响应面法优化D-甘露糖醇改性磷酸镁水泥性能研究OA

Magnesium phosphate cement(MPC)is formed by magnesium-based raw materials(whose main components include magnesium oxide or magnesium hydroxide),phosphates,and retarders.MPC exhibits excellent performances such as rapid setting and hardening,high early strength,superior bonding capability and good volume stability,and it has been widely applied in road rapid repair,airport runway maintenance and special structural rehabilitation.Nevertheless,the traditional retarder borax causes obvious early strength deterioration of MPC when it is incorporated,and it fails to achieve a good balance between working performance and mechanical strength.Moreover,most new retarders still exert adverse impacts on the early mechanical properties of MPC,so their retarding effect and strength development could not be coordinated well.To address the above deficiency,this study adopted response surface methodology to explore the synergistic influence and regulation mechanism of D-mannitol and borax compound system on MPC performances. Borax and D-mannitol content were selected as experimental variables,both ranging in mass fraction from 2.50%to 5.01%.A two-factor,five-level central composite design was adopted,and quadratic polynomial regression models were established to correlate borax content and D-mannitol content with setting time,1 d flexural strength,and 1 d compressive strength.Variance analysis results indicate that all regression models were highly significant,with high coefficients of determination and low coefficients of variation,demonstrating satisfactory fitting accuracy and predictive reliability of the models.Experimental results show that the retarding effect of D-mannitol is more pronounced at a low borax content of 2.50%～3.50%by mass.At a high borax content of 4.50%～5.01%by mass,the early strength initially increases and then decreases with rising D-mannitol content.By contrast,strength declines monotonically as D-mannitol content increases at low borax content.The optimal mix proportion is obtained by model optimization:borax content is 2.50%and D-mannitol content is 4.78%.Under this optimal proportion,the measured setting time is 29.0 min,the 1 d flexural strength is 8.6 MPa,and the 1 d compressive strength is 48.1 MPa.Multiple characterization analyses show that in the optimized composite system,D-mannitol reduces the agglomeration of magnesium oxide particles through its dispersion effect,whereas borax acts as a retarder by forming a protective film on the surfaces of magnesium oxide particles.This dispersion-film formation effect regulates pH evolution,thereby reducing the early hydration rate of MPC.Meanwhile,the optimized composite system accelerates the dissociation of the protective film at specific hydration stages,exposes active sites on magnesium oxide particle surfaces,enhances the generation of hydration products,improves the density of the matrix,and effectively promotes the early strength development of MPC. This study clarifies the synergistic mechanism of D-mannitol and borax,and provides theoretical support and technical reference for the application of D-mannitol-modified MPC.