A Study On Self-contraction And Strength Characteristics Of Magnesium Slag Concrete

Because of the rapid development of the magnesium industry in recent years,magnesium slag emissions increased dramatically,which lead to increasing environmental pollution problems,while restricting the further development of the magnesium industry;in order to pursue the high strength and high fluidity of concrete,it is often mixed with a large number of fillers and admixture,which led to the dimensional stability of concrete is being affected;magnesium slag have a certain hydration activity and its chemical composition is similar to that of cement,the MgO contained in the concrete has an expansibility,so taking the magnesium slag as a concrete admixture not only can improve the strength of concrete but also has a potential compensation for the contraction of concrete,it can reduce the engineering costs and reduce the environmental pollution.Therefore,the project has a high research significance and its study gets the support of the National Natural Science Foundation of China(NSFC).Taking the C30 magnesium slag concrete as the research object,designing a single factor test scheme and the L16(45)orthogonal test scheme which is determined by the factors of the magnesium slag content,the fly ash substitution rate and the ore powder substitution rate and using the trend analysis,range analysis,variance analysis and other analytical methods to analyze the effect of each mineral admixture on the self-contraction of magnesium slag concrete,reveal the mechanism of the effect of magnesium slag on the shrinkage of concrete,and establish the relationship model of the concrete autogenous shrinkage rate in relation with time and the mineral admixture content changes.The study draws the following conclusions:(1)With the increase of the amount of magnesium slag,the self-contraction of concrete reduced gradually.The higher the amount of magnesium slag,the greater the inhibitory effect of magnesium slag on the autogenous shrinkage.Magnesium slag can improve the compressive strength of concrete,but with the increase of the magnesium slag content,the enhancement effect of magnesium slag on compressive strength is gradually reduced.(2)The incorporation of fly ash has an inhibitory effect on the self-contraction of concrete.With the increase of fly ash content,the shrinkage of concrete decreases nearly linearly,and the compressive strength of concrete for 28 days decreases with the increase of fly ash content,and there is a linear relationship between the two.(3)Incorporation of mineral powder will increase the self-contraction of concrete.The mineral powder shows inhibition on the concrete self-contraction in the first three days of the measured age,after that,the mineral powder will promote the development of concrete self-contraction and it can improve the strength of concrete,there is a linear relationship between the two.(4)The order of importance of the mineral admixture to the self-contraction of concrete is:The magnesium slag content>The fly ash substitution rate>The mineral powder substitution rate.(5)The trend of self-contraction of concrete is in accordance with the hyperbolic relationship.The hyperbolic relationship is obvious and the correlation is good,which can accurately predict the self-contraction value of concrete at different ages.