seminario di oggi



Aula Arduino


Siegfried Siegesmund

University of Goettingen, Germany


Marble bowing


For about four decades marble has been used as thin veneer cladding. The

durability of such thin slabs (mostly 30-40 mm) is satisfactory at most

constructions. However, on numerous buildings all over the world, the long-term

deformation (expansion, bowing) of some claddings is associated with structural

weakening and strength loss which led to an inevitable restoration of the affected

facades and to an image problem of marble used as a structural building stone.

Up to now, the existing knowledge about the causes for this special kind of

marble weathering was mostly restricted to research on Carrara marble and to

the effect of individual parameters. This talk summarises the combined influence

of extrinsic (environmental) and intrinsic (material specific) parameters on

marble bowing. The respective impact of these factors on the weathering process

is elucidated by damage mapping of different marble facades. The work focuses

on the influence of the microfabric on the damage dynamics of veneer marble

and particularly considers moisture as an essential climatic parameter.

Generally, the weathering process is promoted by thermal-hygric microcrack

propagation. In case of temperature variations, as occuring during day-night

cycles, the anisotropic strain properties of the main components calcite and/or

dolomite generate stress within the interconnection of grains. This finally leads

to microcracking along fabric discontinuities such as grain boundaries, cleavage

planes or pre-existing cracks. Irreversible residual strain serves as an indicator of

the accumulated extension of microcracks.

Exemplary long-term field data from the facade of the University Library

building in Göttingen as well as weathering simulations of the concerned veneer

marble under laboratory conditions reveal an unbroken progress of slab bowing

there. The detailed knowledge of long-term bowing dynamics and its correlation

with strength loss of veneer panels can provide the basis for risk assessment and

prediction of the service life of damaged marble facades.

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