Design And Performances Of Ultra-high Perfoamance Concrete Based On High Titanium Slag

As a new cementitious material with excellent mechanical properties and high durability,ultra high performance concrete(UHPC)can better utilize the cementitious properties and has a long maintenance-free service life,which is an ideal low carbon,low resource consumption and high quality building material during whole life cycle.However,UHPC has higher requirements for raw materials and production processes,resulting in high cost and energy consumption,which limits its promotion and application.In this paper,ultra-high performance concrete is prepared by high titanium slag powders,sands and crushed stones through the design of the closest stacking ratio,with a view to reduce the costs or dependence of UHPC on high-quality raw materials and promote the utilization of industrial waste.The workability,mechanical properties,hydration characteristics and durability performance of UHPC were systematically studied,results showed that,(1)High-titanium slag sand was used as aggregate to prepare high-titanium slag sand UHPC(TS-UHPC).When the dosage of water reducer was 1.7%,the water-to-binder ratio was 0.22,and the slurry excess factor was 1.3,TS-UHPC exhibited the best overall performance,with a compressive strength of 138.5 MPa at 28 days and a flowability of 215 mm.The mechanical properties,volume stability,carbonation resistance,and freeze-thaw resistance of TS-UHPC were superior to those of natural river sand UHPC(RS-UHPC).The addition of steel fibers improved the strength of TS-UHPC and restrained its shrinkage deformation.With a steel fiber dosage of 1.5%and steam curing,the flexural strength and compressive strength of TS-UHPC reached 32.8 MPa and 187.8 MPa,respectively.It exhibited excellent carbonation resistance and improved freeze-thaw resistance.(2)Steam curing promoted the secondary hydration of TS-UHPC,increased the degree of C-S-H gel polymerization,and enhanced the matrix strength and freeze-thaw resistance.After undergoing 500 cycles of freeze-thaw,the mass losses of TS-UHPC specimens immersed in sodium sulfate solution,sodium chloride solution,and mixed solution(sodium sulfate and sodium chloride)were 0.145%,4.213%,and 1.208%,respectively.(3)Based on the mix design of TS-UHPC,two types of low-activity high-titanium slag micro powder were used to replace fly ash to prepare high-titanium slag sand-micro powder UHPC(Z-UHPC and S-UHPC).High-titanium slag micro powder in the UHPC paste system acted as a filler and nucleation agent,promoting the precipitation of hydration products without affecting the types of hydration products.Z-UHPC and S-UHPC exhibited improved workability,reduced mechanical properties and volume stability,but still possessed excellent carbonation resistance and freeze-thaw resistance.Overall,its performance was superior to RS-UHPC.(4)Furthermore,the introduction of high-titanium slag crushed stone was employed to prepare high-titanium slag crushed stone-sand-micro powder ultra-high performance concrete(UHPC-CA).With a water-to-binder ratio of 0.24 and a slurry excess factor of 1.1,UHPC-CA exhibited the best overall performance,achieving a solid waste proportion of78.5%in the unilateral concrete.Its mechanical properties,carbonation resistance,and freeze-thaw resistance were superior to the RS-UHPC-CA with natural aggregates.Increasing the dosage of steel fibers improved the compressive strength of UHPC-CA,but resulted in a decrease in workability.The optimal steel fiber dosage for UHPC-CA was found to be 1%.Compared to Z-UHPC/S-UHPC,the addition of high-titanium slag crushed stone increased the internal restraint of the concrete,reducing the system shrinkage rate,and significantly reducing the consumption of cementitious materials by 74.7 kg/m~3.