Rheological behavior and early-age reaction kinetics of Portland cement-sulphoaluminate cement blend pastes containing superplasticizer and cellulose ether

The combination of Portland cement (PC) and sulphoaluminate cement (CSA) has the potential to improve the mechanized construction efficiency of cement-based materials, but its rheological behavior still needs to be considered to deeper understand the evolution of workability. Therefore, the blend pastes with different PC-CSA ratio were prepared. To achieve good initial workability, cellulose ether and superplasticizer were added. The shear stress - shear strain rate data of each paste at different resting time was obtained by a rheometer. HerschelBulkley (H-B) model was used to imitate the rheological data, and the evolution curve of yield stress with resting time of each sample was achieved. It was found that sample with higher CSA content showed a faster increase in yield stress over time. Furthermore, isothermal calorimetry was conducted to reveal the reaction kinetics of the rheological evolution of the fresh pastes referring to Johnson-Mehl-Avrami-Kolmogorov model. The results showed that CSA accelerated the nucleation and crystallization process of ettringite (AFt), which is contributed to the yield stress. Meanwhile, a novel technique, 1H low-field nuclear magnetic resonance (NMR), was firstly applied to character the early-age reaction process of PC-CSA blend system by monitoring the evaporative water content changes in the pastes. The result was that the relative content of evaporated water in the paste with higher CSA content decreased faster, which is also beneficial for the yield stress. These methods for evaluating reaction kinetics effectively validated the rheological behavior of the slurry, and established a correlation with the rheological parameter, which had not been identified in previous studies.