Studies On Expansion Induced By Corrosion And Bonding Behavior Of Corroded Reinforced Concrete Under Hoop Constraint And Sustained Load

Concrete durability is a hot issue of civil engineering, and steel corrosion is a main factor which influences the durability of reinforced concrete structures. Surface of concrete will appear longitudinal or transverse cracks and concrete cover will fall off when the steel corrodes; these will lead to the decrese of the bearing capacity and make the structures damage before meeting service life period. The bonding behavior is collaboration of concrete and steel; the degeneration of bonding behavior will influence structure’s safety after steel corrosion. Actually, concrete structures begin corroding under loads and stirrup is taken as hoop constraint in the structure. In this paper, two factors which are the load and hoop constraint(FRP) are considered to study the expansion induced by corrosion and bonding behavior of corroded reinforced concrete on the basis of summarizing the existing research results. The follows is the main research:Through the33same test specimens which were corroded accelerately by electricity, the different corrosion conditions had influences on the cracking of reinforced concrete structures by considering different sustained load, different constraint condition and different corrosion rate; the crack width increased by the increase of corrosion rate; the varying pattern of crack width and hoop constraint with the diffrernt corrosion conditions were analysed on the basis of the above, and the critical corrosion rate was obtained by fitting the crack width and corrosion rate. The results showed that: variation trend of hoop strain was the same to the crack width and they declined by the increase of the load; the critical corrosion rate of concrete cracking declined by the increase of the load, and the critical corrosion rate with hoop constraint was prior to the critical corrosion rate without hoop constraint.According to the reference literatures about models of critical corrosion penetration, the corrosive crack models of different corrosion conditions were established by considering hoop constraint and sustained load; the calculating formulas of critical corrosion rate under four kinds of conditions were acquired: no hoop constraint and no sustained load, hoop constraint and no sustained load, no hoop constraint and sustained load, hoop constraint and sustained load. Besides, the rationality of the calculation formula was verified by comparing the theoretical results and the test results.By means of pull-out test on the corrosion specimens, the different corrosion conditions had influences on the bonding behavior of reinforced concrete structures by considering different sustained load, different constraint condition and different corrosion rate; thus the varying pattern of ultimate bonding strength and bonding stress-slippage curve with the diffrernt corrosion conditions were analysed; and the ultimate bonding strength of different corrosion conditions was amended by correction factor. The results showed that: to the ones with hoop constraint, the ultimate bonding strength went up a little with the rise of sustained load; the ultimate slippage and residual bonding strength of the specimens with hoop constraint was obviously prior to the ones without hoop constraint; the ultimate slippage and residual bonding strength showed the declining trend with the increase of sustained load no matter whether the specimens had the hoop constraint or not.