Study On Corrosion Characteristics Of Steel Bar In Foam Concrete Under Chloride Ion Erosion

Foam concrete has been widely used in reinforced structural elements such as assembled wall panels for its light weight,heat insulation and noise reduction.However,the steel reinforcement in coastal areas and marine environment is highly susceptible to chloride ion erosion,and in recent years,China has been paying attention to the development and utilization of islands and has formulated a series of marine development strategies,so it is significant to reveal the evolution of steel corrosion in foam concrete and to improve the durability.In this paper,we explain the mechanism of reinforcement corrosion in foam concrete from macroscopic,microscopic and electrochemical aspects,and compared with that in ordinary concrete.And explore the optimization of water-cement ratio,fly ash and fiber to improve the performance of foam concrete against reinforcement corrosion.To reserve the basic theory and data for further experimental research on the corrosion performance of reinforcement in foam concrete.the research contents and related conclusions are as follows:（1）The accelerated corrosion test was carried out by using the corrosion rate of reinforcement and the crack width of foam concrete as macro evaluation indexes.The results show that the corrosion rate of reinforcing steel and the crack development rate increase slowly with time and then develop rapidly,and finally grow slowly,and the corrosion resistance of reinforcing steel increases with the increase of density grade of foam concrete.Compared with ordinary concrete,foam concrete has poor corrosion resistance to steel bars,which is due to the introduction of a large number of bubbles in the preparation of foam concrete,and part of the volume is occupied by bubbles,resulting in more internal pores and mutual communication,so its corrosion resistance to steel bars is poor.（2）The polarization curve method was used to obtain information on the morphology of the polarization curves and electrochemical parameters of the steel bars at different corrosion stages.The results showed that the polarization curves gradually shifted to the right with time,the E_corr and R_p values gradually decreased and the I_corrvalue gradually increased,and the corrosion rate of the steel bars kept increasing.More products in the later stage of rusting covered the steel substrate indicating that the reaction was hindered,the slope of the anodic tafel of the polarization curve became larger and the rusting rate slowed down.（3）The electrochemical impedance spectroscopy method was used to obtain the impedance spectra of steel bars at different rusting stages and analyze the electrochemical impedance behavior,and then the best equivalent circuit fitted by Zsimp Win software is R(C（R（Q（R（CR））））.And it was found that the steel bars in foam concrete had three capacitive resistance arcs when they were in the rusting state,and with the increase of corrosion time,the high frequency capacitive reactance arc decreases,and the low frequency capacitive reactance arc impedance shrinks in real steps.（4）With the three factors of water-cement ratio,fly ash and fiber admixture as variables,the macroscopic rusting study and electrochemical mechanism analysis concluded that the steel bar corrosion resistance of foam concrete is best when water-binder ratio is 0.5,and the admixture of fly ash and fiber could significantly improve the anti-rebar rusting performance of foam concrete.When the fly ash and fiber admixture are 20%and 0.6%respectively,the foam concrete has the best anti-reinforcement corrosion performance.（5）Information on the structural morphology and material composition of microscopic corrosion products of steel bars in foam concrete at different corrosion stages was analyzed using scanning electron microscopy and x-ray diffraction.The results showed that the corrosion products on the surface of the bars were relatively dense and showed irregular structure at the initial stage,and gradually became loose with the development of time,and more serious cracks also appeared,and finally showed stacked and fractured distribution.The main components of rust products are hematite（α-Fe₂O₃）,siderite（Fe O）,magnetite（Fe₃O₄）,etc.And Fe OOH can become a new depolarizing agent under anoxic conditions.