Synthesis of lignin-grafted polycarboxylate superplasticizer and the dispersion performance in the cement paste

Abstract

It is common that high-performance concrete is highly viscous, which is not conducive to transportation and pumping. In order to reduce the viscosity of fresh high-performance concrete, a lignin-based polycarboxylate superplasticizer (PCE-ACLx) was synthesized through a novel process and the structure was characterized by FTIR, 1H NMR and GPC. The performance of PCE-ACLx in cement paste was evaluated through the surface tension test, slump test, and the adsorption behavior study. The results show that among the PCE-ACLx, PCE-ACL1 had favorable dispersion effect. At the w/c (ratio of water to cement) ratio of 0.29, the fluidity of cement paste was 283 mm when the PCE-ACL1 dosage was 0.2 wt%. At the w/c ratio of 0.35, the emptying time of fresh paste with 0.2 wt% PCE-ACL1 was 13.9 s, showing good viscosity-reducing effect. Furthermore, the adsorption of PCE-ACLx on the cement particles could be described by Langmuir model and pseudo-second-order model. The saturated adsorption capacity of PCE-ACL1 on the cement particles was less than traditional PCE, but it had thicker adsorption layer, so it had larger steric hindrance. Compared with ordinary PCE polymers, lignin grafted PCE polymers make the polymer as a water reducer have higher easeability and gas-inducing properties, and it will be better to use as a water reducer. Lignin grafted PCE polymer has a relatively large application prospects, in this production process the source of lignin can be papermaking black liquor, which has a relatively large contribution to the protection of the environment.