Experimental Study On Mechanical And Electr Ochemical Properties Of Lightweight Cement Fly Ash Roadbed Filler(LCFF)

For road subgrade in central and northern Shanxi,Durability issues under salt-alkali corrosion and freeze-thaw conditions,And for the purpose of improving the utilization efficiency of fly ash material waste,a lightweight cement fly ash roadbed filler was prepared（LCFF）,By testing the variables such as different fly ash content:LCFF under normal curing conditions,freezing and thawing conditions and salt solution corrosion conditions,unconfined compressive strength and electrochemical parameters were studied.The relationship between the compressive strength and the electrochemical characteristics is discussed,inferred:（1）Through testing the physical properties of LCFF materials:As the proportion of fly ash continues to increase,the density of the material increases first and then decreases,and the water absorption rate and thermal conductivity both increase and then decrease.Unconfined compressive strength also increases first and then decreases.As the proportion of bubbles rises,the density of the material will also decrease,the water absorption rate will decrease,the thermal conductivity will decrease,and the unconfined compressive strength will continue to decrease.Under freeze-thaw conditions,after the proportion of fly ash increases,the unconfined compressive strength of the LCFF material continues to decline.Under salt solution curing conditions,as the concentration of the salt solution increases,the unconfined compressive strength of the LCFF material,the overall intensity is a downward trend.It is concluded that the proportion of fly ash is66.7%,the amount of bubbles is 1200L/m³,and the material performance is the best.（2）Based on the electrochemical system of cement-based materials,the law of unconfined compressive strength and electrochemical parameters of LCFF materials with different proportions of fly ash under freeze-thaw conditions was studied,and equivalent circuit models corresponding to them were matched.It is found that the circuit accessories in the model include（1）Q constant phase angle element（2）R_t porous surface layer transfer resistance（3）W porous surface layer diffusion resistance（4）C_d matrix and stomata contact surface capacitance element;（5）R_l material internal matrix resistance（6）R_selectrolyte solution resistance.The analysis shows that with the increase in the proportion of fly ash,the phenomenon of"slip"between colloids causes the material’s compressive strength to decrease continuously.The Nyquist chart consists of two time constants,high frequency and medium wave,and diffusion impedance in the low frequency region.Corresponding to the equivalent circuit model,Q and C_d continue to decrease,and R_t,W,R_l,and R_s continue to increase.（3）The size of the electrochemical resistance element is closely related to the compressive strength of the LCFF material.R_S can reflect the size of the pores in the material.C_d,R_t,R_l,and Q can all indirectly reflect the hydration process of the material.By fitting the compressive strength with the representative two parameter capacitances Q and the solution resistance R_S,the relationship between the two is exponential.R_s,R_t,and R_l are all negatively related to the compressive strength f_cu of the material,while the capacitances C_d and Q it is positively correlated with the compressive strength f_cu.By analyzing the relationship between the characteristics of the electrochemical parameters and the compressive strength,the basic characteristics of the material can be measured quickly and accurately,and at the same time it can adapt to different project conditions,providing an effective way for actual engineering testing.