Abstract: A prefabricated concrete module and a composite wall structure comprised of an assembly of modules, where the module comprises a generally rectangular front and rear panel, joined by at least one generally trapezoidal partition means. A cellular wall structure is formed by stacking the modules and aligning the partition means on top of each other, thereby forming bins which contain loose material contributing to the weight of the structure. Provisions can be made for slabs which span longitudinally across partition means of vertically contiguous modules. These slabs, which capture an additional amount of loose material, can also, where desired, transfer lateral forces between superposed partition means. In a version of the module, useful whether or not the trapezoidal partition means are employed, the longitudinal distance from a partition to the edge of the front panel, is less than half the distance between partitions.