  Apsidal motion in massive eccentric binaries offers precious information
about the internal structure of the stars. This is especially true for twin
binaries consisting of two nearly identical stars. We make use of the tidally
induced apsidal motion in the twin binary HD152248 to infer constraints on the
internal structure of the O7.5 III-II stars composing this system. We build
stellar evolution models with the code Cl\'es assuming different prescriptions
for the internal mixing occurring inside the stars. We identify the models that
best reproduce the observationally determined present-day properties of the
components of HD152248, as well as their $k_2$, and the apsidal motion rate of
the system. We analyse the impact of some poorly constrained input parameters,
including overshooting, turbulent diffusion, and metallicity. We further build
'single' and 'binary' GENEC models that account for stellar rotation to
investigate the impacts of binarity and rotation. We discuss some effects that
could bias our interpretation of the apsidal motion in terms of the internal
structure constant. Reproducing the observed $k_2$ value and rate of apsidal
motion simultaneously with the other stellar parameters requires a significant
amount of internal mixing or enhanced mass-loss. The results suggest that a
single-star evolution model is sufficient to describe the physics inside this
binary system. Qualitatively, the high turbulent diffusion required to
reproduce the observations could be partly attributed to stellar rotation.
Higher-order terms in the apsidal motion are negligible. Only a very severe
misalignment of the rotation axes could significantly impact the rate of
apsidal motion, but such a high misalignment is highly unlikely in such a
binary system. We infer an age estimate of $5.15\pm0.13$ Myr for the binary and
initial masses of $32.8\pm0.6$ M$_\odot$ for both stars.
