The Research On Formation Mechanism Of Paste-Aggregate Interface Zone Of Geopolymer Concrete Based On Alkali Fusion Method

Due to the great difference between the raw material composition and reaction mechanism of geopolymer and traditional Portland cement,the Interfacial Transition Zone(ITZ),which is widely recognized as the weak link in cement concrete,will also have different composition structure,microscopic morphology and mechanical properties.In order to understand the structure and properties of paste-aggregate interface in geopolymer concrete,the reaction behavior,reaction level and influencing factors of basalt under alkali excitation were studied in this paper,and the microstructure,mechanical properties and formation mechanism of geopolymer concrete paste-aggregate interface were analyzed.The main contents and results of the study are as follows:The chemical composition and content of reactive alumina of basalts were analyzed.The microstructure,mechanical properties and molecular structure of basalts were characterized by XRD,SEM,strength test and FTIR.The effects of alkali fusion process and parameters on the content of activated alumina in basalt were analyzed.The effects of the activator modulus,liquid-solid ratio,alkali fusion activation and metakaolin(MK)content on the reaction level of alkali-activated basalt were studied.Basalt was activated by alkali fusion using dry and wet alkali fusion methods.The alkali fusion effect of basalt under different conditions was investigated by the influence depth of alkali fusion and the elemental analysis before and after alkali fusion.The samples of the interface zone between alkali fused basalt and geopolymer were prepared for the test of macroscopic and microscopic mechanical properties.The interface products were analyzed by FTIR,XRD and EDS,and the formation mechanism of the interface zone was discussed.The results show that the geopolymerization of basalts may occur under alkali activation at a low level.The low content of reactivated alumina in basalt is the restriction of geopolymerization level,and different activator modulus and liquid-solid ratio have no significant effect on the reaction level.Alkali fusion process can effectively increase the content of activated alumina in basalt,and it increases with the increase of NaOH content.After alkali fusion,the reaction level of the basalt is increased to 37.96%under alkali activation,forming a relatively dense hardened slurry structure,and the compressive strength of the basalt at 7 days increases from 2.36MPa to 12.07MPa.The addition of MK can effectively improve the alkali excitation reaction level of basalt,and the higher the dosage of MK,the higher the reaction level of basalt.The amount of alkali has a significant influence on the alkali fusion effect of basalt aggregate,and the effect of wet alkali fusion is better than that of dry alkali fusion.The maximum depth of alkali fusion of wet alkali fusion reaches 1.34mm when the amount of sodium hydroxide reaches 7g,and the closer to the rock surface,the higher the content of reactive elements.The bonding strength between basalt and mortar after alkali fusion treatment is greatly increased from 0.1 MPa to 0.252MPa at most.At the same time,the thickness of the interfacial transition zone increases with the increase of the amount of alkali in the process of alkali fusion,the maximum thickness of the interfacial transition zone increases from less than 30μm to about 100μm,and the bond strength increases with the increase of the thickness of the interfacial transition zone.The formation mechanism of the interface between metakaolin base polymers and basalts may include three parts:mineral activity enhancement,solvation of reactive ions,and geopolymerization.