Effects Of The Activation On Fly Ash-based Geopolymer By Various Activators

Geopolymer is a new-type green and environmentally gel material produced from the reaction of activator and silico-aluminum materials,with the characteristics of extensive researches and applications.Fly ash is often used as the precursor of geopolymer,which can transform the solid waste into resources to a certain extent.However,various activators show different performances when activating fly ash.In this paper,sodium silicate,calcium hydroxide,calcium sulfate,as well as calcium hydroxide+calcium sulfate were used as the activators to study the effects of the activation on fly ash-based geopolymer.Unconfined compressive strength test,X-ray diffraction analysis?XRD?,Fourier transform infrared light?FTIR?,²⁹Si nuclear magnetic resonance(²⁹Si NMR),scanning electron microscope and energy disperse spectroscopy?SEM-EDS?,and physisorption experiment?BET?were carried out to study the effects of various activators with different dosages on the mechanical property and microstructure of fly ash-based geopolymer.The main conclusions are as follows:?1?The main product of the geopolymer activated by sodium silicate is hydrated sodium aluminosilicate.As the modulus decreases and meanwhile the dosage of sodium silicate increases,the reorganization and polymerization of gel products are accelerated so that the integrity and continuity of the microstructure of geopolymer are improved,and then the strength increases.When the modulus of sodium silicate is3.28,the maximum value of the strength is at the dosage of 10%.?2?The strength of geopolymer activated by calcium hydroxide and calcium sulfate respectively increases with the dosage of each activator increasing.The main products by calcium hydroxide are hydrated calcium silicate and calcium hydrated aluminate.With the dosage of calcium hydroxide increasing,the activation of fly ash is accelerated so that the amount of gel products is increased,and the integrity and continuity of the microstructure of geopolymer are improved.The main product by calcium sulfate is ettringite.With the dosage of calcium sulfate increasing,the amount of ettringite is increased,and then the density of the microstructure of geopolymer is improved.Moreover,the activation effect of calcium sulfate is better than calcium hydroxide.?3?The strength of geopolymer activated by composite calcium hydroxide and calcium sulfate decreases with the increase of the dosage of calcium sulfate.The main products during the reaction are hydrated calcium silicate,hydrated calcium aluminate,and ettringite.With the increase of the proportion of calcium sulfate,the amount of ettringite increases but the gel products decrease so that the integrity and continuity of the microstructure of geopolymer gradually decreases.When the mass ration of calcium hydroxide to calcium sulfate is 3:1,the activation effect on fly ash is the best.?4?On the whole,the activation effect from strong to weak is:sodium silicate,calcium hydroxide+calcium sulfate,calcium sulfate,calcium hydroxide.