Marble as building veneer: Weathering dynamics and bowing potentials

Abstract

The veneer cladding of the State and University Library Gottingen is characterised by pronounced deformations after a short time of exposure. The marble cladding displayed clearly visible convex bowing which appeared more distinct in the upper part and on roof level. Direct comparison of bowing data related to measurements from 2000 and 2003 clearly show that the amplitude in bowing had significantly increased. Depending on the bowing panels may show cracks mostly initiated at the dowels. The percentage of visible cracks and breakouts increases with the amplitude of bowing. It seems that a bowing of > 9 mm/m may have a strong control on significant crack initiations and crack growths. The most critical deformed panels were nearly exclusively observed at the roof level. Detailed petrophysical investigations give evidence that with increasing bowing a decrease of rock mechanical properties (flexural strength or breaking load at dowel hole) occurs. Marble degradation is also connected with an increase in porosity and a generally shift of the maximum pore radii to larger pore sizes. On-site damage analyses at the University Library were combined with laboratory tests of the bowing potential to constrain factors that may influence the risk of failure. The experimental data clearly demonstrate that after 40 heating cycles combined with the effect of moisture a certain impact on the decay rate is observed. In the case of demounted panels made from Carrara marble the bowing tests show that already strongly deformed panels from the building exhibit a lower bowing potential than those with lower amplitudes of bowing. Finally, the artificial bowing causes a significant reduction of the flexural strength and the breaking load at the dowel hole. The strength loss of the experimental aged claddings combined with on-site damage analyses had led to conclusions about the risk assessment and lifetime prediction for the investigated marble claddings at the State and University Library.