Corrosion Behavior of Steel Fibers in Reactive Powder Concrete with High Volume of Mineral Admixtures

The corrosion behavior and the effects of temperature on critical chloride content (Ccrit) of steel fibers in RPC were analyzed by a pH meter, ion chromatography, mercury intrusion porosimetry (MIP), and electrochemical techniques. It was found that the suspension pH value, the chloride binding capacity, and the total porosity of RPC were lower than those of high-performance concrete (HPC). The pore structure of RPC mainly consisted of gel pores. The Ccrit values of steel fibers in RPC and HPC at 20 ℃ were 1% and 2%, respectively. When the temperature reached 50 ℃, the Ccrit value of steel fibers in HPC decreased significantly, whereas it remained unchanged in RPC. The corrosion rate of corroded fibers in both RPC and HPC started to decrease with the rise in temperature.

Experimental Study on Fatigue Performance of Reinforced Concrete Beams in Corrosive Environment with Cyclic Loads

In marine environments,reinforced concrete bridge structures are sub-jected to cyclic loads and chloride ingress,which results in corrosion of the rein-forcing bars,early deterioration,durability loss,and a considerable reduction in the fatigue strength.Owing to the complexity of the problem and the difficulty of testing,there are few studies on the fatigue performance of concrete structures under the combined action of corrosion environment and cyclic load.Therefore,a coupling test device for corrosion and cyclic load is designed and fatigue tests of reinforced concrete beams in air environments and chlorine salt corrosive envir-onments are carried out.The fatigue corrosion process,damage mode,and corro-sion features of the test beams as well as chloride ion content in concrete are analyzed.The relationships of deflection,crack,and number of cycles in the dif-ferent environments are given.Results show that the fatigue life of the beam is.greatly reduced under coupled effects of the cyclic load and corrosive environ-ment,the failure fom of the beam is corrosion fatigue damage.The deflection and crack keeps growing with the increase in loading cycles.Under the coupling of cyclic load and corrosion env ironment,the content of chloride ion in concrete is low and there is less variety along the direction of penetration.

Application of machine learning technique for predicting and evaluating chloride ingress in concrete

The degradation of concrete structure in the marine environment is often related to chloride-induced corrosion of reinforcement steel.Therefore,the chloride concentration in concrete is a vital parameter for estimating the corrosion level of reinforcement steel.This research aims at predicting the chloride content in concrete using three hybrid models of gradient boosting(GB),artificial neural network(ANN),and random forest(RF)in combination with particle swarm optimization(PSO).The input variables for modeling include exposure condition,water/binder ratio(W/B),cement content,silica fume,time exposure,and depth of measurement.The results indicate that three models performed well with high accuracy of prediction(R2⩾0.90).Among three hybrid models,the model using GB_PSO achieved the highest prediction accuracy(R2=0.9551,RMSE=0.0327,and MAE=0.0181).Based on the results of sensitivity analysis using SHapley Additive exPlanation(SHAP)and partial dependence plots 1D(PDP-1D),it was found that the exposure condition and depth of measurement were the two most vital variables affecting the prediction of chloride content.When the number of different exposure conditions is larger than two,the exposure significantly impacted the chloride content of concrete because the chloride ion ingress is affected by both chemical and physical processes.This study provides an insight into the evaluation and prediction of the chloride content of concrete in the marine environment.

Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregate concrete

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete(SSRAC)are analyzed by a series of axial compression tests.Two different types of fine(coarse)aggregates are considered:sea sand and river sand(natural and recycled coarse aggregates).Variations in SSRAC properties at different ages are investigated.A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete.Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content.The elastic modulus of SSRAC increases with age.However,the Poisson’s ratio reduces after 2 years.Typical axial stress-strain curves of SSRAC vary with age.Generally,the effect of coarse aggregates on the axial deformation of SSRAC is clear;however,the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand.The aggregate type changes the crack characteristics and propagation of SSRAC.Finally,an analytical expression is suggested to construct the long-term stress-strain curve of SSRAC.