Synthesis And Chloride Resistance Of Alkali-activated Metakaolin-fly Ash Geopolymers

Geopolymer is a novel inorganic cementitious material.Because of its excellent mechanical properties,high temperature resistance and early strength rapid hardening,it has been paid much attention and widely researched in recent years.It has a threedimensional network structure with amorphous and quasicrystal characteristics,formed by the polymerization of silica tetrahedron and aluminum oxygen tetrahedron.It has a wide range of applications in many fields.In the study of concrete durability in the marine environment,the steel corrosion by chloride ions has brought serious safety hazards to the industry,resulting in immeasurable economic losses.Thus,preventing marine corrosion has been becoming a research hotspot in the field of concrete and structural engineering.Therefore,the study of the corrosion resistance of the geopolymer can provide a certain basis for this new material to be put into the marine environment.The main research contents are:(1)The ratio of fly ash – metakaolin composite geopolymer was studied.From the same fluidity aspect,NaOH solution and KOH solution of the same concentration were used as alkaline excitation agents.In the experiment,ten groups of matching ratios were obtained.The compressive strength of the sample was analyzed,the relationship between strength and fly ash ratio,strength and the type of alkaline activator were studied.Under the same fluidity,the time-varying model of the compressive strength and fly ash ratio in the geopolymer material was established.(2)The effect of carbonization on the resistance of geopolymers to chloride ion corrosion was studied.A comparison between the 14 d carbonization and non-carbonization groups of the samples was designed,and the adsorption to chloride ions under different ratio was tested.Solution with different concentrations was set to study the effect of different concentrations on the chloride ions absorption of geopolymers.XRD was used to analyze the composition of samples in the pre-and post-adsorption.Based on the above,the relationship between the chloride ions resistence and composition under different ratios was analyzed.(3)The corrosion resistance to chloride salts of geopolymer in underwater and tidal zone of marine environment was studied.The chloride transport was simulated under natural immersion and dry-wet circulation circumstance.The free chloride ions concentrations in the different depths were obtained after maintaining a certain temperature,humidity and concentration for 30 days,to find out the different corrosion resistance to chloride under natural immersion and dry-wet circulation.Based on the Fick's Second Law,the chloride diffusion coefficient was obtained.