  The eccentric massive binary HD152248 (also known as V1007 Sco), which hosts
two O7.5 III-II(f) stars, is the most emblematic eclipsing O-star binary in the
very young and rich open cluster NGC6231. Its properties render the system an
interesting target for studying tidally induced apsidal motion. Measuring the
rate of apsidal motion in such a binary system gives insight into the internal
structure and evolutionary state of the stars composing it. A large set of
optical spectra was used to reconstruct the spectra of the individual binary
components and establish their radial velocities using a disentangling code.
Radial velocities measured over seven decades were used to establish the rate
of apsidal motion. We furthermore analysed the reconstructed spectra with the
CMFGEN model atmosphere code to determine stellar and wind properties of the
system. Optical photometry was analysed with the Nightfall binary star code. A
complete photometric and radial velocity model was constructed in PHOEBE 2 to
determine robust uncertainties. We find a rate of apsidal motion of
$(1.843^{+0.064}_{-0.083})\deg$ yr$^{-1}$. The photometric data indicate an
orbital inclination of $(67.6^{+0.2}_{-0.1})\deg$ and Roche-lobe filling
factors of both stars of about 0.86. Absolute masses of
$29.5^{+0.5}_{-0.4}$M$_\odot$ and mean stellar radii of
$15.07^{+0.08}_{-0.12}$R$_\odot$ are derived for both stars. We infer an
observational value for the internal structure constant of both stars of
$0.0010\pm0.0001$. Our in-depth analysis of the massive binary HD152248 and the
redetermination of its fundamental parameters can serve as a basis for the
construction of stellar evolution models to determine theoretical rates of
apsidal motion to be compared with the observational one. In addition, the
system hosts two twin stars, which offers a unique opportunity to obtain direct
insight into the internal structure of the stars.
