Context : The eccentric massive binary HD 152 248 ( 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 NGC 6231 .
Its properties render the system an interesting target for studying tidally induced apsidal motion .

Aims : 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 .

Methods : 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 .

Results : We find a rate of apsidal motion of ( 1.843 ^ { +0.064 } _ { -0.083 } ) ^ { \circ } yr ^ { -1 } .
The photometric data indicate an orbital inclination of ( 67.6 ^ { +0.2 } _ { -0.1 } ) ^ { \circ } and Roche-lobe filling factors of both stars of about 0.86 .
Absolute masses of 29.5 ^ { +0.5 } _ { -0.4 } ~ { } \text { M } _ { \odot } and mean stellar radii of 15.07 ^ { +0.08 } _ { -0.12 } ~ { } \text { R } _ { \odot } are derived for both stars .
We infer an observational value for the internal structure constant of both stars of 0.0010 \pm 0.0001 .

Conclusions : Our in-depth analysis of the massive binary HD 152 248 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 .