Influences Of Superplasticizers With Different Anchoring Groups On Properties Of Fresh Cement Pastes

The vigorous construction of infrastructure requires higher and higher construction materials such as cement,and the required functional characteristics are becoming increasingly diverse.Among them,the rheological property is a key indicator that determines the construction quality and durability of cement-based materials.The rheology of cement-based materials is closely related to the internal microstructure of the slurry,and it is also affected by many factors such as the type of superplasticizer,dosage,temperature and construction time.This paper studies the influence of different types and amounts of water reducer on the rheology and temperature sensitivity of fresh cement paste,and reveals the mechanism of action of different water reducers from a microscopic perspective.First,the superplasticizer molecules with four anchoring groups such as carboxyl group,sulfonic acid group,amine group and silane,and prepare fresh cement slurry with different amounts of superplasticizer were prepared at different environmental temperatures;The changes of the expansion degree,yield stress and plastic viscosity of the cement paste with the type,dosage,time and temperature of the superplasticizer were measured separately;the elasticity of different superplasticizers on the freshly mixed slurry was tested with an optical micro-rheometer Index,viscosity index,solid-liquid equilibrium value,storage modulus and loss modulus and other viscoelastic parameters;secondly,Morphologi G3 optical microscope was used to directly observe different types of superplasticizer,admixture and freshly mixed cement slurry at ambient temperature The microstructure characteristics of the body establish the relationship between the microstructure of the slurry and the macro fluidity;afterwards,by testing the amount of superplasticizer adsorbed and its effect on the hydration heat of cement,we explored and clarified the different types of different types at different temperatures The adsorption behavior of the water reducer on the surface of the cement particles and the mechanism of action that affects the hydration of the cement have established an internal relationship between adsorption,hydration and rheology from the perspective of microstructure.The main research conclusions are as follows:(1)The initial expansion of freshly mixed cement paste increases with the addition of superplasticizer agent and then remains constant;the effect of different anchor groups on the superplasticizer is: carboxyl group> silane> sulfonic acid group> amine group The higher the content of carboxyl groups in the liquid,the more significant the increase in initial expansion,and the lower the critical dosage required to achieve the maximum expansion.The initial expansion degree decreases with the increase of temperature;the water reducer with high water reducer content or high carboxyl content will significantly weaken the temperature sensitivity of the initial expansion degree of the slurry,that is,the initial expansion degree is almost not affected by temperature.The change law of initial yield stress and plastic viscosity is completely consistent with the change law of initial expansion degree.(2)The flow retention of the freshly mixed slurry gradually increases with the addition of the superplasticizer,and remains unchanged after reaching the critical dosage;the effect of the superplasticizer of different anchoring groups is: carboxyl group>silane>sulfonic acid group> amine groups;the flow retention of the slurry decreases with increasing temperature;water reducers with high water reducer content or high carboxyl content will significantly weaken the temperature sensitivity of the slurry flow retention.In most cases,the yield stress and plastic viscosity increase with time,and the growth rate decreases with the addition of the superplasticizer,and increases with increasing temperature;the higher the amount of superplasticizer,or the higher the carboxyl content,the increase The lower the amplitude and its temperature sensitivity.(3)The elasticity index increases with time,and the elasticity index grows faster in the early stage and slower in the later stage;as the time increases,the solid-liquid equilibrium value of the slurry decreases continuously until it approaches or equals 0,the solid-liquid equilibrium value is relatively stable in the early stage,and the change range is not large,but the solid-liquid equilibrium value decreases rapidly in the later stage;the macroscopic viscosity index of the slurry increases with time,first increases steadily,then increases rapidly,and finally slowly increases;Comparing the macroscopic viscosity index of the slurry under different water reducer dosages,the higher the dosage,the slower the macro viscosity index of the slurry grows,and vice versa;the elasticity index increases as the temperature increases,and the higher the temperature the elasticity The shorter the time for the index to reach a stable value,the higher the amount of cement paste elasticity index increases when the amount is high,the longer it takes to reach the stable value,that is,the cement when the amount of water reducer is high The elasticity index of the slurry is sensitive to temperature.(4)When the amount of superplasticizer is large and the content of carboxyl group is high,the inhibitory effect on the cement hydration process is more significant;temperature increase can shorten the cement hydration induction period and increase the maximum heat release rate of cement hydration;The adsorption amount of the superplasticizer on the cement surface increases with the increase of the dosage;when the dosage is low,the growth rate is faster,and when the dosage is high,the growth rate is slow;with the increase of the carboxyl content,the peak value of the cement hydration rate decreases sequentially,and the peak value is required The time increases in turn,and the hydration induction period of cement increases in sequence;the increase in the carboxyl content makes the amount of superplasticizer adsorbed on the surface of cement particles increase and the inhibition of cement hydration increases.When the inhibitory effect of the superplasticizer is continuously enhanced,the peak value of the hydration heat release rate is reduced,and the hydration induction period is extended.(5)The microstructure of freshly mixed cement paste shows that the addition of superplasticizer can change the size of the flocculation structure in the cement paste and release a certain amount of free water,which in turn affects the rheological properties of the paste and the cement hydration process.With the increase of the content of carboxyl groups in the water reducer,the dispersion of the cement slurry at 5 min and 60 min increases,and the large-scale flocculation structure decreases;when the superplasticizer with high carboxyl content is added,the size of the flocculation structure increases with time.Prolonged slow growth,that is,the growth of flocculation structure is significantly inhibited.As the temperature increases,the large-size flocculation structure increases,and the small-size flocculation structure decreases,and at 60 min,the size of the flocculation structure in the freshly mixed slurry increases significantly with temperature.