Synergetic effect of superabsorbent polymer and shrinkage reducing admixture on the properties of alkali-activated slag binders

Abstract

This research is to investigate the synergistic effects of superabsorbent polymer (SAP) and shrinkage-reducing admixture (SRA) on autogenous shrinkage, hydration and microstructure of alkali-activated slag system (AAS). Results revealed that the addition of SRA reduced the absorption capacity of SAP, resulting in a smaller size distribution of macrovoids throughout the AAS matrix. Nevertheless, the presence of SAP affected the ability of SRA to effectively reduce the surface tension of the pore solution of AAS. Instead, the addition of SAP resulted in an increase in surface tension by up to 14%. This phenomenon can be explained by the hydrophobic interactions between SAP networks and SRA molecules. The combination of SAP and SRA in AAS exhibited greater effectiveness in controlling autogenous shrinkage compared to using SRA alone, resulting in a reduction of around 53% compared to 46%. On the other hand, incorporating only SAP proved to be more effective, leading to a higher reduction of 90%. However, this combined effect is reported to be counteractive and dependent on the content of each component. Moreover, the hybrid system of SAP and SRA demonstrates a pronounced retardation effect on AAS hydration. The XRD patterns showed no new reaction products were formed. As revealed by SEM analysis, the microstructure of AAS containing SAP and SRA exhibited a distribution of microvoids ranging from 5 to 50 μm. This can explain the reduction of the compressive strength by incorporation a high content of SAP combined with SRA. However, incorporating a lower dosage of SAP is advantageous when combined with SRA in AAS systems. Finally, the integration of SAP and SRA had a positive influence on the properties of AAS mortars, thus compensating for the limitations of each constituent.