In this study, we present the characterisation of damage in polymer concrete using coda waves interferometry (CWI). The latter takes into account the multi-scattered acoustic waves, whose travelling distances are considerably longer than the one corresponding to the direct wave (emitter-receiver direct distance). Experimentally, we prove that CWI is not always appropriate to detect damage. Therefore, we propose an original approach through which the interaction CWI with damage is optimised. This is done using nonlinear resonance (NR) method, where bending modes are excited, at the time when acoustic waves are multi-scattered. Experiments show an important increase in the sensitivity to damage with interesting perspectives in terms of damage location and characterisation.