Influence Mchanism of Nano-silica on the Early-strength of High-fluidity Slag and Desulfurization Gypsum Composite Alkali Activated Material
The high-fluidity slag and desulphurization gypsum composite alkali material with(HSD-AAM)as precursors is one of the new building materials commonly used in the restoration and reinforcement of structures.In order to ensure fluidity,HSD-AAM usually uses a high water-binder ratio,which affects its early strength and thus limits the application of HSD-AAM.To solve this problem,the impact of the amount of nano-silica(NS)on the fluidity,setting time,flexural strength and compressive strength(1d,3d,7d)of HSD-AAM were studied through laboratory experiments,in order to improve the early strength of HSD-AAM without affecting its fluidity;Furthermore,thermogravimetric analysis and differential scanning calorimetry(TG-DSC),X-ray diffraction(XRD),and scanning electronic microscopy(SEM)were used to examine the hydration products and microstructure of the various varieties of HSD-AAM,the mechanism of enhancing the early strength of HSD-AAM by NS content was revealed.The results show that with the increase of NS content,the fluidity and setting time of HSD-AAM decrease,while the early strength increase significantly.When NS content is between 0 and 3％,the fluidity of HSD-AAM decreases by an average of 6.0％with each increase of 1％;the initial and final setting times shorten by 13.7％and 10.0％respectively;1 d flexural strength and compressive strength increase by 10.7％and 20.2％on average;3 d flexural strength and compressive strength increase by 23.3％and 12.4％on average;7 d flexural strength and compressive strength increase by 11.1％and 32.9％on average.This is due to the high pozzolash activity of NS and the hydration reaction with Ca(OH)2 in the slurry in the early stage,which promotes the hydration process and generates a large amount of C-S-H gel,which improves the loose structure of the slurry and makes the microstructure of the slurry more dense in the early stage.
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