Study On The Geopolymer Properties Of CFB Desulfurized Ash

Geopolymer is a kind of three-dimensional network cementitious material,which is composed of Si-O tetrahedron and Al-O tetrahedron.It has the advantages of wide source of raw materials,low price,energy-saving production and environmental protection.In this paper,CFB desulfurization ash geopolymer mortar first is prepared by using the original CFB desulfurization ash and ground CFB desulfurization ash,and the strength was optimized under the same curing conditions;Then,the factors influencing the properties of the materials were studied.In order to prepare the best CFB desulfurization geopolymer materials,the effects of curing system on its properties were analyzed.XRD and SEM were used to analyze the mineral composition and micro morphology of the CFB desulfurization geopolymer in different systems.The results show that,（1）In the same curing system,the strength of the geopolymer prepared from the ground CFB desulfurization ash is higher than that of the original CFB desulfurization ash.（2）The setting time of CFB desulfurization geopolymer is more sensitive to the water-binder ratio,On the premise of ensuring workability,reducing the water-binder ratio can shorten the setting time;the setting time increases first,reaches the maximum value and then decreases with the increase of the amount of alkali activator;the setting time is prolonged with the increase of sodium silicate modulus.（3）In the standard curing condition,the strength of CFB desulfurization geopolymer mortar decreases with the increase of water binder ratio,and the strength is the highest when the content of alkali activator is 32%;the maximum strength can be obtained when the modulus of water glass is 1.5.The compatibility of naphthalene series water reducer and CFB desulfurization ash geopolymer is poor,and the fluidity is basically lost 60 minutes later;naphthalene series water reducer has no effect on the strength of CFB desulfurization ash geopolymer mortar.（4）The strength of each age of standard curing is greater than that of natural curing,and the strength gap decreases after 14 days;the strength of each age is the highest when the steam curing temperature is 80℃,when the steam curing temperature is more than 80℃,the steam curing time is more than 8 hours,and then extend the curing time has little contribution to the strength growth;the effect of increasing steam curing temperature on early strength is greater.After steam curing at 80℃for 16 hours,the compressive strength and flexural strength of CFB desulfurization geopolymer mortar reached 38.7MPa and 7.7MPa respectively in 3days,and the compressive and flexural strength reached 41.3Mpa and 9.0Mpa respectively in28 days.The CFB desulfurization ash geopolymer mortar was steam cured at 80℃for 16h,followed by standard curing to 28d.The mass loss rate and compressive strength loss rate after soaking in water were 3.3%and 25.7%respectively.The CFB desulfurization ash geopolymer mortar was standard cured for 28 days,the mass loss rate and the compression strength loss rate after immersion in water were 3.7%and 40.4%.（5）According to the micro-morphology analysis of the SEM spectrum,it can be seen that the internal structure of the CFB desulfurization ash geopolymer is dense,and the entire interface is gelled;moreover,there are more short rod shaped and flaky irregular particles in the network composed of gelatinous substance.Some particles are embedded into gelatinous substance,which increases the stability of the structure and is conducive to the formation of higher strength.（6）According to the phase analysis of XRD pattern,alkali excitation promotes the transformation of Si O₂ to silicon oxygen tetrahedron,and anhydrite in CFB desulfurization ash participates in the reaction to form AFm.After standard curing for 28d and steam curing for 16h at 80℃continue to the standard curing for 28d,the CFB desulfurization ash geopolymers with two curing systems are the same phase.