| Concrete filled steel tubes have the advantages of high bearing capacity,good durability,and excellent seismic performance.They were widely used in modern high-rise buildings,spatial column structures,and long-span arch bridges.However,the problem that the core concrete was vacant from the wall of the steel pipe was generally not well resolved.This arti-cle mainly studies the effects of the expansion agent,internal curing agent and the composite action on the workability,strength,volume stability and impermeability of the self-compacting steel tube concrete,and reveals the expansion agent and internal curing agent on the self-compacting steel tube through microscopic characterization The mechanism of in-fluence of the macroscopic properties of concrete.By studying the influence of water-binder ratio,sand ratio and water-reducing agent content on the working performance and mechanical strength of self-compacting concrete,it was found that the greater the water-binder ratio and the sand-rubber ratio,the better the workability and the lower the strength.The larger the amount,the better the workability and the higher the strength.The best basic mix ratio of self-compacting concrete was determined,specifically:cement 400 kg,fly ash 60 kg,mineral powder 70 kg,silica fume 30 kg,sand 780kg,crushed stone 890 kg,water 162 kg,water-reducing admixture 2.55%.On the basis of the above research,the effect of the expansion agent,internal curing agent and their combined effect on the volume stability of self-compacting concrete was sys-tematically studied.The results showed that the shrinkage rate of the self-shrinking 7d in the blank group was 444×10-6?m,and when the amount of internal curing agent was from 2%to4%,the shrinkage in 7d was 326×10-6?m,280×10-6?m,178×10-6?m.When the amount of expansion agent was from 3%to 5%,the shrinkage rate at 7 days was 240×10-6?m,205×10-6?m,and 81×10-6?m,respectively.The amount of expansion agent was 5%,and the amount of internal curing agent was compounded by 2%?4%.The self-shrinkage decreases by 102%,104.2%,and 114.2%in 7 days.Studies have shown that self-shrinkage was positively corre-lated with the amount of expansion agent and internal curing agent.The expansion agent has little effect on the porosity of the hardened cement paste in the early stage,and the influence in the later stage.The amount of internal curing agent increases,and the porosity gradually increases.As the amount of expansion agent increases,the internal relative humidity?IRH?of the self-compacting concrete gradually decreases.The greater the amount of internal curing agent,the higher the IRH.Analysis of heat of hydration and electric flux shown that both the expansion agent and the internal curing agent can reduce the heat of hydration,and the reduction effect was more obvious under the combined action.Compared with the blank group,when the expansion agent was 5%and the internal curing agent was 4%,the electric flux at 56d and 90d decreased by 12.9%and 22.4%,respectively.Studies have shown that the porosity gradually decreases with age,and the better the anti-seepage effect.SEM and XRD analysis shown that when the swelling agent and the internal curing agent were mixed,there were a lot of unhydrated fly ash particles in the early stage of hydra-tion,and a small amount of flake Ca?OH?2 grew between the C-S-H gels.At 28 days of hy-dration,a large amount of flaky Ca?OH?2,as well as a small amount of needle-shaped ettring-ite and flocculent C-S-H gel were generated.The types of hydration products in 7d and 28d are basically the same,mainly including Ca?OH?2,AFt,C2S,C3S,C-S-H.Studies have shown that the early generation of Ca?OH?2 was less,and the later generation was more,resulting in lower early strength,and the late strength did not decrease compared with the blank group.In this paper,the self-compacting micro-expansion internal curing steel tube concrete with excellent performance was prepared through the composite action of the expansion agent and the internal curing agent,and a solution was found to suppress the shrinkage of the steel tube concrete. |
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