  Non-resolved thermal infrared observations enable studies of thermal and
physical properties of asteroid surfaces provided the shape and rotational
properties of the target are well determined via thermo-physical models. We
used calibration-programme Herschel PACS data (70, 100, 160 $\mu$m) and
state-of-the-art shape models derived from adaptive-optics observations and/or
optical light curves to constrain for the first time the thermal inertia of
twelve large main-belt asteroids. We also modelled previously
well-characterised targets such as (1) Ceres or (4) Vesta as they constitute
important benchmarks. Using the scale as a free parameter, most targets
required a re-scaling $\sim$5\% consistent with what would be expected given
the absolute calibration error bars. This constitutes a good cross-validation
of the scaled shape models, although some targets required larger re-scaling to
reproduce the IR data. We obtained low thermal inertias typical of large main
belt asteroids studied before, which continues to give support to the notion
that these surfaces are covered by fine-grained insulating regolith. Although
the wavelengths at which PACS observed are longwards of the emission peak for
main-belt asteroids, they proved to be extremely valuable to constrain size and
thermal inertia and not too sensitive to surface roughness. Finally, we also
propose a graphical approach to help examine how different values of the
exponent used for scaling the thermal inertia as a function of heliocentric
distance (i.e. temperature) affect our interpretation of the results.
