Fig. 2

Stress–Strain curves of birch tar made with the condensation method (a), the raised structure including overnight cool down (b) and the raised structure without cool down phase (c). The samples’ shear strength values (i.e., the shear stress values in MPa at which elongation in the samples’ stress–strain diagrams cease to be linear) are marked by black arrows. All values obtained from the three samples are marked with the same letters (a, b, c) in Table 1