Study On The Chemical Activating Strength And Volume Stability Of Geopolymer Based On Circulating Fluidized Bed Combustion Ash And Slag

As a green environmental protection cementitious material,geopolymer has excelent properties such as early strength,fast hardness,high temperature and corrosion resistance.Now it has become a research hotspot in the field of materials.Circula ting fluidized bed de-sulfurization ash(CFBA)has become a large amount of industrial solid waste.From the point of view of chemical composition and mineral composition,it has the synthetic conditions of geopolymer.However,the undesirable volume stability and pozzolanic activity result in its application in geopolymer.In this paper,starting from the undesirable volume stability and low strength of CFBA-geopolymer,the effect of type of activator,dosage of activator,curing condition and composite ratio of CFBA/slag on the volume stability and strength in geopolymer,at the same time,the microstructure of geopolymer was detected with XRD and IR.The main results of the study are as follows:(1)In dry environment,there are no expansion products such as ettringite and gypsum in the water glass or sodium hydroxide or carbonate activated CFBA,the volume deformation is mainly caused by drying shrinkage of C-A-S-H gel.The drying shrinkage of chemically activated CFBA-geopolymer from small to large is: carbonate<sodium hydroxide<water glass.The alkali equivalent in the range of 3 to 7%,the drying shrinkage of CFBA-geopolymer activated by sodium silicate increases with the increase of activator content,the drying shrinkage of CFBA-geopolymer activated by NaOH and carbonate decreases with the increase of activator content.The compressive strength of the chemically activated CFBA-geopolymer from small to large is: water glass<sodium hydroxide<carbonate.The alkali equivalent in the range of 3~7%,the compressive strength of CFBA-geopolymer activated by water glass or carbonate increases with the increase of activator content,the compressive strength of CFBA-geopolymer activated by sodium hydroxide first increases and then decreases with the increase of activator content.Under the condition of water curing,gypsum is formed in the polymer of CFBA by chemical activation,which causes expansion damage to the CFBA-geopolymer,and it is not conducive to the occurrence of polymer polymerization by chemical activatio n of CFBA,resulting in the decrease of C-A-S-H gel production and the reduction of compressive strength.(2)The hydration products of the slag-geopolymer activated by water glass,sodium hydroxide or carbonate are obviously different,the drying shrinkage of slaggeopolymer activated by water glass is the largest,the drying shrinkage of slaggeopolymer activated by sodium hydroxide and carbonate are close.The 28 d compressive strength of the chemically activated slag-geopolymer from small to large is: sodium hydroxide <carbonate < water glass,but when the content of sodium silicate is more than 5%,the strength of slag-geopolymer decreases after 14 days.Under the condition of water curing,the volume deformation law of chemically activated slag geopolymer is the same,the volume of early stage shrinks slightly,and the volume of later stage swels slightly,compared with the dry condition,water curing will make the compressive strength of the slag-geopolymer decrease to a certain extent.(3)The compressive strength of CFBA-slag composite geopolymer increases with the increase of slag composition ratio.The compound ratio of slag increases,and the SiO and Al-O bonds of the CFBA-slag composite geopolymer increase by alternating condensation.The asymmetric stretching of Si-O-Al contributes to the formation of C-SA-H gel.Under drying conditions,the drying shrinkage of CFBA-slag composite geopolymer increases with the increase of the proportion of slag composite.Under the condition of water curing,the linear expansion of CFBA-slag composite geopolymer decreases with the increase of the proportion of slag composite.