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Compressive strength and tensile strength are important mechanical properties of concrete. The long-term strength of concrete under real service environment is an important parameter when evaluating existing buildings, which should also be properly considered in structural design. In this study, the relationship between compressive and splitting tensile strength of old concrete existing for long period under marine environment was investigated. At a deserted harbour, concrete cores samples were drilled by pairs in site. For each pair of samples, the two cores were drilled from the adjacent location and conducted to compressive, splitting tensile test, respectively. 48 compressive and splitting tensile strengths were finally obtained. From the test results, tensile strength presents general uptrend with compressive strength, and the two parameters are well positively correlated. Exponential model generally recommended by building codes or literatures is still capable of describing the relationship between compressive and tensile strength of old deteriorated concrete, when function parameters are properly determined. Based on statistical theory and the experimental result of this study, a method for predicting long-term tensile strength of concrete is developed and an example is given, which may provide a potential way to estimate long-term concrete strength under real marine environment.

External bonding of FRP laminates to the tension soffit of concrete members has become a popular method for flexural strengthening. However, the long-term field performance of FRP-strengthened RC members under service conditions is still a concern, and more work needs to be done. Based on concrete smeared-crack approach, this paper presents a finite-element (FE) model for predicting long-term behavior of FRP-strengthened RC beam, which considers the time-dependent properties of all components including the aging effect of concrete. According to the comparison between theoretical predictions and test results, the validity of the FE model is verified. The interfacial edge stresses in adhesive layer were determined through appropriate mesh refinement near the plate end, and their time-dependent characteristics were investigated. The results show that creep of concrete and epoxy resin cause significant variations of the edge stresses with time. According to the research in this paper, the FE approach is found to be able to properly simulate the long-term behavior of the FRP-strengthened beam and help us better understand the complex changes in the stress state occurring over time.

This paper aims to realize a full scale modelling of reinforced concrete (RC) beam enhanced by externally bonded fibre reinforced polymer (EBRFP), considering both longitudinal bars and stirrups. To this end, several previous revisions to Fick's second law of diffusion were incorporated to establish a revised diffusion model. During the modelling, the following factors were taken into account simultaneously: time-dependent diffusion coefficient, timedependent surface chloride ion content, chloride binding effect, material inhomogeneity and load effect. Then, the boundary conditions were properly changed to fit the enhancement behaviour. Later, the revised diffusion model was numerically solved by the FEA on Abaqus, aiming to reveal the effect of enhancement on chloride diffusion, the effect of longitudinal bars and stirrups on chloride diffusion, and the results and efficiencies of 2D and 3D models. Through the analysis of simulation results, the author drew the following conditions: First, the EBRFP enhancement led to an obvious decrease of chloride ion content, thus extending the initial time of rebar corrosion; Second, the longitudinal rebars greatly boosted the chloride ion content at the front faces of rebars, while the effect of stirrups can be neglected if the longitudinal rebars have been considered; Third, 2D model is more recommended than 3D model if the surface chloride ion content remains invariant along the RC beam.

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