Bowing of marble panels: on-site damage analysis from the Oeconomicum Building at Göttingen (Germany)

Abstract

AbstractThe use of natural stone panels or cladding material for building facades has led to some durability problems, especially with marble slabs. To examine the effects of intrinsic and extrinsic parameters on bowing, a very detailed study was performed on the Oeconomicum Building at the University of Goettingen. In total 1556 panels from the whole building were measured with respect to bowing using a bow-meter. The variation of bowing ranges from concave (up to 23 mm/m) to convex (up to −11 mm/m). The variation is not controlled by the position with respect to the geographical coordinates, height above ground, shadows, temperature etc. On the north facade the different rock structures visible on the panel surfaces are a result of the marble slabs being cut in different directions. The different degrees of bowing are associated with the structure of the marble since all other influencing factors are relatively constant (position, temperature, moisture content, building physics). Experimental data on the expansion behaviour under dry and/or wet conditions reveal different degrees of bowing with respect to the rock fabric and may help to explain the observed differences in bowing. The effect of the rock fabric, especially of the lattice preferred orientation in this case, clearly controls the deterioration of the marble and the degree of bowing. The bowing is also characterized by an increase in the porosity, decreasing values of ultrasonic wave velocities and flexural strength. The loss of cohesion in the strongly deteriorated panels is clearly visible in the microstructure by the open grain boundaries which are interconnected to intergranular microcracks.