Papers by Author: Qiang Li

Abstract: Cracking of the cover concrete due to steel corrosion is considered as one of the major issues of durability of reinforced concrete (RC) structures. This paper tentatively studies the feasibility of DIC to reinforcement corrosion induced concrete fracture and cover cracking measurement. Advantages and limitations of DIC-based non-contact full-field measurement for corrosion induced concrete fracture and cover cracking are discussed. Drawbacks in this test need improvement are pointed out and test method for further study of whole process of simulating the real reinforced concrete cracking is put forward.

Abstract: To study the durability of reinforced concrete structures under coupling effect of load and environmental, an analog device is developed. Device includes sustained loading, accelerated environmental corrosion and measuring systems. The load applied to the column is real-time monitored by the pressure sensor and compensated according to the stiffness degradation and stress relaxation of column due to the rebar corrosion. Electrode is placed in the column so that the arrangement of the measuring instrument is not restricted. Device successfully realizes monitoring the time-varying mechanical performance degradation of reinforced concrete under the coupling effect of load and environment.

Abstract: Cracking of the cover concrete due to steel corrosion is considered as one of the major issues of durability of reinforced concrete (RC) structures. Numerous models have been developed to predict the time from corrosion initiation to cracking of the cover concrete. However, little work has been done on the effects of stirrup on reinforcement corrosion-induced cover cracking. In this paper, the effects of stirrup on reinforcement corrosion-induced cover cracking are investigated. The results of four short columns (section size 100×100 mm, total length 515 mm) subjected to accelerated corrosion clearly show that stirrups not only can effectively postpone and prevent the longitudinal crack initiation but also can restrict the width of cracks caused by corrosion of reinforcement. Therefore, prediction models should account for the effects of stirrup on reinforcement corrosion-induced cover cracking, and even the effects of load on it.

Abstract: Boric acid (H₃BO₃) is often used for cooling the heat in nuclear power plant. Though the drastic measures have been taken, the potential leakage still can not be fully eliminated. Therefore, an attempt to understand the durability mechanism of RC subjected to boric acid is of vital importance. In this paper, specimens cured in a standard moist room at a temperature of 20 ±3 °C after 28days were immersed in three different concentration of boric solution (2000ppm, 8000ppm, 30000ppm) artificially simulated to accelerate the corrosion of acid environment. The hydration products are investigated. Microstructure of reinforced concrete on the surface, 2cm and 4cm away from the surface at ages of 60, 90 and 150 days are examined using X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Results indicate that main hydration product is Ca(BO₂)₂,boric acid corrosion to concrete surface can only be detected from the specimens in 30000ppm solutions at the ages of 150 days and its effect is slight. However, the inner part of the concrete was not affected. The results of XRD coincide with those of SEM.

Abstract: Reaches on durability of concrete has been made great advances over the past decades. However, little works have been done on the corrosion of reinforced concrete exposed to boric acid in cooling pond of heating exchange system of nuclear power plant. The purpose of this study is to experimentally investigate the behavior of reinforced concrete in such circumstance. Tests were carried out on specimens cured in a standard moisture room at a temperature of 20±3°C. Three different concentration of boric solution (2000ppm, 8000ppm, 30000ppm) were simulated to accelerate the corrosion. The compressive and splitting tensile strength,elastic modulus of concrete , mass loss rate of steel bar, bond strength and flexural bearing capacity of reinforced concrete at 60, 90, 120, 150 and 180 days were obtained respectively. The results indicate that the presence of boric acid below 30000ppm does not significantly affect serviceability of concrete. The corrosion is slight for the specimens with crack less than 0.4 mm under flexural loads. Boric acid almost has no effect on the corrosion of the steel bar and bond strength.

Abstract: As a supporting member of concrete structures, the reliability of the columns is of critical importance. To have models targeted to estimating the residual load-bearing capacity of corroded reinforced concrete (R.C.) columns so that inspection procedures and maintenance interventions can be well conducted, a time-dependent capacity model for corroded R.C. column is presented. The model was based on equilibrium equations on which load-bearing capacity of R.C. column at given time (year) can be predicted considering the overall deteriorations of rebar, concrete section, mechanical properties and bond behavior between corroded reinforcement and concrete. The model was verified by published literature test results of corroded R.C. columns served in atmosphere environment for years. The comparison of the model predictions with the test results shows the validity of the model. In the end, considerations for use of the model were suggested.