Drying shrinkage performance of Medium-Ca alkali-activated fly ash and slag pastes

This study focuses on understanding why the drying shrinkage of alkali-activated fly ash and slag (AAFS) paste is much more significant than that of ordinary Portland cement (OPC) paste. Based on the tests of microstructure characterization, a drying shrinkage prediction model is established. By comparing the results of the test and calculation, it can be found that the elastic deformation values of the AAFS paste caused by capillary pore pressure during drying only account for a small part of the drying shrinkage values. The progress of the drying shrinkage in the long term mainly depends on the viscous behaviors of the gel under capillary pore pressure. With the CaO content in the raw materials, the pore structures of the AAFS pastes become denser, resulting in more significant capillary pore pressures. In this case, the micropore closure and gel rearrangement in each AAFS paste were more severe, resulting in the obvious creep of the pastes. The drying shrinkage predictions for the AAFS pastes should consider the creep influence of the pastes under capillary pore pressure, which is greater than that of OPC pastes.

Automated summary

This study investigates the reason why the drying shrinkage of alkali-activated fly ash and slag (AAFS) paste is more significant than that of ordinary Portland cement (OPC) paste. It is found that the long-term progress of drying shrinkage mainly depends on the viscous behaviors of the gel under capillary pore pressure. The closure of micropores and gel rearrangement in AAFS paste are more severe, resulting in obvious creep of the paste.