Synthesis and characterization of high-performance cross-linked polycarboxylate superplasticizers

Cross-linked sustained-release polycarboxylate superplasticizers (SPs) are superior alternative to the comb-type polycarboxylate SPs due to they offer both a high fluidity and a good retention effect for concrete slurry. In this context, a series of cross-linked polycarboxylate superplasticizers were synthesized using acrylic acid, methylallyl polyoxyethylene ether and four different cross-linkers containing ester groups, respectively. The key difference among these four cross-linkers is their molecular weights because they each possessed the different ethoxy content. The fluidity and fluidity retention tests, adsorption performance and scanning electron microscope tests showed that the cross-linked superplasticizers offered good dispersing effects and excellent slump performance. Excitingly, the maximum flow reached up to 394 mm at a water-cement ratio of 0.35 and this high fluidity could be simultaneously maintained for 2 h, which facilitated concrete transport over long distances, therefore improving the practical workability of concrete. Furthermore, it was found that the superplasticizers derived from cross-linkers with higher ethoxy group contents provided cement paste samples with improved fluidity. Evaluation of the hydration heat and setting time demonstrated that the cross-linked polycarboxylate superplasticizers could delay the hydration of cement and the final setting time had been extended by 4 h in comparation with blank samples. After 3, 7 and 28 d, the compressive strength of the cement mortar was improved with increases of molecular weight of the cross-linker in the cross-linked superplasticizers due to the elevation of ethoxy content.