Study On Mechanical Properties Of Corroded Prestressing Strands

At present, corrosion of prestressing strands of prestressed concrete constructs is becoming prominent, but the studies on this subject are poor. So, the mechanical properties of corroded prestressing strands is studied in this paper. Firstly, the prestressing strand specimens were subjected to the artificial climate conditions to obtain different corrosion levels. Then, the tension test was performed to investigate the mechanical properties of corroded prestressing strands, and the constitutive law for corroded strands were established based on the experimental data. Following this, all pits were measured and recorded to investigate its distributed. Finally, the microstructure and fracture characteristics of corroded prestressing strands were observed by scanning electron microscopy. The following research work has been done:(1)The macroscopic and microscopic observation of the fractures show that the failure mode of prestressing strands is similar,the failure mode of uncorroded prestressing strands or slightly corroded prestressing strands are ductility, and the fractures show necking;with the increase of corrosion rate, the failure mode of corroded prestressing strands deteriorates to brittle, and the necking disappears gradually.(2)The results of tension test show that the slight corrosion decreases ultimate strain linearly with increasing corrosion levels, and also decreases slightly the ultimate strength. Strand corrosion has negligible effect on the yield strength and elastic modulus. The failure of corroded strand changed to brittle when the corrosion levels increased beyond to the critical value. The constitutive law for the slightly corroded strand can be expressed as the bilinear elastic-hardening model. For the severely corroded strand as the corrosion levels greater than the critical value, the constitutive law deteriorates to a single linear model.(3)The statistical analysis of the pits size shows that the pit of corroded prestressing strands have three main types: pyramid, ellipsoidal and similar cone. With data analysis and hypothesis testing, the distribution law of dimension parameters are not difficult to be found. The probability distribution of the maximum depth conforms with extremum Ⅰ type distribution, the depth-to-width ratio shows logarithmic normal distribution, and the distribution law of maximum width is not obvious, its value is mainly concentrated in the medium width range [2mm,4mm].(4)The statistical analysis of dimension parameters show: the increase of corrosion rate extends the maximum depth of the pits, but the extend velocity decreases gradually. The increase of corrosion rate also enlarges the depth-to-width ratio, and intensifies the stress concentration of the pits. But, there are no obvious linear relationship between maximum width and corrosion rate.