Ductility ratio and strain energy that are regarded as the characteristic parameters of ductility and toughness were calculated from axial stress-strain curves of plain concrete and HDPE-pipe concrete.Effect of pipe thickness and core-concrete strength on ductility and toughness of HDPE-pipe concrete was studied.The results indicate that the ductility and toughness of HDPE-pipe concrete is much better than those of the plain concrete.The increase in pipe thickness can enhance the ductility and toughness of ...