Study On The Influence Of Welan Gum On Cement And Concrete

Welan gum is a kind of microbial polysaccharide which is rising in recent years.Because of its outstanding nature,it has been widely used in oil exploration and other industries.A large number of studies and applications have found that welan gum has ideal thickening characteristics,when a small amount is added,the solution viscosity will be greatly improved,which can be used as a thickener in engineering,and it also has a good suspension and emulsification effect.Velanjel solution is a typical pseudoplastic fluid with good shear dilution properties.In addition,welan gun has stable properties,strong temperature stability and good acid and alkali resistance.The outstanding characteristics of velanjac make it has a very wide application prospect.At present,studies on the application of welan gum in cement-based materials at home and abroad are very limited,most of them focu on the effect of welan gum on the rheological properties of cement and concrete.Existing research results show that welan gum can significantly improve the performance of concrete mixture,improve the fluidity and water retention.The initial setting and final setting time of cement or concrete can be delayed by delaying the hydration reaction process of cement particles.In this paper,two grades of welan gum appeared in the domestic market:food grade and industrial grade welan gum.They were added to cement respectively,and the effects of two different grades of welan gum on the fluidity,strength,self-shrinkage and early hydration heat release rate of cement-based materials were tested with the admixture method.The microscopic factors causing the differences in macroscopic properties were analyzed and explained by observing the microstructure.Experimental results show that:?1?addition of welan gum can increase water consumption of standard consistency of cement mortar and prolong setting time.The larger the dosage,the more obvious the effect.The effect of food grade welan gum on water consumption of standard consistency is more obvious than that of industrial grade welan gum.The fluidity increases first and then decreases with the increase of dosage.?2?The two kinds of welan gum showed the phenomenon of early inhibition on the strength development,the larger the dosage,the more obvious the inhibition effect,and the more obvious the inhibition effect of industrial grade welan gum.This is related to the fact that welan gum can significantly reduce the 7d hydration reaction rate of cement.The effect of food grade welan gum on the hydration reaction rate was more obvious.The inhibiting effect of industrial-grade welan gum on the 7d hydration reaction rate of cement is slightly weak,and the correlation between the inhibiting effect and the content of cement is poor.The changes of CH,C₃S and C₂S in the XRD test of 3d cement paste can also explain this phenomenon.The effect of two kinds of welan gum on the strength of cement paste at 28d is small.In cement mortar and concrete,food grade welan gum has a significant effect on the strength of concrete at 28d,which increases first and then decreases.The maximum strength occurred in the 0.05%dosage group.The effect of industrial grade welan gum on the strength of colloidal sand for 28d decreased with the increase of dosage.?3?The addition of two kinds of welan gum causes the increase of self-shrinkage of cement mortar.The shrinkage rate of cement mortar in the experimental group with the addition of food-grade welan gum continued to increase on 28d.In the experimental group of industrial grade welan gum,the development rate of self-contraction was faster in the first 7 days,and gradually decreased between 7th day and 28th day.?4?The porosity of cement mortar was measured by mercury injection test.It can be known that with the increase of the content of welan gum,the porosity of cement mortar firstly decreases slightly,then increases rapidly,and the middle pore diameter increases with the increase of the content.Combined with the microscopic analysis by SEM,we know that the addition of welan gum makes the cement particles disperse more evenly through the dispersing effect,resulting in more hydration cores and increased porosity at the same time.However,we can also clearly see that the presence of welan gum inhibited the growth of ettringite,but the inhibitory effect of food grade welan gum in the experimental group was less than that of industrial grade welan gum.However,after the addition of food grade sealant,the porosity level of the specimens was lower than that of the industrial-grade sealant group,and the change trend of intermediate pore diameter was just the opposite.This also explains the different effects of two kinds of welan gums on the development of cement mortar strength from another perspective.