Study On The Performance And Optimization Of High Volume Blast Furnace Slag Powder Cement Based Materials And Concrete

As the hydration reactivity of blast furnace slag (BFS) is low compared with cement clinker, blindly increase the amount of blast furnace slag powder (BFSP) will have a negative impact on the early age mechanical properties of cementitious materials and concrete, which limits the content of BFSP constituting Portland cement in concrete. On the other hand, the grindability of BFS is worse than cement clinker, so it's very difficult to get a desired fineness when ground together, which further affects the reactivity of BFSP. But, high volume BFSP concrete has got more and more attention in concrete construction all over the world due to its excellent durability and the environmental advantages.The influences of Portland cement substituted by BFSP in a high proportion on the performance of cementitious materials were studied in this paper. For the lower early age strength, we choose several activators and selected the industry waste containing sulfate which has optimum activating effect. Composite cementitious materials which can met the requirement of P·S 42.5 cement when the quantity of BFSP powder replaced Portland cement by 70 % and that of P·S 32.5 cement when the content of BFSP powder is up to 80 % were obtained. Other performance of the composite cementitious materials was also experimentally studied, the results show that increasing BFSP content has little effect on standard consistency water quantity, setting time and fluidity, besides, the composite cementitious mortar have small shrinkage and good resistance to sulfate attack.The experimental results studied on mechanical properties and durability of the high volume BFSP concrete and Portland cement concrete show that the high volume BFSP concrete has excellent workability. When the content of BFSP is 50 %, the mechanical properties of BFSP concrete are even better than Portland cement concrete. Furthermore, high volume BFSP concrete has excellent resistance to chloride ion permeability, the permeability coefficient is as low as 29%～36% that of Portland cement concrete. The frost resistance of high volume BFSP concrete is equal to that of Portland cement concrete while the carbonization resistance is poor. Reducing water cement ratio by adding superplasticizer is one of the effective ways to raise the carbonization resistance of the high BFSP concrete.The results of MIP, XRD and SEM analysis on the large amount of slag-cement composite cementitious materials paste and Portland cement paste indicated that secondary hydration reaction of BFSP greatly reduced the amount of Ca (OH)₂ crystal which is bad for microstructure, and increased the number of C-S-H gel which made the hardening paste more dense, pore structure be improved and the pore size distribution more reasonable, sulfate activator effectively stimulated the activity of BFSP, accelerated the ettringite formation, and improved the pore structure.