  Foams made of complex fluids such as particle suspensions have a great
potential for the development of advanced aerated materials. In this paper we
study the rheological behavior of liquid foams loaded with granular
suspensions. We focus on the effect of small particles, i.e. particle-to-bubble
size ratio smaller than 0.1, and we measure the complex modulus as a function
of particle size and particle volume fraction. With respect to previous work,
the results highlight a new elastic regime characterized by unequaled modulus
values as well as independence of size ratio. A careful investigation of the
material microstructure reveals that particles organize through the network
between the gas bubbles and form a granular skeleton structure with tightly
packed particles. The latter is proven to be responsible for the reported new
elastic regime. Rheological probing performed by strain sweep reveals a
two-step yielding of the material: the first one occurs at small strain and is
clearly attributed to yielding of the granular skeleton; the second one
corresponds to the yielding of the bubble assembly, as observed for
particle-free foams. Moreover the elastic modulus measured at small strain is
quantitatively described by models for solid foams in assuming that the
granular skeleton possesses a bulk elastic modulus of order 100 kPa. Additional
rheology experiments performed on the bulk granular material indicate that this
surprisingly high value can be understood as soon as the magnitude of the
confinement pressure exerted by foam bubbles on packed grains is considered.
