Drying shrinkage mitigation of alkali-activated blast furnace slag-copper slag by polyether-based shrinkage reducing admixture and MgO-based expansion agent

Volume stability is a critical challenge for the practical applications of alkali-activated materials. To mitigate the drying shrinkage of alkali-activated blast furnace slag-copper slag (AAS-CS), different contents of polyetherbased shrinkage reducing admixture (PSRA) and MgO-based expansion agent (MEA) are used in this study. The effects of PSRA and MEA on the hydration process, mechanical property and drying shrinkage are investigated. Meanwhile, the mechanisms for drying shrinkage compensation of PSRA and MEA are deeply analyzed by nuclear magnetic resonance (NMR), Fourier transform infrared spectrum (FTIR), thermogravimetry and differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). Results show that the drying shrinkage rate and the compressive strength of AAS-CS gradually decrease with the PSRA content increases from 0 to 2.0 wt%. This is mainly attributed to the coarser pore size and the lower surface tension caused by PSRA. When the content of MEA is 4.0 wt%, AAS-CS exhibits the lower drying shrinkage rate and the higher compressive strength in comparison with the reference sample. The addition of MEA promotes the formation of hydrotalcite (Ht). As an expansive product, an appropriate amount of Ht can exert the filling effect and the shrinkage compensating effect.