Study On Composition Design And Performance Of Fly Ash-based Geopolymer High-strength Mortar

In order to solving the problems of high construction cost of cement pavement,and long road opening time for cement concrete pavement repair materials and poor durability,a fly-ash based Geopolymer mortar was developed.However,the geopolymer mortar prepared with fly ash has shortcomings:easy efflorescence,low strength,high in toughness,these properties seriously affect the application in practical engineering.This passage uses fly ash as the main raw material,the range of Fly ash-based geopolymer mortar is optimized by orthogonal test,through ion titration method measuring the basic ion of the surface,analysing the influence factors of efflorescence of mortar,and based on it design parallel test,verify the inhibitory effect of technical measures on efflorescence.Optimizing polyvinyl alcohol fiber(PVA fiber)and polypropylene fiber(PP fiber),to study the mechanical properties and shrinkage properties of fiber-modified fly ash-based geopolymer mortar,preparing fly ash-based geopolymer high-strength mortar.The conclusions are as follows:1.Analyzing the polymerization mechanism of the fly ash-based geopolymer and the reason of the mortar efflorescence.The main reason of the efflorescence is the low utilization rate of the alkali activator in the Geoash mortar,unused activator escapes out of tiny pores to form a white substance that forms an efflorescence.2.Geoash mortar materials can prepared with the sodium silicate solution with different modulus.When the modulus n=1.2,the effect of inhibiting the efflorescence is significant.The alkali-activator has suitable dosage range,the optimal dosage per kg of powder is 1.8mol sodium silicate solution.3.The addition of slag can significantly inhibit the efflorescence of the material and improve the mechanical properties,and on the basis of adding 10%slag,the compound additions of 0-3%silica fume can effectively inhibit the efflorescence.The lower the water-binder ratio,the lower the efflorescence of the material,when the water-binder ratio was 0.40,the 28 days efflorescence was 675.4mg/L.The inhibition of the efflorescence of the material is evident at a glue to sand ratio of 0.45.4.Comparing with other curing humidity,the efflorescence inhibition effect was best when the curing humidity was above 90%;And the best temperature in steam curing condition is 75 ℃,and curing 24h efflorescence inhibition effect is the best.5.When the PVA fiber content is 0.8%and the length is 6mm,the toughening effect of the fly ash-based geopolymer mortar is the best in the same kind of fiber;when the PP fiber content is 1.6%and the length is 9mm,the toughening effect is the best in the same kind of fiber.6.Using SEM to observe the micro-morphology of fibers in the mortar,it can be found that the PVA fiber has rough surface which can be bonded to the material and the structure is more compact,the modified Geoash mortar compressive strength can reach 63.77MPa,The PP fibers have a regular straight line in the interior of the material,failing to form a cage structure in the mortar interior,which is inferior to the modification effect of the PVA fiber.7.The compressive strength of fly ash based geopolymer high strength mortar prepared in this paper is 63.77 MPa,and the flexural strength is 11.67 MPa.It can be used as a cement concrete pavement material to paved high-grade highway pavement and pavement repair materials.