Comparative study of two PCE superplasticizers with varied charge density in Portland cement and sulfoaluminate cement systems

Two PCEs with acid to ether monomer ratio of 4 and 22, marked as PCE4 and PCE22 respectively were prepared via radical polymerization in order to study their impacts on fluidity and early hydration in Portland cement (OPC) and Sulfoaluminate cement (SAC) systems. Dynamic light scattering measurement reveals that hydrodynamic radius of PCE22 is more sensitive to Ca2+ from being crosslinked. Fluidity tests show that PCE22 exhibits lower initial fluidizing effect than the lower charged PCE4 in OPC paste because of the inter-polymer crosslinking by Ca2+ bridging effect while the opposite comparison is observed in SAC paste due to the lower [Ca2+] in SAC paste than in OPC paste. PCE22 is found to significantly depress the early formation of AFt crystal in SAC paste, indicated by the results of XRD, TGA, BET and calorimetric tests. Thus, PCE22 behaves better in fluidity retention than PCE4 in SAC paste.