Although the ingress of chloride into concrete is normally controlled by absorption and diffusion mechanisms, external loads can affect this process by modifying the microstructure of concrete. To predict the chloride ingress into real structures under service conditions, the effects of external loads on the chloride transport should be considered. In this paper, the effects of compressive and flexural loads on chloride transport were studied. The experimental results indicated that the chloride concentration and apparent chloride diffusion coefficient Dapp decreased with the increase of the compressive stress, up to 55% of the compressive strength, and they increased with the increase of the flexural stress. On the basis of these results, a model for predicting the chloride diffusion process under different loading conditions is established by accounting for various parameters, such as stress level, water-cement ratio, curing time, temperature, concrete age, humidity, and chloride diffusion coefficient. ...

Expansion and cracking induced by the corrosion of reinforcement concrete is the major factor in the failure of concrete durability. Therefore, monitoring of concrete cracking is critical for evaluating the safety of concrete structures. In this paper, we introduce a novel monitoring method combining Brillouin optical time domain analysis (BOTDA) and fiber Bragg grating (FBG), based on mechanical principles of concrete expansion cracking. BOTDA monitors concrete expansion and crack width, while FBG identifies the time and position of cracking. A water-pressure loading simulation test was carried out to determine the relationship between fiber strain, concrete expansion and crack width. An electrical accelerated corrosion test was also conducted to evaluate the ability of this novel sensor to monitor concrete cracking under practical conditions.

Concern has been expressed in the recent decades about the corrosion prediction of concrete structures in a chloride environment. This paper summarises the corrosion prediction models developed for chloride-contaminated concrete, including both the empirical and electrochemical corrosion models. The definition methods of the steel de-passivation process for electrochemical models, such as anode–cathode ratio (A_a/A_c), critical chloride concentration (C_Cl,crit), modification of anodic Tafel slope (β_a) or passive film resistance (R_f), are considered essential and discussed in detail. Furthermore, electrochemical parameters regarding the definition and selection in electrochemical models and experimental measurements are discussed. This study confirms that A_a/A_cand C_Cl,crithave been generally used in recent years, and that the modifications of β_aand R_frelated to free chloride concentration are technically feasible. In addition, the discreteness of electrochemical parameters in electrochemical models and experimental measurements are observed, and time-dependent characteristics of electrochemical parameters are scarcely presented in the existing literature.

The corrosion of reinforcements induced by chloride has resulted to be one of the most frequent causes of their premature damage. Most corrosion sensors were designed to monitor corrosion state in concrete, such as Anode-Ladder-System and Corrowatch System, which are widely used to monitor chloride ingress in marine concrete. However, the monitoring principle of these corrosion sensors is based on the macro-cell test method, so erroneous information may be obtained, especially from concrete under drying or saturated conditions due to concrete resistance taking control in macro-cell corrosion. In this paper, a fast weak polarization method to test corrosion state of reinforcements based on electrochemical polarization dynamics was proposed. Furthermore, a new corrosion sensor for monitoring the corrosion state of concrete cover was developed based on the proposed test method. The sensor was tested in cement mortar, with dry-wet cycle tests to accelerate the chloride ingress rate. The results show that the corrosion sensor can effectively monitor chloride penetration into concrete with little influence of the relative humidity in the concrete. With a reasonable corrosion sensor electrode arrangement, it seems the Ohm-drop effect measured by EIS can be ignored, which makes the tested electrochemical parameters more accurate.

Civil engineering structures can induce various environmental problems during their lifetime. In this paper, the life-cycle environmental impacts of structures, including the emissions to air, water and land, are quantified by environmental cost, and are considered as a part of indirect cost in the life-cycle cost (LCC) model. The computation of environmental cost based on the pollution prevention measures is presented. Using the environmental fines and taxes on various pollutants the environmental costs of construction materials, energy, transportation, and construction equipment are calculated. Structural type selection of a bridge structure is carried out based on the environmental cost-incorporated initial cost. The environmental cost-incorporated LCC model is applied in the life-cycle cost analysis (LCCA) of steel bridge girders. Hurdle discount rates are implemented on future environmental costs. Uncertainties arising from the direct cost and environmental cost are analyzed. The effects of different types of environmental cost discount rates are discussed.

Corrosion cracking of reinforced concrete caused by chloride salt is one of the main determinants of structure durability. Monitoring the entire process of concrete corrosion cracking is critical for assessing the remaining life of the structure and determining if maintenance is needed. Fiber Bragg Grating (FBG) sensing technology is extensively developed in photoelectric monitoring technology and has been used on many projects. FBG can detect the quasi-distribution of strain and temperature under corrosive environments, and thus it is suitable for monitoring reinforced concrete cracking. According to the mechanical principle that corrosion expansion is responsible for the reinforced concrete cracking, a package design of reinforced concrete cracking sensors based on FBG was proposed and investigated in this study. The corresponding relationship between the grating wavelength and strain was calibrated by an equal strength beam test. The effectiveness of the proposed method was verified by an electrically accelerated corrosion experiment. The fiber grating sensing technology was able to track the corrosion expansion and corrosion cracking in real time and provided data to inform decision-making for the maintenance and management of the engineering structure.