Effect Of Lithium Slag On Rheological Properties And Hydration Characteristics Of Cement-Superplasticizer Paste

With the expansion of lithium salt application fields and the rapid growth of market demand,Chinese lithium salt industry has developed rapidly.At the same time,a large amount of lithium slag is generated and its stockpile has increased year by year.The application of lithium slag as a mineral admixture for resource utilization is one of the effective ways to solve that problem.With the progress of hydration,the hydration products in the paste increased and the rheological behavior of the system also changed,i.e.,to a certain extent,the change of rheological properties can reflect the early hydration process,and hydration is also a factor affecting the rheological properties of the system.In order to study the effect of lithium slag dosages and fineness on the rheological properties and hydration characteristics of cement-superplasticizer paste,multi-methods such as fluidity and fluidity loss,rheological parameters(yield shear stress and plastic viscosity),Zeta potential,hydration heat,28 d compressive strength,etc,were used to characterize the impacts of lithium slag.The results showed:(1)Lithium slag is a porous material with a large internal specific surface area,and its pores are mostly large pores.Therefore,the application of lithium slag should pay attention to the absorption of water and the adsorption of the superplasticizers by the pores in the structure.(2)The initial fluidity,fluidity loss,initial yield shear stress and plastic viscosity of the lithium slag-cement composite cementitious material system all decreased with the increase of the dosages of lithium slag,and the effect of the increase of the specific surface area of lithium slag on the rheological properties of the system also presented a similar pattern.When the amount of lithium slag was more than 15%,the shear stress was greatly improved and the rheological properties were deteriorated.The fluidity of the paste had a high correlation with the yield stress,but had little relationship of the plastic viscosity.(3)Superplasticizers were prone to adsorb on the surface of lithium slag which showed a negative zeta potential in pure water,and that caused a further decline in the Zeta potential of paste.With the increase of lithium slag dosages or specific surface area,the initial Zeta potential of the composite cementitious material system decreased.(4)With the increase of lithium slag dosages,the first exothermic peak of composite cementitious material system moved forward and the peak value increased more than the pure cement system,the induction period was prolonged,the second exothermic peak appeared later and the peak value decreased less than the pure cement system,and the total exothermic value of the system gradually decreased.With the increase of the specific surface area of lithium slag,the peak value of the first exothermic peak gradually decreased;the appearance time and duration time of the induction period were almost the same,and the lithium slag fineness had little effect on them.The second exothermic did not move and the second exothermic peak value of the test group with medium fineness lithium slag was the largest.This phenomenon was the result of mutual restriction of factors affecting hydration reaction.When the dosage was constant,the change of the specific surface area of lithium slag had little influence on the total heat release of the composite cementitious material system.(5)The 28d compressive strength of the hardened paste increased first and then decreased with the increase of the amount of lithium slag.The optimum dosage was 15%.Improving the pore structure of hardened paste was the main reason for increasing the strength of hardened paste when the dosage was low.Although the activity index of lithium slag increased with the increase of specific surface area,the increase of specific surface area would also lead to the increase of water demand of the system and decreased the strength of hardened paste for 28d.