The Study On Strength And Hydration Properties Of Geopolymers With Different Oxide Composition

Due to the complex composition of the geopolymer,the strength was different after being excited by the alkaline activator,and the hydration products were also various because of the addition amount of calcium.It was difficult to directly detect the type of gel in the hydration products,which makes it difficult to predict the strength of the geopolymer.In this paper,the titration method was used to detect the content of active oxide in raw materials,and geopolymer was prepared according to the content of SiO2,Al2O3 and CaO.By combining the gray relational analysis and the dichotomy to research the dominant factors of strength,which was the basis to divided geopolymers into two regions.Strength was dominated by the SiO2/Al2O3 ratio in region ?(?cao<25%).However the CaO content had more important effect to strength in the II region(?cao>25%).A series of geopolymers were prepared in region I and region ?,and the intensity in different excitation conditions was projected in the three-dimensional coordinate plot.It was found that the geopolymer with intensity range from 0 to 100 MPa could be prepared in region I,where requires a low modulus sodium silicate as the alkali activator,when the alkali activator modulus range from 1.2 to 1.6.The intensity range of geopolymer in region II was 40?90MPa,and most of the strength were about 70MPa.The larger the alkali activator modulus was in the range from 1.2 to 1.4,the better the strength of geopolymer was.By the hydration heat analysis,it was found that the hydration process of geopolymers in region I(?cao<25%)included start,induction,acceleration,deceleration and stabilization.The process of hydration of geopolymer in region ?(?wcao>25%)went through seven stages:initial phase,induction phase,acceleration phase,deceleration phase,secondary acceleration phase,secondary deceleration phase and stationary phase.CaO in slag will prolong end time of the induction period and advance the end time of the acceleration period.C-S-H and N-A-S-H gels were prepared by sol-gel method and compared with geopolymers.FTIR showed that the structure of geopolymer in region I was similar to that of N-A-S-H gel,which had more-Si-O-Si-non-bridge oxygen bond.The structure of geopolymer in region II was similar to that of layered C-S-H gel,where the-Si-O-bridge oxygen bond incresed,and the chain-like product was increased.TG-DSC and XRD showed that the geopolymers in region I mainly consisted of zeolite structure and N-A-S-H gel.The geopolymer in zone II contained hydrate calcium silicate and zeolite structure.According to mapping analysis geopolymers in region I mainly contain N-A-S-H gel with Si/Al=2,and the spatial distribution was inhomogeneous.Geopolymers in region ? contain a large amount of C-(A)-S-H gel,calcium-rich C-(A)-S-H gel filled defects and cracks in the system,which became more compact.