Three-Dimensional Multi-Phase Microscopic Simulation of Service Life of Recycled Large Aggregate Self-Compacting Concrete

Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environment. A three-dimensional multi-phase mesoscopic numerical model of RLA-SCC was established to simulate the chloride ions transportation in concrete. Experiments of RLA-SCC immersing in chloride solution were carried out to verify the simulation results. The effects of recycled large aggregate (RLA) content and RLA particle size on the service life of concrete were explored. The results indicate that the mesoscopic numerical simulation results are in good agreement with the experimental results. At the same depth, the closer to the surface of the RLA, the greater the chloride ion concentration. The service life of RLA-SCC in marine environment decreases with the increase of RLA content. Compared with the service life of 20% content, the service life of 25% and 30% content decreased by 20% and 42% respectively. Increasing the particle size of RLA can effectively improve the service life of RLA-SCC in chloride environment. Compared with the service life of 50 mm particle size, the service life of 70 mm and 90 mm increased by 61% and 163%, respectively. .

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash（FA）contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio（named as R）of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope（SEM）analyses are consistent with the evaluations by the value of R.

Cellular Automata-based Chloride Ion Diffusion Simulation of Concrete Bridges under Multi-factor Coupling Actions

In order to accurately simulate the diffusion of chloride ion in the existing concrete bridge and acquire the precise chloride ion concentration at given time, a cellular automata （CA）-based model is proposed. The process of chloride ion diffusion is analyzed by the CA-based method and a nonlinear solution of the Fick＇s second law is obtained. Considering the impact of various factors such as stress states, temporal and spatial variability of diffusion parameters and water-cement ratio on the process of chloride ion diffusion, the model of chloride ion diffusion under multi-factor coupling actions is presented. A chloride ion penetrating experiment reported in the literature is used to prove the effectiveness and reasonability of the present method, and a T-type beam is taken as an illustrative example to analyze the process of chloride ion diffusion in practical application. The results indicate that CA-based method can simulate the diffusion of chloride ion in the concrete structures with acceptable precision.

Convolutional Neural Network-Based Regression for Predicting the Chloride Ion Diffusion Coefficient of Concrete

The durability performance of reinforced concrete(RC)building structures is significantly affected by the corrosion of the steel reinforcement due to chloride penetration,thus,the chloride ion diffusion coefficient should be investigated through experiments or theoretical equations to assess the durability of an RC structure.This study aims to predict the chloride ion diffusion coefficient of concrete,a heterogeneous material.A convolutional neural network(CNN)-based regression model that learns the condition of the concrete surface through deep learning,is developed to efficiently obtain the chloride ion diffusion coefficient.For the model implementation to determine the chloride ion diffusion coefficient,concrete mixes with w/c ratios of 0.33,0.40,0.46,0.50,0.62,and 0.68,are cured for 28 days;subsequently,the surface image data of the specimens are collected.Finally,the proposed model predicts the chloride ion diffusion coefficient using the concrete surface image data and exhibits an error of approximately 1.5E−12 m^(2)/s.The results suggest the applicability of proposed model to the field of facility maintenance for estimating the chloride ion diffusion coefficient of concrete using images.

A Time-saving Method for Assessing the Corrosion Inhibitor Efficiency

Corrosion inhibitor is one of the most important technologies to enhance the durability of steel reinforced concrete. A kind of time-saving method was developed to assess the inhibitor efficiency by using a 16 voltage electric field to accelerate the chloride ion diffusion in concrete and inducing corrosion. Both macrocell and microcell current measurements were used to confirm the corrosion initiation status of steel. The comprehensive efficiency of inhibitor shall be assessed in three aspects. The results clearly show the efficiency of different inhibitors, which indicate the reliability of this time-saving method.

Durability of Reinforced Concrete Structures under Coupling Action of Load and Chlorine Erosion

Diffusion behavior of chloride ion in reinforced concrete under bendingmoment was studied by taking the ratio of bending moment to ultimate flexural capacity asload level indicator. The function relationship between load level and chloride iondiffusion coefficient was established, based on that the limit state equation of the chlorideion critical concentration and chloride ion concentration on surface of the steel bar wasestablished. Then by applying Monte-Carlo method the corrosion probability ofreinforcement under different load levels in splash zone was calculated. Calculation resultsdemonstrated that compared with the durability reliability index considering loading effect,the reliability index without considering loading effect could be 100% higher. Inconsideration of requirement for concrete durability, some revision suggestion was putforward. It was recommended that for beam members with different design life in splashzone, the corresponding minimum cover thickness should be adjusted properly as well aswater-cement ratio limit.

Durability problems of lining structures for Xiamen Xiang'an subsea tunnel in China

Durability problem of reinforced concrete for underground structures is a hot issue in the field of structural engineering. For underground structures, the prediction of structural service life and methodology for durability design are needed to estimate structural durability. Taking the case of Xiamen Xiang＇an subsea tunnel as background, which is designed to meet the requirement of lO0-year service life, the influential factors on tunnel lining durability are analyzed. Under the criteria of crack controlling and bearing capacity of linin~ structures, the theoretical service life of Xiamen Xiang＇an subsea tunnel lining is studied. The regulations, which are needed for the diffusion capability of chloride ions in concrete by the relevant diffusion tests, are proposed. After a quick corrosion test, the bearing capacity test on eccentric short columns is implemented to investigate the variation rules in the bearing capacity of models with time. Influence of the corrosion degree of steel bars on the bearing capacity of models is also investigated. Based on the results of model tests, the acceleration ratio between the quick corrosion in laboratory test and the natural corrosion environments is established. Thus, the natural service life of subsea tunnel lining structures can be obtained by means of laboratory tests. Then, the proposed method using this modified model is employed to predict the service life of tunnel lining structures. Finally, the design and construction measures for improving the durability of lining structures of subsea tunnel are introduced. The proposed method in the present study based on a real engineering project is superior to those with only theoretical assumptions, and would be more suitable for similar projects.

A New Method to Quickly Assess the Inhibitor Efficiency

A new method to quickly assess the efficiency of corrosion inhibitor was developed by electrically accelerating chloride ions diffusing onto the surface of the embedded steel bar in concrete and inducing corrosion.Potentiodynamic polarization scanning and linear polarization method were used to evaluate the corrosion states which were compared with the direct observation of the bar surface by breaking the sample.The test duration was about two days and the results clearly show the differences in efficiency of the inhibitors tested.