Characterization Of ITZ Microstructure And Its Relationship With Mechanical Properties Of Concrete

The interface between the aggregate and the paste is a weak link of the concrete,which has an effect on the strength and durability of the concrete.In this paper,the relative content of C-S-H microstructure and different polymerization states were quantitatively characterized by high-resolution NMR,FTIR,XRD and TG.The low of dynamic evolution of the C-S-H structure,CH crystal orientation,size and content in different admixtures and with the curing age is revealed,and the evolution mechanism of the structure is discussed.The dynamic relationship between the interface microstructure and the macroscopic mechanics of the concrete is explored,and the interface microstructure and macro-mechanics model.The parameters of CH crystal were quantitatively characterized by XRD and TG,and the dynamic changes of CH crystal under different admixture and different curing ages were studied.The results show that there is a phenomenon that CH crystal is enriched,oriented growth and crystal size is large,and the pozzolanic effect and physical action of silica fume and fly ash can effectively inhibit this characteristic of CH crystal in the interface.With the increase of the curing age,the CH content of the interface increases,the orientation index and the crystal size decrease.The FTIR and NMR techniques were used to characterize the interface and paste of C-S-H gel structure under different conditions.The mechanism of interface weakening was explored from the perspective of C-S-H gel structure.It was found that the interface had the relative content of Q¹+Q²,the length of [SiO₄] ^4-tetrahedron chain and the degree of polymerization were small,which led to the unstable structure of the interface.However,the incorporation of silicon powder and fly ash increases the average chain length and degree of polymerization of the interface C-S-H gel,thus enhancing the interface performance.With the increase of the age of C-S-H gel,the relative content of Q¹+Q²,the average chain length and the degree of polymerization were increased.The relationship between interface microstructure and macroscopic mechanics was obtained.The relationship between the interface orientation and the average crystal size and flexural strength and compressive strength was established.The relationship between the polymerization degree of C-S-H gel and the macroscopic mechanical properties was investigated.It is found that the flexural and compressive strength decreases linearly with the increase of the orientation index and the average size of the CH crystal.With the increase of the average chain length and the degree of polymerization of the interface C-S-H gel,the flexural and compressive strength is enhanced.