Electrochemical study on semiconductive properties of the passive film on rebar in concrete

The electrochemical behavior of metallic passive film on rebar in concrete is characterized by its semiconductive nature. The charge distribution at the interface between a semiconductor and an electrolyte is often determined by measuring the capacitance of the space-charge layer （Csc） as a function of the electrode potential （E）. When the space charge-layer serves as the depletion layer, the relation of Csc^-2 vs E resembles a Mott-Schottky plot （M-S plot）. The semiconductive properties of the passive film on rebar in concrete were analyzed with M-S plots to study the effect of chloride ions and mineral admixtures on rebar passive films. Some rebar electrodes were immersed in simulated concrete pore solutions, while others were embedded in concrete with/without mineral admixtures. In saturated Ca（OH）, solutions, the relation of Csc^-2-E of rebar electrodes shows linear MottSchottky relationship indicating that the passive film on rebar is a highly disordered n-type semiconductor, with donor density （ND） in the order of 10^26m^-3. After adding chloride ions （Cl wt%〈0.2%） in system solutions, the M-S plot slopes significantly decreased and ND increased, suggesting that chloride ion will cause passive film corrosion and breakdown. The M-S plots of the passive film on rebar electrodes embedded in concrete were similar to those immersed in simulated system solution. However, ND of those in concrete with mineral admixtures tended to be a little smaller, indicating that introducing proper quantity admixtures into concrete could make the rebar passive film have a thicker space-charge layer and therefore a thicker passive film layer.

Research and application of schemes for constructing concrete pillars in large section finishing cut in backfill coal mining

Based on the technology of controlling surrounding rock deformation by constructing concrete pillars in large section finishing cut in backfill coal mining, the characteristics of vertical stress on concrete pillars and main factors influencing pillar stability are analyzed. By building a Winkler elastic foundation mechanical model for the support system constituted of coal pillar, backfill body and concrete pillars, mechanical calculation on stability of concrete pillar is carried out to evaluate the pillar stability and safety. Seven numeral models in three schemes with different pillar sizes, inter-row distances and compression ratios at the stopes were analyzed through numerical simulation according to width reduction principle. The practice of finishing cut at IIIB44 workface at Yangzhuang coal mine shows that： when the actual compression ratio is 86.5%, construction size inside the finishing cut is 2000 mm x 2000 mm and the interval between concrete pillars is 2000 mm x 2000 mm, the pillars can be stable with the maximum movement of two sides of each pillar being only 83 mm and 54 mm, which achieves the expected effect.

Simulation algorithm for spiral case structure in hydropower station

In this study, the damage-plasticity model for concrete that was verified by the model experiment was used to calculate the damage to a spiral case structure based on the damage mechanics theory. The concrete structure surrounding the spiral case was simulated with a three-dimensional finite element model. Then, the distribution and evolution of the structural damage were studied. Based on investigation of the change of gap openings between the steel liner and concrete structure, the impact of the non-uniform variation of gaps on the load-beating ratio between the steel liner and concrete structure was analyzed. The comparison of calculated results of the simplified and simulation algorithms shows that the simulation algorithm is a feasible option for the calculation of spiral case structures. In addition, the shell-spring model was introduced for optimization analysis, and the results were reasonable.

High corrosion resistance film on rebar by cerium modification

A cerium film was prepared on the surface of rebar by chemical conversion method to enhance its corrosion resistance.The film in the simulated concrete pore solution was measured by electrochemical method,transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS).The effect of temperature on film formation was studied,and the optimum temperature was determined at 35℃.The film produced by too high formation temperature has more defects,resulting in the lower corrosion resistance.The Ce film resistance increased with time evolution until 800 h,then decreased and stabilized.The Ce film layer has a double-layer film structure,the upper layer is an oxide of cerium,and the underlayer is an oxide of iron.Results revealed that after being immersed in the simulated concrete pore solution,the corrosion resistance of the Ce film was enhanced by self-densification.