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The article presents a study which examined the cracking of concrete cover based on a three-period model of steel bar corrosion in reinforced concrete. The research focused on the two corrosion points, namely, the void to be filled was exactly filled and the concrete cover was exactly cracked. Also mentioned are the theory of elastic mechanics and the relationship between crack width of concrete cover and the steel corrosion depth.

In this work, a total of 20 beam type concrete specimens were prepared to investigate bond behavior of glass fiber reinforced polymer (GFRP) bar embedded in marine concrete. The influence of sustained loads (load level: 0.25, 0.45 and 0.65 ultimate load (P u)) and stirrup on bond properties was investigated. After sustained load period, flexural bond test was conducted to determine bond stress and slip. Test results indicate that bond strength of GFRP bars shows decreased trend with increasing sustained loading. Compared with specimen not subjected to sustained load, bond strength significantly decreased under 0.25, 0.45 and 0.65 P u. Also, sustained load deteriorates the bond stiffness and bond toughness. What' s more, differences in failure modes and bond strength of steel bar and GFRP bars in flexural bonding tests were analyzed and compared. All GFRP bar specimens subjected to sustained load exhibit bars pull-out failure. In contrast to steel bar, the influence of stirrups on GFRP bar-marine concrete bond strength is relatively limited (specimens with stirrups exhibited only 1.8 % increase over specimens without stirrups), due to GFRP bars lower rib heights and weaker mechanical interlocking with concrete. Characterization of different stages of bond-slip curves of GFRP bar beam specimen subjected to sustained loads was carried out and bond-slip curves of GFRP shows two peaks. According bond strength and slip test data, bond stress-slip mathematical relationship model between GFRP bar and marine concrete under sustained load has been fitted. • Bond strength of GFRP bars shows decreasing trend with increasing sustained load. • Influence of stirrups on bond strength of GFRP - marine concrete is relatively limited. • Bond stress-slip mathematical relationship model under sustained load has been fitted. [ABSTRACT FROM AUTHOR]

Reinforced-concrete (RC) structures are inevitably subjected to sustained loads during their service life. In the natural environment, the exposed surfaces of RC members often experience dry–wet cycles due to rainfall and tides. An important parameter in structural design is the the bond behaviour between steel bars and concrete, and this is affected by the coupled effect of sustained loads and dry–wet cycles. In this study, 32 RC beam specimens were subjected to different levels of sustained load (25%, 50% and 75% of ultimate load) and dry–wet cycles for a period of 120 d. The immediate slip and time-dependent slip (TDS) between the steel bar and concrete during testing were recorded and analysed. It was found that the TDS increased with an increase in the duration of sustained loading and greater sustained load levels resulted in larger TDSs. After long-term testing, the bond strength and bond stress–strain were investigated using a flexural-bond test. The results showed that bond strength increased due to the coupled effects of sustained load and dry–wet cycles. Based on the test results, an empirical model for steel bar–concrete TDS considering the effect of sustained load and dry–wet cycles was developed. [ABSTRACT FROM AUTHOR]

Twenty-seven reinforced concrete beam specimens were cast to study the bond properties between steel bars and concrete under the coupling of chloride ion erosion and repeated load (0, 0.25, 0.45, and 0.65 of ultimate load) for 210 days. The bond strength and slip of steel bars embedded in concrete were measured by the flexural bond test. Based on the test results, the higher the level of repeated load alone, the lower the bond strength. The bond strength of beam specimens under the coupling of repeated load and chloride ion erosion is lower than that under repeated load alone or chloride ion erosion alone. The bond strength decreases gradually when the corrosion ratio exceeds 1.5%. The slip between steel bars and concrete decreases with the increase of repeated load level under the coupling of chloride ion erosion and repeated load when splitting failure occurs. Based on the test results, the bond strength-slip constitutive relationship was proposed. [ABSTRACT FROM AUTHOR]

• Beam type specimen. • Sustained load. • Accelerate corrosion. • Instantaneous slip and time-dependent slip. • Prediction model of bond strength. The degradation of bond behavior between corroded steel bars and concrete under sustained load is among the main issue for the durability of structures. In this study, the impressed current method was used to achieve target corrosion levels of tensile steel bar (0%, 1%, 3%, and 5%), while specimens bearing the sustained load (0%, 25%, 45%, and 65% ultimate load). The sustained load lasted for 60 days, during which the instantaneous slip and time-dependent slip were recorded. Finally, the bond strength of all kinds of specimens was measured by the flexural-bond test. The test results show that corrosion and load significantly affect the slip and bond strength between steel bar and concrete. Slight corrosion (less than 1%) leads to higher bond strength, up to 1.22 times that of the control group, while severe corrosion (more than 2.42%) leads to lower. Additionally, the strength reduction caused by the coupling of load and corrosion is more obvious than the single, by up to 45.66%. In addition, based on the test results, the time-dependent slip and bond strength prediction model were proposed, which can be used for predicting the service life of structures in the erosive environment. [ABSTRACT FROM AUTHOR]

• Beam type specimen. • Reciprocating loading history. • Steel bar corrosion. • Bond stress-slip relationship. • Degradation model of bond strength. The bond between steel bars and concrete can be deteriorated by corrosion. A series of beam specimens with initial cracks were cast to study the effects of corrosion on bond behavior. The current-induced accelerated corrosion technique was used to reach four levels of corrosion (0%, 3%, 5% and 7%), and different amplitudes of reciprocating load (0%, 10%, 20% and 30% of ultimate load) were applied on the specimens. Finally, the flexural-bond test was carried out on specimens to obtain the bond strength and bond stress-slip relationships. The results show that the bond strength decreases with the increase in corrosion rate, and deterioration under the coupling condition of reciprocating load and corrosion is more significant, which can be reduced over 50%. And the higher the corrosion level, the faster the slip increases. In addition, the bond stress-slip relationship and the bond strength degradation model are proposed, which can be used to predict the changes of bond behavior under corresponding working conditions. [ABSTRACT FROM AUTHOR]

• Bond properties of specimen subjected to different working condition was analyzed. • The existence of reciprocating load and chloride cause the bond strength deterioration. • The mathematical model of bond strength-slip has been proposed. This work presented an experimental investigation on bond behavior of corroded steel bars embedded in concrete under the action of three different levels of reciprocating loads (25%, 45% and 65% of ultimate load) and sustained chloride attack using 51 RC beam specimens with dimensions of 100 mm × 150 mm × 550 mm. In the test, the steel is corroded by the method of energized accelerated corrosion (theoretical corrosion ratio of steel is set as 2%, 4% and 6%). Test results show that the effect of reciprocating load will cause the bond strength between uncorroded steel bars and concrete to decrease in the chloride environment, but the effect is not significant. Under the coupled effect of reciprocating loads and energized accelerated corrosion, when the corrosion ratio of longitudinal reinforcement is constant, as the increase of the reciprocating load level, the bond strength between the steel bar and concrete of the specimen decreases. When the theoretical corrosion ratio of steel bars is small, the bond strength between steel bars and concrete gradually increases with the increase of the corrosion ratio; as the corrosion ratio of steel bars further increases, the bond strength shows a downward trend. The theoretical corrosion ratio of steel bars reaches a peak of about 2%. In this paper, the mathematical model of bond strength-slip has been proposed. This work provided an important theoretical basis for correctly assessing the durability of buildings or structures subjected to reciprocating loads in coastal areas. [ABSTRACT FROM AUTHOR]