Influence of Sequence Structure of Polycarboxylate Superplasticizers on Early Age Properties of Cement Paste: Fid-Bau Portal

Influence of Sequence Structure of Polycarboxylate Superplasticizers on Early Age Properties of Cement Paste

Shu, Xin

AbstractDifferent polycarboxylate (PC) superplasticizers have been successfully synthesized by varying side-chain density as well as sequence structure through free radical polymerization and reversible addition-fragmentation chain transfer polymerization (RAFT), respectively. Characteristic connections between molecular structure and early age properties of cement paste have been systematically evaluated by various methods, such as adsorption, flowability, calorimetric measurements, amount of hydration product, and dissolution of cement grains. The results show that block PC adsorbs faster with a larger adsorption amount onto cement particle surfaces than random PC, thereby having a better initial flowability and faster loss of workability. Moreover, the dormant period of cement paste with block PC could be effectively shortened by 3 h with block PC as well as the onset of the acceleratory period could be promoted. The results from X-ray diffraction (XRD)-Rietveld refinement show that block PC promotes both C3A and C3S reaction than that of random PC. In addition, a larger number of clusters of C-S-H is formed on the cement particle surfaces at the very early age with block PC and then C-S-H clusters developed a continuous structure with prolonged time, which may increase the early strength of cement paste. Furthermore, the dissolution rate of cement minerals is drastically faster with block PC compared with random PC. All these findings are helpful not only for understanding the relationship of the molecular structure of PC and the early age properties of cement paste, but also further designing the optimum molecular structure of PC to meet the requirement of continuous materials with early strength.