Transient damage spreading and anomalous scaling in mortar crack surfaces

The scaling properties of a post-mortem mortar crack surface are investigated. The root mean square of the height fluctuations is found to obey anomalous scaling properties, but with three exponents, two of them characterizing the local roughness (zeta~=0.79 and zetae~=0.41) and the third one driving the global roughness (zetag~=1.60). The critical exponent zeta~=0.79 is conjectured to reflect damage screening occurring for length scales smaller than the process zone size, while the exponent zetae~=0.41 characterizes roughness at larger length scales, i.e., at length scales where the material can be considered as linear elastic. Finally, we argue that the global roughness exponent could be material dependent contrary to both local roughness exponents (zeta~=0.8 and zetae~=0.4) which can be considered as universal.