AbstractA new kind of retarding polycarboxylate superplasticizer (M20S80) was prepared through the modification of black liquor and polycarboxylate superplasticizer (S) through an Fe2+-H2O2 reaction system. The synthesis process of M20S80 was introduced. Infrared spectrum analysis (FT-IR) was used to investigate the changes in functional groups in M20S80. At the same time, a mixture of LM20S80 was made by mixing black liquor and S at a mass ratio of 1:4 directly at room temperature. In comparison with S and LM20S80, the influences of M20S80 on the properties of concrete were studied. The results indicate that M20S80 had a better water reduction rate in concrete than LM20280 and was close to S under the same conditions. Furthermore, M20S80 had a retarding effect on the early strength development of concrete, but no negative influence on strength after 28 d of curing. Finally, M20S80 with dosages of 0.45% appeared to be more effective in improving the pore structure of concrete.