  We investigate the implications of Nambu-Goto (NG), L\"uscher-Weisz (LW) and
Polyakov-Kleinert (PK) string actions for the Casimir energy of the QCD
flux-tube at one and two loop order at finite temperature. We perform our
numerical study on the 4-dim pure SU(3) Yang-Mills lattice gauge theory at
finite temperature $\beta=6.0$. The static quark-antiquark potential is
calculated using link-integrated Polyakov loop correlators. At a high
temperature-close to the critical point- We find that the rigidity and
self-interactions effects of the QCD string to become detectable. The
remarkable feature of this model is that it retrieves a correct dependency of
the renormalized string tension on the temperature. Good fit to static
potential data at source separations $R \ge 0.5$ fm is obtained when including
additional two-boundary terms of (LW) action. On the other-hand, at a lower
temperature-near the QCD plateau- We detect signatures of two boundary terms of
the L\"uscher-Weisz (LW) string action. The (LW) string with boundary action is
yielding a static potential which is in a good agreement with the lattice data,
however, for color source separation as short as $R=0.3$ fm.
