Influence Of Alkali To Sulfate Ratio On The Rheological Property And Hydration And Hardening Of Portland Cement

The performance of cement is related to many factors,especially the content of alkali and sulfate in cement.In recent years,the content of sulfate and the content of alkali in cement have been raised.Although sulfate and alkali are small components in cement,they play an important role in hydration and hardening of cement.Sulfate generally has a serious influence on the formation of ettringite in the initial age of hydration of the cement,prolonging the setting time,and promoting the development of early strength.Alkali accelerates the progress of hydration of cement,affecting the liquid-phase properties of cement and making the rheology and workability of cement paste worse.In the actual project,alkali and sulfate often affect the performance of cement,and the synergistic effect of alkali and sulfate in cement should be considered.The effect of alkali to sulfate ratio on the early rheological properties and hydration and hardening of cement were studied by this paper,the suitable alkali to sulfate ratio variation range is determined so as to optimize the rheological properties of cement and meet the construction and other performance requirements of cement or concrete.This study selected three kinds of clinker with alkali content of 0.10%,0.34%,and0.64%,and adjusted the alkali to sulfate ratio?R/S=Na₂O_e/SO₃,molar ratio?of cement by adding alkali sulfate and gypsum.And analyze the viscosity,fluidity,strength and hydration products of cement to reflect the effect of different alkali to sulfate ratio on rheological properties and hydration and hardening of cement.The results showed that the viscosity of the low-alkali cement with alkali content of 0.10%first decreased and then increased with the increase of the alkali to sulfate ratio.The inflection point appeared when the alkali to sulfate ratio was 0.4,and while for the cement of 0.64%of the alkali content.The viscosity of cement paste decreases with increasing alkali to sulfate ratio,when the cement with 0.34%alkali content has a gentler change in the viscosity of cement paste with increasing alkali to sulfate ratio,but showing a slight increasing trend;the changes of fluidity also show the same regularity,and the loss of fluidity by the time is not related to the alkali to sulfate ratio;The fluidity,sulfate content and alkali to sulfate ratio of the cement is analyzed by response surface methodology by Design Expert experimental design software,it shows that when the alkali to sulfate ratio ranges from 0.4 to 0.7,the sulfate content ranges from 2.5%to4.0%,the cement with 0.1%alkali content of clinker has the best fluidity;when the alkali to sulfate ratio is less than 0.35,the cement with 0.64%alkali content of clinker has the best fluidity when the sulfate content is ranges from 2.4%to 4.0%.The cement with alkali content of 0.34%of clinker,alkali to sulfate ratio in the range of 0.3 to0.6,sulfate content ranges from 2.0%to 3.5%,it has good fluidity performance,the difference is not obvious.The mechanical properties of cement are related to the alkali content of clinker.For low-alkali cement with alkali content of 0.10%,increase the alkali to sulfate ratio to 0.2,the compressive strength of the cement paste in the early and later age were be increased.When the alkali to sulfate ratio is higher than 0.2,the compressive strength is increased in 1 day and 3 days,The later strength decreases;For the low-alkali cement mortar compressive strength,increase the alkali sulfate ratio to 0.35,and it promote the development of strength,when the alkali to sulfate ratio is greater than 0.35,it is not conducive to the later strength development.Cements with alkali content of 0.34%and0.64%of clinker with an increase in the alkali to sulfate ratio,which improves the early compressive strength and decreases the strength of the later age.because the increase of alkali to sulfate ratio makes the floccular C-S-H gel crystal particles decrease and the cement porosity increase.It can be considered that the alkali to sulfate ratio affects the rheological properties of the cement within a certain range,or the alkali to sulfate ratio can be improved by adjusting the alkali to sulfate ratio when the cement is actually used.However,the alkali to sulfate ratio of the cement is related to the initial alkali content of the clinker.For low-alkali cement,increasing the alkali to sulfate ratio in an appropriate range can promote the development of strength.