Effect Of Steel Slag Powder And Compound Admixture On Mixture Properties And Strength Of Self-compacting Concrete

With the development of economy and society,more and more waste residues are produced in industrial production.Steel slag is a large amount of industrial waste slag discharged in our country at present.Its actual utilization rate is still relatively low.A large amount of steel slag is still in the state of storage and landfill,which not only occupies a large amount of land,wastes land resources,but also easily causes environmental pollution.Therefore,it is necessary to further strengthen the research and application of steel slag resource utilization.At present,converter slag is the main steel slag produced in China.Because it contains mineral components similar to Portland cement clinker minerals and has weak hydraulicity,it is one of the main ways to use steel slag as concrete admixture by grinding converter steel slag.High performance concrete is a kind of sustainable development"green concrete",and self-compacting concrete is an important variety of high performance concrete.At present,steel slag powder is mainly used in ordinary concrete as concrete admixture,but the application of steel slag powder in self-compacting concrete is still lack of research.Starting from expanding the reuse of steel slag,this paper takes the micro-powder of steel slag produced by Maanshan Limin Spark Metallurgical Slag Environmental Protection Technology Development Company as the main research object。The influence of steel slag powder and compound admixture（admixture made of steel slag powder and other admixtures）on cement setting time,water consumption for standard consistency,mortar fluidity and mortar strength was studied through comparative experiments.The mechanism of influence on cement setting time was analyzed by hydration heat test;The effects of steel slag powder and compound admixtures on the mixtures properties and strength of self-compacting concrete were studied by means of mixtures test and compressive strength test,and the micro-analysis was carried out by SEM.The results show that the self-compacting concrete with satisfactory performance can be prepared by using steel slag powder and compound admixture with appropriate proportion.The research results have theoretical significance and practical value for further studying the technical properties of steel slag powder and expanding the application of steel slag powder and composite admixtures in self-compacting concrete engineering.The main research results of this paper are as follows:（1）The steel slag powder has obvious retarding effect on cement paste.The addition of steel slag powder prolongs the setting time of cement.The larger the amount of steel slag powder,the longer the setting time of cement.The retarding effect of steel slag powder on cement paste is significantly greater than that of fly ash,silica fume and slag powder.The main reason is that there are more P₂O₅ in steel slag powder,which has great influence on cement hydration.When the compound admixture is mixed with steel slag powder,silica fume and slag powder,the setting time of cement is longer than that of benchmark test group,but the prolonged value is obviously reduced;The results of cement hydration heat measurement show that the early hydration reaction rate of each test group mixed with steel slag powder is lower than that of the reference test group.When steel slag powder is mixed with silica fume and slag powder,the hydration rate increases and the retarding effect of steel slag powder on cement is improved.The water consumption for standard consistency of cement paste mixed with steel slag powder has little change compared with the standard test group.When the compound admixture containing fly ash is added,the water consumption for standard consistency of cement can be reduced,while when the compound admixture containing silica fume is added,the water consumption for standard consistency of cement paste will be increased;（2）At the same water-binder ratio,the fluidity of cement mortar can be improved by adding steel slag powder,fly ash and slag powder.Fly ash has better effect on improving the fluidity of cement mortar.The fluidity of cement mortar decreases obviously with the addition of silica fume.The fluidity of cement mortar with steel slag powder and fly ash compound admixture is higher than that with steel slag powder alone.The compressive strength of cement mortar decreases by 7d and 28 d with the addition of steel slag powder and fly ash,and fly ash has a greater influence on the early strength of cement.The compressive strength of cement mortar can be improved obviously by adding the compound admixture containing silica fume and slag powder.The compressive strength of cement mortar at 7d and 28d increased by 7.8%and 14.2%respectively when 30%and 2:1 steel slag powder-silica fume compound admixtures were added;（3）The slump-flow values of each test group of self-compacting concrete mixed with steel slag powder and compound admixture can meet the filling requirements of SF1 self-compacting concrete.However,the variety and proportion of admixtures in the compound admixtures have a significant impact on the slump-flow value.The filling performance of the test groups mixed with steel slag powder and fly ash is higher than that of the benchmark test group.The setting time of self-compacting concrete depends on the setting time of cement.Because steel slag powder has retarding effect on cement paste,the setting time of self-compacting concrete mixed with steel slag powder is obviously longer than that of reference self-compacting concrete.The larger the content of steel slag powder,the longer the setting time of self-compacting concrete.When the total amount of admixture is the same,the effect of compound admixture on the setting time of self-compacting concrete mixtures is obviously less than that of steel slag powder,and the effect of 1:1 ratio of steel slag powder to slag powder is the smallest;（4）The compressive strength of self-compacting concrete decreases in 7d and 28d with the addition of steel slag powder alone,and the compressive strength of self-compacting concrete can be improved with the addition of compound admixtures.The compressive strength of self-compacting concrete with steel slag powder-slag powder-silica fume compound admixture on 7d and 28d increased by 12.8%and 4.6%respectively compared with the benchmark test group.SEM micro-morphology analysis shows that the binary compound admixture and ternary compound admixture mixed with steel slag powder,slag powder and silica fume can improve the microstructure of self-compacting concrete.The effect of ternary compound admixture is more obvious,and the early compressive strength of self-compacting concrete is obviously improved.