Corrosion Behavour Of Reinforcement In Alkali Activated Concrete

The cementitious material cement used in ordinary concrete will produce a large amount of carbon dioxide in the process of production.Alkali-activated slag as concrete cementitious material can reduce carbon dioxide emissions,and realize the resource utilization of solid waste slag and other resources,which is a kind of energy saving and environmental friendly building material.Alkali-activated slag concrete must be combined with steel bar to be used as bearing member in building structure.The composition and pH value of the alkali-activated slag concrete pore solution are significantly different from those of the ordinary concrete,which will inevitably affect the formation process and the microstructure of passive film,Thereby affecting the corrosion behavior of steel bars.This investigation tested the four activators:sodium hydroxide,sodium silicate,sodium carbonate and sodium sulfate,compound with slag powder as cementitious material to make alkali-activated slag concrete?hereinafter referred to as PSH,PSS,PSC,PSF?The ordinary portland cement concrete?OPC?was used as the control group,studying the passivation behavior of passive film in simulated pore solution,the destruction of steel passive films and corrosion processes under chloride corrosion environment,and steel corrosion behavior in alkali-activated slag concrete in both low carbon steel rebar?LC?and corrosion resistant steel bar?CR?.The main conclusions of this paper are as follows:?1?The electrochemical tests of the passivation of the steel in the simulated pore solution and the depassivation behavior in the simulated pore solution and the chloride containing compound solution show that the formation and damage process of the steel passivation film are highly dependent on the PH value of the pore solution,The higher the PH value,the faster the formation rate of the passivation film,the more stable the passivation film is,the stronger the erosion resistance.The ability of steel bars to resist chloride ion destruction in different pore solutions is:PSH>PSS>PSC>OPC.Due to the composition of Cr,Mo and other alloys,the passivation film of CR forms a more compact cover and owns better resistant of chloride-induced corrosion than LC.?2?Atomic force microscopy?AFM?and XPS measurements of the passivation film during the growth and failure of the steel in the simulated pore solution showed that the passivation film of the steel in the simulated pore solution of the alkali-activated slag was more compact and resistant to chloride ion attack than the ordinary concrete and the best ingredient is PSH.The outer layer in LC and CR contains Fe²⁺?FeO/Fe?OH?₂?and Fe³⁺?Fe₂O₃/FeOOH?.And LC contains only Fe²⁺in the inner layer of the passivation film.The inner and outer layers of the passivation steel in CR detected Cr₂O₃ and Cr?OH?₃,and Cr₂O₃ is mainly in the inner layer.?3?The thickness of passive film of low carbon steel rebar is about 12nanometers in ordinary concrete simulated pore solution;the thickness of the passive film of sodium hydroxide,sodium silicate,sodium carbonate,sodium sulfate activated slag simulated pore solutions were respectively 18nm,12nm,12nm,6nm;The thickness of corrosion resistant steel rebar passive film in the simulated pore solution of sodium hydroxide activated slag is about 18nm,while it is about 12nm in the other four kinds of simulated pore solutions.?4?The compressive strength,drying shrinkage and impermeability of different alkali activated slag concrete and ordinary portland cement concrete were analyzed,showing that the strength of alkali activated slag concrete were lower than ordinary portland cement concrete,but the strength of alkali activated slag concrete is more developed than ordinary portland cement concrete in later strength;The drying shrinkage of concrete is:PSS>PSC>PSH>OPC>PSF;According to the capillary water absorption tests,the impermeability of concrete is as follows:PSH>OPC>PSS>PSC>PSF;The RCM test showed that the chloride ion penetration resistance of concrete is as follows:PSH>PSS>PSC>PSF>OPC;The chlorine ion transmission rule under different corrosion zones of the ocean is analyzed through the real sea exposure,it can be seen that the resistance to chloride ion penetration of alkali activated slag concretes are superior to ordinary Portland cement concrete under different corrosion zones,among them,sodium silicate and sodium hydroxide activated slag concrete have the best resistance to chloride ion penetration.At the same time,it is also found that the corrosion degree of concrete in different corrosion areas is splash zone>underwater area>atmospheric area.?5?According to the different alkali-activated slag concrete embedded steel electrical accelerated corrosion test,it is showed that the corrosion rate of steel in concrete is PSF>PSC>PSS>PSH>OPC;The scanning electron microscope and EDS were used to analyze the rust spot,showing that reinforced outer rust layer microstructure mainly scaly,acicular,honeycomb.The surface is uneven and the structure is loose.The reinforced outer rust layer of PSH,PSC and PSF is more looser while it is more denser in ordinary concrete.The main elements of steel corrosion products are Fe and O,and the ratio of Fe/O atoms in corrosion products are different from eath other.