Study On Corrosion Of Reinforcement In Cracked Concrete Under Marine Environment

Reinforced concrete is the most widely used building materials of social construction nowadays.The steel corrosion in concrete is extremely serious in marine environment.Reinforced concrete structure with cracks is ubiquitous,Therefore,it has enormous significance to study the influence of cracks on corrosion of steel bars in concrete,which is of great significance to prevent the corrosion of steel bars in reinforced concrete structures and improve its durability.In this paper,the reinforced concrete corrosion with cracks is quantitatively and qualitatively analyzed by marine exposure and electric acceleration method,and the corrosion mechanism of steel bars is revealed.The main results are as follows:1.The electrochemical impedance spectroscopy(EIS)was adopted to study the corrosion behavior of different types of steel bars in different marine exposure environments,transverse fracture scales and concrete ratios.Conclusions are gotten by comparing with the corrosion degree of corrosion resistant steel bars made of ordinary round steel and sand steel,it is found that corrosion resistant steel has stronger corrosion resistance.The influence of transverse fracture scale on the corrosion rate of steel bars is 0.1mm <0.15 mm <0.2mm <0.3mm.The influence of transverse spacing on the corrosion rate of steel bars is 0.15 mm <0.15mm@60mm <0.15mm@30mm.In the case of the same scale of fractures,the influence of different exposed areas on the corrosion rate of steel bars is: Seawater zone <Tide zone<Splash zone.2.Based on the method of AC impedance spectroscopy,the corrosion behavior of different types of steel bars in different marine exposure environments,longitudinal fracture scales and concrete ratios was studied.The following conclusions can be drawn by experiment: The influence of longitudinal fracture scale on the corrosion rate of steel is 0.1mm <0.3mm <0.5mm <1mm.In the case of the same scale fractures,the influence of different marine exposure areas on the corrosion rate of steel bars is: submerged zone <tidal area < splash zone.The incorporation of pulverized coal and fly ash in concrete can slow down the steel bars corrosion.In contrast to the superabsorbent resin,the incorporation of a small amount of resin will slow down the corrosion of the steel bars in the concrete and if the SAP content is high,the honeycomb pores will be left in the concrete and the corrosion will be serious.The effect of different proportions on the corrosion rate of steel bars in concrete under the same area is: LF50SP1 <LF50 <LF50SP2 <LF50SP3 <L50.3.The effect of cracks on steel bars corrosion under electrical acceleration was studied by adopting the self-designed prefabricated fracture device to make concrete samples with cracked concrete.In the early stage of electrical acceleration,the surface of steel bar is constantly generating rust,and after a certain period of time,the rust is diffused along the protective layer.Concrete protection layer continues to expand until the penetration because corrosion caused by rust corrosion is greater than the concrete compressive stress caused by cracks.By monitoring the Nyquist diagram,it is found that the anti-arc of the low frequency zone is shrinking continuously during the energization process,which indicates that the polarization resistance of the steel is decreasing,the passivation film of the steel is changed from the passivated state to the active erosion state,and the rebar begins to corrode.The effect of transverse fracture on the corrosion of steel bars is: 0.1mm <0.15 mm <0.2mm <0.3mm.The effect of longitudinal fracture scale on the corrosion of steel bars is: 0.1mm <0.2mm <0.3mm <1mm.Through the constant potential to accelerate the corrosion of steel,real-time monitoring of the specimen current changes,the current are gradually reduced after the first mutation to a larger value tends to stabilize after the trend.The current and time of cracking of the concrete are obtained from the abrupt point of the current,which is consistent with the time at which the macroscopic observation of the concrete is cracked.