| At present,reinforced concrete structure is mainly used in large lifeline projects;however,the durability of reinforced concrete structure in the marine environment is becoming more and more serious,which has caused great harm to the life of lifeline projects.Corrosion of steel bars is the main factor that causes the durability damage of concrete.The concrete is highly alkaline in normal circumstances,and a stable passivation film will form on the surface of the steel bar in the concrete.If there is a large amount of chlorine salt or carbonation in the concrete,the passivation film on the surface of the steel bar will be destroyed,which will lead to the corrosion of the steel bar.In order to inhibit the corrosion of harmful substances on steel bars,it is an economic,effective and simple way to mix steel bar rust inhibitor into concrete.The corrosion inhibitor used in this paper is a compound corrosion inhibitor with nitrite as the main rust inhibitor applied in a station of Qingdao Metro.Through the electrochemical test of carbon steel in simulated concrete pore solution with different corrosion inhibitor content and p H value,and the tests of SEM,AFM and XPS were carried out on the surface of carbon steel to study the effect and mechanism of corrosion inhibitor.Through the compressive strength,RCM,rapid carbonation and salt water drying and soaking cycle test of concrete with different content of corrosion inhibitor,combined with the SEM,XRD and MIP test of concrete,the effect of corrosion inhibitor on the performance of concrete was studied;Molecular dynamics was used to simulate the transport process of different nitrite solution in the nano channel of hydrated calcium silicate(CSH),and the existing forms of ions in different nitrite were studied from the microscopic point of view.The results are as follows:(1)The electrochemical test of carbon steel in the simulated concrete pore solution with different content of corrosion inhibitor and p H value of solution shows that corrosion inhibitor can effectively adsorb and form film on the surface of carbon steel;with the increase of the content of corrosion inhibitor,the corrosion inhibition efficiency gradually increases;when the content of corrosion inhibitor is more than 6%,the increase of corrosion inhibition efficiency tends to be gentle;at different p H value,corrosion inhibitor can achieve good corrosion inhibition effect.When the p H value of the solution is 10.3,the corrosion inhibition efficiency is the highest,reaching 89.84%.SEM,AFM and XPS were used to observe and analyze the surface of carbon steel with and without corrosion inhibitor.The results showed that corrosion inhibitor could make the passivation film more smooth and stable.(2)The results of compressive strength test,chloride ion electromigration test and rapid carbonation test of concrete with different content of corrosion inhibitor show that the larger the content of corrosion inhibitor is,the better the performance of concrete is;when the content of corrosion inhibitor is 4%,it has a significant improvement effect on the performance of concrete,and the increase of the content tends to be gentle;the 28 d salt water drying immersion cycle test of mortar with different content of corrosion inhibitor show that the average corrosion current density(Icorr)decreased significantly with the increase of the content of corrosion inhibitor.The addition of corrosion inhibitor can effectively protect the reinforcement.The results of SEM and XRD show that the addition of corrosion inhibitor can promote the hydration reaction and enhance the compactness of concrete.The results of MIP show that with the increase of the content of corrosion inhibitor,the pore structure is more refined and the concrete is more dense,so the performance of concrete is improved.Combined with the electrochemical test results,it is suggested that the engineering dosage is 6% wt.of cementitious materials.(3)Based on the existence form of nitrite solution in the concrete nanochannels,the free state can be transferred to the surface of the steel bar and thus play a role of corrosion inhibition.In this paper,a model of nitrite solution in pore water transport process of CSH gel nanochannels is established,which explains the dissociation and adsorption mechanism of NO2-in the nanoparticle channel.Compared with three nitrite solutions,the adsorption capacity of NO2-in the solution of Li NO2,Na NO2 and Ca(NO2)2 at the interface of CSH nanopore is the worst,so the free NO2-ions in the pore are the most,the movement speed of the ions to the surface of the reinforcement is the fastest,and they can be more effectively transmitted to the surface of the reinforcement to prevent corrosion. |
