The present research brings new insights on the role of admixed corrosion inhibitors in the processes of cement hydration and rebar corrosion. The admixing of NaCl and the corrosion inhibitors in fresh mortar was foun...The present research brings new insights on the role of admixed corrosion inhibitors in the processes of cement hydration and rebar corrosion. The admixing of NaCl and the corrosion inhibitors in fresh mortar was found to alter the morphology and microstructure of the hardened mortar at the steel-mortar interfacial region. The admixing of the inhibitors increased the risk of carbonation of cement hydrates at the steel-mortar interfacial region, but partially displaced chloride ions. Chloride and the admixed inhibitors facilitated the formation of different cement hydrates and affected chloride binding at the steel-mortar interfacial region. The admixing of all three inhibitors was found to increase the polarization resistance of steel, indicating reduced corrosion rate of the steel over 48-day exposures to salt ponding.展开更多
Steel rebar normally forms an oxide or rusty skin before it is embedded into concrete and the passivation properties of this skin will be heavily influenced by temperature. To study the effect of temperature on the pa...Steel rebar normally forms an oxide or rusty skin before it is embedded into concrete and the passivation properties of this skin will be heavily influenced by temperature. To study the effect of temperature on the passivation properties of steel rebar under different surface conditions, we conducted scanning electron microscopy （SEM） observations and electrochemical measurements, such as measurements of the free corrosion potential and polarization curves of HPB235 steel rebar. These measurements identified three kinds of surfaces： polished, oxide skin, and rusty skin. Our results show that the passivation properties of all the surface types decrease with the increase of temperature. Temperature has the greatest effect on the rusty-skin rebar and least effect on the polished steel rebar, because of cracks and crevices on the mill scale on the steel rebar＇s surface. The rusty-skin rebar exhibits the highest corrosion rate because crevice corrosion can accelerate the corrosion of the steel rehar, particularly at high temperature. The results also indicate that the threshold temperatures of passivation for the oxide-skin rebar and the rusty-skin rebar are 37℃and 20℃, respectively.展开更多
Corrosion of steel rebar is the most important durability problem of reinforced concrete. The aim of this research was to investigate the corrosion behavior of steel rebar in simulated pore solutions and gangue-blende...Corrosion of steel rebar is the most important durability problem of reinforced concrete. The aim of this research was to investigate the corrosion behavior of steel rebar in simulated pore solutions and gangue-blended cement mortar. The simulated pore solutions were based on the pore solution composition of gangue-blended cement. The pH and Cl-concentration of simulated pore solutions had significant effects on corrosion potential. However,an increase in pH reduced the influence of Cl-concentra-tion on corrosion potential. The corrosion behavior of steel rebar in gangue-blended cement is different from that in simulated solutions. The gangue cementitious mortar surrounding steel rebar provides stable passivity environments for steel,leading to a decrease in ion diffusion coefficients. Alternating current impedance (ACI) analysis results indicated that the indicator Rc for concrete resistivity is higher for gangue mortar than for ordinary Portland cement (OPC),which improves its corrosion potential. The results from energy dispersive X-ray analysis (EDX) showed more aluminates and silicates at the rebar interface for gangue-blended cement. These aluminates improve the chloride binding capacity of hydrates in mortar,and increase the corrosion protection of steel rebar.展开更多
基金Supported by the Research and Innovative Technology Administration under the U.S. Department of Transportation through the University Transportation Center
文摘The present research brings new insights on the role of admixed corrosion inhibitors in the processes of cement hydration and rebar corrosion. The admixing of NaCl and the corrosion inhibitors in fresh mortar was found to alter the morphology and microstructure of the hardened mortar at the steel-mortar interfacial region. The admixing of the inhibitors increased the risk of carbonation of cement hydrates at the steel-mortar interfacial region, but partially displaced chloride ions. Chloride and the admixed inhibitors facilitated the formation of different cement hydrates and affected chloride binding at the steel-mortar interfacial region. The admixing of all three inhibitors was found to increase the polarization resistance of steel, indicating reduced corrosion rate of the steel over 48-day exposures to salt ponding.
文摘Steel rebar normally forms an oxide or rusty skin before it is embedded into concrete and the passivation properties of this skin will be heavily influenced by temperature. To study the effect of temperature on the passivation properties of steel rebar under different surface conditions, we conducted scanning electron microscopy （SEM） observations and electrochemical measurements, such as measurements of the free corrosion potential and polarization curves of HPB235 steel rebar. These measurements identified three kinds of surfaces： polished, oxide skin, and rusty skin. Our results show that the passivation properties of all the surface types decrease with the increase of temperature. Temperature has the greatest effect on the rusty-skin rebar and least effect on the polished steel rebar, because of cracks and crevices on the mill scale on the steel rebar＇s surface. The rusty-skin rebar exhibits the highest corrosion rate because crevice corrosion can accelerate the corrosion of the steel rehar, particularly at high temperature. The results also indicate that the threshold temperatures of passivation for the oxide-skin rebar and the rusty-skin rebar are 37℃and 20℃, respectively.
基金Project supported by the National Natural Science Foundation of China (No. 50674062)the National Science & Technology Pillar Program (No. 2006BAC21B03)the Beijing Science and Tech-nology Plan Projects (No. D07040300690000), China
文摘Corrosion of steel rebar is the most important durability problem of reinforced concrete. The aim of this research was to investigate the corrosion behavior of steel rebar in simulated pore solutions and gangue-blended cement mortar. The simulated pore solutions were based on the pore solution composition of gangue-blended cement. The pH and Cl-concentration of simulated pore solutions had significant effects on corrosion potential. However,an increase in pH reduced the influence of Cl-concentra-tion on corrosion potential. The corrosion behavior of steel rebar in gangue-blended cement is different from that in simulated solutions. The gangue cementitious mortar surrounding steel rebar provides stable passivity environments for steel,leading to a decrease in ion diffusion coefficients. Alternating current impedance (ACI) analysis results indicated that the indicator Rc for concrete resistivity is higher for gangue mortar than for ordinary Portland cement (OPC),which improves its corrosion potential. The results from energy dispersive X-ray analysis (EDX) showed more aluminates and silicates at the rebar interface for gangue-blended cement. These aluminates improve the chloride binding capacity of hydrates in mortar,and increase the corrosion protection of steel rebar.
