Experimental Study On Transportation And Filling Of Corrosion Products In Reinforcement Concrete

During the service of reinforced concrete structures,the corrosion of steel bars is one of the main reasons for the deterioration of structural durability.The volume expansion caused by reinforcement corrosion makes concrete crack,which not only leads to structural deterioration,but also provides a channel for harmful medium erosion,further intensifying reinforcement corrosion.A part of corrosion products form rust layer on the surface of reinforcement,and different rust layer distribution will produce different rust expansion stress distribution on concrete.Others are transmitted into the concrete after formation,filled in the pores and cracks of the concrete,or even lost to the external environment through the protective layer,and do not produce corrosion expansion stress in the concrete.Once the proportion of this part is too large,it will lead to overestimation of the durability of the structure,causing accidents.Therefore,it is very important to study the transmission and filling rules of corrosion products in concrete for accurately predicting the time of corrosion cracking of concrete cover and correctly evaluating the durability of structures.This paper takes this as the main line of research.Through experiments,it deeply analyzes the influence of different kinds of concrete on reinforcement corrosion and the transmission and filling rules of corrosion products,analyzes the soluble intermediate substances that control the transmission of reinforcement corrosion products,the transmission range and quality of corrosion products.The main research contents of this paper are as follows:(1)The corrosion degree and the distribution of corrosion products around reinforcement of three kinds of ordinary concrete with different water cement ratio and concrete with fly ash and mineral powder admixture under dry wet cycle conditions were studied.The porosity of concrete was measured by mercury intrusion method.The effect of porosity on the corrosion rate of steel bars was observed by CT and SEM.The distribution of corrosion products around reinforcement is divided into three situations,and a three-stage model of reinforcement corrosion,transport,oxidation and precipitation is established to explain the reasons for the three different situations,and explain the transport and filling rules of corrosion products.(2)The chemical composition of solid and liquid corrosion products of reinforcement immersed in simulated concrete pore solution in ordinary sealed box and in situ Raman electrochemical cell was determined by Raman spectroscopy.Compared with the existing research data,it is found that the soluble intermediate product green rust appears in the in-situ Raman electrochemical cell completely isolated from air,which proves that green rust can appear in the concrete and dissolve in the solution to control the transport of corrosion products,and gives the material transformation process of steel bar corrosion products in the simulated pore solution.(3)The EDTA titration method is used to quantify the iron content of the steel bar,the steel /mortar interface,and each position of the mortar section in the mortar test block mixed with chlorine salt and circulated dry and wet.By comparing the mass loss of rebar before and after corrosion and the iron mass corresponding to the rust layer obtained by titrating acid pickling solution,the iron mass corresponding to the rust product transferred to the mortar was obtained.Drill holes in blocks on the mortar section to get powder,measure the iron content at each position by EDTA titration,and draw a cloud chart to obtain the transmission range of corrosion products in the mortar and the corresponding iron mass.