Study On Rheology And Modification Mechanism Of Cement Pastes With Alkanolamines

As a kind of common grinding aids in cement produce,alkanolamines can significantly reduce the energy consumption of cement grinding,and also improve the early performance of cement.Several typical alkanolamines,including triethanolamine（TEA）,triisopropanolamine（TIPA）and diethanol-isopropanolamine（DEIPA）,have been widely studied by many experts and scholars for their effects on the mechanical properties,micro morphology and pore structure of cement.However,the effects of alkanolamines on the rheological properties and early hydration of cement-based materials are rarely studied.In this paper,the influence of three alkanolamines（TEA,TIPA,DEIPA）on the early rheological properties of cement was studied,and the rheological properties were also controlled by changing the content of SO₃（using gypsum）.I have revealed the action mechanisms of alkanolamines in cement to a certain extent from micro perspective by the analysis of heat of hydration experiment,X-ray diffraction and ion concentration in the cement liquid phase.The main research contents and results are as follows:（1）The effect of alkanolamines on the early rheological properties of cement paste was studied.The results show that after the alkanolamine is incorporated into cement,the initial fluidity of the cement paste is not significantly affected,but the fluidity loss of the cement paste will increase over time,especially the fluidity loss over time in the first 30minutes.And the fluidity loss over time increases with the increase of the dosage of alkanolamines.In general,the shear stress and apparent viscosity of cement paste increase with the increase of the content.The system is a typical Hereshel-Buikley fluid,with power law coefficient less than 1,appearing as obvious shear thinning behavior.With the increase of the content of alkanolamines,the apparent viscosity of the pastes rise significantly,and the shear stress growth within 120 minutes is also significantly higher than that of the control group.（2）The effect of alkanolamines on the early rheological properties of cement paste after adjusting the SO₃ content by change the dosage of gypsum was studied.After adding a proper amount of gypsum,when the dosage of alkanolamines is low（0.02%,0.05%）,the time loss of fluidity of the cement paste is significantly decreased,and when the dosage of alkanolamines is higher（0.1%）,it can also be partially decreased.Rotary viscometer test results show that when the shear rate is 204.3s^-1 and the dosage of alkanolamines is 0.1%,after adding water for 120 minutes,the shear stress of TEA group drops from 56.2Pa to 47.7Pa,and the shear stress of TIPA group is also reduced from56.2Pa to 47.7Pa,and the shear stress of DEIPA group decreased from 50.2Pa to 49.4Pa.（3）The rheological behavior and regulation mechanism of cement paste under the effect of alkanolamines were studied by heat of hydration test,ICP-OES,X-ray diffraction and other methods.The results of the heat of hydration show that TEA prolongs the induction period of cement hydration,delays the hydration of C₃S,and slightly reduces the accumulated heat in the early stage.TIPA promotes the conversion of ettringite to AFm,and the secondary ettringite heat release in the DEIPA group is sharper than the TEA and TIPA groups.After adding gypsum,the aluminate reaction accelerated by alkanolamine is regulated,and the reaction rate is significantly slowed down.ICP-OES results show that alkanolamines increase the dissolution of Fe³⁺and Al³⁺in the cement liquid phase,which is the reason for the acceleration of early cement hydration.XRD results show that alkanolamines can promote the formation of ettringite in the early stage of cement hydration.Increasing the content of SO₃ in cement can reduce the amount of ettringite formed in the same time.From this,it can be concluded that the rheological behavior and modification mechanism of cement pastes under the effect of alkanolamines are mainly as follows:alkanolamines significantly promote the dissolution of iron and aluminum phases in cement clinker minerals,promote aluminate reaction,and can form more ettringite,affect the rheological behavior of cement pastes,especially the fluidity loss.The increase of SO₃ content in cement significantly reduces the aluminate reaction rate in the early hydration of cement,and the formation of ettringite decreases in the same time,which can slow down the influence of alkanolamines on the rheological behavior of cement pastes to a certain extent.