Study On Preparation And Performance Of Super High Strength Concrete Filled Steel Tubes With High Titanium Heavy Slag Sand

Ultra-high-strength concrete-filled steel tube is a composite material in which ultra-high-strength concrete（strength grade>80MPa）is poured into steel pipes.It has the advantages of good seismic resistance and material saving.It has broad application prospects in the western mountainous areas with high seismic intensity and poor traffic conditions.The paper aims at the characteristics of ultra-high-strength concrete with low water-to-binder ratio,large shrinkage,unstable strength development and other issues such as easy debonding and voiding of ultra-high-strength concrete filled steel tubes.Based on the porous properties of high-titanium heavy slag sand,the internal curing effect is used to replace The super-high-strength concrete-filled steel tube was prepared with machine-made sand,and its performance was systematically studied,and the following research results were obtained:（1）The law of water absorption and release of high-titanium heavy slag sand was proved,the influence of high-titanium heavy slag sand on the performance of ultra-high strength concrete was clarified,and the design and preparation method of high-titanium heavy slag sand for ultra-high-strength concrete filled steel tube was proposed.Research shows that:the water absorption rate of high-titanium heavy slag sand is about 1.5 times that of machine-made sand;the water release rate increases with the increase of temperature;the high-titanium heavy slag sand can store water and has the function of"water storage-release".With the increase of the water withholding rate,the initial working performance of concrete deteriorates,and the working performance will be amplified after 2h;the mechanical properties increase with the increase of the water withholding rate;the working performance of concrete deteriorates with the increase of the replacement amount.When the water-binder ratio is 0.18,the total rubber material is 700kg/m³,the sand rate is 41%,the water deduction rate of high-titanium heavy slag sand is 85%,and the replacement amount is 60%,ultra-high-strength,high-fluidity,low-shrinkage concrete can be prepared:concrete expansion Degree of 630mm,360d compressive strength of 141.3MPa,90d expansion rate of 165.8×10^-4.（2）The internal curing mechanism of high-titanium heavy slag sand for ultra-high-strength concrete-filled steel tube is revealed.The analysis shows that:the porous structure promotes the close combination of cement slurry and aggregate to form a"thromb-eliminating"structure,which increases the interfacial cohesion;the high-titanium heavy slag sand has the function of"water release-water storage"and"internal curing"effect,Ensure the hydration of the expansion agent in the later stage,promote the hydration of cement and other minerals in the early stage,accelerate the consumption of Ca（OH）₂ crystals in the later stage,and promote the conversion of Ca（OH）₂ with C₂S and C₃S to form a higher strength low alkali The AFt phase and C-S-H gel prevent the enrichment of Ca（OH）₂,improve the interface transition zone,and optimize the pore structure.（3）The influence of high-titanium heavy slag sand on the mechanical properties of ultra-high-strength concrete-filled steel tube short columns under axial compression is clarified.The results show that the replacement amount of high-titanium heavy slag sand has no significant effect on the failure form,load-displacement relationship,and stress-strain relationship of the concrete-filled steel tube specimens.The specimens are all shear failures,and the peak load is added with high-titanium heavy slag sands.The bearing capacity reaches the maximum when the replacement amount is 60%;the actual bearing capacity has a small gap with the bearing capacity value obtained by the bearing capacity formula in the standard,which can meet the design and use requirements.