International audienceUltrasonic waves propagating in solids have stress-dependent velocities. The relation between stress (or strain) and velocity forms the basis of non-linear acoustics. In homogeneous solids, conventional time-of-flight techniques have measured this dependence with spectacular precision. In heterogeneous media like concrete, the direct (ballistic) wave around 500~kHz is strongly attenuated and conventional techniques are less efficient. In this manuscript, the effect of weak stress changes on the late arrivals constituting the acoustic diffuse coda is tracked. A resolution of 2.10−5 in relative velocity change is attained which corresponds to a sensitivity to stress change of better than 50 kPa. Therefore the technique described here provides an original way to measure the non-linear parameter with stress variations on the order of tens of kPa
