Another feature which is different for the specimens with dissimilar building orientation is the arrangement of their weak links and defects in the macrostructure, as shown in Fig. 8. In vertical specimens, weak interfacial links of successive layers and the axis of linear and planar defects are normal to the loading direction. This arrangement results in the maximum stress concentrations on these defects and provides more accessible paths for voids to grow and coalesce (Fig. 8C). According to Fig. 8C, in vertical samples subjected to external loadings, sharp corners of planar defects are normal to the stress flow and this alignment results in higher stress concentrations in these locations, while the sharp