The stiffness of foam concrete depends primarily on the added porosity. Nevertheless, by performing 3D elastic numerical simulations on artificial unit cells in the frame of periodic homogenization, it is shown that describing foam concrete as a porous material is not sufficient to explain the experimental measurements of the Young modulus for added porosity higher than 40%. Indeed, introducing sand as a third phase enables to recover accurate estimates of the Young Modulus. Furthermore, for highly porous concrete foams, it is shown that the stress concentrates in thin members deprived of stiff sand particles, thus leading to a softer overall stiffness.

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