Abstract: Punching behavior of eight compound concrete slabs was experimentally studied，and the influences of demolished concrete lumps，reinforcement ratio，thickness of slab and span of slab on the slab's punching perfor- mance were investigated． Validity of different design codes for predicting the punching shear capacity of the com- pound concrete slabs was discussed，and a correction coefficient was suggested． It finds that: (a) when the strength of demolished concrete is lower than that of fresh concrete，the initial stiffness of the compound concrete slab is almost the same as that of the conventional concrete slab，but the punching shear strength of the former is slightly smaller than the latter; (b) when the reinforcement ratio and span-to-thickness ratio keep unchanged， increasing the thickness of slab is more effective to enhance the slab's punching shear strength than reducing the span of slab; (c) it is very necessary to take the steel bars into account during the calculation of the slab's punching shear strength，when the span-to-thickness ratio is relatively small，the formulae for the punching shear capacity specified in current design codes need to be improved further; and (d) to make the predicted punching shear strength of the compound concrete slab has similar safety margin to conventional concrete slab，a reduction factor of 0. 95 is suggested to the former．

Key words: concrete slab, demolished concrete lumps, punching test, punching shear strength