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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]

• 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]

• The allowable content of microfines can be relaxed. • Coupled effects of content and MBV of microfines has a decisive influence. • A correlation theory was established to calculate the coupled effects. This study investigated the coupled influences of the content and methylene blue value (MBV) of microfines on the comprehensive performance of manufactured sand concrete. The results show that microfines with a low MBV improve the workability of fresh concrete and the compactness of hardened concrete, thus improving certain properties of the concrete. In contrast, microfines with a high MBV are detrimental to frost resistance and shrinkage. Furthermore, the requirements regarding the allowable content of microfines can be relaxed depending on the associated MBV in order to make full use of microfines in manufactured sand concrete. Finally, this study calculates the coefficient of the coupled effects of the content and MBV of microfines on the performance of manufactured sand concrete based on the correlation theory and provides the basis for updating the content and MBV requirements for microfines in actual engineering. Sand can be replaced with microfines in traditional construction, transportation engineering and bridge engineering, thereby alleviating shortages of river sand. [ABSTRACT FROM AUTHOR]