Study On Preparation And Early Cracking Of Self-compacting Concrete With Steel Slag

In this paper,taking advantage of high value-added steel slag as a principle.The magnetic separation tailings after milling,removing iron is selected as fine aggregate to produce the self-compacting concrete with magnetic separation tailing.Then,the effects of Magnetic separation tailings replacement ratio,consistency of mortar and admixture on the workability,mechanical properties and early cracking property of self-compacting concrete with magnetic separation tailings were studied.And on this basis,the comparative analysis on the effect of steel fiber anti-cracking material was made.The following conclusions are drawn by the experimental studies:(1)Compared to ordinary concrete,magnetic separation slag has rough surface,high apparent density and high water absorption rate.For achieving nice workability of concrete,it is necessary to increase the consistency of mortar and content of cement in concrete.(2)It is feasible to prepare self-compacting concrete which meets the code by magnetic separation tailings.When the content of polycarboxylate superplasticizer is 0.3%and the mortar consistency is 0.45,the optimal performance of the mixture can be achieved.When volume replacement rate of magnetic separation tailings is 50%,the mixture has nice workability.When the replacement rate is up to 75%,the workability of mixture can still meet the specifications.(3)The magnetic separation tailings replacement rate greatly affects the compressive strength and splitting tensile strength of concrete at various curing ages.The early strength of self-compacting concrete with magnetic separation tailings develop slowly and the latter strength increases rapidly.When the content of magnetic separation tailings is 75%,the compressive strength and splitting tensile strength of self-compacting concrete are the highest.(4)The magnetic separation tailings can significantly improve the early cracking performance of self-compacting concrete with magnetic separation tailings,including: the initial cracking time of concrete,crack size,the total cracking area per unit area decreases.(5)Steel fiber can reduce the workability of concrete,but can improve the strength and crack resistance of concrete,and this phenomenon is more obvious with the increase of steel fiber content.The test results show that the workability of mixture is reduced for steel fiber,but the test results are still in conformity with the standard.The increase rate of strength of concrete is 1.9%~20.5% because of steel fiber.Steel fiber can improve the crack resistanceof concrete by transferring the stress and reducing stress concentration.And when the steel fiber content is 0.5%,the crack resistance of concrete is the best.(6)The length of steel fiber has great influence on the performance of concrete.The unfavorable effect of short steel fiber on workability of concrete mixture is greater than that of long steel fiber,but the test results are still in conformity with the standard,However,the short steel fiber is superior to the long steel fiber in terms of strength and crack resistance.When the steel fiber content is 0.5%,the strength growth rate of concrete with short steel fiber is higher 4.5%(compressive strength)and 6.9%(splitting tensile strength)than that of concrete with long steel fiber,and no cracks appear in concrete with steel fiber.