Study On Cement Strength Development And Hydration Mechanism With Alkanolamines

As the main components of cement grinding aids,alkanolamines can not only improve the grinding efficiency of cement,but also significantly affect the hydration process and performance of cement.In recent years,supplementary cementitious materials（SCMs）have been widely used,They play an important role in reducing the cost of raw materials and improving the properties of cement based materials.However,at present,the research on alkanolamines mainly focus on the field of cement clinker mineral phase hydration,and the research on the interaction between alkanolamines and SCMs is not systematic.This paper aims to investigate the effect of triethanolamine（TEA）and triisopropanolamine（TIPA）on hydration of cement and fly ash/limestone composite cement,and to study on its strength development law and hydration mechanism.The main research contents and results are as follows:（1）Thermodynamic modeling was applied to investigate the influence of fly ash/limestone on the hydrate assemblage.The results showed that fly ash promoted the conversion of ettringite（AFt）to monosulfate（Ms）,and limestone powder leaded to the formation of monocarbonate at the expense of Ms and thereby stabilized the AFt,fly ash also enhanced the chemical reaction of limestone powder and leaded to the presence of more calcium carboaluminate.The results of thermodynamic modeling were in good agreement with those of XRD,which can accurately predict the types and development of hydration products of composite cement.（2）The hydration mechanism of cement with TEA and TIPA was studied.The results showed that TEA and TIPA can change the early hydration kinetics of cement,also can improve the hydration of cement clinker and hasten the conversion of AFt to Ms.The effect of TEA on the hydration of intermediate phases（C₃A/C₄AF）was significant only in the early stages（1d）,while the effect of TIPA on the dissolution of C₄AF can last to28d.In addition,at 3d curing age,the addition of TEA and TIPA promoted the formation of coarse sulphoaluminate clusters and the number of the internal C-S-H gel decreased or disappeared completely.（3）Design of experiments（Do E）was used to investigate the influence of TEA and TIPA on the strength development law of the fly ash-limestone composite cement.The results showed that limestone powder was more effective than fly ash in enhancing early strength of cement,while fly ash was effective in enhancing the 28d strength than limesone powder.The synergistic effect between fly ash and limestone powder is not significant without chemical additives.The addition of TEA and TIPA improved the early strength of fly ash-limestone composite cement,and enhanced the synergistic effect between fly ash and limestone powder,particularly TIPA,resulting in the high volume of fly ash and limestone powder in composite cement without loss of strength.（4）The synergistic effect between fly ash and limestone powder with TEA and TIPA was studied.TEA and TIPA were able to significantly promote the hydration of C₃A/C₄AF and increase the hydration degree of cement clinker in the early stages,resulting in the more formation of aluminate hydrates and more portlandite to react with fly ash.At the same time,the complexation of TEA and TIPA can also promote the dissolution of fly ash,so fly ash showed high hydration activity.In addition,the Al³⁺provided by fly ash further enhanced the chemical action of limestone powder and formed more calcium carboaluminate.These hydration products further filled the pores and refined the microstructure,the structure of the hardened cement paste was dense,which resulting in strength improvement of composite cement.TIPA was better than TEA because it can continuously promote the dissolution of C₄AF and increse the overall hydration of cement clinker,generate more portlandite to activate the hydration activity of fly ash,and more Al³⁺to react with limestone powder.Therefore,TIPA can further improve the reaction degree of fly ash and limestone powder.