124 (1991). 6. Winkler E. M. Weathering of crystalline marble. In Engineering Geology of Ancient Works and Historical Sites. (Edited by Marinos and Koukis), pp. 717-721 (1988). 7. Winkler E. M. Stone: Properties, Durability in Man's Environment, p. 250. Springer, Vienna (1973).